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Network Working Group C. Adams
Request for Comments: 2510 Entrust Technologies
Category: Standards Track S. Farrell
SSE
March 1999
Internet X.509 Public Key Infrastructure
Certificate Management Protocols
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document describes the Internet X.509 Public Key Infrastructure
(PKI) Certificate Management Protocols. Protocol messages are defined
for all relevant aspects of certificate creation and management.
Note that "certificate" in this document refers to an X.509v3
Certificate as defined in [COR95, X509-AM].
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC2119].
Introduction
The layout of this document is as follows:
- Section 1 contains an overview of PKI management;
- Section 2 contains discussion of assumptions and restrictions;
- Section 3 contains data structures used for PKI management messages;
- Section 4 defines the functions that are to be carried out in PKI
management by conforming implementations;
- Section 5 describes a simple protocol for transporting PKI messages;
- the Appendices specify profiles for conforming implementations and
provide an ASN.1 module containing the syntax for all messages
defined in this specification.
Adams & Farrell Standards Track [Page 1]
RFC 2510 PKI Certificate Management Protocols March 1999
1 PKI Management Overview
The PKI must be structured to be consistent with the types of
individuals who must administer it. Providing such administrators
with unbounded choices not only complicates the software required but
also increases the chances that a subtle mistake by an administrator
or software developer will result in broader compromise. Similarly,
restricting administrators with cumbersome mechanisms will cause them
not to use the PKI.
Management protocols are REQUIRED to support on-line interactions
between Public Key Infrastructure (PKI) components. For example, a
management protocol might be used between a Certification Authority
(CA) and a client system with which a key pair is associated, or
between two CAs that issue cross-certificates for each other.
1.1 PKI Management Model
Before specifying particular message formats and procedures we first
define the entities involved in PKI management and their interactions
(in terms of the PKI management functions required). We then group
these functions in order to accommodate different identifiable types
of end entities.
1.2 Definitions of PKI Entities
The entities involved in PKI management include the end entity (i.e.,
the entity to be named in the subject field of a certificate) and the
certification authority (i.e., the entity named in the issuer field
of a certificate). A registration authority MAY also be involved in
PKI management.
1.2.1 Subjects and End Entities
The term "subject" is used here to refer to the entity named in the
subject field of a certificate; when we wish to distinguish the tools
and/or software used by the subject (e.g., a local certificate
management module) we will use the term "subject equipment". In
general, the term "end entity" (EE) rather than subject is preferred
in order to avoid confusion with the field name.
It is important to note that the end entities here will include not
only human users of applications, but also applications themselves
(e.g., for IP security). This factor influences the protocols which
the PKI management operations use; for example, application software
is far more likely to know exactly which certificate extensions are
required than are human users. PKI management entities are also end
entities in the sense that they are sometimes named in the subject
Adams & Farrell Standards Track [Page 2]
RFC 2510 PKI Certificate Management Protocols March 1999
field of a certificate or cross-certificate. Where appropriate, the
term "end-entity" will be used to refer to end entities who are not
PKI management entities.
All end entities require secure local access to some information --
at a minimum, their own name and private key, the name of a CA which
is directly trusted by this entity and that CA's public key (or a
fingerprint of the public key where a self-certified version is
available elsewhere). Implementations MAY use secure local storage
for more than this minimum (e.g., the end entity's own certificate or
application-specific information). The form of storage will also vary
-- from files to tamper-resistant cryptographic tokens. Such local
trusted storage is referred to here as the end entity's Personal
Security Environment (PSE).
Though PSE formats are beyond the scope of this document (they are
very dependent on equipment, et cetera), a generic interchange format
for PSEs is defined here - a certification response message MAY be
used.
1.2.2 Certification Authority
The certification authority (CA) may or may not actually be a real
"third party" from the end entity's point of view. Quite often, the
CA will actually belong to the same organization as the end entities
it supports.
Again, we use the term CA to refer to the entity named in the issuer
field of a certificate; when it is necessary to distinguish the
software or hardware tools used by the CA we use the term "CA
equipment".
The CA equipment will often include both an "off-line" component and
an "on-line" component, with the CA private key only available to the
"off-line" component. This is, however, a matter for implementers
(though it is also relevant as a policy issue).
We use the term "root CA" to indicate a CA that is directly trusted
by an end entity; that is, securely acquiring the value of a root CA
public key requires some out-of-band step(s). This term is not meant
to imply that a root CA is necessarily at the top of any hierarchy,
simply that the CA in question is trusted directly.
A "subordinate CA" is one that is not a root CA for the end entity in
question. Often, a subordinate CA will not be a root CA for any
entity but this is not mandatory.
Adams & Farrell Standards Track [Page 3]
RFC 2510 PKI Certificate Management Protocols March 1999
1.2.3 Registration Authority
In addition to end-entities and CAs, many environments call for the
existence of a Registration Authority (RA) separate from the
Certification Authority. The functions which the registration
authority may carry out will vary from case to case but MAY include
personal authentication, token distribution, revocation reporting,
name assignment, key generation, archival of key pairs, et cetera.
This document views the RA as an OPTIONAL component - when it is not
present the CA is assumed to be able to carry out the RA's functions
so that the PKI management protocols are the same from the end-
entity's point of view.
Again, we distinguish, where necessary, between the RA and the tools
used (the "RA equipment").
Note that an RA is itself an end entity. We further assume that all
RAs are in fact certified end entities and that RAs have private keys
that are usable for signing. How a particular CA equipment identifies
some end entities as RAs is an implementation issue (i.e., this
document specifies no special RA certification operation). We do not
mandate that the RA is certified by the CA with which it is
interacting at the moment (so one RA may work with more than one CA
whilst only being certified once).
In some circumstances end entities will communicate directly with a
CA even where an RA is present. For example, for initial registration
and/or certification the subject may use its RA, but communicate
directly with the CA in order to refresh its certificate.
1.3 PKI Management Requirements
The protocols given here meet the following requirements on PKI
management.
1. PKI management must conform to the ISO 9594-8 standard and the
associated amendments (certificate extensions)
2. PKI management must conform to the other parts of this series.
3. It must be possible to regularly update any key pair without
affecting any other key pair.
4. The use of confidentiality in PKI management protocols must be
kept to a minimum in order to ease regulatory problems.
Adams & Farrell Standards Track [Page 4]
RFC 2510 PKI Certificate Management Protocols March 1999
5. PKI management protocols must allow the use of different
industry-standard cryptographic algorithms, (specifically
including RSA, DSA, MD5, SHA-1) -- this means that any given
CA, RA, or end entity may, in principle, use whichever
algorithms suit it for its own key pair(s).
6. PKI management protocols must not preclude the generation of
key pairs by the end-entity concerned, by an RA, or by a CA --
key generation may also occur elsewhere, but for the purposes
of PKI management we can regard key generation as occurring
wherever the key is first present at an end entity, RA, or CA.
7. PKI management protocols must support the publication of
certificates by the end-entity concerned, by an RA, or by a CA.
Different implementations and different environments may choose
any of the above approaches.
8. PKI management protocols must support the production of
Certificate Revocation Lists (CRLs) by allowing certified end
entities to make requests for the revocation of certificates -
this must be done in such a way that the denial-of-service
attacks which are possible are not made simpler.
9. PKI management protocols must be usable over a variety of
"transport" mechanisms, specifically including mail, http,
TCP/IP and ftp.
10. Final authority for certification creation rests with the CA;
no RA or end-entity equipment can assume that any certificate
issued by a CA will contain what was requested -- a CA may
alter certificate field values or may add, delete or alter
extensions according to its operating policy. In other words,
all PKI entities (end-entities, RAs, and CAs) must be capable
of handling responses to requests for certificates in which
the actual certificate issued is different from that requested
(for example, a CA may shorten the validity period requested).
Note that policy may dictate that the CA must not publish or
otherwise distribute the certificate until the requesting
entity has reviewed and accepted the newly-created certificate
(typically through use of the PKIConfirm message).
11. A graceful, scheduled change-over from one non-compromised CA
key pair to the next (CA key update) must be supported (note
that if the CA key is compromised, re-initialization must be
performed for all entities in the domain of that CA). An end
entity whose PSE contains the new CA public key (following a
CA key update) must also be able to verify certificates
verifiable using the old public key. End entities who directly
Adams & Farrell Standards Track [Page 5]
RFC 2510 PKI Certificate Management Protocols March 1999
trust the old CA key pair must also be able to verify
certificates signed using the new CA private key. (Required
for situations where the old CA public key is "hardwired" into
the end entity's cryptographic equipment).
12. The Functions of an RA may, in some implementations or
environments, be carried out by the CA itself. The protocols
must be designed so that end entities will use the same
protocol (but, of course, not the same key!) regardless of
whether the communication is with an RA or CA.
13. Where an end entity requests a certificate containing a given
public key value, the end entity must be ready to demonstrate
possession of the corresponding private key value. This may be
accomplished in various ways, depending on the type of
certification request. See Section 2.3, "Proof of Possession
of Private Key", for details of the in-band methods defined
for the PKIX-CMP (i.e., Certificate Management Protocol)
messages.
PKI Management Operations
The following diagram shows the relationship between the entities
defined above in terms of the PKI management operations. The letters
in the diagram indicate "protocols" in the sense that a defined set
of PKI management messages can be sent along each of the lettered
lines.
