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Internet Engineering Task Force (IETF) H. Brockhaus
Request for Comments: 9483 D. von Oheimb
Category: Standards Track S. Fries
ISSN: 2070-1721 Siemens
November 2023
Lightweight Certificate Management Protocol (CMP) Profile
Abstract
This document aims at simple, interoperable, and automated PKI
management operations covering typical use cases of industrial and
Internet of Things (IoT) scenarios. This is achieved by profiling
the Certificate Management Protocol (CMP), the related Certificate
Request Message Format (CRMF), and transfer based on HTTP or
Constrained Application Protocol (CoAP) in a succinct but
sufficiently detailed and self-contained way. To make secure
certificate management for simple scenarios and constrained devices
as lightweight as possible, only the most crucial types of operations
and options are specified as mandatory. More specialized or complex
use cases are supported with optional features.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9483.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
1.1. How to Read This Document
1.2. Conventions and Terminology
1.3. Motivation for a Lightweight Profile of CMP
1.4. Special Requirements of Industrial and IoT Scenarios
1.5. Existing CMP Profiles
1.6. Compatibility with Existing CMP Profiles
1.7. Use of CMP in SZTP and BRSKI Environments
1.8. Scope of This Document
1.9. Structure of This Document
2. Solution Architecture
3. Generic Aspects of PKI Messages and PKI Management Operations
3.1. General Description of the CMP Message Header
3.2. General Description of the CMP Message Protection
3.3. General Description of CMP Message ExtraCerts
3.4. Generic PKI Management Operation Prerequisites
3.5. Generic Validation of a PKI Message
3.6. Error Handling
3.6.1. Reporting Error Conditions Upstream
3.6.2. Reporting Error Conditions Downstream
3.6.3. Handling Error Conditions on Nested Messages Used for
Batching
3.6.4. PKIStatusInfo and Error Messages
4. PKI Management Operations
4.1. Enrolling End Entities
4.1.1. Enrolling an End Entity to a New PKI
4.1.2. Enrolling an End Entity to a Known PKI
4.1.3. Updating a Valid Certificate
4.1.4. Enrolling an End Entity Using a PKCS #10 Request
4.1.5. Using MAC-Based Protection for Enrollment
4.1.6. Adding Central Key Pair Generation to Enrollment
4.1.6.1. Using the Key Transport Key Management Technique
4.1.6.2. Using the Key Agreement Key Management Technique
4.1.6.3. Using the Password-Based Key Management Technique
4.2. Revoking a Certificate
4.3. Support Messages
4.3.1. Get CA Certificates
4.3.2. Get Root CA Certificate Update
4.3.3. Get Certificate Request Template
4.3.4. CRL Update Retrieval
4.4. Handling Delayed Delivery
5. PKI Management Entity Operations
5.1. Responding to Requests
5.1.1. Responding to a Certificate Request
5.1.2. Responding to a Confirmation Message
5.1.3. Responding to a Revocation Request
5.1.4. Responding to a Support Message
5.1.5. Initiating Delayed Delivery
5.2. Forwarding Messages
5.2.1. Not Changing Protection
5.2.2. Adding Protection and Batching of Messages
5.2.2.1. Adding Protection to a Request Message
5.2.2.2. Batching Messages
5.2.3. Replacing Protection
5.2.3.1. Not Changing Proof-of-Possession
5.2.3.2. Using raVerified
5.3. Acting on Behalf of Other PKI Entities
5.3.1. Requesting a Certificate
5.3.2. Revoking a Certificate
6. CMP Message Transfer Mechanisms
6.1. HTTP Transfer
6.2. CoAP Transfer
6.3. Piggybacking on Other Reliable Transfer
6.4. Offline Transfer
6.4.1. File-Based Transfer
6.4.2. Other Asynchronous Transfer Protocols
7. Conformance Requirements
7.1. PKI Management Operations
7.2. Message Transfer
8. IANA Considerations
9. Security Considerations
10. References
10.1. Normative References
10.2. Informative References
Appendix A. Example CertReqTemplate
Acknowledgements
Authors' Addresses
1. Introduction
This document specifies PKI management operations supporting machine-
to-machine and IoT use cases. Its focus is to maximize automation
and interoperability between all involved PKI entities, ranging from
end entities (EEs) over any number of intermediate PKI management
entities, such as registration authorities (RAs), to the Certificate
Management Protocol (CMP) [RFC4210] endpoints of certification
authority (CA) systems. This profile makes use of the concepts and
syntax specified in CMP [RFC4210] [RFC9480] [RFC9481], Certificate
Request Message Format (CRMF) [RFC4211] [RFC9045], Cryptographic
Message Syntax (CMS) [RFC5652] [RFC8933], HTTP transfer for CMP
[RFC6712], and CoAP transfer for CMP [RFC9482]. CMP, CRMF, and CMS
are feature-rich specifications, but most application scenarios use
only a limited subset of the same specified functionality.
Additionally, the standards are not always precise enough on how to
interpret and implement the described concepts. Therefore, this
document aims to tailor the available options and specify how to use
them in adequate detail to make the implementation of interoperable
automated certificate management as straightforward and lightweight
as possible.
While this document was being developed, documents intended to
obsolete RFC 4210 [PKIX-CMP] and RFC 6712 [HTTP-CMP] were posted, and
they include the full set of changes described in CMP Updates
[RFC9480].
1.1. How to Read This Document
This document has become longer than the authors would have liked it
to be. Yet apart from studying Section 3, which contains general
requirements, the reader does not have to work through the whole
document. The guidance in Sections 1.9 and 7 should be used to
figure out which parts of Sections 4 to 6 are relevant for the target
certificate management solution, depending on the PKI management
operations, their variants, and types of message transfer needed.
Since conformity to this document can be achieved by implementing
only the functionality declared mandatory in Section 7, the profile
can still be called lightweight because, in particular for end
entities, the mandatory-to-implement set of features is rather
limited.
1.2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The term "PROHIBITED" is to be interpreted to mean that the
respective ASN.1 field SHALL NOT be present or used.
Technical terminology is used in conformance with [RFC4210],
[RFC4211], [RFC5280], and IEEE 802.1AR [IEEE.802.1AR_2018]. The
following terminology is used:
CA: Certification authority, which issues certificates.
RA: Registration authority, an optional PKI component to which a
CA delegates certificate management functions, such as end
entity authentication and authorization checks for incoming
requests. An RA can also provide conversion between various
certificate management protocols and other protocols providing
some operations related to certificate management.
LRA: Local registration authority, a specific form of RA with
proximity to the end entities.
Note: For ease of reading, this document also uses the term
"RA" for LRAs in all cases where the difference is not
relevant.
KGA: Key generation authority, an optional system component,
typically colocated with an RA or CA, that offers key
generation services to end entities.
EE: End entity, typically a device or service that holds a public-
private key pair for which it manages a public key
certificate. An identifier for the EE is given as the subject
of its certificate.
The following terminology is reused from [RFC4210] as follows:
PKI management operation: All CMP messages belonging to a single
transaction. The transaction is
identified by the transactionID field of
the message headers.
PKI management entity: A non-EE PKI entity, i.e., an RA or a
CA.
PKI entity: An EE or PKI management entity.
CMP messages are referred to by the names of PKIBody choices defined
in Section 5.1.2 of [RFC4210] and are further described in Section 4
of this document.
The following terms are introduced in this document:
CMP protection key: The private key used to sign a CMP
message.
CMP protection certificate: The certificate related to the CMP
protection key. If the keyUsage
extension is present, it MUST include
digitalSignature.
1.3. Motivation for a Lightweight Profile of CMP
CMP was standardized in 1999 and is implemented in several PKI
products. In 2005, a completely reworked and enhanced version 2 of
CMP [RFC4210] and CRMF [RFC4211] has been published, followed by a
document specifying a transfer mechanism for CMP messages using HTTP
[RFC6712] in 2012.
CMP is a capable protocol and could be used more widely. CMP
[RFC4210] and CMP Updates [RFC9480] offer a very large set of
features and options. On one hand, this makes CMP applicable to a
very wide range of scenarios; on the other hand, a full
implementation supporting all options is not realistic because this
would take undue effort.
In order to reduce complexity, the set of mandatory PKI management
operations and variants required by this specification has been kept
lean. This limits development efforts and minimizes resource needs,
which is particularly important for memory-constrained devices. To
this end, when there was design flexibility to either have necessary
complexity on the EE or in the PKI management entity, this profile
chose to include it in the PKI management entities where typically
more computational resources are available. Additional recommended
PKI management operations and variants support some more complex
scenarios that are considered beneficial for environments with more
specific demands or boundary conditions. The optional PKI management
operations support less common scenarios and requirements.
Moreover, many details of the Certificate Management Protocol have
been left open or have not been specified in full preciseness. The
profiles specified in Appendices D and E of [RFC4210] define some
more detailed PKI management operations. Yet the specific needs of
highly automated scenarios for machine-to-machine communication are
not covered sufficiently.
Profiling is a way to reduce feature richness and complexity of
standards to what is needed for specific use cases. 3GPP and UNISIG
already use profiling of CMP as a way to cope with these challenges.
To profile means to take advantage of the strengths of the given
protocol while explicitly narrowing down the options it provides to
those needed for the purpose(s) at hand and eliminating all
identified ambiguities. In this way, the general aspects of the
protocol are utilized and only the special requirements of the target
scenarios need to be dealt with using distinct features the protocol
offers.
Defining a profile for a new target environment takes high effort
because the range of available options needs to be well understood
and the selected options need to be consistent with each other and
suitably cover the intended application scenario. Since most
industrial PKI management use cases typically have much in common, it
is worth sharing this effort, which is the aim of this document.
Other standardization bodies can reference this document and further
tailor the PKI management operations to their needs to avoid coming
up with individual profiles from scratch.
1.4. Special Requirements of Industrial and IoT Scenarios
The profiles specified in Appendices D and E of [RFC4210] have been
developed particularly for managing certificates of human end
entities. With the evolution of distributed systems and client-
server architectures, certificates for machines and applications on
them have become widely used. This trend has strengthened even more
in emerging industrial and IoT scenarios. CMP is sufficiently
flexible to support them well.
Today's IT security architectures for industrial solutions typically
use certificates for endpoint authentication within protocols like
IPsec, TLS, or Secure Shell (SSH). Therefore, the security of these
architectures highly relies upon the security and availability of the
implemented certificate management operations.
Due to increasing security and availability needs in operational
technology, especially when used for critical infrastructures and
systems with a high number of certificates, a state-of-the-art
certificate management system must be constantly available and cost-
efficient, which calls for high automation and reliability.
Consequently, "Framework for Improving Critical Infrastructure
Cybersecurity" [NIST.CSWP.04162018] refers to proper processes for
issuance, management, verification, revocation, and audit of
authorized devices, users, and processes involving identity and
credential management. According to commonly accepted best
practices, such PKI management operations are also required in
[IEC.62443-3-3] for security level 2 and higher.
Further challenges in many industrial systems are network
segmentation and asynchronous communication. Also, PKI management
entities like certification authorities (CAs) are not typically
deployed on-site but in a highly protected data center environment,
e.g., operated according to ETSI Policy and security requirements for
Trust Service Providers issuing certificates [ETSI-EN.319411-1].
Certificate management must be able to cope with such network
architectures. CMP offers the required flexibility and
functionality, namely authenticated self-contained messages,
efficient polling, and support for asynchronous message transfer
while retaining end-to-end authentication.
1.5. Existing CMP Profiles
As already stated, [RFC4210] contains profiles with mandatory and
optional PKI management operations in Appendices D and E of
[RFC4210]. Those profiles focus on management of human user
certificates and only partly address the specific needs of
certificate management automation for unattended devices or machine-
to-machine application scenarios.
Both Appendices D and E of [RFC4210] focus on PKI management
operations between an EE and an RA or CA. They do not address
further profiling of RA-to-CA communication, which is typically
needed for full backend automation. All requirements regarding
algorithm support for Appendices D and E of [RFC4210] have been
updated by Section 7.1 of CMP Algorithms [RFC9481].
3GPP makes use of CMP [RFC4210] in its Technical Specification 33.310
[ETSI-3GPP.33.310] for automatic management of IPsec certificates in
3G, LTE, and 5G backbone networks. Since 2010, a dedicated CMP
profile for initial certificate enrollment and certificate update
operations between EEs and RAs/CAs is specified in that document.
In 2015, UNISIG included a CMP profile for enrollment of TLS
certificates in the Subset-137 specifying the ETRAM/ETCS online key
management for train control systems [UNISIG.Subset-137].
Both standardization bodies tailor CMP [RFC4210], CRMF [RFC4211], and
HTTP transfer for CMP [RFC6712] for highly automated and reliable PKI
management operations for unattended devices and services.
1.6. Compatibility with Existing CMP Profiles
The profile specified in this document is compatible with Appendices
D and E of [RFC4210], with the following exceptions:
* signature-based protection is the default protection; an initial
PKI management operation may also use protection based on the
message authentication code (MAC),
* certification of a second key pair within the same PKI management
operation is not supported,
* proof-of-possession (POP) with the self-signature of the certReq
containing the certTemplate (according to [RFC4211], Section 4.1,
clause 3) is the recommended default POP method (deviations are
possible for EEs when requesting central key generation, for RAs
when using raVerified, and if the newly generated keypair is
technically not capable to generate digital signatures),
* confirmation of newly enrolled certificates may be omitted, and
* all PKI management operations consist of request-response message
pairs originating at the EE, i.e., announcement messages
(requiring a push model, a CMP server on the EE) are excluded in
favor of a lightweight implementation on the EE.
The profile specified in this document is compatible with the CMP
profile for 3G, LTE, and 5G network domain security and
authentication framework [ETSI-3GPP.33.310], except that:
* protection of initial PKI management operations may be MAC-based,
* the subject field is mandatory in certificate templates, and
* confirmation of newly enrolled certificates may be omitted.
The profile specified in this document is compatible with the CMP
profile for online key management in rail networks as specified in
[UNISIG.Subset-137], except that:
* A certificate enrollment request message consists of only one
certificate request (CertReqMsg).
* [RFC4210] requires that the messageTime is Greenwich Mean Time
coded as generalizedTime.
Note: As Table 5 of [UNISIG.Subset-137] explicitly states that the
messageTime is required to be "UTC time", it is not clear if this
means a coding as UTCTime or generalizedTime and if time zones
other than Greenwich Mean Time shall be allowed. Both time
formats are described in Section 4.1.2.5 of [RFC5280].
* The same type of protection is required to be used for all
messages of one PKI management operation. This means, in case the
request message protection is MAC-based, the response, certConf,
and pkiConf messages must also have MAC-based protection.
* Use of caPubs is not required but is typically allowed in
combination with MAC-based protected PKI management operations.
On the other hand, Table 12 of [UNISIG.Subset-137] requires using
caPubs.
Note: It remains unclear from UNISIG Subset-137 which
certificate(s) for the caPubs field should be used. For security
reasons, it cannot be used for delivering the root CA certificate
needed to validate the signature-based protection of the given
response message (as stated indirectly also in Section 6.3.1.5.2 b
of [UNISIG.Subset-137]).
* This profile requires that the certConf message have one
CertStatus element where the statusInfo field is recommended.
Note: In contrast, Table 18 of [UNISIG.Subset-137] requires that
the certConf message has one CertStatus element where the
statusInfo field must be absent. This precludes sending a
negative certConf message in case the EE rejects the newly
enrolled certificate. This results in violating the general rule
that a certificate request transaction must include a certConf
message (moreover, since using implicitConfirm is not allowed
there either).
1.7. Use of CMP in SZTP and BRSKI Environments
In Secure Zero Touch Provisioning (SZTP) [RFC8572] and other
environments using Network Configuration Protocol (NETCONF) / YANG
modules, [SZTP-CSR] offers a YANG module that includes several types
of certificate requests to obtain a public key certificate for a
locally generated key pair. Such messages are of the form ietf-ztp-
types:cmp-csr from module ietf-ztp-csr and offer both proof-of-
possession and proof-of-identity. To allow PKI management entities
that use the module ietf-ztp-csr and also wish to comply with this
profile, the ir, cr, kur, or p10cr message MUST be formatted by the
EE as described in Section 4.1, and it MAY be forwarded, as specified
in Section 5.2.
In Bootstrapping Remote Secure Key Infrastructure (BRSKI) [RFC8995]
environments, "BRSKI-AE: Alternative Enrollment Protocols in BRSKI"
[BRSKI-AE] describes a generalization regarding the employed
enrollment protocols to allow alternatives to Enrollment over Secure
Transport (EST) [RFC7030]. For the use of CMP, it requires adherence
to this profile.
1.8. Scope of This Document
On one hand, this profile intends to reduce the flexibility of CMP to
the generic needs of automated certificate management of machine end
entities. On the other hand, it offers a variety of PKI management
operations and options relevant for industrial use cases. Therefore,
it is still a framework that supports further profiling by those
addressing a specific use case or scenario, e.g., 3GPP/ETSI or
UNISIG. There is room to further tailor this profile. This enables
stricter profiling to meet the concrete needs in application areas.
To minimize ambiguity and complexity through needless variety, this
document specifies exhaustive requirements for generating PKI
management messages on the sender side. However, it gives only
minimal requirements on checks by the receiving side and how to
handle error cases.
Especially on the EE side, this profile aims at a lightweight
implementation. This means that the number of PKI management
operation implementations are reduced to a reasonable minimum to
support typical certificate management use cases in industrial
machine-to-machine environments. On the EE side, only limited
resources are expected, while on the side of the PKI management
entities, the profile accepts higher requirements.
For the sake of interoperability and robustness, implementations
should, so long as security is not affected, adhere to Postel's law:
"Be conservative in what you do, be liberal in what you accept from
others" (often reworded as: "Be conservative in what you send, be
liberal in what you receive").
Fields used in ASN.1 syntax in Sections 3, 4, or 5 are specified in
CMP [RFC4210] [RFC9480], CRMF [RFC4211], and CMS [RFC5652] [RFC8933].
When these sections do not explicitly discuss a field, then the field
SHOULD NOT be used by the sending entity. The receiving entity MUST
NOT require the absence of such a field and, if the field is present,
MUST handle it gracefully.
1.9. Structure of This Document
Section 2 introduces the general PKI architecture and approach to
certificate management that is assumed in this document.
Section 3 profiles the generic aspects of the PKI management
operations specified in detail in Sections 4 and 5 to minimize
redundancy in the description and to ease implementation. This
covers the general structure and protection of messages, as well as
generic prerequisites, validation, and error handling.
Section 4 profiles the exchange of CMP messages between an EE and the
PKI management entity. There are various flavors of certificate
enrollment requests, optionally with polling, central key generation,
revocation, and general support PKI management operations.
Section 5 profiles responding to requests, exchanges between PKI
management entities, and operations on behalf of other PKI entities.
This may include delayed delivery of messages, which involves polling
for responses, and nesting of messages.
Section 6 outlines several mechanisms for CMP message transfer,
including HTTP-based transfer [RFC6712] optionally using TLS, CoAP-
based transfer [RFC9482] optionally using DTLS, and offline file-
based transport.
Section 7 defines which parts of the profile are mandatory,
recommended, optional, or not relevant to implement for which type of
entity.
2. Solution Architecture
To facilitate secure automatic certificate enrollment, the device
hosting an EE is typically equipped with a manufacturer-issued device
certificate. Such a certificate is typically installed during
production and is meant to identify the device throughout its
lifetime. This certificate can be used to protect the initial
enrollment of operational certificates after installation of the EE
in its operational environment. In contrast to the manufacturer-
issued device certificate, operational certificates are issued by the
owner or operator of the device to identify the device or one of its
components for operational use, e.g., in a security protocol like
IPsec, TLS, or SSH. In IEEE 802.1AR [IEEE.802.1AR_2018], a
manufacturer-issued device certificate is called an Initial Device
Identifier (IDevID) certificate and an operational certificate is
called a Locally Significant Device Identifier (LDevID) certificate.
Note: The owner or operator using the manufacturer-issued device
certificate for authenticating the device during initial enrollment
of operational certificates MUST trust the respective trust anchor
provided by the manufacturer.
Note: According to IEEE 802.1AR [IEEE.802.1AR_2018], a DevID
comprises the triple of the certificate, the corresponding private
key, and the certificate chain.
All certificate management operations specified in this document
follow the pull model, i.e., they are initiated by an EE (or by an RA
acting as an EE). The EE creates a CMP request message, protects it
using some asymmetric credential or shared secret information, and
sends it to a PKI management entity. This PKI management entity may
be a CA or more typically an RA, which checks the request and
responds to it itself or forwards the request upstream to the next
PKI management entity. In case an RA changes the CMP request message
header or body or wants to demonstrate successful verification or
authorization, it can apply a protection of its own. The
communication between an LRA and RA can be performed synchronously or
asynchronously. Asynchronous communication typically leads to
delayed message delivery as described in Section 4.4.
+-----+ +-----+ +-----+ +-----+
| | | | | | | |
| EE |<---------->| LRA |<-------------->| RA |<---------->| CA |
| | | | | | | |
+-----+ +-----+ +-----+ +-----+
synchronous (a)synchronous (a)synchronous
+----connection----+------connection------+----connection----+
operators service partner
+---------on site---------+---back-end services--+---trust center--+
<--- downstream <--- | ---> upstream --->
Figure 1: Certificate Management Architecture Example
In operational environments, the certificate management architecture
can have multiple LRAs bundling requests from multiple EEs at
dedicated locations and one (or more than one) central RA aggregating
the requests from the LRAs. Every LRA in this scenario has shared
secret information (one per EE) for MAC-based protection or a CMP
protection key and certificate, allowing it to protect CMP messages
it processes using its own credentials. The figure above shows an
architectural example with one LRA, RA, and CA. It is also possible
not to have an RA or LRA or that there is no CA with a CMP interface.
Depending on the network infrastructure, the message transfer between
PKI management entities may be based on synchronous online
connections, asynchronous connections, or even offline (e.g., file-
based) transfer.
Note: In contrast to the pull model used in this document, other
specifications could use the messages specified in this document to
implement the push model. In this case, the EE is pushed (triggered)
by the PKI management entity to provide the CMP request; therefore,
the EE acts as the receiver, not initiating the interaction with the
PKI. For example, when the device itself only acts (as a server as
described in BRSKI with Pledge in Responder Mode [BRSKI-PRM]),
support of certificate enrollment in a push model is needed. While
BRSKI-PRM currently utilizes its own format for the exchanges, CMP in
general and the messages specified in this profile offer all required
capabilities. Nevertheless, the message flow and state machine as
described in Section 4 must be adapted to implement a push model.
Note: Third-party CAs not conforming to this document may implement
other variants of CMP, different standardized protocols, or even
proprietary interfaces for certificate management. In such cases, an
RA needs to adapt the exchanged CMP messages to the flavor of
certificate management interaction required by such a nonconformant
CA.
3. Generic Aspects of PKI Messages and PKI Management Operations
This section covers the generic aspects of the PKI management
operations specified in Sections 4 and 5 as upfront general
requirements to minimize redundancy in the description and to ease
implementation.
As described in Section 5.1 of [RFC4210], all CMP messages have the
following general structure:
+--------------------------------------------+
| PKIMessage |
| +----------------------------------------+ |
| | header | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | body | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | protection (OPTIONAL) | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | extraCerts (OPTIONAL) | |
| +----------------------------------------+ |
+--------------------------------------------+
Figure 2: CMP Message Structure
The general contents of the message header, protection, and
extraCerts fields are specified in the following three subsections.
In case a specific PKI management operation needs different contents
in the header, protection, or extraCerts fields, the differences are
described in the respective subsections of Sections 4 and 5.
The CMP message body contains the PKI management operation-specific
information. It is described in Sections 4 and 5.
Note: In the description of CMP messages, the presence of some fields
is stated as OPTIONAL or RECOMMENDED. The following text that states
requirements on such a field applies only if the field is present.
The generic prerequisites needed by the PKI entities in order to
perform PKI management operations are described in Section 3.4.
The generic validation steps to be performed by PKI entities upon
receiving a CMP message are described in Section 3.5.
The generic aspects of handling and reporting errors are described in
Section 3.6.
3.1. General Description of the CMP Message Header
This section describes the generic header fields of all CMP messages.
Any fields or variations specific to PKI management operation are
described in Sections 4 and 5.
header
pvno REQUIRED
-- MUST be 3 to indicate CMP v3 in all cases where EnvelopedData
-- is supported and expected to be used in the current
-- PKI management operation
-- MUST be 3 to indicate CMP v3 in certConf messages when using
-- the hashAlg field
-- MUST be 2 to indicate CMP v2 in all other cases
-- For details on version negotiation, see [RFC9480]
sender REQUIRED
-- Contains a name representing the originator, which also
-- protects the message
-- For signature-based protection, MUST be the subject field of
-- the CMP protection certificate
-- For MAC-based protection, MUST contain a name the PKI
-- management entity can use to identify the shared secret
-- information. This name MUST be placed in the commonName
-- field of the directoryName choice.
-- In a multihop scenario, the receiving entity cannot rely
-- on the correctness of the sender field.
recipient REQUIRED
-- SHOULD be the name of the intended recipient; otherwise, the
-- NULL-DN MUST be used
-- In the first message of a PKI management operation, SHOULD be
-- the subject DN of the CA the PKI management operation is
-- requested from
-- In all other messages, SHOULD contain the value of the sender
-- field of the previous message in the same PKI management
-- operation
-- The recipient field shall be handled gracefully by the
-- receiving entity, because in a multihop scenario, its
-- correctness cannot be guaranteed.
messageTime OPTIONAL
-- MUST be present if the confirmWaitTime field is present
-- MUST be the time at which the message was produced, if present
-- MAY be set by a PKI management entity to provide the current
-- time
-- MAY be used by the end entity for time synchronization if the
-- response was received within a short time frame
protectionAlg REQUIRED
-- MUST be an algorithm identifier indicating the algorithm
-- used for calculating the protection bits
-- If it is a signature algorithm, its type MUST be
-- MSG_SIG_ALG as specified in Section 3 of [RFC9481] and
-- MUST be consistent with the subjectPublicKeyInfo field of
-- the CMP protection certificate
-- If it is a MAC algorithm, its type MUST be MSG_MAC_ALG, as
-- specified in [RFC9481], Section 6.1
senderKID RECOMMENDED
-- For signature-based protection, MUST be used and contain the
-- value of the SubjectKeyIdentifier if present in the CMP
-- protection certificate
-- For MAC-based protection, MUST be used and contain the same
-- name as in the commonName field of the sender field
transactionID REQUIRED
-- In the first message of a PKI management operation, MUST be
-- 128 bits of random data to minimize the probability of
-- having the transactionID already in use at the server
-- In all other messages, MUST be the value from the previous
-- message in the same PKI management operation
senderNonce REQUIRED
-- MUST be cryptographically secure and fresh 128 random bits
recipNonce RECOMMENDED
-- If this is the first message of a transaction, MUST be absent
-- If this is a delayed response message, MUST be present and
-- contain the value of the senderNonce of the respective
-- request message in the same transaction
-- In all other messages, MUST be present and contain the value
-- of the senderNonce of the previous message in the same
-- transaction
generalInfo OPTIONAL
implicitConfirm OPTIONAL
-- RECOMMENDED in ir/cr/kur/p10cr messages,
-- OPTIONAL in ip/cp/kup response messages, and
-- PROHIBITED in other types of messages
-- Added to request messages to request omission of the certConf
-- message
-- Added to response messages to grant omission of the certConf
-- message
-- See [RFC4210], Section 5.1.1.1.
ImplicitConfirmValue REQUIRED
-- ImplicitConfirmValue MUST be NULL
confirmWaitTime OPTIONAL
-- RECOMMENDED in ip/cp/kup messages if implicitConfirm is
-- not included
-- PROHIBITED if implicitConfirm is included
-- See [RFC4210], Section 5.1.1.2.
ConfirmWaitTimeValue REQUIRED
-- ConfirmWaitTimeValue MUST be a GeneralizedTime value
-- specifying the point in time up to which the PKI management
-- entity will wait for the certConf message. The accepted
-- length of the waiting period will vary by use case.
certProfile OPTIONAL
-- MAY be present in ir/cr/kur/p10cr and in genm messages of type
-- id-it-certReqTemplate
-- MUST be omitted in all other messages
-- See [RFC9480].
CertProfileValue REQUIRED
-- MUST contain a sequence of one UTF8String element
-- MUST contain the name of a certificate profile
3.2. General Description of the CMP Message Protection
This section describes the generic protection field contents of all
CMP messages. For signature-based protection, which is the default
protection mechanism for all CMP messages described in this profile,
the CMP protection key and CMP protection certificate are used. For
MAC-based protection, shared secret information is used as described
in Section 4.1.5.
protection
-- If present, the same kind of protection MUST be used for all
-- messages of that PKI management operation.
-- MUST be present, except if protection is not possible for
-- error messages as described in Section 3.6.4
-- For signature-based protection, MUST contain the signature
-- calculated using the CMP protection key of the entity
-- protecting the message
-- For MAC-based protection, MUST contain a MAC calculated using
-- the shared secret information
-- The protection algorithm used MUST be given in the
-- protectionAlg field.
The CMP message protection provides, if available, message origin
authentication and integrity protection for the header and body. The
CMP message extraCerts field is not covered by this protection.
Note: The extended key usages described in Section 2.2 of CMP Updates
[RFC9480] can be used for authorization of a sending PKI management
entity.
3.3. General Description of CMP Message ExtraCerts
This section describes the generic extraCerts field of all CMP
messages. Any specific requirements on the extraCerts are specified
in the respective PKI management operation.
extraCerts
-- MUST be present for signature-based protection and contain the
-- CMP protection certificate together with its chain for the
-- first request and response message of a PKI management
-- operation. MAY be omitted in certConf, PKIConf, pollReq,
-- and pollRep messages. The first certificate in this field
-- MUST be the CMP protection certificate followed by its
-- chain, where each element should directly certify the one
-- immediately preceding it.
-- MUST be present in ip, cp, and kup messages and contain the
-- chain of a newly issued certificate.
-- Self-signed certificates should be omitted from extraCerts and
-- MUST NOT be trusted based on their inclusion in any case
Note: One reason for adding a self-signed certificate to extraCerts
is if it is the CMP protection certificate or a successor root CA
self-signed certificate as indicated in the HashOfRootKey extension
of the current root CA certificate; see [RFC8649]. Another reason
for including self-signed certificates in the extraCerts is, for
instance, due to storage limitations. A receiving PKI entity may not
have the complete trust anchor information available but just a
unique identification of it and thus needs the full trust anchor
information carried in a self-signed certificate for further
processing (see Section 9).
For maximum interoperability, all implementations SHOULD be prepared
to handle potentially additional certificates and arbitrary orderings
of the certificates.
3.4. Generic PKI Management Operation Prerequisites
This subsection describes what is generally needed by the PKI
entities to be able to perform PKI management operations.
Identification of PKI entities:
* For signature-based protection, each EE knows its own identity
from the CMP protection certificate; for MAC-based protection, it
MAY know its identity to fill the sender field.
* Each EE MAY know the intended recipient of its requests to fill
the recipient field, e.g., the name of the addressed CA.
Note: This name may be established using an enrollment voucher (as
described in [RFC8366]), the issuer field from a CertReqTemplate
response message content, or by other configuration means.
Routing of CMP messages:
* Each PKI entity sending messages upstream MUST know the address
needed for transferring messages to the next PKI management entity
in case online transfer is used.
Note: This address may depend on the recipient, the certificate
profile, and the used transfer mechanism.
Authentication of PKI entities:
* Each PKI entity MUST have credentials to authenticate itself. For
signature-based protection, it MUST have a private key and the
corresponding certificate along with its chain.
* Each PKI entity MUST be able to establish trust in the PKI it
receives responses from. When signature-based protection is used,
it MUST have the trust anchor(s) and any certificate status
information needed to perform path validation of CMP protection
certificates used for signature-based protection.
Note: A trust anchor is usually a root certificate of the PKI
addressed by the requesting EE. It may be established by
configuration or in an out-of-band manner. For an EE, it may be
established using an enrollment voucher [RFC8366] or in-band of
CMP by the caPubs field in a certificate response message.
Authorization of PKI management operations:
* Each EE or RA MUST have sufficient information to be able to
authorize the PKI management entity to perform the upstream PKI
management operation.
Note: This may be achieved, for example, by using the cmcRA
extended key usage in server certificates, by local configuration
(such as specific name patterns for subject Distinguished Name
(DN) or Subject Alternative Name (SAN) portions that may identify
an RA) and/or by having a dedicated root CA usable only for
authenticating PKI management entities.
* Each PKI management entity MUST have sufficient information to be
able to authorize the downstream PKI entity requesting the PKI
management operation.
Note: For authorizing an RA, the same examples apply as above.
The authorization of EEs can be very specific to the application
domain based on local PKI policy.
3.5. Generic Validation of a PKI Message
This section describes generic validation steps of each PKI entity
receiving a PKI request or response message before any further
processing or forwarding. If a PKI management entity decides to
terminate a PKI management operation because a check failed, it MUST
send a negative response or an error message as described in
Section 3.6. The PKIFailureInfo bits given below in parentheses MAY
be used in the failInfo field of the PKIStatusInfo as described in
Section 3.6.4; also see Appendix F of [RFC4210].
All PKI message header fields not mentioned in this section, like the
recipient and generalInfo fields, SHOULD be handled gracefully upon
receipt.
The following list describes the basic set of message input
validation steps. Without these checks, the protocol becomes
dysfunctional.
* The formal ASN.1 syntax of the whole message MUST be compliant
with the definitions given in CMP [RFC4210] [RFC9480], CRMF
[RFC4211], and CMS [RFC5652] [RFC8933]. (failInfo: badDataFormat)
* The pvno MUST be cmp2000(2) or cmp2021(3). (failInfo bit:
unsupportedVersion)
* The transactionID MUST be present. (failInfo bit: badDataFormat)
* The PKI message body type MUST be one of the message types
supported by the receiving PKI entity and MUST be allowed in the
current state of the PKI management operation identified by the
given transactionID. (failInfo bit: badRequest)
The following list describes the set of message input validation
steps required to ensure secure protocol operation:
* The senderNonce MUST be present and MUST contain at least 128 bits
of data. (failInfo bit: badSenderNonce)
* Unless the PKI message is the first message of a PKI management
operation,
- the recipNonce MUST be present and MUST equal the senderNonce
of the previous message or equal the senderNonce of the most
recent request message for which the response was delayed, in
case of delayed delivery as specified in Section 4.4. (failInfo
bit: badRecipientNonce)
* Messages without protection MUST be rejected except for error
messages as described in Section 3.6.4.
* The message protection MUST be validated when present, and
messages with an invalid protection MUST be rejected.
- The protection MUST be signature-based except if MAC-based
protection is used as described in Sections 4.1.5 and 4.1.6.3.
(failInfo bit: wrongIntegrity)
- If present, the senderKID MUST identify the key material needed
for verifying the message protection. (failInfo bit:
badMessageCheck)
- If signature-based protection is used, the CMP protection
certificate MUST be successfully validated, including path
validation using a trust anchor, and MUST be authorized
according to local policies. If the keyUsage extension is
present in the CMP protection certificate, the digitalSignature
bit MUST be set. (failInfo bit: badAlg, badMessageCheck, or
signerNotTrusted)
- The sender of a request message MUST be authorized to request
the operation according to PKI policies. (failInfo bit:
notAuthorized)
Note: The requirements for checking certificates given in [RFC5280]
MUST be followed for signature-based CMP message protection. Unless
the message is a positive ip/cp/kup, where the issuing CA certificate
of the newly enrolled certificate is the same as the CMP protection
certificate of that message, certificate status checking SHOULD be
performed on the CMP protection certificates. If the response
message contains the caPubs field to transfer new trust anchor
information, the CMP protection is crucial and certificate status
checking is REQUIRED. For other cases, it MAY be acceptable to omit
certificate status checking when respective information is not
available.
Depending on local policies, one or more of the input validation
checks described below need to be implemented:
* If signature-based protection is used, the sender field MUST match
the subject of the CMP protection certificate. (failInfo bit:
badMessageCheck)
* If the messageTime is present and
- the receiving system has a reliable system time, the
messageTime MUST be close to the current time of the receiving
system, where the threshold will vary by use case. (failInfo
bit: badTime)
- the receiving system does not have a reliable system time, the
messageTime MAY be used for time synchronization.