Adams & Farrell Standards Track [Page 6]
RFC 2510 PKI Certificate Management Protocols March 1999
+---+ cert. publish +------------+ j
| | <--------------------- | End Entity | <-------
| C | g +------------+ "out-of-band"
| | | ^ loading
| e | | | initial
| r | a | | b registration/
| t | | | certification
| | | | key pair recovery
| / | | | key pair update
| | | | certificate update
| C | PKI "USERS" V | revocation request
| R | -------------------+-+-----+-+------+-+-------------------
| L | PKI MANAGEMENT | ^ | ^
| | ENTITIES a | | b a | | b
| | V | | |
| R | g +------+ d | |
| e | <------------ | RA | <-----+ | |
| p | cert. | | ----+ | | |
| o | publish +------+ c | | | |
| s | | | | |
| i | V | V |
| t | g +------------+ i
| o | <------------------------| CA |------->
| r | h +------------+ "out-of-band"
| y | cert. publish | ^ publication
| | CRL publish | |
+---+ | | cross-certification
e | | f cross-certificate
| | update
| |
V |
+------+
| CA-2 |
+------+
Figure 1 - PKI Entities
At a high level the set of operations for which management messages
are defined can be grouped as follows.
1 CA establishment: When establishing a new CA, certain steps are
required (e.g., production of initial CRLs, export of CA public
key).
2 End entity initialization: this includes importing a root CA
public key and requesting information about the options
supported by a PKI management entity.
Adams & Farrell Standards Track [Page 7]
RFC 2510 PKI Certificate Management Protocols March 1999
3 Certification: various operations result in the creation of new
certificates:
3.1 initial registration/certification: This is the process
whereby an end entity first makes itself known to a CA or
RA, prior to the CA issuing a certificate or certificates
for that end entity. The end result of this process (when it
is successful) is that a CA issues a certificate for an end
entity's public key, and returns that certificate to the end
entity and/or posts that certificate in a public repository.
This process may, and typically will, involve multiple
"steps", possibly including an initialization of the end
entity's equipment. For example, the end entity's equipment
must be securely initialized with the public key of a CA, to
be used in validating certificate paths. Furthermore, an
end entity typically needs to be initialized with its own
key pair(s).
3.2 key pair update: Every key pair needs to be updated
regularly (i.e., replaced with a new key pair), and a new
certificate needs to be issued.
3.3 certificate update: As certificates expire they may be
"refreshed" if nothing relevant in the environment has
changed.
3.4 CA key pair update: As with end entities, CA key pairs need
to be updated regularly; however, different mechanisms are
required.
3.5 cross-certification request: One CA requests issuance of a
cross-certificate from another CA. For the purposes of this
standard, the following terms are defined. A "cross-
certificate" is a certificate in which the subject CA and
the issuer CA are distinct and SubjectPublicKeyInfo contains
a verification key (i.e., the certificate has been issued
for the subject CA's signing key pair). When it is
necessary to distinguish more finely, the following terms
may be used: a cross-certificate is called an "inter-domain
cross-certificate" if the subject and issuer CAs belong to
different administrative domains; it is called an "intra-
domain cross-certificate" otherwise.
Adams & Farrell Standards Track [Page 8]
RFC 2510 PKI Certificate Management Protocols March 1999
Notes:
Note 1. The above definition of "cross-certificate" aligns with the
defined term "CA-certificate" in X.509. Note that this term is not
to be confused with the X.500 "cACertificate" attribute type, which
is unrelated.
Note 2. In many environments the term "cross-certificate", unless
further qualified, will be understood to be synonymous with "inter-
domain cross-certificate" as defined above.
Note 3. Issuance of cross-certificates may be, but is not
necessarily, mutual; that is, two CAs may issue cross-certificates
for each other.
3.6 cross-certificate update: Similar to a normal certificate
update but involving a cross-certificate.
4 Certificate/CRL discovery operations: some PKI management
operations result in the publication of certificates or CRLs:
4.1 certificate publication: Having gone to the trouble of
producing a certificate, some means for publishing it is
needed. The "means" defined in PKIX MAY involve the
messages specified in Sections 3.3.13 - 3.3.16, or MAY
involve other methods (LDAP, for example) as described in
the "Operational Protocols" documents of the PKIX series of
specifications.
4.2 CRL publication: As for certificate publication.
5 Recovery operations: some PKI management operations are used
when an end entity has "lost" its PSE:
5.1 key pair recovery: As an option, user client key materials
(e.g., a user's private key used for decryption purposes)
MAY be backed up by a CA, an RA, or a key backup system
associated with a CA or RA. If an entity needs to recover
these backed up key materials (e.g., as a result of a
forgotten password or a lost key chain file), a protocol
exchange may be needed to support such recovery.
6 Revocation operations: some PKI operations result in the
creation of new CRL entries and/or new CRLs:
6.1 revocation request: An authorized person advises a CA of an
abnormal situation requiring certificate revocation.
Adams & Farrell Standards Track [Page 9]
RFC 2510 PKI Certificate Management Protocols March 1999
7 PSE operations: whilst the definition of PSE operations (e.g.,
moving a PSE, changing a PIN, etc.) are beyond the scope of this
specification, we do define a PKIMessage (CertRepMessage) which
can form the basis of such operations.
Note that on-line protocols are not the only way of implementing the
above operations. For all operations there are off-line methods of
achieving the same result, and this specification does not mandate
use of on-line protocols. For example, when hardware tokens are
used, many of the operations MAY be achieved as part of the physical
token delivery.
Later sections define a set of standard messages supporting the above
operations. The protocols for conveying these exchanges in different
environments (file based, on-line, E-mail, and WWW) is also
specified.
2. Assumptions and restrictions
2.1 End entity initialization
The first step for an end entity in dealing with PKI management
entities is to request information about the PKI functions supported
and to securely acquire a copy of the relevant root CA public key(s).
2.2 Initial registration/certification
There are many schemes that can be used to achieve initial
registration and certification of end entities. No one method is
suitable for all situations due to the range of policies which a CA
may implement and the variation in the types of end entity which can
occur.
We can however, classify the initial registration / certification
schemes that are supported by this specification. Note that the word
"initial", above, is crucial - we are dealing with the situation
where the end entity in question has had no previous contact with the
PKI. Where the end entity already possesses certified keys then some
simplifications/alternatives are possible.
Having classified the schemes that are supported by this
specification we can then specify some as mandatory and some as
optional. The goal is that the mandatory schemes cover a sufficient
number of the cases which will arise in real use, whilst the optional
schemes are available for special cases which arise less frequently.
In this way we achieve a balance between flexibility and ease of
implementation.
Adams & Farrell Standards Track [Page 10]
RFC 2510 PKI Certificate Management Protocols March 1999
We will now describe the classification of initial registration /
certification schemes.
2.2.1 Criteria used
2.2.1.1 Initiation of registration / certification
In terms of the PKI messages which are produced we can regard the
initiation of the initial registration / certification exchanges as
occurring wherever the first PKI message relating to the end entity
is produced. Note that the real-world initiation of the registration
/ certification procedure may occur elsewhere (e.g., a personnel
department may telephone an RA operator).
The possible locations are at the end entity, an RA, or a CA.
2.2.1.2 End entity message origin authentication
The on-line messages produced by the end entity that requires a
certificate may be authenticated or not. The requirement here is to
authenticate the origin of any messages from the end entity to the
PKI (CA/RA).
In this specification, such authentication is achieved by the PKI
(CA/RA) issuing the end entity with a secret value (initial
authentication key) and reference value (used to identify the
transaction) via some out-of-band means. The initial authentication
key can then be used to protect relevant PKI messages.
We can thus classify the initial registration/certification scheme
according to whether or not the on-line end entity -> PKI messages
are authenticated or not.
Note 1: We do not discuss the authentication of the PKI -> end entity
messages here as this is always REQUIRED. In any case, it can be
achieved simply once the root-CA public key has been installed at the
end entity's equipment or it can be based on the initial
authentication key.
Note 2: An initial registration / certification procedure can be
secure where the messages from the end entity are authenticated via
some out- of-band means (e.g., a subsequent visit).
2.2.1.3 Location of key generation
In this specification, "key generation" is regarded as occurring
wherever either the public or private component of a key pair first
occurs in a PKIMessage. Note that this does not preclude a
Adams & Farrell Standards Track [Page 11]
RFC 2510 PKI Certificate Management Protocols March 1999
centralized key generation service - the actual key pair MAY have
been generated elsewhere and transported to the end entity, RA, or CA
using a (proprietary or standardized) key generation request/response
protocol (outside the scope of this specification).
There are thus three possibilities for the location of "key
generation": the end entity, an RA, or a CA.
2.2.1.4 Confirmation of successful certification
Following the creation of an initial certificate for an end entity,
additional assurance can be gained by having the end entity
explicitly confirm successful receipt of the message containing (or
indicating the creation of) the certificate. Naturally, this
confirmation message must be protected (based on the initial
authentication key or other means).
This gives two further possibilities: confirmed or not.
2.2.2 Mandatory schemes
The criteria above allow for a large number of initial registration /
certification schemes. This specification mandates that conforming CA
equipment, RA equipment, and EE equipment MUST support the second
scheme listed below. Any entity MAY additionally support other
schemes, if desired.
2.2.2.1 Centralized scheme
In terms of the classification above, this scheme is, in some ways,
the simplest possible, where:
- initiation occurs at the certifying CA;
- no on-line message authentication is required;
- "key generation" occurs at the certifying CA (see Section 2.2.1.3);
- no confirmation message is required.
In terms of message flow, this scheme means that the only message
required is sent from the CA to the end entity. The message must
contain the entire PSE for the end entity. Some out-of-band means
must be provided to allow the end entity to authenticate the message
received and decrypt any encrypted values.
Adams & Farrell Standards Track [Page 12]
RFC 2510 PKI Certificate Management Protocols March 1999
2.2.2.2 Basic authenticated scheme
In terms of the classification above, this scheme is where:
- initiation occurs at the end entity;
- message authentication is REQUIRED;
- "key generation" occurs at the end entity (see Section 2.2.1.3);
- a confirmation message is REQUIRED.
In terms of message flow, the basic authenticated scheme is as
follows:
End entity RA/CA
========== =============
out-of-band distribution of Initial Authentication
Key (IAK) and reference value (RA/CA -> EE)
Key generation
Creation of certification request
Protect request with IAK
-->>--certification request-->>--
verify request
process request
create response
--<<--certification response--<<--
handle response
create confirmation
-->>--confirmation message-->>--
verify confirmation
(Where verification of the confirmation message fails, the RA/CA MUST
revoke the newly issued certificate if it has been published or
otherwise made available.)
2.3 Proof of Possession (POP) of Private Key
In order to prevent certain attacks and to allow a CA/RA to properly
check the validity of the binding between an end entity and a key
pair, the PKI management operations specified here make it possible
for an end entity to prove that it has possession of (i.e., is able
to use) the private key corresponding to the public key for which a
certificate is requested. A given CA/RA is free to choose how to
enforce POP (e.g., out-of-band procedural means versus PKIX-CMP in-
band messages) in its certification exchanges (i.e., this may be a
policy issue). However, it is REQUIRED that CAs/RAs MUST enforce POP
by some means because there are currently many non-PKIX operational
protocols in use (various electronic mail protocols are one example)
that do not explicitly check the binding between the end entity and
the private key. Until operational protocols that do verify the
Adams & Farrell Standards Track [Page 13]
RFC 2510 PKI Certificate Management Protocols March 1999
binding (for signature, encryption, and key agreement key pairs)
exist, and are ubiquitous, this binding can only be assumed to have
been verified by the CA/RA. Therefore, if the binding is not verified
by the CA/RA, certificates in the Internet Public-Key Infrastructure
end up being somewhat less meaningful.
POP is accomplished in different ways depending upon the type of key
for which a certificate is requested. If a key can be used for
multiple purposes (e.g., an RSA key) then any appropriate method MAY
be used (e.g., a key which may be used for signing, as well as other
purposes, SHOULD NOT be sent to the CA/RA in order to prove
possession).
This specification explicitly allows for cases where an end entity
supplies the relevant proof to an RA and the RA subsequently attests
to the CA that the required proof has been received (and validated!).
For example, an end entity wishing to have a signing key certified
could send the appropriate signature to the RA which then simply
notifies the relevant CA that the end entity has supplied the
required proof. Of course, such a situation may be disallowed by some
policies (e.g., CAs may be the only entities permitted to verify POP
during certification).
2.3.1 Signature Keys
For signature keys, the end entity can sign a value to prove
possession of the private key.
2.3.2 Encryption Keys
For encryption keys, the end entity can provide the private key to
the CA/RA, or can be required to decrypt a value in order to prove
possession of the private key (see Section 3.2.8). Decrypting a value
can be achieved either directly or indirectly.
The direct method is for the RA/CA to issue a random challenge to
which an immediate response by the EE is required.
The indirect method is to issue a certificate which is encrypted for
the end entity (and have the end entity demonstrate its ability to
decrypt this certificate in the confirmation message). This allows a
CA to issue a certificate in a form which can only be used by the
intended end entity.
This specification encourages use of the indirect method because this
requires no extra messages to be sent (i.e., the proof can be
demonstrated using the {request, response, confirmation} triple of
messages).
Adams & Farrell Standards Track [Page 14]
RFC 2510 PKI Certificate Management Protocols March 1999
2.3.3 Key Agreement Keys
For key agreement keys, the end entity and the PKI management entity
(i.e., CA or RA) must establish a shared secret key in order to prove
that the end entity has possession of the private key.
Note that this need not impose any restrictions on the keys that can
be certified by a given CA -- in particular, for Diffie-Hellman keys
the end entity may freely choose its algorithm parameters -- provided
that the CA can generate a short-term (or one-time) key pair with the
appropriate parameters when necessary.
2.4 Root CA key update
This discussion only applies to CAs that are a root CA for some end
entity.
The basis of the procedure described here is that the CA protects its
new public key using its previous private key and vice versa. Thus
when a CA updates its key pair it must generate two extra
cACertificate attribute values if certificates are made available
using an X.500 directory (for a total of four: OldWithOld;
OldWithNew; NewWithOld; and NewWithNew).
When a CA changes its key pair those entities who have acquired the
old CA public key via "out-of-band" means are most affected. It is
these end entities who will need access to the new CA public key
protected with the old CA private key. However, they will only
require this for a limited period (until they have acquired the new
CA public key via the "out-of-band" mechanism). This will typically
be easily achieved when these end entities' certificates expire.
The data structure used to protect the new and old CA public keys is
a standard certificate (which may also contain extensions). There are
no new data structures required.
Note 1. This scheme does not make use of any of the X.509 v3
extensions as it must be able to work even for version 1
certificates. The presence of the KeyIdentifier extension would make
for efficiency improvements.
Note 2. While the scheme could be generalized to cover cases where
the CA updates its key pair more than once during the validity period
of one of its end entities' certificates, this generalization seems
of dubious value. Not having this generalization simply means that
the validity period of a CA key pair must be greater than the
validity period of any certificate issued by that CA using that key
pair.
Adams & Farrell Standards Track [Page 15]
RFC 2510 PKI Certificate Management Protocols March 1999
Note 3.This scheme forces end entities to acquire the new CA public
key on the expiry of the last certificate they owned that was signed
with the old CA private key (via the "out-of-band" means).
Certificate and/or key update operations occurring at other times do
not necessarily require this (depending on the end entity's
equipment).
2.4.1 CA Operator actions
To change the key of the CA, the CA operator does the following:
1. Generate a new key pair;
2. Create a certificate containing the old CA public key signed
with the new private key (the "old with new" certificate);
3. Create a certificate containing the new CA public key signed
with the old private key (the "new with old" certificate);
4. Create a certificate containing the new CA public key signed
with the new private key (the "new with new" certificate);
5. Publish these new certificates via the directory and/or other
means (perhaps using a CAKeyUpdAnn message);
6. Export the new CA public key so that end entities may acquire
it using the "out-of-band" mechanism (if required).
The old CA private key is then no longer required. The old CA public
key will however remain in use for some time. The time when the old
CA public key is no longer required (other than for non-repudiation)
will be when all end entities of this CA have securely acquired the
new CA public key.
The "old with new" certificate must have a validity period starting
at the generation time of the old key pair and ending at the expiry
date of the old public key.
The "new with old" certificate must have a validity period starting
at the generation time of the new key pair and ending at the time by
which all end entities of this CA will securely possess the new CA
public key (at the latest, the expiry date of the old public key).
The "new with new" certificate must have a validity period starting
at the generation time of the new key pair and ending at the time by
which the CA will next update its key pair.
Adams & Farrell Standards Track [Page 16]
RFC 2510 PKI Certificate Management Protocols March 1999
2.4.2 Verifying Certificates.
Normally when verifying a signature, the verifier verifies (among
other things) the certificate containing the public key of the
signer. However, once a CA is allowed to update its key there are a
range of new possibilities. These are shown in the table below.
Repository contains NEW Repository contains only OLD
and OLD public keys public key (due to, e.g.,
delay in publication)
PSE PSE Contains PSE Contains PSE Contains
Contains OLD public NEW public OLD public
NEW public key key key
key
Signer's Case 1: Case 3: Case 5: Case 7:
certifi- This is In this case Although the In this case
cate is the the verifier CA operator the CA
protected standard must access has not operator has
using NEW case where the updated the not updated
public the directory in directory the the directory
key verifier order to get verifier can and so the
can the value of verify the verification
directly the NEW certificate will FAIL
verify the public key directly -
certificate this is thus
without the same as
using the case 1.
directory
Signer's Case 2: Case 4: Case 6: Case 8:
certifi- In this In this case The verifier Although the
cate is case the the verifier thinks this CA operator
protected verifier can directly is the has not
using OLD must verify the situation of updated the
public access the certificate case 2 and directory the
key directory without will access verifier can
in order using the the verify the
to get the directory directory; certificate
value of however, the directly -
the OLD verification this is thus
public key will FAIL the same as
case 4.
Adams & Farrell Standards Track [Page 17]
RFC 2510 PKI Certificate Management Protocols March 1999
2.4.2.1 Verification in cases 1, 4, 5 and 8.
In these cases the verifier has a local copy of the CA public key
which can be used to verify the certificate directly. This is the
same as the situation where no key change has occurred.
Note that case 8 may arise between the time when the CA operator has
generated the new key pair and the time when the CA operator stores
the updated attributes in the directory. Case 5 can only arise if the
CA operator has issued both the signer's and verifier's certificates
during this "gap" (the CA operator SHOULD avoid this as it leads to
the failure cases described below).
2.4.2.2 Verification in case 2.
In case 2 the verifier must get access to the old public key of the
CA. The verifier does the following:
1. Look up the caCertificate attribute in the directory and pick
the OldWithNew certificate (determined based on validity
periods);
2. Verify that this is correct using the new CA key (which the
verifier has locally);
3. If correct, check the signer's certificate using the old CA
key.
Case 2 will arise when the CA operator has issued the signer's
certificate, then changed key and then issued the verifier's
certificate, so it is quite a typical case.
2.4.2.3 Verification in case 3.
In case 3 the verifier must get access to the new public key of the
CA. The verifier does the following:
1. Look up the CACertificate attribute in the directory and pick
the NewWithOld certificate (determined based on validity
periods);
2. Verify that this is correct using the old CA key (which the
verifier has stored locally);
3. If correct, check the signer's certificate using the new CA
key.
Case 3 will arise when the CA operator has issued the verifier's
certificate, then changed key and then issued the signer's
certificate, so it is also quite a typical case.
Adams & Farrell Standards Track [Page 18]
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2.4.2.4 Failure of verification in case 6.
In this case the CA has issued the verifier's PSE containing the new
key without updating the directory attributes. This means that the
verifier has no means to get a trustworthy version of the CA's old
key and so verification fails.