3.6. Error Handling
This section describes how a PKI entity handles error conditions on
messages it receives. Each error condition should be logged
appropriately to allow root-cause analysis of failure cases.
3.6.1. Reporting Error Conditions Upstream
An EE SHALL NOT send error messages. PKI management entities SHALL
NOT send error messages in the upstream direction either.
In case an EE rejects a newly issued certificate contained in an ip,
cp, or kup message and implicit confirmation has not been granted,
the EE MUST report this using a certConf message with "rejection"
status and await the pkiConf response as described in Section 4.1.1.
On all other error conditions regarding response messages, the EE or
PKI management entity MUST regard the current PKI management
operation as terminated with failure. The error conditions include:
* invalid response message header, body type, protection, or
extraCerts, according to the checks described in Section 3.5,
* any issue detected with response message contents,
* receipt of an error message from upstream,
* timeout occurred while waiting for a response, and
* rejection of a newly issued certificate while implicit
confirmation has been granted.
Upstream PKI management entities will not receive any CMP message to
learn that the PKI management operation has been terminated. In case
they expect a further message from the EE, a connection interruption
or timeout will occur. The value set for such timeouts will vary by
use case. Then they MUST also regard the current PKI management
operation as terminated with failure and MUST NOT attempt to send an
error message downstream.
3.6.2. Reporting Error Conditions Downstream
In case the PKI management entity detects an error condition, e.g.,
rejecting the request due to policy decision, in the body of an ir,
cr, p10cr, kur, or rr message received from downstream, it MUST
report the error in the specific response message, i.e., an ip, cp,
kup, or rp with "rejection" status, as described in Sections 4.1.1
and 4.2. This can also happen in case of polling.
In case the PKI management entity detects any other error condition
on requests (including pollReq, certConf, genm, and nested messages)
received from downstream and on responses received from upstream
(such as invalid message header, body type, protection, or
extraCerts, according to the checks described in Section 3.5), it
MUST report them downstream in the form of an error message as
described in Section 3.6.4.
3.6.3. Handling Error Conditions on Nested Messages Used for Batching
Batching of messages using nested messages as described in
Section 5.2.2.2 requires special error handling.
If the error condition is on an upstream nested message containing
batched requests, it MUST NOT attempt to respond to the individual
requests included in it but to the nested message itself.
In case a PKI management entity receives an error message in response
to a nested message, it must propagate the error by responding with
an error message to each of the request messages contained in the
nested message.
In case a PKI management entity detects an error condition on the
downstream nested message received in response to a nested message
sent before and the body of the received nested message still parses,
it MAY ignore this error condition and handle the included responses
as described in Section 5.2.2.2. Otherwise, it MUST propagate the
error by responding with an error message to each of the requests
contained in the nested message it sent originally.
3.6.4. PKIStatusInfo and Error Messages
When sending any kind of negative response, including error messages,
a PKI entity MUST indicate the error condition in the PKIStatusInfo
structure of the respective message as described below. Then it MUST
regard the current PKI management operation as terminated with
failure.
The PKIStatusInfo structure is used to report errors. It may be part
of various message types, in particular, ip, cp, kup, certConf, and
error. The PKIStatusInfo structure consists of the following fields:
status: Here, the PKIStatus value "rejection" MUST be used in case
an error was detected. When a PKI management entity indicates
delayed delivery of a CMP response message to the EE with an error
message as described in Section 4.4, the status "waiting" MUST be
used there.
statusString: Here, any human-readable valid value for logging or to
display via a user interface should be added.
failInfo: Here, the PKIFailureInfo bits MAY be used in the way
explained in Appendix F of [RFC4210]. PKIFailureInfo bits
regarding the validation described in Section 3.5 are referenced
there. The PKIFailureInfo bits referenced in Sections 5.1 and 6
are described here:
badCertId: A kur, certConf, or rr message references an unknown
certificate.
badPOP: An ir/cr/kur/p10cr contains an invalid proof-of-
possession.
certRevoked: Revocation is requested for a certificate that is
already revoked.
badCertTemplate: The contents of a certificate request are not
accepted, e.g., a field is missing or has an unacceptable value
or the given public key is already in use in some other
certificate (depending on policy).
transactionIdInUse: This is sent by a PKI management entity in
case the received request contains a transactionID that is
currently in use for another transaction. An EE receiving such
an error message should resend the request in a new transaction
using a different transactionID.
notAuthorized: The sender of a request message is not authorized
for requesting the operation.
systemUnavail: This is sent by a PKI management entity in case a
back-end system is not available.
systemFailure: This is sent by a PKI management entity in case a
back-end system is currently not functioning correctly.
An EE receiving a systemUnavail or systemFailure failInfo should
resend the request in a new transaction after some time.
Detailed Message Description:
Error Message -- error
Field Value
header
-- As described in Section 3.1
body
-- The message indicating the error that occurred
error REQUIRED
pKIStatusInfo REQUIRED
status REQUIRED
-- MUST have the value "rejection"
statusString OPTIONAL
-- This field should contain any human-readable text for
-- debugging, for logging, or to display in a GUI
failInfo OPTIONAL
-- MAY be present and contain the relevant PKIFailureInfo bits
protection RECOMMENDED
-- As described in Section 3.2
extraCerts RECOMMENDED
-- As described in Section 3.3
Protecting the error message may not be technically feasible if it is
not clear which credential the recipient will be able to use when
validating this protection, e.g., in case the request message was
fundamentally broken. In these exceptional cases, the protection of
the error message MAY be omitted.
4. PKI Management Operations
This section focuses on the communication of an EE with the PKI
management entity it directly talks to. Depending on the network and
PKI solution, this can be an RA or directly a CA. Handling of a
message by a PKI management entity is described in Section 5.
The PKI management operations specified in this section cover the
following:
* requesting a certificate with variations like initial enrollment,
certificate updates, central key generation, and MAC-based
protection
* revoking a certificate
* support messages
* polling for delayed response messages
These operations mainly specify the message body of the CMP messages
and utilize the specification of the message header, protection, and
extraCerts, as specified in Section 3. The messages are named by the
respective field names in PKIBody, like ir, ip, cr, cp, etc.; see
Section 5.1.2 of [RFC4210].
The following diagram shows the EE state machine covering all PKI
management operations described in this section, including negative
responses, error messages described in Section 3.6.4, ip/cp/kup/error
messages with status "waiting", and pollReq and pollRep messages as
described in Section 4.4.
On receiving messages from upstream, the EE MUST perform the general
validation checks described in Section 3.5. In case an error occurs,
the behavior is described in Section 3.6.
End Entity State Machine:
start
|
| send ir/cr/kur/p10cr/rr/genm
v
waiting for response
v
+--------------------------+--------------------------+
| | |
| receives ip/cp/kup with | received ip/cp/kup/error | received
| status "accepted" or | with status "waiting" | rp/genp or
| "grantedWithMods" | | ip/cp/kup/
| v | error
| +-------> polling | with status
| | | | "rejection"
| | received | send |
| | pollRep | pollReq |
| | v |
| | waiting for response |
| | v |
| +------------+--------+ |
| | | |
| received ip/cp/kup | | received |
| with status "accepted" | | rp/genp or |
| or "grantedWithMods" | | ip/cp/kup/error |
| | | with status |
+---------->+<-------------+ | "rejection" |
v | |
+-----------+-----+ | |
| | | |
| implicitConfirm | implicitConfirm | |
| granted | not granted | |
| | | |
| | send certConf | |
| v | |
| waiting for pkiConf*) | |
| | | |
| | received | |
| v pkiConf v |
+---------------->+------->+<-------+<----------------+
|
v
end
*) In case of a delayed delivery of pkiConf responses, the same
polling mechanism is initiated as for rp or genp messages by
sending an error message with status "waiting".
Note: All CMP messages belonging to the same PKI management operation
MUST have the same transactionID because the message receiver
identifies the elements of the operation in this way.
This section is aligned with CMP [RFC4210], CMP Updates [RFC9480],
and CMP Algorithms [RFC9481].
Guidelines as well as an algorithm use profile for this document are
available in CMP Algorithms [RFC9481].
4.1. Enrolling End Entities
There are various approaches for requesting a certificate from a PKI.
These approaches differ in the way the EE authenticates itself to the
PKI, in the form of the request being used, and how the key pair to
be certified is generated. The authentication mechanisms may be as
follows:
* using a certificate from an external PKI, e.g., a manufacturer-
issued device certificate, and the corresponding private key
* using a private key and certificate issued from the same PKI that
is addressed for requesting a certificate
* using the certificate to be updated and the corresponding private
key
* using shared secret information known to the EE and the PKI
management entity
An EE requests a certificate indirectly or directly from a CA. When
the PKI management entity handles the request as described in
Section 5.1.1 and responds with a message containing the requested
certificate, the EE MUST reply with a confirmation message unless
implicitConfirm was granted. The PKI management entity MUST then
handle it as described in Section 5.1.2 and respond with a
confirmation, closing the PKI management operation.
The message sequences described in this section allow the EE to
request certification of a locally or centrally generated public-
private key pair. The public key and the subject name identifying
the EE MUST be present in the certTemplate of the certificate request
message.
Note: If the EE does not know for which subject name to request the
certificate, it can use the subject name from the CMP protection
certificate in case of signature-based protection or the identifier
of the shared secret in case of MAC-based protection.
Typically, the EE provides a signature-based proof-of-possession of
the private key associated with the public key contained in the
certificate request, as defined by [RFC4211], Section 4.1, clause 3.
To this end, it is assumed that the private key can technically be
used for signing. This is the case for the most common algorithms
RSA, ECDSA, and EdDSA, regardless of potentially intended
restrictions of the key usage.
Note: Section 4 of [RFC4211] allows for providing proof-of-possession
using any method that a key can be used for. In conformance with
Section 8.1.5.1.1.2 of [NIST.SP.800-57p1r5], the newly generated
private key may be used for self-signature, if technically possible,
even if the keyUsage extension requested in the certificate request
prohibits generation of digital signatures.
The requesting EE provides the binding of the proof-of-possession to
its identity by signature-based or MAC-based protection of the CMP
request message containing that POP. An upstream PKI management
entity should verify whether this EE is authorized to obtain a
certificate with the requested subject and other fields and
extensions.
The proof-of-possession is provided by signing the certReq containing
the certTemplate with the subject name and public key. To bind this
proof-of-possession to the proof-of-identity of the requesting EE,
the subject name in the certTemplate needs to identify the same
entity as the subject name in the CMP protection certificate or match
the identifier used with MAC-based protection.
Note: This binding may be lost if a PKI management entity reprotects
this request message.
The EE MAY indicate the certificate profile to use in the certProfile
extension of the generalInfo field in the PKIHeader of the
certificate request message as described in Section 3.1.
In case the EE receives a CA certificate in the caPubs field for
installation as a new trust anchor, it MUST properly authenticate the
message and authorize the sender as a trusted source of the new trust
anchor. This authorization is typically indicated using shared
secret information for protecting an Initialization Response (ip)
message. Authorization can also be signature-based, using a
certificate issued by another PKI that is explicitly authorized for
this purpose. A certificate received in caPubs MUST NOT be accepted
as a trust anchor if it is the root CA certificate of the certificate
used for protecting the message.
4.1.1. Enrolling an End Entity to a New PKI
This PKI management operation should be used by an EE to request a
certificate from a new PKI using an existing certificate from an
external PKI, e.g., a manufacturer-issued IDevID certificate
[IEEE.802.1AR_2018], to authenticate itself to the new PKI.
Note: In Bootstrapping Remote Secure Key Infrastructure (BRSKI)
[RFC8995] environments, "BRSKI-AE: Alternative Enrollment Protocols
in BRSKI" [BRSKI-AE] describes a generalization regarding enrollment
protocols alternative to EST [RFC7030]. As replacement of EST
simpleenroll, BRSKI-AE uses this PKI management operation for
bootstrapping LDevID certificates.
Specific prerequisites augmenting the prerequisites in Section 3.4
are as follows:
* The certificate of the EE MUST have been enrolled by an external
PKI, e.g., a manufacturer-issued device certificate.
* The PKI management entity MUST have the trust anchor of the
external PKI.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
Message Flow:
Step# EE PKI management entity
1 format ir
2 -> ir ->
3 handle or
forward ir
4 format or receive ip
5 possibly grant
implicitConfirm
6 <- ip <-
7 handle ip
----------------- if implicitConfirm not granted -----------------
8 format certConf
9 -> certConf ->
10 handle or
forward certConf
11 format or receive pkiConf
12 <- pkiConf <-
13 handle pkiConf
For this PKI management operation, the EE MUST include a sequence of
one CertReqMsg in the ir. If more certificates are required, further
requests MUST be sent using separate PKI management operations.
The EE MUST include the generalInfo field implicitConfirm in the
header of the ir message as described in Section 3.1, unless it
requires certificate confirmation. This leaves the PKI management
entities the choice of whether or not the EE must send a certConf
message upon receiving a new certificate. Depending on the PKI
policy and requirements for managing EE certificates, it can be
important for PKI management entities to learn if the EE accepted the
new certificate. In such cases, when responding with an ip message,
the PKI management entity MUST NOT include the implicitConfirm
extension. In case the EE included the generalInfo field
implicitConfirm in the request message and the PKI management entity
does not need any explicit confirmation from the EE, the PKI
management entity MUST include the generalInfo field implicitConfirm
in the response message. This prevents explicit certificate
confirmation and saves the overhead of a further message round trip.
Otherwise, the PKI management entity SHOULD include confirmWaitTime
as described in Section 3.1.
If the EE did not request implicit confirmation or implicit
confirmation was not granted by the PKI management entity,
certificate confirmation MUST be performed as follows. If the EE
successfully received the certificate, it MUST send a certConf
message in due time. On receiving a valid certConf message, the PKI
management entity MUST respond with a pkiConf message. If the PKI
management entity does not receive the expected certConf message in
time, it MUST handle this like a rejection by the EE. In case of
rejection, depending on its policy, the PKI management entity MAY
revoke the newly issued certificate, notify a monitoring system, or
log the event internally.
Note: Depending on PKI policy, a new certificate may be published by
a PKI management entity, and explicit confirmation may be required.
In this case, it is advisable not to do the publication until a
positive certificate confirmation has been received. This way, the
need to revoke the certificate on negative confirmation can be
avoided.
If the certificate request was rejected by the CA, the PKI management
entity MUST return an ip message containing the status code
"rejection" as described in Section 3.6, and the certifiedKeyPair
field SHALL be omitted. The EE MUST NOT react to such an ip message
with a certConf message, and the PKI management operation MUST be
terminated.
Detailed Message Description:
Initialization Request -- ir
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE for a new certificate
ir REQUIRED
-- MUST contain a sequence of one CertReqMsg
-- If more certificates are required, further PKI management
-- operations needs to be initiated
certReq REQUIRED
certReqId REQUIRED
-- MUST be 0
certTemplate REQUIRED
version OPTIONAL
-- MUST be 2 if supplied
subject REQUIRED
-- The EE's identity MUST be carried in the subject field
-- and/or the subjectAltName extension.
-- If subject name is present only in the subjectAltName
-- extension, then the subject field MUST be NULL-DN
publicKey OPTIONAL
-- MUST be present if local key generation is used
-- MAY be absent if central key generation is requested
algorithm OPTIONAL
-- MUST be present if local key generation is used and MUST
-- include the subject public key algorithm identifier
-- MAY be present if central key generation is requested and,
-- if present, informs the KGA of algorithm and parameter
-- preferences regarding the to-be-generated key pair
subjectPublicKey REQUIRED
-- MUST contain the public key to be certified in case of local
-- key generation
-- MUST be a zero-length BIT STRING if central key generation
-- is requested
extensions OPTIONAL
-- MAY include end-entity-specific X.509 extensions of the
-- requested certificate, like subject alternative name, key
-- usage, and extended key usage
-- The subjectAltName extension MUST be present if the EE subject
-- name includes a subject alternative name.
popo OPTIONAL
-- MUST be present if local key generation is used
-- MUST be absent if central key generation is requested
signature OPTIONAL
-- MUST be used by an EE if the key can be used for signing, and
-- if used, it MUST have the type POPOSigningKey
poposkInput PROHIBITED
-- MUST NOT be used; it is not needed because subject and
-- publicKey are both present in the certTemplate
algorithmIdentifier REQUIRED
-- The signature algorithm MUST be consistent with the publicKey
-- algorithm field of the certTemplate
signature REQUIRED
-- MUST contain the signature value computed over the DER-encoded
-- certReq
raVerified OPTIONAL
-- MAY be used by an RA after verifying the proof-of-possession
-- provided by the EE
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
Initialization Response -- ip
Field Value
header
-- As described in Section 3.1
body
-- The response of the CA to the request as appropriate
ip REQUIRED
caPubs OPTIONAL
-- MAY be used if the certifiedKeyPair field is present
-- If used, it MUST contain only a trust anchor, e.g., root
-- certificate, of the certificate contained in certOrEncCert
response REQUIRED
-- MUST contain a sequence of one CertResponse
certReqId REQUIRED
-- MUST be 0
status REQUIRED
-- PKIStatusInfo structure MUST be present
status REQUIRED
-- positive values allowed: "accepted", "grantedWithMods"
-- negative values allowed: "rejection"
-- "waiting" only allowed with a polling use case as described
-- in Section 4.4
statusString OPTIONAL
-- MAY be any human-readable text for debugging, for logging, or
-- to display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if status is "accepted" or "grantedWithMods"
certifiedKeyPair OPTIONAL
-- MUST be present if status is "accepted" or "grantedWithMods"
-- MUST be absent if status is "rejection"
certOrEncCert REQUIRED
-- MUST be present if status is "accepted" or "grantedWithMods"
certificate REQUIRED
-- MUST be present when certifiedKeyPair is present
-- MUST contain the newly enrolled X.509 certificate
privateKey OPTIONAL
-- MUST be absent in case of local key generation or "rejection"
-- MUST contain the encrypted private key in an EnvelopedData
-- structure as specified in Section 4.1.6 in case the
-- private key was generated centrally
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
-- MUST contain the chain of the certificate present in
-- certOrEncCert
-- Duplicate certificates MAY be omitted
Certificate Confirmation -- certConf
Field Value
header
-- As described in Section 3.1
body
-- The message of the EE sends a confirmation to the PKI
-- management entity to accept or reject the issued
-- certificates
certConf REQUIRED
-- MUST contain a sequence of one CertStatus
CertStatus REQUIRED
certHash REQUIRED
-- The hash algorithm to use MUST be the hash algorithm indicated
-- in the below hashAlg field. If the hashAlg field is not
-- set, it MUST be the hash algorithm defined by the algorithm
-- identifier of the certificate signature or the dedicated
-- hash algorithm defined in [RFC9481] for the used certificate
-- signature algorithm.
certReqId REQUIRED
-- MUST be 0
statusInfo OPTIONAL
-- PKIStatusInfo structure should be present
-- Omission indicates acceptance of the indicated certificate
status REQUIRED
-- positive values allowed: "accepted"
-- negative values allowed: "rejection"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, for logging, or
-- to display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if status is "accepted"
hashAlg OPTIONAL
-- The hash algorithm to use for calculating the above certHash
-- If used, the pvno field in the header MUST be cmp2021 (3).
-- For backward compatibility, use of this field is
-- NOT RECOMMENDED if the hash algorithm to use can be
-- identified by other means; see above.
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first request message
-- of this PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and the PKI
-- management entity caches the CMP protection certificate from
-- the first request message of this PKI management operation
PKI Confirmation -- pkiConf
Field Value
header
-- As described in Section 3.1
body
pkiconf REQUIRED
-- The content of this field MUST be NULL
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first response
-- message of this PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and the EE has
-- cached the CMP protection certificate from the first
-- response message of this PKI management operation
4.1.2. Enrolling an End Entity to a Known PKI
This PKI management operation should be used by an EE to request an
additional certificate of the same PKI it already has certificates
from. The EE uses one of these existing certificates to authenticate
itself by signing its request messages using the respective private
key.
Specific prerequisites augmenting the prerequisites in Section 3.4
are as follows:
* The certificate used by the EE MUST have been enrolled by the PKI
it requests another certificate from.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1, with the following changes:
1. The body of the first request and response SHOULD be cr and cp.
Otherwise, ir and ip MUST be used.
Note: Since the difference between ir/ip and cr/cp is
syntactically not essential, an ir/ip may be used in this PKI
management operation.
2. The caPubs field in the certificate response message MUST be
absent.
4.1.3. Updating a Valid Certificate
This PKI management operation should be used by an EE to request an
update for one of its certificates that is still valid. The EE uses
the certificate it wishes to update as the CMP protection
certificate. Both for authenticating itself and for proving
ownership of the certificate to be updated, it signs the request
messages with the corresponding private key.
Specific prerequisites augmenting the prerequisites in Section 3.4
are as follows:
* The certificate the EE wishes to update MUST NOT be expired or
revoked and MUST have been issued by the addressed CA.
* A new public-private key pair should be used.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1, with the following changes:
1. The body of the first request and response MUST be kur and kup,
respectively.
2. Protection of the kur MUST be performed using the certificate to
be updated.
3. The subject field and/or the subjectAltName extension of the
certTemplate MUST contain the EE subject name of the existing
certificate to be updated, without modifications.
4. The certTemplate SHOULD contain the subject and/or subjectAltName
extension and publicKey of the EE only.
5. The oldCertId control MAY be used to make clear which certificate
is to be updated.
6. The caPubs field in the kup message MUST be absent.
As part of the certReq structure of the kur, the oldCertId control is
added after the certTemplate field.
controls
type RECOMMENDED
-- MUST be the value id-regCtrl-oldCertID, if present
value
issuer REQUIRED
serialNumber REQUIRED
-- MUST contain the issuer and serialNumber of the certificate
-- to be updated
4.1.4. Enrolling an End Entity Using a PKCS #10 Request
This PKI management operation can be used by an EE to request a
certificate using the PKCS #10 [RFC2986] format to interoperate with
CAs not supporting CRMF [RFC4211]. This offers a variation of the
PKI management operations specified in Sections 4.1.1 to 4.1.3.
In this PKI management operation, the public key and all further
certificate template data MUST be contained in the subjectPKInfo and
other certificationRequestInfo fields of the PKCS #10 structure.
The prerequisites are the same as given in Section 4.1.2.
The message sequence for this PKI management operation is identical
to that given in Sections 4.1.1 to 4.1.3, with the following changes:
1. The body of the first request and response MUST be p10cr and cp,
respectively.
2. The certReqId in the cp message MUST be -1.
Detailed Message Description:
Certification Request -- p10cr
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE for a new certificate using a PKCS #10
-- certificate request
p10cr REQUIRED
certificationRequestInfo REQUIRED
version REQUIRED
-- MUST be 0 to indicate PKCS #10 v1.7
subject REQUIRED
-- The EE subject name MUST be carried in the subject field
-- and/or the subjectAltName extension.
-- If subject name is present only in the subjectAltName
-- extension, then the subject field MUST be NULL-DN
subjectPKInfo REQUIRED
algorithm REQUIRED
-- MUST include the subject public key algorithm identifier
subjectPublicKey REQUIRED
-- MUST include the public key to be certified
attributes OPTIONAL
-- MAY include end-entity-specific X.509 extensions of the
-- requested certificate like subject alternative name,
-- key usage, and extended key usage
-- The subjectAltName extension MUST be present if the EE
-- subject name includes a subject alternative name.
signatureAlgorithm REQUIRED
-- The signature algorithm MUST be consistent with the
-- subjectPKInfo field.
signature REQUIRED
-- MUST contain the self-signature for proof-of-possession
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described for the underlying PKI management operation
4.1.5. Using MAC-Based Protection for Enrollment
This is a variant of the PKI management operations described in
Sections 4.1.1, 4.1.2, and 4.1.4. It should be used by an EE to
request a certificate of a new PKI in case it does not have a
certificate to prove its identity to the target PKI but has some
secret information shared with the PKI management entity. Therefore,
the request and response messages are MAC-protected using this shared
secret information. The distribution of this shared secret is out of
scope for this document. The PKI management entity checking the MAC-
based protection MUST replace this protection according to
Section 5.2.3, as the next hop may not know the shared secret
information.
Note: The entropy of the shared secret information is crucial for the
level of protection when using MAC-based protection. Further
guidance is available in the security considerations updated by CMP
Updates [RFC9480].
Specific prerequisites augmenting the prerequisites in Section 3.4
are as follows:
* Rather than using private keys, certificates, and trust anchors,
the EE and the PKI management entity MUST share secret
information.
Note: The shared secret information MUST be established out of
band, e.g., by a service technician during initial local
configuration.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Sections 4.1.1, 4.1.2, and 4.1.4, with the following
changes:
1. The protection of all messages MUST be MAC-based. Therefore,
extraCerts fields of all messages do not contain CMP protection
certificates and associated chains.
2. The sender field MUST contain a name the PKI management entity
can use to identify the shared secret information used for
message protection. This name MUST be placed in the commonName
field of the directoryName choice. The senderKID MUST contain
the same name as in the commonName field of the sender field. In
case the sending entity does not yet know for which name to
request the certificate, it can use this commonName in the
subject field of the certTemplate.
See Section 6 of CMP Algorithms [RFC9481] for details on message
authentication code algorithms (MSG_MAC_ALG) to use. Typically,
parameters are part of the protectionAlg field, e.g., used for key
derivation, like a salt and an iteration count. Such parameters
should remain constant for message protection throughout this PKI
management operation to reduce the computational overhead.
4.1.6. Adding Central Key Pair Generation to Enrollment
This is a variant of the PKI management operations described in
Sections 4.1.1 to 4.1.4 and the variant described in Section 4.1.5.
It needs to be used in case an EE is not able to generate its new
public-private key pair itself or central generation of the EE key
material is preferred. Which PKI management entity will act as Key
Generation Authority (KGA) and perform the key generation is a matter
of the local implementation. This PKI management entity MUST use a
certificate containing the additional extended key usage extension
id-kp-cmKGA in order to be accepted by the EE as a legitimate key
generation authority.
Note: As described in Section 5.3.1, the KGA can use the PKI
management operation described in Section 4.1.2 to request the
certificate for this key pair on behalf of the EE.
When an EE requests central key generation for a certificate update
using a kur message, the KGA cannot use a kur message to request the
certificate on behalf of the EE, as the old EE credential is not
available to the KGA for protecting this message. Therefore, if the
EE uses the PKI management operation described in Section 4.1.3, the
KGA MUST act as described in Section 4.1.2 to request the certificate
for the newly generated key pair on behalf of the EE from the CA.
Generally speaking, it is strongly preferable to generate public-
private key pairs locally at the EE. This is advisable to make sure
that the entity identified in the newly issued certificate is the
only entity that knows the private key.
Reasons for central key generation may include the following:
* lack of sufficient initial entropy
Note: Good random numbers are not only needed for key generation
but also for session keys and nonces in any security protocol.
Therefore, a decent security architecture should anyways support
good random number generation on the EE side or provide enough
initial entropy for the random number generator seed to guarantee
good pseudorandom number generation. Yet maybe this is not the
case at the time of requesting an initial certificate during
manufacturing.
* lack of computational resources, in particular, for RSA key
generation
Note: Since key generation could be performed in advance to the
certificate enrollment communication, it is often not time
critical.
Note: As mentioned in Section 2, central key generation may be
required in a push model, where the certificate response message is
transferred by the PKI management entity to the EE without a previous
request message.
The EE requesting central key generation MUST omit the publicKey
field from the certTemplate or, in case it has a preference on the
key type to be generated, provide this preference in the algorithm
sub-field and fill the subjectPublicKey sub-field with a zero-length
BIT STRING. Both variants indicate to the PKI management entity that
a new key pair shall be generated centrally on behalf of the EE.
Note: As the protection of centrally generated keys in the response
message has been extended to EncryptedKey by Section 2.7 of CMP
Updates [RFC9480], EnvelopedData is the preferred alternative to
EncryptedValue. In CRMF [RFC4211], Section 2.1, point 9, the use of
EncryptedValue has been deprecated in favor of the EnvelopedData
structure. Therefore, this profile requires using EnvelopedData, as
specified in Section 6 of CMS [RFC5652]. When EnvelopedData is to be
used in a PKI management operation, CMP v3 MUST be indicated in the
message header already for the initial request message; see
Section 2.20 of CMP Updates [RFC9480].
+----------------------------------+
| EnvelopedData |
| [RFC5652], Section 6 |
| +------------------------------+ |
| | SignedData | |
| | [RFC5652], Section 5 | |
| | +--------------------------+ | |
| | | AsymmetricKeyPackage | | |
| | | [RFC5958] | | |
| | | +----------------------+ | | |
| | | | private key | | | |
| | | +----------------------+ | | |
| | +--------------------------+ | |
| +------------------------------+ |
+----------------------------------+
Figure 3: Encrypted Private Key Container
The PKI management entity delivers the private key in the privateKey
field in the certifiedKeyPair structure of the response message also
containing the newly issued certificate.
The private key MUST be provided as an AsymmetricKeyPackage structure
as defined in [RFC5958].
This AsymmetricKeyPackage structure MUST be wrapped in a SignedData
structure, as specified in Section 5 of CMS [RFC5652] and [RFC8933],
and signed by the KGA generating the key pair. The signature MUST be
performed using a private key related to a certificate asserting the
extended key usage id-kp-cmKGA, as described in Section 2.2 of CMP
Updates [RFC9480], to demonstrate authorization to generate key pairs
on behalf of an EE. For response messages using signature-based
protection, the EE MUST validate the signer certificate contained in
the SignedData structure and SHOULD authorize the KGA considering any
given id-kp-cmKGA extended key usage in the signer certificate. For
response messages using MAC-based protection, the EE MAY omit the
validation as it may not be possible or meaningful to the EE. In
this case, the EE authorizes the KGA using the shard secret
information.
The SignedData structure MUST be wrapped in an EnvelopedData
structure, as specified in Section 6 of CMS [RFC5652], encrypting it
using a newly generated symmetric content-encryption key.
This content-encryption key MUST be securely provided as part of the
EnvelopedData structure to the EE using one of three key management
techniques. The choice of the key management technique to be used by
the PKI management entity depends on the authentication mechanism the
EE chose to protect the request message. See Section 2.7 of CMP
Updates [RFC9480] for details on which key management technique to
use.
* Signature-based protection of the request message:
In this case, the choice depends on the type of public key in the
CMP protection certificate used by the EE in its request.
- The content-encryption key SHALL be protected using the key
transport key management technique (see Section 4.1.6.1) if the
key type supports this.
- The content-encryption key SHALL be protected using the key
agreement key management technique (see Section 4.1.6.2) if the
key type supports this.
* MAC-based protection of the request message:
- The content-encryption key SHALL be protected using the
password-based key management technique (see Section 4.1.6.3)
if and only if the EE used MAC-based protection for the request
message.
Specific prerequisites augmenting those of the respective certificate
enrollment PKI management operations are as follows:
* If signature-based protection is used, the EE MUST be able to
authenticate and authorize the KGA using suitable information,
which includes a trust anchor.
* If MAC-based protection is used, the KGA MUST also know the shared
secret information to protect the encrypted transport of the newly
generated key pair. Consequently, the EE can also authorize the
KGA.
* The PKI management entity MUST have a certificate containing the
additional extended key usage extension id-kp-cmKGA for signing
the SignedData structure containing the private key package.
* For encrypting the SignedData structure, a fresh content-
encryption key to be used by the symmetric encryption algorithm
MUST be generated with sufficient entropy.
Note: The security strength of the protection of the generated
private key should be similar or higher than the security strength
of the generated private key.
Detailed Description of the privateKey Field:
privateKey REQUIRED
-- MUST be an EnvelopedData structure, as specified in
-- Section 6 of CMS [RFC5652]
version REQUIRED
-- MUST be 2 for recipientInfo type KeyAgreeRecipientInfo and
-- KeyTransRecipientInfo
-- MUST be 0 for recipientInfo type PasswordRecipientInfo
recipientInfos REQUIRED
-- MUST contain a sequence of one RecipientInfo, which MUST be
-- ktri of type KeyTransRecipientInfo (see Section 4.1.6.1),
-- kari of type KeyAgreeRecipientInfo (see Section 4.1.6.2), or
-- pwri of type PasswordRecipientInfo (see Section 4.1.6.3)
encryptedContentInfo
REQUIRED
contentType REQUIRED
-- MUST be id-signedData
contentEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the algorithm used for
-- content encryption
-- The algorithm type MUST be PROT_SYM_ALG as specified in
-- [RFC9481], Section 5
encryptedContent REQUIRED
-- MUST be the SignedData structure, as specified in Section 5
-- of CMS [RFC5652] and [RFC8933], in encrypted form
version REQUIRED
-- MUST be 3
digestAlgorithms
REQUIRED
-- MUST contain a sequence of one AlgorithmIdentifier element
-- MUST be the algorithm identifier of the digest algorithm
-- used for generating the signature and match the signature
-- algorithm specified in signatureAlgorithm; see [RFC8933]
encapContentInfo
REQUIRED
-- MUST contain the content that is to be signed
eContentType REQUIRED
-- MUST be id-ct-KP-aKeyPackage as specified in [RFC5958]
eContent REQUIRED
-- MUST be of type AsymmetricKeyPackage and
-- MUST contain a sequence of one OneAsymmetricKey element
version REQUIRED
-- MUST be 1 (indicating v2)
privateKeyAlgorithm
REQUIRED
-- The privateKeyAlgorithm field MUST contain the algorithm
-- identifier of the asymmetric key pair algorithm
privateKey REQUIRED
publicKey REQUIRED
-- MUST contain the public key corresponding to the private key
-- for simplicity and consistency with v2 of OneAsymmetricKey
certificates REQUIRED
-- MUST contain the certificate for the private key used to sign
-- the signedData content, together with its chain
-- The first certificate in this field MUST be the KGA
-- certificate used for protecting this content
-- Self-signed certificates should not be included and MUST NOT
-- be trusted based on their inclusion in any case
signerInfos REQUIRED
-- MUST contain a sequence of one SignerInfo element
version REQUIRED
-- MUST be 3
sid REQUIRED
subjectKeyIdentifier
REQUIRED
-- MUST be the subjectKeyIdentifier of the KGA certificate
digestAlgorithm
REQUIRED
-- MUST be the same as in the digestAlgorithms field of
-- encryptedContent
signedAttrs REQUIRED
-- MUST contain an id-contentType attribute containing the value
-- id-ct-KP-aKeyPackage
-- MUST contain an id-messageDigest attribute containing the
-- message digest of eContent
-- MAY contain an id-signingTime attribute containing the time
-- of a signature. It SHOULD be omitted if the transactionTime
-- field is not present in the PKIHeader.
-- For details on the signed attributes, see Sections 5.3 and
-- 11 of CMS [RFC5652] and [RFC8933]
signatureAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the signature algorithm
-- used for calculation of the signature bits
-- The signature algorithm type MUST be MSG_SIG_ALG, as
-- specified in [RFC9481], Section 3, and MUST be consistent
-- with the subjectPublicKeyInfo field of the KGA certificate
signature REQUIRED
-- MUST be the digital signature of the encapContentInfo
As stated in Section 1.8, all fields of the ASN.1 syntax that are
defined in [RFC5652] but are not explicitly specified here SHOULD NOT
be used.
4.1.6.1. Using the Key Transport Key Management Technique
This variant can be applied in combination with the PKI management
operations specified in Sections 4.1.1 to 4.1.3 using signature-based
protection of CMP messages. The EE certificate used for the
signature-based protection of the request message MUST contain a
public key supporting key transport and allow for the key usage
"keyEncipherment". The related key pair MUST be used for
encipherment of the content-encryption key. For this key management
technique, the KeyTransRecipientInfo structure MUST be used in the
contentInfo field.
The KeyTransRecipientInfo structure included into the EnvelopedData
structure is specified in Section 6.2.1 of CMS [RFC5652].
Detailed Description of the KeyTransRecipientInfo Structure:
ktri REQUIRED
-- MUST be KeyTransRecipientInfo as specified in Section 6.2.1
-- of CMS [RFC5652]
version REQUIRED
-- MUST be 2
rid REQUIRED
-- MUST contain the subjectKeyIdentifier of the CMP protection
-- certificate, if available, in the rKeyId choice, and the
-- subjectKeyIdentifier MUST equal the senderKID in the
-- PKIHeader.
-- If the CMP protection certificate does not contain a
-- subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
-- be used.