Note that the failure is the CA operator's fault.
2.4.2.5 Failure of verification in case 7.
In this case the CA has issued the signer's certificate protected
with the new key without updating the directory attributes. This
means that the verifier has no means to get a trustworthy version of
the CA's new key and so verification fails.
Note that the failure is again the CA operator's fault.
2.4.3 Revocation - Change of CA key
As we saw above the verification of a certificate becomes more
complex once the CA is allowed to change its key. This is also true
for revocation checks as the CA may have signed the CRL using a newer
private key than the one that is within the user's PSE.
The analysis of the alternatives is as for certificate verification.
3. Data Structures
This section contains descriptions of the data structures required
for PKI management messages. Section 4 describes constraints on their
values and the sequence of events for each of the various PKI
management operations. Section 5 describes how these may be
encapsulated in various transport mechanisms.
3.1 Overall PKI Message
All of the messages used in this specification for the purposes of
PKI management use the following structure:
PKIMessage ::= SEQUENCE {
header PKIHeader,
body PKIBody,
protection [0] PKIProtection OPTIONAL,
extraCerts [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL
}
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RFC 2510 PKI Certificate Management Protocols March 1999
The PKIHeader contains information which is common to many PKI
messages.
The PKIBody contains message-specific information.
The PKIProtection, when used, contains bits that protect the PKI
message.
The extraCerts field can contain certificates that may be useful to
the recipient. For example, this can be used by a CA or RA to present
an end entity with certificates that it needs to verify its own new
certificate (if, for example, the CA that issued the end entity's
certificate is not a root CA for the end entity). Note that this
field does not necessarily contain a certification path - the
recipient may have to sort, select from, or otherwise process the
extra certificates in order to use them.
3.1.1 PKI Message Header
All PKI messages require some header information for addressing and
transaction identification. Some of this information will also be
present in a transport-specific envelope; however, if the PKI message
is protected then this information is also protected (i.e., we make
no assumption about secure transport).
The following data structure is used to contain this information:
PKIHeader ::= SEQUENCE {
pvno INTEGER { ietf-version2 (1) },
sender GeneralName,
-- identifies the sender
recipient GeneralName,
-- identifies the intended recipient
messageTime [0] GeneralizedTime OPTIONAL,
-- time of production of this message (used when sender
-- believes that the transport will be "suitable"; i.e.,
-- that the time will still be meaningful upon receipt)
protectionAlg [1] AlgorithmIdentifier OPTIONAL,
-- algorithm used for calculation of protection bits
senderKID [2] KeyIdentifier OPTIONAL,
recipKID [3] KeyIdentifier OPTIONAL,
-- to identify specific keys used for protection
transactionID [4] OCTET STRING OPTIONAL,
-- identifies the transaction; i.e., this will be the same in
-- corresponding request, response and confirmation messages
senderNonce [5] OCTET STRING OPTIONAL,
recipNonce [6] OCTET STRING OPTIONAL,
-- nonces used to provide replay protection, senderNonce
Adams & Farrell Standards Track [Page 20]
RFC 2510 PKI Certificate Management Protocols March 1999
-- is inserted by the creator of this message; recipNonce
-- is a nonce previously inserted in a related message by
-- the intended recipient of this message
freeText [7] PKIFreeText OPTIONAL,
-- this may be used to indicate context-specific instructions
-- (this field is intended for human consumption)
generalInfo [8] SEQUENCE SIZE (1..MAX) OF
InfoTypeAndValue OPTIONAL
-- this may be used to convey context-specific information
-- (this field not primarily intended for human consumption)
}
PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
-- text encoded as UTF-8 String (note: each UTF8String SHOULD
-- include an RFC 1766 language tag to indicate the language
-- of the contained text)
The pvno field is fixed (at one) for this version of this
specification.
The sender field contains the name of the sender of the PKIMessage.
This name (in conjunction with senderKID, if supplied) should be
usable to verify the protection on the message. If nothing about the
sender is known to the sending entity (e.g., in the init. req.
message, where the end entity may not know its own Distinguished Name
(DN), e-mail name, IP address, etc.), then the "sender" field MUST
contain a "NULL" value; that is, the SEQUENCE OF relative
distinguished names is of zero length. In such a case the senderKID
field MUST hold an identifier (i.e., a reference number) which
indicates to the receiver the appropriate shared secret information
to use to verify the message.
The recipient field contains the name of the recipient of the
PKIMessage. This name (in conjunction with recipKID, if supplied)
should be usable to verify the protection on the message.
The protectionAlg field specifies the algorithm used to protect the
message. If no protection bits are supplied (note that PKIProtection
is OPTIONAL) then this field MUST be omitted; if protection bits are
supplied then this field MUST be supplied.
senderKID and recipKID are usable to indicate which keys have been
used to protect the message (recipKID will normally only be required
where protection of the message uses Diffie-Hellman (DH) keys).
Adams & Farrell Standards Track [Page 21]
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The transactionID field within the message header MAY be used to
allow the recipient of a response message to correlate this with a
previously issued request. For example, in the case of an RA there
may be many requests "outstanding" at a given moment.
The senderNonce and recipNonce fields protect the PKIMessage against
replay attacks.
The messageTime field contains the time at which the sender created
the message. This may be useful to allow end entities to correct
their local time to be consistent with the time on a central system.
The freeText field may be used to send a human-readable message to
the recipient (in any number of languages). The first language used
in this sequence indicates the desired language for replies.
The generalInfo field may be used to send machine-processable
additional data to the recipient.
3.1.2 PKI Message Body
PKIBody ::= CHOICE { -- message-specific body elements
ir [0] CertReqMessages, --Initialization Request
ip [1] CertRepMessage, --Initialization Response
cr [2] CertReqMessages, --Certification Request
cp [3] CertRepMessage, --Certification Response
p10cr [4] CertificationRequest, --PKCS #10 Cert. Req.
-- the PKCS #10 certification request (see [PKCS10])
popdecc [5] POPODecKeyChallContent, --pop Challenge
popdecr [6] POPODecKeyRespContent, --pop Response
kur [7] CertReqMessages, --Key Update Request
kup [8] CertRepMessage, --Key Update Response
krr [9] CertReqMessages, --Key Recovery Request
krp [10] KeyRecRepContent, --Key Recovery Response
rr [11] RevReqContent, --Revocation Request
rp [12] RevRepContent, --Revocation Response
ccr [13] CertReqMessages, --Cross-Cert. Request
ccp [14] CertRepMessage, --Cross-Cert. Response
ckuann [15] CAKeyUpdAnnContent, --CA Key Update Ann.
cann [16] CertAnnContent, --Certificate Ann.
rann [17] RevAnnContent, --Revocation Ann.
crlann [18] CRLAnnContent, --CRL Announcement
conf [19] PKIConfirmContent, --Confirmation
nested [20] NestedMessageContent, --Nested Message
genm [21] GenMsgContent, --General Message
genp [22] GenRepContent, --General Response
error [23] ErrorMsgContent --Error Message
}
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The specific types are described in Section 3.3 below.
3.1.3 PKI Message Protection
Some PKI messages will be protected for integrity. (Note that if an
asymmetric algorithm is used to protect a message and the relevant
public component has been certified already, then the origin of
message can also be authenticated. On the other hand, if the public
component is uncertified then the message origin cannot be
automatically authenticated, but may be authenticated via out-of-band
means.)
When protection is applied the following structure is used:
PKIProtection ::= BIT STRING
The input to the calculation of PKIProtection is the DER encoding of
the following data structure:
ProtectedPart ::= SEQUENCE {
header PKIHeader,
body PKIBody
}
There MAY be cases in which the PKIProtection BIT STRING is
deliberately not used to protect a message (i.e., this OPTIONAL field
is omitted) because other protection, external to PKIX, will instead
be applied. Such a choice is explicitly allowed in this
specification. Examples of such external protection include PKCS #7
[PKCS7] and Security Multiparts [RFC1847] encapsulation of the
PKIMessage (or simply the PKIBody (omitting the CHOICE tag), if the
relevant PKIHeader information is securely carried in the external
mechanism); specification of external protection using PKCS #7 will
be provided in a separate document. It is noted, however, that many
such external mechanisms require that the end entity already
possesses a public-key certificate, and/or a unique Distinguished
Name, and/or other such infrastructure-related information. Thus,
they may not be appropriate for initial registration, key-recovery,
or any other process with "boot-strapping" characteristics. For
those cases it may be necessary that the PKIProtection parameter be
used. In the future, if/when external mechanisms are modified to
accommodate boot-strapping scenarios, the use of PKIProtection may
become rare or non-existent.
Depending on the circumstances the PKIProtection bits may contain a
Message Authentication Code (MAC) or signature. Only the following
cases can occur:
Adams & Farrell Standards Track [Page 23]
RFC 2510 PKI Certificate Management Protocols March 1999
- shared secret information
In this case the sender and recipient share secret information
(established via out-of-band means or from a previous PKI management
operation). PKIProtection will contain a MAC value and the
protectionAlg will be the following:
PasswordBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 13}
PBMParameter ::= SEQUENCE {
salt OCTET STRING,
owf AlgorithmIdentifier,
-- AlgId for a One-Way Function (SHA-1 recommended)
iterationCount INTEGER,
-- number of times the OWF is applied
mac AlgorithmIdentifier
-- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
} -- or HMAC [RFC2104, RFC2202])
In the above protectionAlg the salt value is appended to the shared
secret input. The OWF is then applied iterationCount times, where the
salted secret is the input to the first iteration and, for each
successive iteration, the input is set to be the output of the
previous iteration. The output of the final iteration (called
"BASEKEY" for ease of reference, with a size of "H") is what is used
to form the symmetric key. If the MAC algorithm requires a K-bit key
and K <= H, then the most significant K bits of BASEKEY are used. If
K > H, then all of BASEKEY is used for the most significant H bits of
the key, OWF("1" || BASEKEY) is used for the next most significant H
bits of the key, OWF("2" || BASEKEY) is used for the next most
significant H bits of the key, and so on, until all K bits have been
derived. [Here "N" is the ASCII byte encoding the number N and "||"
represents concatenation.]