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key transport
-- algorithm. The algorithm type MUST be KM_KT_ALG as
-- specified in [RFC9481], Section 4.2
encryptedKey REQUIRED
-- MUST be the encrypted content-encryption key
4.1.6.2. Using the Key Agreement Key Management Technique
This variant can be applied in combination with the PKI management
operations specified in Sections 4.1.1 to 4.1.3, using signature-
based protection of CMP messages. The EE certificate used for the
signature-based protection of the request message MUST contain a
public key supporting key agreement and allow for the key usage
"keyAgreement". The related key pair MUST be used for establishment
of the content-encryption key. For this key management technique,
the KeyAgreeRecipientInfo structure MUST be used in the contentInfo
field.
The KeyAgreeRecipientInfo structure included into the EnvelopedData
structure is specified in Section 6.2.2 of CMS [RFC5652].
Detailed Description of the KeyAgreeRecipientInfo Structure:
kari REQUIRED
-- MUST be KeyAgreeRecipientInfo as specified in Section
-- 6.2.2 of CMS [RFC5652]
version REQUIRED
-- MUST be 3
originator REQUIRED
-- MUST contain the subjectKeyIdentifier of the CMP protection
-- certificate, if available, in the subjectKeyIdentifier
-- choice, and the subjectKeyIdentifier MUST equal the
-- senderKID in the PKIHeader.
-- If the CMP protection certificate does not contain a
-- subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
-- be used.
ukm RECOMMENDED
-- MUST be used when 1-Pass Elliptic Curve Menezes-Qu-Vanstone
-- (ECMQV) is used; see [RFC5753]
-- SHOULD be present to ensure uniqueness of the key
-- encryption key
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key agreement
-- algorithm
-- The algorithm type MUST be KM_KA_ALG as specified in
-- [RFC9481], Section 4.1
-- The parameters field of the key agreement algorithm MUST
-- contain the key wrap algorithm. The algorithm type
-- MUST be KM_KW_ALG as specified in [RFC9481], Section 4.3
recipientEncryptedKeys
REQUIRED
-- MUST contain a sequence of one RecipientEncryptedKey
rid REQUIRED
-- MUST contain the subjectKeyIdentifier of the CMP protection
-- certificate, if available, in the rKeyId choice, and the
-- subjectKeyIdentifier MUST equal the senderKID in the
-- PKIHeader.
-- If the CMP protection certificate does not contain a
-- subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
-- be used
encryptedKey
REQUIRED
-- MUST be the encrypted content-encryption key
4.1.6.3. Using the Password-Based Key Management Technique
This variant can be applied in combination with the PKI management
operation specified in Section 4.1.5, using MAC-based protection of
CMP messages. The shared secret information used for the MAC-based
protection MUST also be used for the encryption of the content-
encryption key but with a different salt value applied in the key
derivation algorithm. For this key management technique, the
PasswordRecipientInfo structure MUST be used in the contentInfo
field.
Note: The entropy of the shared secret information is crucial for the
level of protection when using a password-based key management
technique. For centrally generated key pairs, the entropy of the
shared secret information SHALL NOT be less than the security
strength of the centrally generated key pair. Further guidance is
available in Section 9.
The PasswordRecipientInfo structure included into the EnvelopedData
structure is specified in Section 6.2.4 of CMS [RFC5652].
Detailed Description of the PasswordRecipientInfo Structure:
pwri REQUIRED
-- MUST be PasswordRecipientInfo as specified in
-- Section 6.2.4 of CMS [RFC5652]
version REQUIRED
-- MUST be 0
keyDerivationAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key derivation
-- algorithm
-- The algorithm type MUST be KM_KD_ALG as specified in
-- [RFC9481], Section 4.4
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key wrap algorithm
-- The algorithm type MUST be KM_KW_ALG as specified in
-- [RFC9481], Section 4.3
encryptedKey REQUIRED
-- MUST be the encrypted content-encryption key
4.2. Revoking a Certificate
This PKI management operation should be used by an entity to request
revocation of a certificate. Here, the revocation request is used by
an EE to revoke one of its own certificates.
The revocation request message MUST be signed using the certificate
that is to be revoked to prove the authorization to revoke. The
revocation request message is signature-protected using this
certificate. This requires that the EE still possesses the private
key. If this is not the case, the revocation has to be initiated by
other means, e.g., revocation by the RA, as specified in
Section 5.3.2.
An EE requests revoking a certificate of its own at the CA that
issued this certificate. The PKI management entity handles the
request as described in Section 5.1.3, and responds with a message
that contains the status of the revocation from the CA.
The specific prerequisite augmenting the prerequisites in Section 3.4
is as follows:
* The certificate the EE wishes to revoke is not yet expired or
revoked.
Message Flow:
Step# EE PKI management entity
1 format rr
2 -> rr ->
3 handle or forward rr
4 format or receive rp
5 <- rp <-
6 handle rp
For this PKI management operation, the EE MUST include a sequence of
one RevDetails structure in the rr message body. In the case no
generic error occurred, the response to the rr MUST be an rp message
containing a single status field.
Detailed Message Description:
Revocation Request -- rr
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE to revoke its certificate
rr REQUIRED
-- MUST contain a sequence of one element of type RevDetails
-- If more revocations are desired, further PKI management
-- operations need to be initiated
certDetails REQUIRED
-- MUST be present and is of type CertTemplate
serialNumber REQUIRED
-- MUST contain the certificate serialNumber attribute of the
-- certificate to be revoked
issuer REQUIRED
-- MUST contain the issuer attribute of the certificate to be
-- revoked
crlEntryDetails REQUIRED
-- MUST contain a sequence of one reasonCode of type CRLReason
-- (see [RFC5280], Section 5.3.1)
-- If the reason for this revocation is not known or shall not
-- be published, the reasonCode MUST be 0 (unspecified)
protection REQUIRED
-- As described in Section 3.2 and using the private key related
-- to the certificate to be revoked
extraCerts REQUIRED
-- As described in Section 3.3
Revocation Response -- rp
Field Value
header
-- As described in Section 3.1
body
-- The response of the PKI management entity to the request as
-- appropriate
rp REQUIRED
status REQUIRED
-- MUST contain a sequence of one element of type PKIStatusInfo
status REQUIRED
-- positive value allowed: "accepted"
-- negative value allowed: "rejection"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, for logging, or
-- to display in a GUI
failInfo OPTIONAL
-- MAY be present if the status is "rejection"
-- MUST be absent if the status is "accepted"
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
4.3. Support Messages
The following support messages offer on-demand, in-band delivery of
content relevant to the EE provided by a PKI management entity. CMP
general messages and general response are used for this purpose.
Depending on the environment, these requests may be answered by an RA
or CA (see also Section 5.1.4).
The general messages and general response messages contain
InfoTypeAndValue structures. In addition to those infoType values
defined in [RFC4210] and CMP Updates [RFC9480], further OIDs MAY be
used to define new PKI management operations or new general-purpose
support messages as needed in specific environments.
The following contents are specified in this document:
* Get CA certificates.
* Get root CA certificate update.
* Get certificate request template.
* Get new Certificate Revocation Lists (CRLs).
The following message flow and contents are common to all general
message (genm) and general response (genp) messages.
Message Flow:
Step# EE PKI management entity
1 format genm
2 -> genm ->
3 handle or forward genm
4 format or receive genp
5 <- genp <-
6 handle genp
Detailed Message Description:
General Message -- genm
Field Value
header
-- As described in Section 3.1
body
-- A request by the EE for information
genm REQUIRED
-- MUST contain a sequence of one element of type
-- InfoTypeAndValue
infoType REQUIRED
-- MUST be the OID identifying one of the specific PKI
-- management operations described below
infoValue OPTIONAL
-- MUST be as specified for the specific PKI management operation
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
General Response -- genp
Field Value
header
-- As described in Section 3.1
body
-- The response of the PKI management entity providing
-- information
genp REQUIRED
-- MUST contain a sequence of one element of type
-- InfoTypeAndValue
infoType REQUIRED
-- MUST be the OID identifying the specific PKI management
-- operation described below
infoValue OPTIONAL
-- MUST be as specified for the specific PKI management operation
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
4.3.1. Get CA Certificates
This PKI management operation can be used by an EE to request CA
certificates from the PKI management entity.
An EE requests CA certificates, e.g., for chain construction, from a
PKI management entity by sending a general message with OID id-it-
caCerts, as specified in Section 2.14 of CMP Updates [RFC9480]. The
PKI management entity responds with a general response with the same
OID that either contains a SEQUENCE of certificates populated with
the available intermediate and issuing CA certificates or no content
in case no CA certificate is available.
No specific prerequisites apply in addition to those specified in
Section 3.4.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1. the infoType OID to use is id-it-caCerts
2. the infoValue of the request MUST be absent
3. if present, the infoValue of the response MUST contain a sequence
of certificates
Detailed Description of the infoValue Field of genp:
infoValue OPTIONAL
-- MUST be absent if no CA certificate is available
-- MUST be present if CA certificates are available
-- if present, MUST be a sequence of CMPCertificate
4.3.2. Get Root CA Certificate Update
This PKI management operation can be used by an EE to request an
updated root CA certificate as described in Section 4.4 of [RFC4210].
An EE requests an update of a root CA certificate from the PKI
management entity by sending a general message with OID id-it-
rootCaCert. If needed for unique identification, the EE MUST include
the old root CA certificate in the message body as specified in
Section 2.15 of CMP Updates [RFC9480]. The PKI management entity
responds with a general response with OID id-it-rootCaKeyUpdate that
either contains the update of the root CA certificate consisting of
up to three certificates or no content in case no update is
available.
Note: This mechanism may also be used to update trusted non-root
certificates, e.g., directly trusted intermediate or issuing CA
certificates.
The newWithNew certificate is the new root CA certificate and is
REQUIRED to be present if available. The newWithOld certificate is
REQUIRED to be present in the response message because it is needed
for the receiving entity trusting the old root CA certificate to gain
trust in the new root CA certificate. The oldWithNew certificate is
OPTIONAL because it is only needed in rare scenarios where other
entities may not already trust the old root CA.
No specific prerequisites apply in addition to those specified in
Section 3.4.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1. the infoType OID to use is id-it-rootCaCert in the request and
id-it-rootCaKeyUpdate in the response
2. the infoValue of the request SHOULD contain the root CA
certificate the update is requested for
3. if present, the infoValue of the response MUST be a
RootCaKeyUpdateContent structure
Detailed Description of the infoValue Field of genm:
infoValue RECOMMENDED
-- MUST contain the root CA certificate to be updated if needed
-- for unique identification
Detailed Description of the infoValue Field of genp:
infoValue OPTIONAL
-- MUST be absent if no update of the root CA certificate is
-- available
-- MUST be present if an update of the root CA certificate
-- is available and MUST be of type RootCaKeyUpdateContent
newWithNew REQUIRED
-- MUST be present if infoValue is present
-- MUST contain the new root CA certificate
newWithOld REQUIRED
-- MUST be present if infoValue is present
-- MUST contain a certificate containing the new public
-- root CA key signed with the old private root CA key
oldWithNew OPTIONAL
-- MAY be present if infoValue is present
-- MUST contain a certificate containing the old public
-- root CA key signed with the new private root CA key
4.3.3. Get Certificate Request Template
This PKI management operation can be used by an EE to request a
template with parameters for future certificate requests.
An EE requests certificate request parameters from the PKI management
entity by sending a general message with OID id-it-certReqTemplate as
specified in Section 2.16 of CMP Updates [RFC9480]. The EE MAY
indicate the certificate profile to use in the id-it-certProfile
extension of the generalInfo field in the PKIHeader of the general
message as described in Section 3.1. The PKI management entity
responds with a general response with the same OID that either
contains requirements on the certificate request template or no
content in case no specific requirements are imposed by the PKI. The
CertReqTemplateValue contains requirements on certificate fields and
extensions in a certTemplate. Optionally, it contains a keySpec
field containing requirements on algorithms acceptable for key pair
generation.
The EE SHOULD follow the requirements from the received CertTemplate
by including in the certificate requests all the fields requested,
taking over all the field values provided and filling in any
remaining fields values. The EE SHOULD NOT add further fields, name
components, and extensions or their (sub)components. If deviating
from the recommendations of the template, the certificate request
might be rejected.
Note: We deliberately do not use "MUST" or "MUST NOT" here in order
to allow more flexibility in case the rules given here are not
sufficient for specific scenarios. The EE can populate the
certificate request as wanted and ignore any of the requirements
contained in the CertReqTemplateValue. On the other hand, a PKI
management entity is free to ignore or replace any parts of the
content of the certificate request provided by the EE. The
CertReqTemplate PKI management operation offers means to ease a joint
understanding of which fields and/or which field values should be
used. An example is provided in Appendix A.
In case a field of type Name, e.g., subject, is present in the
CertTemplate but has the value NULL-DN (i.e., has an empty list of
relative distinguished name (RDN) components), the field SHOULD be
included in the certificate request and filled with content provided
by the EE. Similarly, in case an X.509v3 extension is present but
its extnValue is empty, this means that the extension SHOULD be
included and filled with content provided by the EE. In case a Name
component, for instance, a common name or serial number, is given but
has an empty string value, the EE SHOULD fill in a value. Similarly,
in case an extension has subcomponents (e.g., an IP address in a
SubjectAltName field) with empty values, the EE SHOULD fill in a
value.
The EE MUST ignore (i.e., not include) empty fields, extensions, and
subcomponents that it does not understand or does not know suitable
values to fill in.
The publicKey field of type SubjectPublicKeyInfo in the CertTemplate
of the CertReqTemplateValue MUST be omitted. In case the PKI
management entity wishes to make a stipulation on algorithms the EE
may use for key generation, this MUST be specified using the keySpec
field as specified in Section 2.16 of CMP Updates [RFC9480].
The keySpec field, if present, specifies the public key types
optionally with parameters and/or RSA key lengths for which a
certificate may be requested.
The value of a keySpec element with the OID id-regCtrl-algId, as
specified in Section 2.16 of CMP Updates [RFC9480], MUST be of type
AlgorithmIdentifier and give an algorithm other than RSA. For
Elliptic Curve (EC) keys, the curve information MUST be specified as
described in the respective standard documents.
The value of a keySpec element with the OID id-regCtrl-rsaKeyLen, as
specified in Section 2.16 of CMP Updates [RFC9480], MUST be a
positive integer value and give an RSA key length.
In the CertTemplate of the CertReqTemplateValue, the serialNumber,
signingAlg, issuerUID, and subjectUID fields MUST be omitted.
The specific prerequisites augmenting the prerequisites in
Section 3.4 is as follows:
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1. the infoType OID to use is id-it-certReqTemplate
2. the id-it-certProfile generalInfo field in the header of the
request MAY contain the name of the requested certificate request
template
3. the infoValue of the request MUST be absent
4. if present, the infoValue of the response MUST be a
CertReqTemplateValue containing a CertTemplate structure and an
optional keySpec field
Detailed Description of the infoValue Field of genp:
InfoValue OPTIONAL
-- MUST be absent if no requirements are available
-- MUST be present if the PKI management entity has any
-- requirements on the contents of the certificate template
certTemplate REQUIRED
-- MUST be present if infoValue is present
-- MUST contain the required CertTemplate structure elements
-- The SubjectPublicKeyInfo field MUST be absent
keySpec OPTIONAL
-- MUST be absent if no requirements on the public key are
-- available
-- MUST be present if the PKI management entity has any
-- requirements on the keys generated
-- MUST contain a sequence of one AttributeTypeAndValue per
-- supported algorithm with attribute id-regCtrl-algId or
-- id-regCtrl-rsaKeyLen
4.3.4. CRL Update Retrieval
This PKI management operation can be used by an EE to request a new
CRL. If a CA offers methods to access a CRL, it may include CRL
distribution points or authority information access extensions into
the issued certificates as specified in [RFC5280]. In addition, CMP
offers CRL provisioning functionality as part of the PKI management
operation.
An EE requests a CRL update from the PKI management entity by sending
a general message with OID id-it-crlStatusList. The EE MUST include
the CRL source identifying the requested CRL and, if available, the
thisUpdate time of the most current CRL instance it already has, as
specified in Section 2.17 of CMP Updates [RFC9480]. The PKI
management entity MUST respond with a general response with OID id-
it-crls.
The EE MUST identify the requested CRL either by a CRL distribution
point name or issuer name.
Note: CRL distribution point names can be obtained from a
cRLDistributionPoints extension of a certificate to be validated or
from an issuingDistributionPoint extension of the CRL to be updated.
CRL issuer names can be obtained from the cRLDistributionPoints
extension of a certificate, from the issuer field of the authority
key identifier extension of a certificate or CRL, and from the issuer
field of a certificate or CRL.
If a thisUpdate value was given, the PKI management entity MUST
return the latest CRL available from the referenced source if this
CRL is more recent than the given thisUpdate time. If no thisUpdate
value was given, it MUST return the latest CRL available from the
referenced source. In all other cases, the infoValue in the response
message MUST be absent.
The PKI management entity should treat a CRL distribution point name
as an internal pointer to identify a CRL that is directly available
at the PKI management entity. It is not intended as a way to fetch
an arbitrary CRL from an external location, as this location may be
unavailable to that PKI management entity.
In addition to the prerequisites specified in Section 3.4, the EE
MUST know which CRL to request.
Note: If the EE does not want to request a specific CRL, it MAY
instead use a general message with OID id-it-currentCrl as specified
in Section 5.3.19.6 of [RFC4210].
The message sequence for this PKI management operation is as given
above, with the following specific content:
1. the infoType OID to use is id-it-crlStatusList in the request and
id-it-crls in the response
2. the infoValue of the request MUST be present and contain a
sequence of one CRLStatus structure
3. if present, the infoValue of the response MUST contain a sequence
of one CRL
Detailed Description of the infoValue Field of genm:
infoValue REQUIRED
-- MUST contain a sequence of one CRLStatus element
source REQUIRED
-- MUST contain the dpn choice of type DistributionPointName if
-- the CRL distribution point name is available
-- Otherwise, MUST contain the issuer choice identifying the CA
-- that issues the CRL. It MUST contain the issuer DN in the
-- directoryName field of a GeneralName element.
thisUpdate OPTIONAL
-- MUST contain the thisUpdate field of the latest CRL the EE
-- has gotten from the issuer specified in the given dpn or
-- issuer field
-- MUST be omitted if the EE does not have any instance of the
-- requested CRL
Detailed Description of the infoValue Field of genp:
infoValue OPTIONAL
-- MUST be absent if no CRL to be returned is available
-- MUST contain a sequence of one CRL update from the referenced
-- source if a thisUpdate value was not given or a more recent
-- CRL is available
4.4. Handling Delayed Delivery
This is a variant of all PKI management operations described in this
document. It is initiated in case a PKI management entity cannot
respond to a request message in a timely manner, typically due to
offline or asynchronous upstream communication or due to delays in
handling the request. The polling mechanism has been specified in
Section 5.3.22 of [RFC4210] and updated by [RFC9480].
Depending on the PKI architecture, the entity initiating delayed
delivery is not necessarily the PKI management entity directly
addressed by the EE.
When initiating delayed delivery of a message received from an EE,
the PKI management entity MUST respond with a message including the
status "waiting". In response to an ir/cr/kur/p10cr message, it must
place the status "waiting" in an ip/cp/kup message and for responses
to other request message types in an error message. On receiving
this response, the EE MUST store in its transaction context the
senderNonce of the preceding request message because this value will
be needed for checking the recipNonce of the final response to be
received after polling. It sends a poll request with certReqId 0 if
referring to the CertResponse element contained in the ip/cp/kup
message, else -1 to refer to the whole message. In case the final
response is not yet available, the PKI management entity that
initiated the delayed delivery MUST answer with a poll response with
the same certReqId. The included checkAfter time value indicates the
minimum number of seconds that should elapse before the EE sends a
new pollReq message to the PKI management entity. Polling earlier
than indicated by the checkAfter value may increase the number of
message round trips. This is repeated until a final response is
available or any party involved gives up on the current PKI
management operation, i.e., a timeout occurs.
When the PKI management entity that initiated delayed delivery can
provide the final response for the original request message of the
EE, it MUST send this response to the EE. Using this response, the
EE can continue the current PKI management operation as usual.
No specific prerequisites apply in addition to those of the
respective PKI management operation.
Message Flow:
Step# EE PKI management entity
1 format request
message
2 -> request ->
3 handle or forward
request
4 format ip/cp/kup/error
with status "waiting"
response in case no
immediate final response
is available
5 <- ip/cp/kup/error <-
6 handle
ip/cp/kup/error
with status
"waiting"
-------------------------- start polling --------------------------
7 format pollReq
8 -> pollReq ->
9 handle or forward pollReq
10 in case the final response
for the original request
is available, continue
with step 14
otherwise, format or
receive pollRep with
checkAfter value
11 <- pollRep <-
12 handle pollRep
13 let checkAfter
time elapse and
continue with
step 7
----------------- end polling, continue as usual ------------------
14 format or receive
final response on
the original request
15 <- response <-
16 handle final
response
Detailed Message Description:
Response with Status "waiting" -- ip/cp/kup/error
Field Value
header
-- As described in Section 3.1
body
-- As described for the respective PKI management operation, with
-- the following adaptations:
status REQUIRED -- in case of ip/cp/kup
pKIStatusInfo REQUIRED -- in case of error response
-- PKIStatusInfo structure MUST be present
status REQUIRED
-- MUST be status "waiting"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, for logging, or
-- to display in a GUI
failInfo PROHIBITED
protection REQUIRED
-- As described in Section 3.2
extraCerts OPTIONAL
-- As described in Section 3.3
Polling Request -- pollReq
Field Value
header
-- As described in Section 3.1
body
-- The message of the EE asking for the final response or for a
-- time to check again
pollReq REQUIRED
certReqId REQUIRED
-- MUST be 0 if referring to a CertResponse element, else -1
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first request message
-- of the PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and the PKI
-- management entity caches the CMP protection certificate from
-- the first request message of the PKI management operation
Polling Response -- pollRep
Field Value
header
-- As described in Section 3.1
body
-- The message indicates the delay after which the EE SHOULD
-- send another pollReq message for this transaction
pollRep REQUIRED
certReqId REQUIRED
-- MUST be 0 if referring to a CertResponse element, else -1
checkAfter REQUIRED
-- MUST be the time in seconds to elapse before a new pollReq
-- should be sent
reason OPTIONAL
-- MAY be any human-readable text for debugging, for logging, or
-- to display in a GUI
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first response
-- message of the PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and the EE has
-- cached the CMP protection certificate from the first
-- response message of the PKI management operation
Final Response - Any Type of Response Message
Field Value
header
-- MUST be the header, as described for the response message
-- of the respective PKI management operation
body
-- The response of the PKI management entity to the initial
-- request, as described in the respective PKI management
-- operation
protection REQUIRED
-- MUST be as described for the response message of the
-- respective PKI management operation
extraCerts REQUIRED
-- MUST be as described for the response message of the
-- respective PKI management operation
5. PKI Management Entity Operations
This section focuses on request processing by a PKI management
entity. Depending on the network and PKI solution design, this can
be an RA or CA, any of which may include protocol conversion or
central key generation (i.e., acting as a KGA).
A PKI management entity may directly respond to request messages from
downstream and report errors. In case the PKI management entity is
an RA, it typically forwards the received request messages upstream
after checking them and forwards respective response messages
downstream. Besides responding to messages or forwarding them, a PKI
management entity may request or revoke certificates on behalf of
EEs. A PKI management entity may also need to manage its own
certificates and thus act as an EE using the PKI management
operations specified in Section 4.
5.1. Responding to Requests
The PKI management entity terminating the PKI management operation at
CMP level MUST respond to all received requests by returning a
related CMP response message or an error. Any intermediate PKI
management entity MAY respond, depending on the PKI configuration and
policy.
In addition to the checks described in Section 3.5, the responding
PKI management entity MUST check that a request that initiates a new
PKI management operation does not use a transactionID that is
currently in use. The failInfo bit value to use is
transactionIdInUse as described in Section 3.6.4. If any of these
verification steps or any of the essential checks described in
Section 3.5 and in the following subsections fails, the PKI
management entity MUST proceed as described in Section 3.6.
The responding PKI management entity MUST copy the sender field of
the request to the recipient field of the response, MUST copy the
senderNonce of the request to the recipNonce of the response, and
MUST use the same transactionID for the response.
5.1.1. Responding to a Certificate Request
An ir/cr/kur/p10cr message is used to request a certificate as
described in Section 4.1. The responding PKI management entity MUST
proceed as follows unless it initiates delayed delivery as described
in Section 5.1.5.
The PKI management entity MUST check the message body according to
the applicable requirements from Section 4.1. Possible failInfo bit
values used for error reporting in case a check failed include
badCertId and badCertTemplate. It MUST verify the presence and value
of the proof-of-possession (failInfo bit: badPOP) unless central key
generation is requested. If a signature-based proof-of-possession is
present, the PKI management entity MUST verify, based on local PKI
policy, that the subject name in the certTemplate identifies the same
entity as the subject name in the CMP protection certificate or
matches the identifier used with MAC-based protection. In case this
verification fails, the message MUST have been protected by an
authorized PKI management entity (failInfo bit: notAuthorized). If
the special POP value "raVerified" is given, the PKI management
entity should check that the request message was signed using a
certificate containing the cmcRA extended key usage (failInfo bit:
notAuthorized). The PKI management entity should also perform any
further checks on the certTemplate contents (failInfo:
badCertTemplate) according to any applicable PKI policy and
certificate profile.
If the requested certificate is available, the PKI management entity
MUST respond with a positive ip/cp/kup message as described in
Section 4.1.
Note: If central key generation is performed by the responding PKI
management entity, the responding PKI management entity MUST include
the private key in encrypted form in the response as specified in
Section 4.1.6.
The prerequisites of the respective PKI management operation
specified in Section 4.1 apply.
If the EE requested omission of the certConf message, the PKI
management entity MUST handle it as described in Section 4.1.1.
Therefore, it MAY grant this by including the implicitConfirm
generalInfo field or including the confirmWaitTime field in the
response header.
5.1.2. Responding to a Confirmation Message
A PKI management entity MUST handle a certConf message if it has
responded before with a positive ip/cp/kup message not granting
implicit confirmation. It should check the message body according to
the requirements given in Section 4.1.1 (failInfo bit: badCertId) and
MUST react as described there.
The prerequisites of the respective PKI management operation
specified in Section 4.1 apply.
5.1.3. Responding to a Revocation Request
An rr message is used to request revocation of a certificate. The
responding PKI management entity should check the message body
according to the requirements in Section 4.2. It MUST make sure that
the referenced certificate exists (failInfo bit: badCertId), has been
issued by the addressed CA, and is not already expired or revoked
(failInfo bit: certRevoked). On success, it MUST respond with a
positive rp message, as described in Section 4.2.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.1.4. Responding to a Support Message
A genm message is used to retrieve extra content. The responding PKI
management entity should check the message body according to the
applicable requirements in Section 4.3 and perform any further checks
depending on the PKI policy. On success, it MUST respond with a genp
message as described there.
Note: The responding PKI management entity may generate the response
from scratch or reuse the contents of previous responses. Therefore,
it may be worth caching the body of the response message as long as
the contained information is valid and current, such that further
requests for the same contents can be answered immediately.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.1.5. Initiating Delayed Delivery
This functional extension can be used by a PKI management entity in
case the response to a request takes longer than usual. In this
case, the PKI management entity should completely validate the
request as usual and then start processing the request itself or
forward it further upstream as soon as possible. In the meantime, it
MUST respond with an ip/cp/kup/error message including the status
"waiting" and handle subsequent polling as described in Section 4.4.
Typically, as stated in Section 5.2.3, an intermediate PKI management
entity should not change the sender and recipient nonces even in case
it modifies a request or a response message. In the special case of
delayed delivery initiated by an intermediate PKI management entity,
there is an exception. Between the EE and this PKI management
entity, pollReq and pollRep messages are exchanged handling the
nonces as usual. Yet when the final response from upstream has
arrived at the PKI management entity, this response contains the
recipNonce copied (as usual) from the senderNonce in the original
request message. The PKI management entity that initiated the
delayed delivery MAY replace the recipNonce in the response message
with the senderNonce of the last received pollReq because the
downstream entities, including the EE, might expect it in this way.
Yet the check specified in Section 3.5 allows alternate use of the
senderNonce of the original request.
No specific prerequisites apply in addition to those of the
respective PKI management operation.
5.2. Forwarding Messages
In case the PKI solution consists of intermediate PKI management
entities (i.e., LRA or RA), each CMP request message coming from an
EE or any other downstream PKI management entity MUST either be
forwarded to the next (upstream) PKI management entity as described
in this section, or answered as described in Section 5.1. Any
received response message or a locally generated error message MUST
be forwarded to the next (downstream) PKI entity.
In addition to the checks described in Section 3.5, the forwarding
PKI management entity MAY verify the proof-of-possession for
ir/cr/kur/p10cr messages. If one of these verification procedures
fails, the RA proceeds as described in Section 3.6.
A PKI management entity SHOULD NOT change the received message unless
its role in the PKI system requires it. This is because changes to
the message header or body imply reprotection. Changes to the
protection breaks end-to-end authentication of the message source.
Changes to the certificate template in a certificate request breaks
proof-of-possession. More details are available in the following
subsections. Concrete PKI system specifications may define when to
do so in more detail.
This is particularly relevant in the upstream communication of a
request message.
Each forwarding PKI management entity has one or more
functionalities. It may:
* verify the identities of EEs and make authorization decisions for
certification request processing based on local PKI policy,
* add or modify fields of certificate request messages,
* replace a MAC-based protection with a signature-based protection
that can also be verified further upstream and vice versa,
* double-check if the messages transferred back and forth are
properly protected and well-formed,
* provide an authentic indication that it has performed all required
checks,
* initiate a delayed delivery due to delays transferring messages or
handling requests, or
* collect messages from multiple RAs and forward them jointly.
Note: PKI management entities forwarding messages may also store data
from a message in a database for later usage or audit purposes. They
may also support traversal of a network boundary.
The decision if a message should be forwarded is:
* unchanged with the original protection,
* unchanged with an additional protection, or
* changed with an additional protection
depending on the PKI solution design and the associated security
policy, e.g., as defined in the certificate policy (CP) /
certification practice statement (CPS) documents [RFC3647].
A PKI management entity SHOULD add or MAY replace a protection of a
message if it
* needs to securely indicate that it has done checks or validations
on the message to one of the next (upstream) PKI management
entities or
* needs to protect the message using a key and certificate from a
different PKI.
If retaining end-to-end message authentication is required, an
additional protection SHALL be added instead of replacing the
original protection.
A PKI management entity MUST replace a protection of a message if it
* performs changes to the header or the body of the message or
* needs to convert from or to a MAC-based protection.
This is particularly relevant in the upstream communication of
certificate request messages.
Note that the message protection covers only the header and the body
and not the extraCerts. The PKI management entity MAY change the
extraCerts in any of the following message adaptations, e.g., to
sort, add, or delete certificates to support subsequent PKI entities.
This may be particularly helpful to augment upstream messages with
additional certificates or to reduce the number of certificates in
downstream messages when forwarding to constrained devices.
5.2.1. Not Changing Protection
This variant means that a PKI management entity forwards a CMP
message without changing the header, body, or protection. In this
case, the PKI management entity acts more like a proxy, e.g., on a
network boundary, implementing no specific RA-like security
functionality that requires an authentic indication to the PKI.
Still, the PKI management entity might implement checks that result
in refusing to forward the request message and instead responding as
specified in Section 3.6.
This variant of forwarding a message or the one described in
Section 5.2.2.1 MUST be used for kur messages and for central key
generation.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.2.2. Adding Protection and Batching of Messages
This variant of forwarding a message means that a PKI management
entity adds another protection to PKI management messages before
forwarding them.
The nested message is a PKI management message containing a
PKIMessages sequence as its body, containing one or more CMP
messages.
As specified in the updated Section 5.1.3.4 of [RFC4210] (also see
Section 2.6 of CMP Updates [RFC9480]), there are various use cases
for adding another protection by a PKI management entity. Specific
procedures are described in more detail in the following sections.
Detailed Message Description:
Nested Message - nested
Field Value
header
-- As described in Section 3.1
body
-- Container to provide additional protection to original
-- messages and to bundle request messages or alternatively
-- response messages
PKIMessages REQUIRED
-- MUST be a sequence of one or more CMP messages
protection REQUIRED
-- As described in Section 3.2, using the CMP protection key of
-- the PKI management entity
extraCerts REQUIRED
-- As described in Section 3.3
5.2.2.1. Adding Protection to a Request Message
This variant means that a PKI management entity forwards a CMP
message while authentically indicating successful validation and
approval of a request message without changing the original message
authentication.
By adding a protection using its own CMP protection key, the PKI
management entity provides a proof of verifying and approving the
message, as described above. Thus, the PKI management entity acts as
an actual registration authority (RA), which implements important
security functionality of the PKI. Applying an additional protection
is specifically relevant when forwarding a message that requests a
certificate update or central key generation. This is because the
original protection of the EE needs to be preserved while adding an
indication of approval by the PKI management entity.
The PKI management entity wrapping the original request message in a
nested message structure MUST copy the values of the senderNonce and
transactionID header fields of the original message to the respective
header fields of the nested message and apply signature-based
protection. The additional signature serves as proof of verification
and authorization by this PKI management entity.
The PKI management entity receiving such a nested message that
contains a single request message MUST validate the additional
protection signature on the nested message and check the
authorization for the approval it implies. Other fields in the
header of the nested message can be ignored.
The PKI management entity responding to the request contained in the
nested message sends the response message as described in
Section 5.1, without wrapping it in a nested message.
Note: When responding to the inner request message, it must be
considered that the verification and approval activity described in
this section has already been performed by the PKI management entity
that protected the nested message.
Note: This form of nesting messages is characterized by the fact that
the transactionID in the header of the nested message is the same as
the one used in the included message.
The specific prerequisite augmenting the prerequisites in Section 3.4
is as follows:
* The PKI management entity MUST be able to validate the respective
request and have the authorization to perform approval of the
request according to the PKI policies.
Message Flow:
Step# PKI management entity PKI management entity
1 format nested
2 -> nested ->
3 handle or forward nested
4 format or receive response
5 <- response <-
6 forward response
5.2.2.2. Batching Messages
A PKI management entity MAY bundle any number of PKI management
messages for batch processing or to transfer a bulk of PKI management
messages using the nested message structure. In this use case,
nested messages are used both on the upstream interface for
transferring request messages towards the next PKI management entity
and on its downstream interface for response messages.
This PKI management operation is typically used on the interface
between an LRA and an RA to bundle several messages for offline or
asynchronous delivery. In this case, the LRA needs to initiate
delayed delivery, as described in Section 5.1.5. If the RA needs
different routing information per the nested PKI management message
provided upstream, a suitable mechanism may need to be implemented to
ensure that the downstream delivery of the response is done to the
right requester. Since this mechanism strongly depends on the
requirements of the target architecture, it is out of scope of this
document.
A nested message containing requests is generated locally at the PKI
management entity. For the upstream nested message, the PKI
management entity acts as a protocol endpoint; therefore, a fresh
transactionID and a fresh senderNonce MUST be used in the header of
the nested message. An upstream nested message may contain request
messages, e.g., ir, cr, p10cr, kur, pollReq, certConf, rr, or genm.
While building the upstream nested message, the PKI management entity
must store the sender, transactionID, and senderNonce fields of all
bundled messages together with the transactionID of the upstream
nested message.
Such an upstream nested message is sent to the next PKI management
entity. The upstream PKI management entity that unbundles it MUST
handle each of the included request messages as usual. It MUST
answer with a downstream nested message. This downstream nested
message MUST use the transactionID of the upstream nested message and
return the senderNonce of the upstream nested message as the
recipNonce of the downstream nested message. The downstream nested
message MUST bundle all available individual response messages (e.g.,
ip, cp, kup, pollRep, pkiConf, rp, genp, or error) for all original
request messages of the upstream nested message. While unbundling
the downstream nested message, the former PKI management entity must
determine lost and unexpected responses based on the previously
stored transactionIDs. When it forwards the unbundled responses, any
extra messages MUST be dropped, and any missing response message MUST
be answered with an error message (failInfo bit: systemUnavail) to
inform the respective requester about the failed certificate
management operation.
Note: This form of nesting messages is characterized by the fact that
the transactionID in the header of the nested message is different to
those used in the included messages.
The protection of the nested messages MUST NOT be regarded as an
indication of verification or approval of the bundled PKI request
messages.