- DH key pairs
Where the sender and receiver possess Diffie-Hellman certificates
with compatible DH parameters, then in order to protect the message
the end entity must generate a symmetric key based on its private DH
key value and the DH public key of the recipient of the PKI message.
PKIProtection will contain a MAC value keyed with this derived
symmetric key and the protectionAlg will be the following:
Adams & Farrell Standards Track [Page 24]
RFC 2510 PKI Certificate Management Protocols March 1999
DHBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 30}
DHBMParameter ::= SEQUENCE {
owf AlgorithmIdentifier,
-- AlgId for a One-Way Function (SHA-1 recommended)
mac AlgorithmIdentifier
-- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
} -- or HMAC [RFC2104, RFC2202])
In the above protectionAlg OWF is applied to the result of the
Diffie-Hellman computation. The OWF output (called "BASEKEY" for ease
of reference, with a size of "H") is what is used to form the
symmetric key. If the MAC algorithm requires a K-bit key and K <= H,
then the most significant K bits of BASEKEY are used. If K > H, then
all of BASEKEY is used for the most significant H bits of the key,
OWF("1" || BASEKEY) is used for the next most significant H bits of
the key, OWF("2" || BASEKEY) is used for the next most significant H
bits of the key, and so on, until all K bits have been derived. [Here
"N" is the ASCII byte encoding the number N and "||" represents
concatenation.]
- signature
Where the sender possesses a signature key pair it may simply sign
the PKI message. PKIProtection will contain the signature value and
the protectionAlg will be an AlgorithmIdentifier for a digital
signature (e.g., md5WithRSAEncryption or dsaWithSha-1).
- multiple protection
In cases where an end entity sends a protected PKI message to an RA,
the RA MAY forward that message to a CA, attaching its own protection
(which MAY be a MAC or a signature, depending on the information and
certificates shared between the RA and the CA). This is accomplished
by nesting the entire message sent by the end entity within a new PKI
message. The structure used is as follows.
NestedMessageContent ::= PKIMessage
3.2 Common Data Structures
Before specifying the specific types that may be placed in a PKIBody
we define some data structures that are used in more than one case.
Adams & Farrell Standards Track [Page 25]
RFC 2510 PKI Certificate Management Protocols March 1999
3.2.1 Requested Certificate Contents
Various PKI management messages require that the originator of the
message indicate some of the fields that are required to be present
in a certificate. The CertTemplate structure allows an end entity or
RA to specify as much as it wishes about the certificate it requires.
CertTemplate is identical to a Certificate but with all fields
optional.
Note that even if the originator completely specifies the contents of
a certificate it requires, a CA is free to modify fields within the
certificate actually issued. If the modified certificate is
unacceptable to the requester, the Confirmation message may be
withheld, or an Error Message may be sent (with a PKIStatus of
"rejection").
See [CRMF] for CertTemplate syntax.
3.2.2 Encrypted Values
Where encrypted values (restricted, in this specification, to be
either private keys or certificates) are sent in PKI messages the
EncryptedValue data structure is used.
See [CRMF] for EncryptedValue syntax.
Use of this data structure requires that the creator and intended
recipient respectively be able to encrypt and decrypt. Typically,
this will mean that the sender and recipient have, or are able to
generate, a shared secret key.
If the recipient of the PKIMessage already possesses a private key
usable for decryption, then the encSymmKey field MAY contain a
session key encrypted using the recipient's public key.
3.2.3 Status codes and Failure Information for PKI messages
All response messages will include some status information. The
following values are defined.
PKIStatus ::= INTEGER {
granted (0),
-- you got exactly what you asked for
grantedWithMods (1),
-- you got something like what you asked for; the
-- requester is responsible for ascertaining the differences
rejection (2),
-- you don't get it, more information elsewhere in the message
Adams & Farrell Standards Track [Page 26]
RFC 2510 PKI Certificate Management Protocols March 1999
waiting (3),
-- the request body part has not yet been processed,
-- expect to hear more later
revocationWarning (4),
-- this message contains a warning that a revocation is
-- imminent
revocationNotification (5),
-- notification that a revocation has occurred
keyUpdateWarning (6)
-- update already done for the oldCertId specified in
-- the key update request message
}
Responders may use the following syntax to provide more information
about failure cases.
PKIFailureInfo ::= BIT STRING {
-- since we can fail in more than one way!
-- More codes may be added in the future if/when required.
badAlg (0),
-- unrecognized or unsupported Algorithm Identifier
badMessageCheck (1),
-- integrity check failed (e.g., signature did not verify)
badRequest (2),
-- transaction not permitted or supported
badTime (3),
-- messageTime was not sufficiently close to the system time,
-- as defined by local policy
badCertId (4),
-- no certificate could be found matching the provided criteria
badDataFormat (5),
-- the data submitted has the wrong format
wrongAuthority (6),
-- the authority indicated in the request is different from the
-- one creating the response token
incorrectData (7),
-- the requester's data is incorrect (used for notary services)
missingTimeStamp (8),
-- when the timestamp is missing but should be there (by policy)
badPOP (9)
-- the proof-of-possession failed
}
PKIStatusInfo ::= SEQUENCE {
status PKIStatus,
statusString PKIFreeText OPTIONAL,
failInfo PKIFailureInfo OPTIONAL
}
Adams & Farrell Standards Track [Page 27]
RFC 2510 PKI Certificate Management Protocols March 1999
3.2.4 Certificate Identification
In order to identify particular certificates the CertId data
structure is used.
See [CRMF] for CertId syntax.
3.2.5 "Out-of-band" root CA public key
Each root CA must be able to publish its current public key via some
"out-of-band" means. While such mechanisms are beyond the scope of
this document, we define data structures which can support such
mechanisms.
There are generally two methods available: either the CA directly
publishes its self-signed certificate; or this information is
available via the Directory (or equivalent) and the CA publishes a
hash of this value to allow verification of its integrity before use.
OOBCert ::= Certificate
The fields within this certificate are restricted as follows:
- The certificate MUST be self-signed (i.e., the signature must be
verifiable using the SubjectPublicKeyInfo field);
- The subject and issuer fields MUST be identical;
- If the subject field is NULL then both subjectAltNames and
issuerAltNames extensions MUST be present and have exactly the same
value;
- The values of all other extensions must be suitable for a self-
signed certificate (e.g., key identifiers for subject and issuer
must be the same).
OOBCertHash ::= SEQUENCE {
hashAlg [0] AlgorithmIdentifier OPTIONAL,
certId [1] CertId OPTIONAL,
hashVal BIT STRING
-- hashVal is calculated over the self-signed
-- certificate with the identifier certID.
}
The intention of the hash value is that anyone who has securely
received the hash value (via the out-of-band means) can verify a
self- signed certificate for that CA.
Adams & Farrell Standards Track [Page 28]
RFC 2510 PKI Certificate Management Protocols March 1999
3.2.6 Archive Options
Requesters may indicate that they wish the PKI to archive a private
key value using the PKIArchiveOptions structure
See [CRMF] for PKIArchiveOptions syntax.
3.2.7 Publication Information
Requesters may indicate that they wish the PKI to publish a
certificate using the PKIPublicationInfo structure.
See [CRMF] for PKIPublicationInfo syntax.
3.2.8 Proof-of-Possession Structures
If the certification request is for a signing key pair (i.e., a
request for a verification certificate), then the proof of possession
of the private signing key is demonstrated through use of the
POPOSigningKey structure.
See [CRMF] for POPOSigningKey syntax, but note that
POPOSigningKeyInput has the following semantic stipulations in this
specification.
POPOSigningKeyInput ::= SEQUENCE {
authInfo CHOICE {
sender [0] GeneralName,
-- from PKIHeader (used only if an authenticated identity
-- has been established for the sender (e.g., a DN from a
-- previously-issued and currently-valid certificate))
publicKeyMAC [1] PKMACValue
-- used if no authenticated GeneralName currently exists for
-- the sender; publicKeyMAC contains a password-based MAC
-- (using the protectionAlg AlgId from PKIHeader) on the
-- DER-encoded value of publicKey
},
publicKey SubjectPublicKeyInfo -- from CertTemplate
}
On the other hand, if the certification request is for an encryption
key pair (i.e., a request for an encryption certificate), then the
proof of possession of the private decryption key may be demonstrated
in one of three ways.
1) By the inclusion of the private key (encrypted) in the
CertRequest (in the PKIArchiveOptions control structure).
Adams & Farrell Standards Track [Page 29]
RFC 2510 PKI Certificate Management Protocols March 1999
2) By having the CA return not the certificate, but an encrypted
certificate (i.e., the certificate encrypted under a randomly-
generated symmetric key, and the symmetric key encrypted under
the public key for which the certification request is being
made) -- this is the "indirect" method mentioned previously in
Section 2.3.2. The end entity proves knowledge of the private
decryption key to the CA by MACing the PKIConfirm message using
a key derived from this symmetric key. [Note that if more than
one CertReqMsg is included in the PKIMessage, then the CA uses
a different symmetric key for each CertReqMsg and the MAC uses
a key derived from the concatenation of all these keys.] The
MACing procedure uses the PasswordBasedMac AlgId defined in
Section 3.1.
3) By having the end entity engage in a challenge-response
protocol (using the messages POPODecKeyChall and
POPODecKeyResp; see below) between CertReqMessages and
CertRepMessage -- this is the "direct" method mentioned
previously in Section 2.3.2. [This method would typically be
used in an environment in which an RA verifies POP and then
makes a certification request to the CA on behalf of the end
entity. In such a scenario, the CA trusts the RA to have done
POP correctly before the RA requests a certificate for the end
entity.] The complete protocol then looks as follows (note
that req' does not necessarily encapsulate req as a nested
message):
EE RA CA
---- req ---->
<--- chall ---
---- resp --->
---- req' --->
<--- rep -----
---- conf --->
<--- rep -----
---- conf --->
This protocol is obviously much longer than the 3-way exchange given
in choice (2) above, but allows a local Registration Authority to be
involved and has the property that the certificate itself is not
actually created until the proof of possession is complete.
If the cert. request is for a key agreement key (KAK) pair, then the
POP can use any of the 3 ways described above for enc. key pairs,
with the following changes: (1) the parenthetical text of bullet 2)
is replaced with "(i.e., the certificate encrypted under the
symmetric key derived from the CA's private KAK and the public key
for which the certification request is being made)"; (2) the first
Adams & Farrell Standards Track [Page 30]
RFC 2510 PKI Certificate Management Protocols March 1999
parenthetical text of the challenge field of "Challenge" below is
replaced with "(using PreferredSymmAlg (see Appendix B6) and a
symmetric key derived from the CA's private KAK and the public key
for which the certification request is being made)". Alternatively,
the POP can use the POPOSigningKey structure given in [CRMF] (where
the alg field is DHBasedMAC and the signature field is the MAC) as a
fourth alternative for demonstrating POP if the CA already has a D-H
certificate that is known to the EE.
The challenge-response messages for proof of possession of a private
decryption key are specified as follows (see [MvOV97, p.404] for
details). Note that this challenge-response exchange is associated
with the preceding cert. request message (and subsequent cert.
response and confirmation messages) by the nonces used in the
PKIHeader and by the protection (MACing or signing) applied to the
PKIMessage.
POPODecKeyChallContent ::= SEQUENCE OF Challenge
-- One Challenge per encryption key certification request (in the
-- same order as these requests appear in CertReqMessages).
Challenge ::= SEQUENCE {
owf AlgorithmIdentifier OPTIONAL,
-- MUST be present in the first Challenge; MAY be omitted in any
-- subsequent Challenge in POPODecKeyChallContent (if omitted,
-- then the owf used in the immediately preceding Challenge is
-- to be used).
witness OCTET STRING,
-- the result of applying the one-way function (owf) to a
-- randomly-generated INTEGER, A. [Note that a different
-- INTEGER MUST be used for each Challenge.]
challenge OCTET STRING
-- the encryption (under the public key for which the cert.
-- request is being made) of Rand, where Rand is specified as
-- Rand ::= SEQUENCE {
-- int INTEGER,
-- - the randomly-generated INTEGER A (above)
-- sender GeneralName
-- - the sender's name (as included in PKIHeader)
-- }
}
POPODecKeyRespContent ::= SEQUENCE OF INTEGER
-- One INTEGER per encryption key certification request (in the
-- same order as these requests appear in CertReqMessages). The
-- retrieved INTEGER A (above) is returned to the sender of the
-- corresponding Challenge.
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3.3 Operation-Specific Data Structures
3.3.1 Initialization Request
An Initialization request message contains as the PKIBody an
CertReqMessages data structure which specifies the requested
certificate(s). Typically, SubjectPublicKeyInfo, KeyId, and Validity
are the template fields which may be supplied for each certificate
requested (see Appendix B profiles for further information). This
message is intended to be used for entities first initializing into
the PKI.
See [CRMF] for CertReqMessages syntax.
3.3.2 Initialization Response
An Initialization response message contains as the PKIBody an
CertRepMessage data structure which has for each certificate
requested a PKIStatusInfo field, a subject certificate, and possibly
a private key (normally encrypted with a session key, which is itself
encrypted with the protocolEncKey).
See Section 3.3.4 for CertRepMessage syntax. Note that if the PKI
Message Protection is "shared secret information" (see Section
3.1.3), then any certificate transported in the caPubs field may be
directly trusted as a root CA certificate by the initiator.
3.3.3 Registration/Certification Request
A Registration/Certification request message contains as the PKIBody
a CertReqMessages data structure which specifies the requested
certificates. This message is intended to be used for existing PKI
entities who wish to obtain additional certificates.
See [CRMF] for CertReqMessages syntax.
Alternatively, the PKIBody MAY be a CertificationRequest (this
structure is fully specified by the ASN.1 structure
CertificationRequest given in [PKCS10]). This structure may be
required for certificate requests for signing key pairs when
interoperation with legacy systems is desired, but its use is
strongly discouraged whenever not absolutely necessary.
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3.3.4 Registration/Certification Response
A registration response message contains as the PKIBody a
CertRepMessage data structure which has a status value for each
certificate requested, and optionally has a CA public key, failure
information, a subject certificate, and an encrypted private key.
CertRepMessage ::= SEQUENCE {
caPubs [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL,
response SEQUENCE OF CertResponse
}
CertResponse ::= SEQUENCE {
certReqId INTEGER,
-- to match this response with corresponding request (a value
-- of -1 is to be used if certReqId is not specified in the
-- corresponding request)
status PKIStatusInfo,
certifiedKeyPair CertifiedKeyPair OPTIONAL,
rspInfo OCTET STRING OPTIONAL
-- analogous to the id-regInfo-asciiPairs OCTET STRING defined
-- for regInfo in CertReqMsg [CRMF]
}
CertifiedKeyPair ::= SEQUENCE {
certOrEncCert CertOrEncCert,
privateKey [0] EncryptedValue OPTIONAL,
publicationInfo [1] PKIPublicationInfo OPTIONAL
}
CertOrEncCert ::= CHOICE {
certificate [0] Certificate,
encryptedCert [1] EncryptedValue
}
Only one of the failInfo (in PKIStatusInfo) and certificate (in
CertifiedKeyPair) fields can be present in each CertResponse
(depending on the status). For some status values (e.g., waiting)
neither of the optional fields will be present.
Given an EncryptedCert and the relevant decryption key the
certificate may be obtained. The purpose of this is to allow a CA to
return the value of a certificate, but with the constraint that only
the intended recipient can obtain the actual certificate. The benefit
of this approach is that a CA may reply with a certificate even in
the absence of a proof that the requester is the end entity which can
use the relevant private key (note that the proof is not obtained
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until the PKIConfirm message is received by the CA). Thus the CA will
not have to revoke that certificate in the event that something goes
wrong with the proof of possession.
3.3.5 Key update request content
For key update requests the CertReqMessages syntax is used.
Typically, SubjectPublicKeyInfo, KeyId, and Validity are the template
fields which may be supplied for each key to be updated. This
message is intended to be used to request updates to existing (non-
revoked and non-expired) certificates.
See [CRMF] for CertReqMessages syntax.
3.3.6 Key Update response content
For key update responses the CertRepMessage syntax is used. The
response is identical to the initialization response.
See Section 3.3.4 for CertRepMessage syntax.
3.3.7 Key Recovery Request content
For key recovery requests the syntax used is identical to the
initialization request CertReqMessages. Typically,
SubjectPublicKeyInfo and KeyId are the template fields which may be
used to supply a signature public key for which a certificate is
required (see Appendix B profiles for further information).
See [CRMF] for CertReqMessages syntax. Note that if a key history is
required, the requester must supply a Protocol Encryption Key control
in the request message.
3.3.8 Key recovery response content
For key recovery responses the following syntax is used. For some
status values (e.g., waiting) none of the optional fields will be
present.
KeyRecRepContent ::= SEQUENCE {
status PKIStatusInfo,
newSigCert [0] Certificate OPTIONAL,
caCerts [1] SEQUENCE SIZE (1..MAX) OF
Certificate OPTIONAL,
keyPairHist [2] SEQUENCE SIZE (1..MAX) OF
CertifiedKeyPair OPTIONAL
}
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3.3.9 Revocation Request Content
When requesting revocation of a certificate (or several certificates)
the following data structure is used. The name of the requester is
present in the PKIHeader structure.
RevReqContent ::= SEQUENCE OF RevDetails
RevDetails ::= SEQUENCE {
certDetails CertTemplate,
-- allows requester to specify as much as they can about
-- the cert. for which revocation is requested
-- (e.g., for cases in which serialNumber is not available)
revocationReason ReasonFlags OPTIONAL,
-- the reason that revocation is requested
badSinceDate GeneralizedTime OPTIONAL,
-- indicates best knowledge of sender
crlEntryDetails Extensions OPTIONAL
-- requested crlEntryExtensions
}
3.3.10 Revocation Response Content
The response to the above message. If produced, this is sent to the
requester of the revocation. (A separate revocation announcement
message MAY be sent to the subject of the certificate for which
revocation was requested.)
RevRepContent ::= SEQUENCE {
status SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
-- in same order as was sent in RevReqContent
revCerts [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
-- IDs for which revocation was requested (same order as status)
crls [1] SEQUENCE SIZE (1..MAX) OF CertificateList OPTIONAL
-- the resulting CRLs (there may be more than one)
}
3.3.11 Cross certification request content
Cross certification requests use the same syntax (CertReqMessages) as
for normal certification requests with the restriction that the key
pair MUST have been generated by the requesting CA and the private
key MUST NOT be sent to the responding CA.
See [CRMF] for CertReqMessages syntax.
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3.3.12 Cross certification response content
Cross certification responses use the same syntax (CertRepMessage) as
for normal certification responses with the restriction that no
encrypted private key can be sent.
See Section 3.3.4 for CertRepMessage syntax.
3.3.13 CA Key Update Announcement content
When a CA updates its own key pair the following data structure MAY
be used to announce this event.