No specific prerequisites apply in addition to those specified in
Section 3.4.
Message Flow:
Step# PKI management entity PKI management entity
1 format nested
2 -> nested ->
3 handle or forward nested
4 format or receive nested
5 <- nested <-
6 handle nested
5.2.3. Replacing Protection
The following two alternatives can be used by any PKI management
entity forwarding a CMP message with or without changes while
providing its own protection and, in this way, asserting approval of
the message.
If retaining end-to-end message authentication is required, an
additional protection SHALL be added instead of replacing the
original protection.
By replacing the existing protection using its own CMP protection
key, the PKI management entity provides a proof of verifying and
approving the message as described above. Thus, the PKI management
entity acts as an actual registration authority (RA), which
implements important security functionality of the PKI such as
verifying the proof of requester identity and authorization.
Note: By replacing the message protection, the binding of a
signature-based proof-of-possession to the proof-of-identity given by
the original message protection gets lost. To enable the CA to
verify this binding, the original message can be provided in the
origPKIMessage generalInfo field.
Before replacing the existing protection with a new protection, the
PKI management entity:
* MUST validate the protection of the received message,
* should check the content of the message,
* may do any modifications that it wants to perform, and
* MUST check that the sender of the original message, as
authenticated by the message protection, is authorized for the
given operation.
* for certificate requests, MUST verify the binding of signature-
based proof-of-possession to the proof-of-identity as described in
Section 5.1.1.
These message adaptations MUST NOT be applied to kur messages
described in Section 4.1.3 since their original protection using the
key and certificate to be updated needs to be preserved.
These message adaptations MUST NOT be applied to certificate request
messages described in Section 4.1.6 for central key generation since
their original protection needs to be preserved up to the KGA, which
needs to use it for encrypting the new private key for the EE.
In both the kur and central key generation cases, if a PKI management
entity needs to state its approval of the original request message,
it MUST provide this using a nested message as specified in
Section 5.2.2.1.
When an intermediate PKI management entity modifies a message, it
MUST NOT change the transactionID, the senderNonce, or the
recipNonce, apart from the exception for the recipNonce given in
Section 5.1.5.
5.2.3.1. Not Changing Proof-of-Possession
This variant of forwarding a message means that a PKI management
entity forwards a CMP message with or without modifying the message
header or body while preserving any included proof-of-possession.
This variant is typically used when an RA replaces an existing MAC-
based protection with its own signature-based protection; because the
upstream PKI management entity does not know the respective shared
secret information, replacing the protection is useful.
Note: A signature-based proof-of-possession of a certificate request
will be broken if any field in the certTemplate structure is changed.
In case the PKI management entity breaks an existing proof-of-
possession, the message adaptation described in Section 5.2.3.2 needs
to be applied instead.
The specific prerequisite augmenting the prerequisites in Section 3.4
is as follows:
* The PKI management entity MUST be able to validate the respective
request and have the authorization to perform approval of the
request according to the PKI policies.
5.2.3.2. Using raVerified
This variant of forwarding a message needs to be used if a PKI
management entity breaks any included proof-of-possession in a
certificate request message, for instance, because it forwards an ir
or cr message with modifications of the certTemplate, i.e.,
modification, addition, or removal of fields.
The PKI management entity MUST verify the proof-of-possession
contained in the original message using the included public key. If
successful, the PKI management entity MUST change the popo field
value to raVerified.
Specific prerequisites augmenting the prerequisites in Section 3.4
are as follows:
* The PKI management entity MUST be authorized to replace the proof-
of-possession (after verifying it) with raVerified.
* The PKI management entity MUST be able to validate the respective
request and have the authorization to perform approval of the
request according to the PKI policies.
Detailed Description of the popo Field of the certReq Structure:
popo
raVerified REQUIRED
-- MUST have the value NULL and indicates that the PKI
-- management entity verified the popo of the original message
5.3. Acting on Behalf of Other PKI Entities
A PKI management entity may need to request a PKI management
operation on behalf of another PKI entity. In this case, the PKI
management entity initiates the respective PKI management operation
as described in Section 4, acting in the role of the EE.
Note: The request message protection will not authenticate the EE,
but it will authenticate the RA acting on behalf of the EE.
5.3.1. Requesting a Certificate
A PKI management entity may use one of the PKI management operations
described in Section 4.1 to request a certificate on behalf of
another PKI entity. It either generates the key pair itself and
inserts the new public key in the subjectPublicKey field of the
request certTemplate, or it uses a certificate request received from
downstream, e.g., by means of a different protocol. In the latter
case, it MUST verify the received proof-of-possession if this proof
breaks, e.g., due to transformation from PKCS #10 [RFC2986] to CRMF
[RFC4211]. It MUST also verify, based on local PKI policy, that the
subject name in the certTemplate identifies the EE.
No specific prerequisites apply in addition to those specified in
Section 4.1.
Note: An upstream PKI management entity will not be able to
differentiate this PKI management operation from the one described in
Section 5.2.3 because, in both cases, the message is protected by the
PKI management entity.
The message sequence for this PKI management operation is identical
to the respective PKI management operation given in Section 4.1, with
the following changes:
1. The request messages MUST be signed using the CMP protection key
of the PKI management entity taking the role of the EE in this
operation.
2. If inclusion of a proper proof-of-possession is not possible, the
PKI management entity MUST verify the POP provided from
downstream and use "raVerified" in its upstream request.
3. The binding of the proof-of-possession to the proof-of-identity
of the requesting EE cannot be provided when acting on behalf of
the EE.
5.3.2. Revoking a Certificate
A PKI management entity may use the PKI management operation
described in Section 4.2 to revoke a certificate of another PKI
entity. This revocation request message MUST be signed by the PKI
management entity using its own CMP protection key to prove to the
PKI authorization to revoke the certificate on behalf of that PKI
entity.
No specific prerequisites apply in addition to those specified in
Section 4.2.
Note: An upstream PKI management entity will not be able to
differentiate this PKI management operation from the ones described
in Section 5.2.3.
The message sequence for this PKI management operation is identical
to that given in Section 4.2, with the following changes:
1. The rr message MUST be signed using the CMP protection key of the
PKI management entity acting on behalf of the EE in this
operation.
6. CMP Message Transfer Mechanisms
CMP messages are designed to be self-contained, such that, in
principle, any reliable transfer mechanism can be used. EEs will
typically support only one transfer mechanism. PKI management
entities SHOULD offer HTTP and MAY offer CoAP where required.
Piggybacking of CMP messages on any other reliable transfer protocol
MAY be used, and file-based transfer MAY be used in case offline
transfer is required.
Independently of the means of transfer, it can happen that messages
are lost or that a communication partner does not respond. To
prevent waiting indefinitely, each PKI entity that sends CMP requests
should use a configurable per-request timeout, and each PKI
management entity that handles CMP requests should use a configurable
timeout in case a further request message is to be expected from the
client side within the same transaction. In this way, a hanging
transaction can be closed cleanly with an error as described in
Section 3.6 (failInfo bit: systemUnavail), and related resources (for
instance, any cached extraCerts) can be freed.
Moreover, there are various situations where the delivery of messages
gets delayed. For instance, a serving PKI management entity might
take longer than expected to form a response due to administrative
processes, resource constraints, or upstream message delivery delays.
The transport layer itself may cause delays, for instance, due to
offline transport, network segmentation, or intermittent network
connectivity. Part of these issues can be detected and handled at
CMP level using pollReq and pollRep messages as described in
Section 4.4, while others are better handled at transfer level.
Depending on the transfer protocol and system architecture, solutions
for handling delays at transfer level may be present and can be used
for CMP connections, for instance, connection reestablishment and
message retransmission.
Note: Long timeout periods are helpful to maximize chances to handle
minor delays at lower layers without the need for polling.
Note: When using TCP and similar reliable connection-oriented
transport protocols, which is typical in conjunction with HTTP, there
is the option to keep the connection alive over multiple request-
response message pairs. This may improve efficiency.
When conveying CMP messages in HTTP, CoAP, or MIME-based transfer
protocols, the Internet media type "application/pkixcmp" MUST be set
for transfer encoding as specified in Section 3.4 of CMP over HTTP
[RFC6712] and Section 2.3 of CMP over CoAP [RFC9482].
6.1. HTTP Transfer
This transfer mechanism can be used by a PKI entity to transfer CMP
messages over HTTP. If HTTP transfer is used, the specifications
described in [RFC6712] and updated by CMP Updates [RFC9480] MUST be
followed.
PKI management operations MUST use a URI path consisting of '/.well-
known/cmp' or '/.well-known/cmp/p/<name>' as specified in Section 3.3
of CMP Updates [RFC9480]. It SHOULD be followed by an operation
label depending on the type of PKI management operation.
+============================+====================+=========+
| PKI Management Operation | URI Path Segment | Details |
+============================+====================+=========+
| Enrolling an End Entity to | initialization | Section |
| a New PKI | | 4.1.1 |
+----------------------------+--------------------+---------+
| Enrolling an End Entity to | certification | Section |
| a Known PKI | | 4.1.2 |
+----------------------------+--------------------+---------+
| Updating a Valid | keyupdate | Section |
| Certificate | | 4.1.3 |
+----------------------------+--------------------+---------+
| Enrolling an End Entity | pkcs10 | Section |
| Using a PKCS #10 Request | | 4.1.4 |
+----------------------------+--------------------+---------+
| Revoking a Certificate | revocation | Section |
| | | 4.2 |
+----------------------------+--------------------+---------+
| Get CA Certificates | getcacerts | Section |
| | | 4.3.1 |
+----------------------------+--------------------+---------+
| Get Root CA Certificate | getrootupdate | Section |
| Update | | 4.3.2 |
+----------------------------+--------------------+---------+
| Get Certificate Request | getcertreqtemplate | Section |
| Template | | 4.3.3 |
+----------------------------+--------------------+---------+
| CRL Update Retrieval | getcrls | Section |
| | | 4.3.4 |
+----------------------------+--------------------+---------+
| Batching Messages | nested | Section |
| | | 5.2.2.2 |
| Note: This path element is | | |
| applicable only between | | |
| PKI management entities. | | |
+----------------------------+--------------------+---------+
Table 1: HTTP URI Path Segment <operation>
If operation labels are used:
* independently of any variants used (see Sections 4.1.5, 4.1.6, and
4.4), the operation label corresponding to the PKI management
operation SHALL be used.
* any certConf or pollReq messages SHALL be sent to the same
endpoint as determined by the PKI management operation.
* when a single request message is nested as described in
Section 5.2.2.1, the label to use SHALL be the same as for the
underlying PKI management operation.
By sending a request to its preferred endpoint, the PKI entity will
recognize, via the HTTP response status code, whether a configured
URI is supported by the PKI management entity.
In case a PKI management entity receives an unexpected HTTP status
code from upstream, it MUST respond downstream with an error message
as described in Section 3.6, using a failInfo bit corresponding to
the status code, e.g., systemFailure.
For certificate management, the major security goal is integrity and
data origin authentication. For delivery of centrally generated
keys, confidentiality is also a must. These goals are sufficiently
achieved by CMP itself, also in an end-to-end fashion.
If a second line of defense is required or general privacy concerns
exist, TLS can be used to provide confidentiality on a hop-by-hop
basis. TLS should be used with certificate-based authentication to
further protect the HTTP transfer as described in [RFC9110]. In
addition, the recommendations provided in [RFC9325] should be
followed.
Note: The requirements for checking certificates given in [RFC5280]
and either [RFC5246] or [RFC8446] must be followed for the TLS layer.
Certificate status checking should be used for the TLS certificates
of all communication partners.
TLS with mutual authentication based on shared secret information may
be used in case no suitable certificates for certificate-based
authentication are available, e.g., a PKI management operation with
MAC-based protection is used.
Note: The entropy of the shared secret information is crucial for the
level of protection available using shard secret information-based
TLS authentication. A pre-shared key (PSK) mechanism may be used
with shared secret information with an entropy of at least 128 bits.
Otherwise, a password-authenticated key exchange (PAKE) protocol is
recommended.
Note: The provisioning of client certificates and PSKs is out of
scope of this document.
6.2. CoAP Transfer
This transfer mechanism can be used by a PKI entity to transfer CMP
messages over CoAP [RFC7252], e.g., in constrained environments. If
CoAP transfer is used, the specifications described in CMP over CoAP
[RFC9482] MUST be followed.
PKI management operations MUST use a URI path consisting of '/.well-
known/cmp' or '/.well-known/cmp/p/<name>' as specified in Section 2.1
of CMP over CoAP [RFC9482]. It SHOULD be followed by an operation
label depending on the type of PKI management operation.
+=======================================+=========+=========+
| PKI Management Operation | URI | Details |
| | Path | |
| | Segment | |
+=======================================+=========+=========+
| Enrolling an End Entity to a New PKI | ir | Section |
| | | 4.1.1 |
+---------------------------------------+---------+---------+
| Enrolling an End Entity to a Known | cr | Section |
| PKI | | 4.1.2 |
+---------------------------------------+---------+---------+
| Updating a Valid Certificate | kur | Section |
| | | 4.1.3 |
+---------------------------------------+---------+---------+
| Enrolling an End Entity Using a PKCS | p10 | Section |
| #10 Request | | 4.1.4 |
+---------------------------------------+---------+---------+
| Revoking a Certificate | rr | Section |
| | | 4.2 |
+---------------------------------------+---------+---------+
| Get CA Certificates | crts | Section |
| | | 4.3.1 |
+---------------------------------------+---------+---------+
| Get Root CA Certificate Update | rcu | Section |
| | | 4.3.2 |
+---------------------------------------+---------+---------+
| Get Certificate Request Template | att | Section |
| | | 4.3.3 |
+---------------------------------------+---------+---------+
| CRL Update Retrieval | crls | Section |
| | | 4.3.4 |
+---------------------------------------+---------+---------+
| Batching Messages | nest | Section |
| | | 5.2.2.2 |
| Note: This path element is applicable | | |
| only between PKI management entities. | | |
+---------------------------------------+---------+---------+
Table 2: CoAP URI Path Segment <operation>
If operation labels are used:
* independently of any variants used (see Sections 4.1.5, 4.1.6, and
4.4), the operation label corresponding to the PKI management
operation SHALL be used.
* any certConf or pollReq messages SHALL be sent to the same
endpoint, as determined by the PKI management operation.
* when a single request message is nested as described in
Section 5.2.2.1, the label to use SHALL be the same as for the
underlying PKI management operation.
By sending a request to its preferred endpoint, the PKI entity will
recognize, via the CoAP response status code, whether a configured
URI is supported by the PKI management entity. The CoAP-inherent
discovery mechanisms MAY also be used.
In case a PKI management entity receives an unexpected CoAP status
code from upstream, it MUST respond downstream with an error message,
as described in Section 3.6, using a failInfo bit corresponding to
the status code, e.g., systemFailure.
Like for HTTP transfer, to offer a second line of defense or to
provide hop-by-hop privacy protection, DTLS may be utilized as
described in CMP over CoAP [RFC9482]. If DTLS is utilized, the same
boundary conditions (peer authentication, etc.) as those stated for
TLS to protect HTTP transfer in Section 6.1 apply to DTLS likewise.
Note: The provisioning of client certificates and PSKs is out of
scope of this document.
6.3. Piggybacking on Other Reliable Transfer
CMP messages MAY also be transferred on some other reliable protocol,
e.g., Extensible Authentication Protocol (EAP) or Message Queuing
Telemetry Transport (MQTT). Connection, delay, and error handling
mechanisms similar to those specified for HTTP in [RFC6712] need to
be implemented.
A more detailed specification is out of scope of this document and
would need to be given, for instance, in the scope of the transfer
protocol used.
6.4. Offline Transfer
For transferring CMP messages between PKI entities, any mechanism
that is able to store and forward binary objects of sufficient length
and with sufficient reliability while preserving the order of
messages for each transaction can be used.
The transfer mechanism should be able to indicate message loss,
excessive delay, and possibly other transmission errors. In such
cases, the PKI entities MUST report an error as specified in
Section 3.6, as far as possible.
6.4.1. File-Based Transfer
CMP messages MAY be transferred between PKI entities using file-based
mechanisms, for instance, when an EE is offline or a PKI management
entity performs delayed delivery. Each file MUST contain the ASN.1
DER encoding of one CMP message only, where the message may be
nested. There MUST be no extraneous header or trailer information in
the file. The filename extension ".pki" MUST be used.
6.4.2. Other Asynchronous Transfer Protocols
Other asynchronous transfer protocols, e.g., email or website upload/
download, MAY transfer CMP messages between PKI entities. A MIME
wrapping is defined for those environments that are MIME-native. The
MIME wrapping is specified in Section 3.1 of [RFC8551].
The ASN.1 DER encoding of the CMP messages MUST be transferred using
the "application/pkixcmp" content type and base64-encoded content
transfer encoding, as specified in Section 3.4 of CMP over HTTP
[RFC6712]. A filename MUST be included either in a "content-type" or
a "content-disposition" statement. The filename extension ".pki"
MUST be used.
7. Conformance Requirements
This section defines which level of support for the various features
specified in this profile is required for each type of PKI entity.
7.1. PKI Management Operations
The following table provides an overview of the PKI management
operations specified in Sections 4 and 5 and states whether support
by conforming EE, RA, and CA implementations is mandatory,
recommended, optional, or not applicable. Variants amend or change
behavior of base PKI management operations and are therefore also
included.
The PKI management operation specifications in Section 4 assume that
either the RA or CA is the PKI management entity that terminates the
Certificate Management Protocol. If the RA terminates CMP, it either
responds directly as described in Section 5.1, or it forwards the
certificate management operation towards the CA not using CMP.
Section 5.2 describes different options of how an RA can forward a
CMP message using CMP. Section 5.3 offers the option that an RA
operates on behalf on an EE and therefore takes the role of the EE in
Section 4.