CAKeyUpdAnnContent ::= SEQUENCE {
oldWithNew Certificate, -- old pub signed with new priv
newWithOld Certificate, -- new pub signed with old priv
newWithNew Certificate -- new pub signed with new priv
}
3.3.14 Certificate Announcement
This structure MAY be used to announce the existence of certificates.
Note that this message is intended to be used for those cases (if
any) where there is no pre-existing method for publication of
certificates; it is not intended to be used where, for example, X.500
is the method for publication of certificates.
CertAnnContent ::= Certificate
3.3.15 Revocation Announcement
When a CA has revoked, or is about to revoke, a particular
certificate it MAY issue an announcement of this (possibly upcoming)
event.
RevAnnContent ::= SEQUENCE {
status PKIStatus,
certId CertId,
willBeRevokedAt GeneralizedTime,
badSinceDate GeneralizedTime,
crlDetails Extensions OPTIONAL
-- extra CRL details(e.g., crl number, reason, location, etc.)
}
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A CA MAY use such an announcement to warn (or notify) a subject that
its certificate is about to be (or has been) revoked. This would
typically be used where the request for revocation did not come from
the subject concerned.
The willBeRevokedAt field contains the time at which a new entry will
be added to the relevant CRLs.
3.3.16 CRL Announcement
When a CA issues a new CRL (or set of CRLs) the following data
structure MAY be used to announce this event.
CRLAnnContent ::= SEQUENCE OF CertificateList
3.3.17 PKI Confirmation content
This data structure is used in three-way protocols as the final
PKIMessage. Its content is the same in all cases - actually there is
no content since the PKIHeader carries all the required information.
PKIConfirmContent ::= NULL
3.3.18 PKI General Message content
InfoTypeAndValue ::= SEQUENCE {
infoType OBJECT IDENTIFIER,
infoValue ANY DEFINED BY infoType OPTIONAL
}
-- Example InfoTypeAndValue contents include, but are not limited to:
-- { CAProtEncCert = {id-it 1}, Certificate }
-- { SignKeyPairTypes = {id-it 2}, SEQUENCE OF AlgorithmIdentifier }
-- { EncKeyPairTypes = {id-it 3}, SEQUENCE OF AlgorithmIdentifier }
-- { PreferredSymmAlg = {id-it 4}, AlgorithmIdentifier }
-- { CAKeyUpdateInfo = {id-it 5}, CAKeyUpdAnnContent }
-- { CurrentCRL = {id-it 6}, CertificateList }
-- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
-- This construct MAY also be used to define new PKIX Certificate
-- Management Protocol request and response messages, or general-
-- purpose (e.g., announcement) messages for future needs or for
-- specific environments.
GenMsgContent ::= SEQUENCE OF InfoTypeAndValue
-- May be sent by EE, RA, or CA (depending on message content).
-- The OPTIONAL infoValue parameter of InfoTypeAndValue will typically
-- be omitted for some of the examples given above. The receiver is
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-- free to ignore any contained OBJ. IDs that it does not recognize.
-- If sent from EE to CA, the empty set indicates that the CA may send
-- any/all information that it wishes.
3.3.19 PKI General Response content
GenRepContent ::= SEQUENCE OF InfoTypeAndValue
-- The receiver is free to ignore any contained OBJ. IDs that it does
-- not recognize.
3.3.20 Error Message content
ErrorMsgContent ::= SEQUENCE {
pKIStatusInfo PKIStatusInfo,
errorCode INTEGER OPTIONAL,
-- implementation-specific error codes
errorDetails PKIFreeText OPTIONAL
-- implementation-specific error details
}
4. Mandatory PKI Management functions
The PKI management functions outlined in Section 1 above are
described in this section.
This section deals with functions that are "mandatory" in the sense
that all end entity and CA/RA implementations MUST be able to provide
the functionality described (perhaps via one of the transport
mechanisms defined in Section 5). This part is effectively the
profile of the PKI management functionality that MUST be supported.
Note that not all PKI management functions result in the creation of
a PKI message.
4.1 Root CA initialization
[See Section 1.2.2 for this document's definition of "root CA".]
A newly created root CA must produce a "self-certificate" which is a
Certificate structure with the profile defined for the "newWithNew"
certificate issued following a root CA key update.
In order to make the CA's self certificate useful to end entities
that do not acquire the self certificate via "out-of-band" means, the
CA must also produce a fingerprint for its public key. End entities
that acquire this fingerprint securely via some "out-of-band" means
can then verify the CA's self-certificate and hence the other
attributes contained therein.
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The data structure used to carry the fingerprint is the OOBCertHash.
4.2 Root CA key update
CA keys (as all other keys) have a finite lifetime and will have to
be updated on a periodic basis. The certificates NewWithNew,
NewWithOld, and OldWithNew (see Section 2.4.1) are issued by the CA
to aid existing end entities who hold the current self-signed CA
certificate (OldWithOld) to transition securely to the new self-
signed CA certificate (NewWithNew), and to aid new end entities who
will hold NewWithNew to acquire OldWithOld securely for verification
of existing data.
4.3 Subordinate CA initialization
[See Section 1.2.2 for this document's definition of "subordinate
CA".]
From the perspective of PKI management protocols the initialization
of a subordinate CA is the same as the initialization of an end
entity. The only difference is that the subordinate CA must also
produce an initial revocation list.
4.4 CRL production
Before issuing any certificates a newly established CA (which issues
CRLs) must produce "empty" versions of each CRL which is to be
periodically produced.
4.5 PKI information request
When a PKI entity (CA, RA, or EE) wishes to acquire information about
the current status of a CA it MAY send that CA a request for such
information.
The CA must respond to the request by providing (at least) all of the
information requested by the requester. If some of the information
cannot be provided then an error must be conveyed to the requester.
If PKIMessages are used to request and supply this PKI information,
then the request must be the GenMsg message, the response must be the
GenRep message, and the error must be the Error message. These
messages are protected using a MAC based on shared secret information
(i.e., PasswordBasedMAC) or any other authenticated means (if the end
entity has an existing certificate).
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4.6 Cross certification
The requester CA is the CA that will become the subject of the
cross-certificate; the responder CA will become the issuer of the
cross-certificate.
The requester CA must be "up and running" before initiating the
cross-certification operation.
4.6.1 One-way request-response scheme:
The cross-certification scheme is essentially a one way operation;
that is, when successful, this operation results in the creation of
one new cross-certificate. If the requirement is that cross-
certificates be created in "both directions" then each CA in turn
must initiate a cross-certification operation (or use another
scheme).
This scheme is suitable where the two CAs in question can already
verify each other's signatures (they have some common points of
trust) or where there is an out-of-band verification of the origin of
the certification request.
Detailed Description:
Cross certification is initiated at one CA known as the responder.
The CA administrator for the responder identifies the CA it wants to
cross certify and the responder CA equipment generates an
authorization code. The responder CA administrator passes this
authorization code by out-of-band means to the requester CA
administrator. The requester CA administrator enters the
authorization code at the requester CA in order to initiate the on-
line exchange.
The authorization code is used for authentication and integrity
purposes. This is done by generating a symmetric key based on the
authorization code and using the symmetric key for generating Message
Authentication Codes (MACs) on all messages exchanged.
The requester CA initiates the exchange by generating a random number
(requester random number). The requester CA then sends to the
responder CA the cross certification request (ccr) message. The
fields in this message are protected from modification with a MAC
based on the authorization code.
Upon receipt of the ccr message, the responder CA checks the protocol
version, saves the requester random number, generates its own random
number (responder random number) and validates the MAC. It then
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generates (and archives, if desired) a new requester certificate that
contains the requester CA public key and is signed with the responder
CA signature private key. The responder CA responds with the cross
certification response (ccp) message. The fields in this message are
protected from modification with a MAC based on the authorization
code.
Upon receipt of the ccp message, the requester CA checks that its own
system time is close to the responder CA system time, checks the
received random numbers and validates the MAC. The requester CA
responds with the PKIConfirm message. The fields in this message are
protected from modification with a MAC based on the authorization
code. The requester CA writes the requester certificate to the
Repository.
Upon receipt of the PKIConfirm message, the responder CA checks the
random numbers and validates the MAC.
Notes:
1. The ccr message must contain a "complete" certification request,
that is, all fields (including, e.g., a BasicConstraints
extension) must be specified by the requester CA.
2. The ccp message SHOULD contain the verification certificate of the
responder CA - if present, the requester CA must then verify this
certificate (for example, via the "out-of-band" mechanism).
4.7 End entity initialization
As with CAs, end entities must be initialized. Initialization of end
entities requires at least two steps:
- acquisition of PKI information
- out-of-band verification of one root-CA public key
(other possible steps include the retrieval of trust condition
information and/or out-of-band verification of other CA public keys).
4.7.1 Acquisition of PKI information
The information REQUIRED is:
- the current root-CA public key
- (if the certifying CA is not a root-CA) the certification path
from the root CA to the certifying CA together with appropriate
revocation lists
- the algorithms and algorithm parameters which the certifying CA
supports for each relevant usage
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Additional information could be required (e.g., supported extensions
or CA policy information) in order to produce a certification request
which will be successful. However, for simplicity we do not mandate
that the end entity acquires this information via the PKI messages.
The end result is simply that some certification requests may fail
(e.g., if the end entity wants to generate its own encryption key but
the CA doesn't allow that).
The required information MAY be acquired as described in Section 4.5.
4.7.2 Out-of-Band Verification of Root-CA Key
An end entity must securely possess the public key of its root CA.
One method to achieve this is to provide the end entity with the CA's
self-certificate fingerprint via some secure "out-of-band" means. The
end entity can then securely use the CA's self-certificate.
See Section 4.1 for further details.