+==========+=============================+========+========+========+
| ID | PKI Management Operations | EE | RA | CA |
| | and Variants | | | |
+==========+=============================+========+========+========+
| Generic | Generic Aspects of PKI | MUST | MUST | MUST |
| | Messages and PKI | | | |
| | Management Operations, | | | |
| | Section 3 | | | |
+----------+-----------------------------+--------+--------+--------+
| IR | Enrolling an End Entity to | MUST | MAY | MUST |
| | a New PKI, Section 4.1.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| CR | Enrolling an End Entity to | MAY | MAY | MAY |
| | a Known PKI, Section 4.1.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| KUR | Updating a Valid | MUST | MAY | MUST |
| | Certificate, Section 4.1.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| P10CR | Enrolling an End Entity | MAY | MAY | MAY |
| | Using a PKCS #10 Request, | | | |
| | Section 4.1.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| MAC | Using MAC-Based Protection | MAY | SHOULD | MAY |
| | for Enrollment (IR, CR, | | 1) | |
| | and P10CR if supported), | | | |
| | Section 4.1.5 | | | |
+----------+-----------------------------+--------+--------+--------+
| CKeyGen | Adding Central Key Pair | MAY | MAY | MAY |
| | Generation to Enrollment | | | |
| | (IR, CR, KUR, and P10CR if | | | |
| | supported), Section 4.1.6 | | | |
+----------+-----------------------------+--------+--------+--------+
| RR | Revoking a Certificate, | SHOULD | SHOULD | SHOULD |
| | Section 4.2 | | 2) | 3) |
+----------+-----------------------------+--------+--------+--------+
| CACerts | Get CA Certificates, | MAY | MAY | MAY |
| | Section 4.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| RootUpd | Get Root CA Certificate | MAY | MAY | MAY |
| | Update, Section 4.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| ReqTempl | Get Certificate Request | MAY | MAY | MAY |
| | Template, Section 4.3.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| CRLUpd | CRL Update Retrieval, | MAY | MAY | MAY |
| | Section 4.3.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| Polling | Handling Delayed Delivery, | MAY | MAY | MAY |
| | Section 4.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertResp | Responding to a | N/A | MAY | MUST |
| | Certificate Request (IR, | | | |
| | CR, KUR, and P10CR if | | | |
| | supported), Section 5.1.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertConf | Responding to a | N/A | MAY | MUST |
| | Confirmation Message, | | | |
| | Section 5.1.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| RevResp | Responding to a Revocation | N/A | MAY | SHOULD |
| | Request, Section 5.1.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| GenResp | Responding to a Support | N/A | MAY | MAY |
| | Message (CACerts, RootUpd, | | | |
| | ReqTempl, CRLUpd if | | | |
| | supported), Section 5.1.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| InitPoll | Initiating Delayed | N/A | MAY | MAY |
| | Delivery, Section 5.1.5 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdKeep | Forwarding Messages - Not | N/A | MUST | N/A |
| | Changing Protection, | | | |
| | Section 5.2.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdAddS | Forwarding Messages - | N/A | MUST | MUST |
| | Adding Protection to a | | | |
| | Request Message, | | | |
| | Section 5.2.2.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdAddB | Forwarding Messages - | N/A | MAY | MAY |
| | Batching Messages, | | | |
| | Section 5.2.2.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdReqKP | Forwarding Messages - Not | N/A | SHOULD | N/A |
| | Changing Proof-of- | | 1) | |
| | Possession, | | | |
| | Section 5.2.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdReqBP | Forwarding Messages - | N/A | MAY | MAY |
| | Using raVerified, | | | |
| | Section 5.2.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertROnB | Acting on Behalf of Other | N/A | MAY | N/A |
| | PKI Entities - Requesting | | | |
| | a Certificate, | | | |
| | Section 5.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| RevROnB | Acting on Behalf of Other | N/A | SHOULD | SHOULD |
| | PKI Entities - Revoking a | | 2) | 3) |
| | Certificate, Section 5.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
Table 3: Level of Support for PKI Management Operations and Variants
1) The RA should be able to change the CMP message protection from
MAC-based to signature-based protection; see Section 5.2.3.1.
2) The RA should be able to request certificate revocation on behalf
of an EE (see Section 5.3.2), e.g., in order to handle incidents.
3) An alternative would be to perform revocation at the CA without
using CMP, for instance, using a local administration interface.
7.2. Message Transfer
CMP does not have specific needs regarding message transfer, except
that, for each request message sent, eventually a sequence of one
response message should be received. Therefore, virtually any
reliable transfer mechanism can be used, such as HTTP, CoAP, and
file-based offline transfer. Thus, this document does not require
any specific transfer protocol to be supported by conforming
implementations.
On different links between PKI entities (e.g., EE-RA and RA-CA),
different transfer mechanisms, as specified in Section 6, may be
used.
HTTP SHOULD be supported and CoAP MAY be supported at all PKI
entities for maximizing general interoperability at transfer level.
Yet full flexibility is retained to choose whatever transfer
mechanism is suitable, for instance, for devices and system
architectures with specific constraints.
The following table lists the name and level of support specified for
each transfer mechanism.
+=========+=======================+========+========+========+
| ID | Message Transfer Type | EE | RA | CA |
+=========+=======================+========+========+========+
| HTTP | HTTP Transfer, | SHOULD | SHOULD | SHOULD |
| | Section 6.1 | | | |
+---------+-----------------------+--------+--------+--------+
| CoAP | CoAP Transfer, | MAY | MAY | MAY |
| | Section 6.2 | | | |
+---------+-----------------------+--------+--------+--------+
| Piggyb | Piggybacking on Other | MAY | MAY | MAY |
| | Reliable Transfer, | | | |
| | Section 6.3 | | | |
+---------+-----------------------+--------+--------+--------+
| Offline | Offline Transfer, | MAY | MAY | MAY |
| | Section 6.4 | | | |
+---------+-----------------------+--------+--------+--------+
Table 4: Level of Support for Message Transfer Types
8. IANA Considerations
IANA has registered the following content in the "CMP Well-Known URI
Path Segments" registry (see <https://www.iana.org/assignments/cmp>),
as defined in [RFC8615].
+====================+==========================+===============+
| Path Segment | Description | Reference |
+====================+==========================+===============+
| initialization | Enrolling an End Entity | RFC 9483, |
| | to a New PKI over HTTP | Section 4.1.1 |
+--------------------+--------------------------+---------------+
| certification | Enrolling an End Entity | RFC 9483, |
| | to a Known PKI over HTTP | Section 4.1.2 |
+--------------------+--------------------------+---------------+
| keyupdate | Updating a Valid | RFC 9483, |
| | Certificate over HTTP | Section 4.1.3 |
+--------------------+--------------------------+---------------+
| pkcs10 | Enrolling an End Entity | RFC 9483, |
| | Using a PKCS #10 Request | Section 4.1.4 |
| | over HTTP | |
+--------------------+--------------------------+---------------+
| revocation | Revoking a Certificate | RFC 9483, |
| | over HTTP | Section 4.2 |
+--------------------+--------------------------+---------------+
| getcacerts | Get CA Certificates over | RFC 9483, |
| | HTTP | Section 4.3.1 |
+--------------------+--------------------------+---------------+
| getrootupdate | Get Root CA Certificate | RFC 9483, |
| | Update over HTTP | Section 4.3.2 |
+--------------------+--------------------------+---------------+
| getcertreqtemplate | Get Certificate Request | RFC 9483, |
| | Template over HTTP | Section 4.3.3 |
+--------------------+--------------------------+---------------+
| getcrls | CRL Update Retrieval | RFC 9483, |
| | over HTTP | Section 4.3.4 |
+--------------------+--------------------------+---------------+
| nested | Batching Messages over | RFC 9483, |
| | HTTP | Section |
| | | 5.2.2.2 |
+--------------------+--------------------------+---------------+
| ir | Enrolling an End Entity | RFC 9483, |
| | to a New PKI over CoAP | Section 4.1.1 |
+--------------------+--------------------------+---------------+
| cr | Enrolling an End Entity | RFC 9483, |
| | to a Known PKI over CoAP | Section 4.1.2 |
+--------------------+--------------------------+---------------+
| kur | Updating a Valid | RFC 9483, |
| | Certificate over CoAP | Section 4.1.3 |
+--------------------+--------------------------+---------------+
| p10 | Enrolling an End Entity | RFC 9483, |
| | Using a PKCS #10 Request | Section 4.1.4 |
| | over CoAP | |
+--------------------+--------------------------+---------------+
| rr | Revoking a Certificate | RFC 9483, |
| | over CoAP | Section 4.2 |
+--------------------+--------------------------+---------------+
| crts | Get CA Certificates over | RFC 9483, |
| | CoAP | Section 4.3.1 |
+--------------------+--------------------------+---------------+
| rcu | Get Root CA Certificate | RFC 9483, |
| | Update over CoAP | Section 4.3.2 |
+--------------------+--------------------------+---------------+
| att | Get Certificate Request | RFC 9483, |
| | Template over CoAP | Section 4.3.3 |
+--------------------+--------------------------+---------------+
| crls | CRL Update Retrieval | RFC 9483, |
| | over CoAP | Section 4.3.4 |
+--------------------+--------------------------+---------------+
| nest | Batching Messages over | RFC 9483, |
| | CoAP | Section |
| | | 5.2.2.2 |
+--------------------+--------------------------+---------------+
Table 5: New "CMP Well-Known URI Path Segments" Registry Entries
9. Security Considerations
The security considerations laid out in CMP [RFC4210] and updated by
CMP Updates [RFC9480], CMP Algorithms [RFC9481], CRMF [RFC4211],
Algorithm Requirements Update [RFC9045], CMP over HTTP [RFC6712], and
CMP over CoAP [RFC9482] apply.
Trust anchors for chain validations are often provided in the form of
self-signed certificates. All trust anchors MUST be stored on the
device with integrity protection. In some cases, a PKI entity may
not have sufficient storage for the complete certificates. In such
cases, it may only store, e.g., a hash of each self-signed
certificate and require receiving the certificate in the extraCerts
field, as described in Section 3.3. If such self-signed certificates
are provided in-band in the messages, they MUST be verified using
information from the trust store of the PKI entity.
For TLS using shared secret information-based authentication, both
PSK and PAKE provide the same amount of protection against a real-
time authentication attack, which is directly the amount of entropy
in the shared secret. The difference between a pre-shared key (PSK)
and a password-authenticated key exchange (PAKE) protocol is in the
level of long-term confidentiality of the TLS messages against brute-
force decryption, where a PSK-based cipher suite only provides
security according to the entropy of the shared secret, while a PAKE-
based cipher suite provides full security independent of the entropy
of the shared secret.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
<https://www.rfc-editor.org/info/rfc4211>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<https://www.rfc-editor.org/info/rfc5958>.
[RFC6712] Kause, T. and M. Peylo, "Internet X.509 Public Key
Infrastructure -- HTTP Transfer for the Certificate
Management Protocol (CMP)", RFC 6712,
DOI 10.17487/RFC6712, September 2012,
<https://www.rfc-editor.org/info/rfc6712>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC8933] Housley, R., "Update to the Cryptographic Message Syntax
(CMS) for Algorithm Identifier Protection", RFC 8933,
DOI 10.17487/RFC8933, October 2020,
<https://www.rfc-editor.org/info/rfc8933>.
[RFC9045] Housley, R., "Algorithm Requirements Update to the
Internet X.509 Public Key Infrastructure Certificate
Request Message Format (CRMF)", RFC 9045,
DOI 10.17487/RFC9045, June 2021,
<https://www.rfc-editor.org/info/rfc9045>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/info/rfc9325>.
[RFC9480] Brockhaus, H., von Oheimb, D., and J. Gray, "Certificate
Management Protocol (CMP) Updates", RFC 9480,
DOI 10.17487/RFC9480, November 2023,
<https://www.rfc-editor.org/info/rfc9480>.
[RFC9481] Brockhaus, H., Aschauer, H., Ounsworth, M., and J. Gray,
"Certificate Management Protocol (CMP) Algorithms",
RFC 9481, DOI 10.17487/RFC9481, November 2023,
<https://www.rfc-editor.org/info/rfc9481>.
[RFC9482] Sahni, M., Ed. and S. Tripathi, Ed., "Constrained
Application Protocol (CoAP) Transfer for the Certificate
Management Protocol", RFC 9482, DOI 10.17487/RFC9482,
November 2023, <https://www.rfc-editor.org/info/rfc9482>.
10.2. Informative References
[BRSKI-AE] von Oheimb, D., Fries, S., and H. Brockhaus, "BRSKI-AE:
Alternative Enrollment Protocols in BRSKI", Work in
Progress, Internet-Draft, draft-ietf-anima-brski-ae-05, 28
June 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-anima-brski-ae-05>.
[BRSKI-PRM]
Fries, S., Werner, T., Lear, E., and M. Richardson, "BRSKI
with Pledge in Responder Mode (BRSKI-PRM)", Work in
Progress, Internet-Draft, draft-ietf-anima-brski-prm-10,
23 October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-anima-brski-prm-10>.
[ETSI-3GPP.33.310]
3GPP, "Network Domain Security (NDS); Authentication
Framework (AF)", 3GPP TS 33.310 16.6.0, December 2020,
<http://www.3gpp.org/ftp/Specs/html-info/33310.htm>.
[ETSI-EN.319411-1]
ETSI, "Electronic Signatures and Infrastructures (ESI);
Policy and security requirements for Trust Service
Providers issuing certificates; Part 1: General
requirements", V1.3.1, ETSI EN 319 411-1, May 2021,
<https://www.etsi.org/deliver/
etsi_en/319400_319499/31941101/01.03.01_60/
en_31941101v010301p.pdf>.
[HTTP-CMP] Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- HTTP Transfer
for the Certificate Management Protocol (CMP)", Work in
Progress, Internet-Draft, draft-ietf-lamps-rfc6712bis-03,
10 February 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-lamps-rfc6712bis-03>.
[IEC.62443-3-3]
IEC, "Industrial communication networks - Network and
system security - Part 3-3: System security requirements
and security levels", IEC 62443-3-3:2013, August 2013,
<https://webstore.iec.ch/publication/7033>.
[IEEE.802.1AR_2018]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Secure Device Identity", IEEE Std 802.1AR-2018,
DOI 10.1109/IEEESTD.2018.8423794, August 2018,
<https://ieeexplore.ieee.org/document/8423794>.
[NIST.CSWP.04162018]
National Institute of Standards and Technology (NIST),
"Framework for Improving Critical Infrastructure
Cybersecurity", Version 1.1,
DOI 10.6028/NIST.CSWP.04162018, April 2018,
<http://nvlpubs.nist.gov/nistpubs/CSWP/
NIST.CSWP.04162018.pdf>.
[NIST.SP.800-57p1r5]
Barker, E., "Recommendation for Key Management: Part 1 -
General", DOI 10.6028/NIST.SP.800-57pt1r5, May 2020,
<https://doi.org/10.6028/NIST.SP.800-57pt1r5>.
[PKIX-CMP] Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- Certificate
Management Protocol (CMP)", Work in Progress, Internet-
Draft, draft-ietf-lamps-rfc4210bis-07, 19 June 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
rfc4210bis-07>.
[RFC3647] Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S.
Wu, "Internet X.509 Public Key Infrastructure Certificate
Policy and Certification Practices Framework", RFC 3647,
DOI 10.17487/RFC3647, November 2003,
<https://www.rfc-editor.org/info/rfc3647>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve
Cryptography (ECC) Algorithms in Cryptographic Message
Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January
2010, <https://www.rfc-editor.org/info/rfc5753>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", RFC 8551, DOI 10.17487/RFC8551,
April 2019, <https://www.rfc-editor.org/info/rfc8551>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
[RFC8649] Housley, R., "Hash Of Root Key Certificate Extension",
RFC 8649, DOI 10.17487/RFC8649, August 2019,
<https://www.rfc-editor.org/info/rfc8649>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
[SZTP-CSR] Watsen, K., Housley, R., and S. Turner, "Conveying a
Certificate Signing Request (CSR) in a Secure Zero Touch
Provisioning (SZTP) Bootstrapping Request", Work in
Progress, Internet-Draft, draft-ietf-netconf-sztp-csr-14,
2 March 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-netconf-sztp-csr-14>.
[UNISIG.Subset-137]
UNISIG, "ERTMS/ETCS On-line Key Management FFFIS", Subset-
137, V1.0.0, December 2015,
<https://www.era.europa.eu/system/files/2023-01/
sos3_index083_-_subset-137_v100.pdf>.
Appendix A. Example CertReqTemplate
Suppose the server requires that the certTemplate contains:
* the issuer field with a value to be filled in by the EE,
* the subject field with a common name to be filled in by the EE and
two organizational unit fields with given values "myDept" and
"myGroup",
* the publicKey field contains an Elliptic Curve Cryptography (ECC)
key on curve secp256r1 or an RSA public key of length 2048,
* the subjectAltName extension with DNS name "www.myServer.com" and
an IP address to be filled in,
* the keyUsage extension marked critical with the value
digitalSignature and keyAgreement, and
* the extKeyUsage extension with values to be filled in by the EE.
Then the infoValue with certTemplate and keySpec fields returned to
the EE will be encoded as follows:
SEQUENCE {
SEQUENCE {
[3] {
SEQUENCE {}
}
[5] {
SEQUENCE {
SET {
SEQUENCE {
OBJECT IDENTIFIER commonName (2 5 4 3)
UTF8String ""
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myDept"
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myGroup"
}
}
}
}
[9] {
SEQUENCE {
OBJECT IDENTIFIER subjectAltName (2 5 29 17)
OCTET STRING, encapsulates {
SEQUENCE {
[2] "www.myServer.com"
[7] ""
}
}
}
SEQUENCE {
OBJECT IDENTIFIER keyUsage (2 5 29 15)
BOOLEAN TRUE
OCTET STRING, encapsulates {
BIT STRING 3 unused bits
"10001"B
}
}
SEQUENCE {
OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
OCTET STRING, encapsulates {
SEQUENCE {}
}
}
}
}
SEQUENCE {
SEQUENCE {
OBJECT IDENTIFIER algId (1 3 6 1 5 5 7 5 1 11)
SEQUENCE {
OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
OBJECT IDENTIFIER secp256r1 (1 2 840 10045 3 1 7)
}
}
SEQUENCE {
OBJECT IDENTIFIER rsaKeyLen (1 3 6 1 5 5 7 5 1 12)
INTEGER 2048
}
}
}
Acknowledgements
We thank the various reviewers of this document.
Authors' Addresses
Hendrik Brockhaus
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: hendrik.brockhaus@siemens.com
URI: https://www.siemens.com
David von Oheimb
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: david.von.oheimb@siemens.com
URI: https://www.siemens.com
Steffen Fries
Siemens AG
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: steffen.fries@siemens.com
URI: https://www.siemens.com