4.8 Certificate Request
An initialized end entity MAY request a certificate at any time (as
part of an update procedure, or for any other purpose). This request
will be made using the certification request (cr) message. If the
end entity already possesses a signing key pair (with a corresponding
verification certificate), then this cr message will typically be
protected by the entity's digital signature. The CA returns the new
certificate (if the request is successful) in a CertRepMessage.
4.9 Key Update
When a key pair is due to expire the relevant end entity MAY request
a key update - that is, it MAY request that the CA issue a new
certificate for a new key pair. The request is made using a key
update request (kur) message. If the end entity already possesses a
signing key pair (with a corresponding verification certificate),
then this message will typically be protected by the entity's digital
signature. The CA returns the new certificate (if the request is
successful) in a key update response (kup) message, which is
syntactically identical to a CertRepMessage.
5. Transports
The transport protocols specified below allow end entities, RAs and
CAs to pass PKI messages between them. There is no requirement for
specific security mechanisms to be applied at this level if the PKI
messages are suitably protected (that is, if the OPTIONAL
PKIProtection parameter is used as specified for each message).
Adams & Farrell Standards Track [Page 42]
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5.1 File based protocol
A file containing a PKI message MUST contain only the DER encoding of
one PKI message, i.e., there MUST be no extraneous header or trailer
information in the file.
Such files can be used to transport PKI messages using, e.g., FTP.
5.2 Direct TCP-Based Management Protocol
The following simple TCP-based protocol is to be used for transport
of PKI messages. This protocol is suitable for cases where an end
entity (or an RA) initiates a transaction and can poll to pick up the
results.
If a transaction is initiated by a PKI entity (RA or CA) then an end
entity must either supply a listener process or be supplied with a
polling reference (see below) in order to allow it to pick up the PKI
message from the PKI management component.
The protocol basically assumes a listener process on an RA or CA
which can accept PKI messages on a well-defined port (port number
829). Typically an initiator binds to this port and submits the
initial PKI message for a given transaction ID. The responder replies
with a PKI message and/or with a reference number to be used later
when polling for the actual PKI message response.
If a number of PKI response messages are to be produced for a given
request (say if some part of the request is handled more quickly than
another) then a new polling reference is also returned.
When the final PKI response message has been picked up by the
initiator then no new polling reference is supplied.
The initiator of a transaction sends a "direct TCP-based PKI message"
to the recipient. The recipient responds with a similar message.
A "direct TCP-based PKI message" consists of:
length (32-bits), flag (8-bits), value (defined below)
The length field contains the number of octets of the remainder of
the message (i.e., number of octets of "value" plus one). All 32-bit
values in this protocol are specified to be in network byte order.
Message name flag value
pkiMsg '00'H DER-encoded PKI message
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RFC 2510 PKI Certificate Management Protocols March 1999
-- PKI message
pollRep '01'H polling reference (32 bits),
time-to-check-back (32 bits)
-- poll response where no PKI message response ready; use polling
-- reference value (and estimated time value) for later polling
pollReq '02'H polling reference (32 bits)
-- request for a PKI message response to initial message
negPollRep '03'H '00'H
-- no further polling responses (i.e., transaction complete)
partialMsgRep '04'H next polling reference (32 bits),
time-to-check-back (32 bits),
DER-encoded PKI message
-- partial response to initial message plus new polling reference
-- (and estimated time value) to use to get next part of response
finalMsgRep '05'H DER-encoded PKI message
-- final (and possibly sole) response to initial message
errorMsgRep '06'H human readable error message
-- produced when an error is detected (e.g., a polling reference is
-- received which doesn't exist or is finished with)
Where a PKIConfirm message is to be transported (always from the
initiator to the responder) then a pkiMsg message is sent and a
negPollRep is returned.
The sequence of messages which can occur is then:
a) end entity sends pkiMsg and receives one of pollRep, negPollRep,
partialMsgRep or finalMsgRep in response. b) end entity sends
pollReq message and receives one of negPollRep, partialMsgRep,
finalMsgRep or errorMsgRep in response.
The "time-to-check-back" parameter is a 32-bit integer, defined to be
the number of seconds which have elapsed since midnight, January 1,
1970, coordinated universal time. It provides an estimate of the
time that the end entity should send its next pollReq.
5.3 Management Protocol via E-mail
This subsection specifies a means for conveying ASN.1-encoded
messages for the protocol exchanges described in Section 4 via
Internet mail.
A simple MIME object is specified as follows.
Content-Type: application/pkixcmp
Content-Transfer-Encoding: base64
<<the ASN.1 DER-encoded PKIX-CMP message, base64-encoded>>
Adams & Farrell Standards Track [Page 44]
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This MIME object can be sent and received using common MIME
processing engines and provides a simple Internet mail transport for
PKIX-CMP messages. Implementations MAY wish to also recognize and
use the "application/x-pkixcmp" MIME type (specified in earlier
versions of this document) in order to support backward compatibility
wherever applicable.
5.4 Management Protocol via HTTP
This subsection specifies a means for conveying ASN.1-encoded
messages for the protocol exchanges described in Section 4 via the
HyperText Transfer Protocol.
A simple MIME object is specified as follows.
Content-Type: application/pkixcmp
<<the ASN.1 DER-encoded PKIX-CMP message>>
This MIME object can be sent and received using common HTTP
processing engines over WWW links and provides a simple browser-
server transport for PKIX-CMP messages. Implementations MAY wish to
also recognize and use the "application/x-pkixcmp" MIME type
(specified in earlier versions of this document) in order to support
backward compatibility wherever applicable.
SECURITY CONSIDERATIONS
This entire memo is about security mechanisms.
One cryptographic consideration is worth explicitly spelling out. In
the protocols specified above, when an end entity is required to
prove possession of a decryption key, it is effectively challenged to
decrypt something (its own certificate). This scheme (and many
others!) could be vulnerable to an attack if the possessor of the
decryption key in question could be fooled into decrypting an
arbitrary challenge and returning the cleartext to an attacker.
Although in this specification a number of other failures in security
are required in order for this attack to succeed, it is conceivable
that some future services (e.g., notary, trusted time) could
potentially be vulnerable to such attacks. For this reason we re-
iterate the general rule that implementations should be very careful
about decrypting arbitrary "ciphertext" and revealing recovered
"plaintext" since such a practice can lead to serious security
vulnerabilities.
Adams & Farrell Standards Track [Page 45]
RFC 2510 PKI Certificate Management Protocols March 1999
Note also that exposing a private key to the CA/RA as a proof-of-
possession technique can carry some security risks (depending upon
whether or not the CA/RA can be trusted to handle such material
appropriately). Implementers are advised to exercise caution in
selecting and using this particular POP mechanism.
References
[COR95] ISO/IEC JTC 1/SC 21, Technical Corrigendum 2 to ISO/IEC
9594-8: 1990 & 1993 (1995:E), July 1995.
[CRMF] Myers, M., Adams, C., Solo, D. and D. Kemp, "Certificate
Request Message Format", RFC 2511, March 1999.
[MvOV97] A. Menezes, P. van Oorschot, S. Vanstone, "Handbook of
Applied Cryptography", CRC Press, 1997.
[PKCS7] RSA Laboratories, "The Public-Key Cryptography Standards
(PKCS)", RSA Data Security Inc., Redwood City, California,
November 1993 Release.
[PKCS10] RSA Laboratories, "The Public-Key Cryptography Standards
(PKCS)", RSA Data Security Inc., Redwood City, California,
November 1993 Release.
[PKCS11] RSA Laboratories, "The Public-Key Cryptography Standards -
PKCS #11: Cryptographic token interface standard", RSA
Data Security Inc., Redwood City, California, April 28,
1995.
[RFC1847] Galvin, J., Murphy, S. Crocker, S. and N. Freed, "Security
Multiparts for MIME: Multipart/Signed and Multipart/
Encrypted", RFC 1847, October 1995.
[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2202] Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
SHA-1", RFC 2202, September 1997.
[X509-AM] ISO/IEC JTC1/SC 21, Draft Amendments DAM 4 to ISO/IEC
9594-2, DAM 2 to ISO/IEC 9594-6, DAM 1 to ISO/IEC 9594-7,
and DAM 1 to ISO/IEC 9594-8 on Certificate Extensions, 1
December, 1996.
Adams & Farrell Standards Track [Page 46]
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Acknowledgements
The authors gratefully acknowledge the contributions of various
members of the PKIX Working Group. Many of these contributions
significantly clarified and improved the utility of this
specification.
Authors' Addresses
Carlisle Adams
Entrust Technologies
750 Heron Road, Suite E08,
Ottawa, Ontario
Canada K1V 1A7
EMail: cadams@entrust.com
Stephen Farrell
Software and Systems Engineering Ltd.
Fitzwilliam Court
Leeson Close
Dublin 2
IRELAND
EMail: stephen.farrell@sse.ie
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APPENDIX A: Reasons for the presence of RAs
The reasons which justify the presence of an RA can be split into
those which are due to technical factors and those which are
organizational in nature. Technical reasons include the following.
-If hardware tokens are in use, then not all end entities will have
the equipment needed to initialize these; the RA equipment can
include the necessary functionality (this may also be a matter of
policy).
-Some end entities may not have the capability to publish
certificates; again, the RA may be suitably placed for this.
-The RA will be able to issue signed revocation requests on behalf
of end entities associated with it, whereas the end entity may not
be able to do this (if the key pair is completely lost).
Some of the organizational reasons which argue for the presence of an
RA are the following.
-It may be more cost effective to concentrate functionality in the
RA equipment than to supply functionality to all end entities
(especially if special token initialization equipment is to be
used).
-Establishing RAs within an organization can reduce the number of
CAs required, which is sometimes desirable.
-RAs may be better placed to identify people with their
"electronic" names, especially if the CA is physically remote from
the end entity.
-For many applications there will already be in place some
administrative structure so that candidates for the role of RA are
easy to find (which may not be true of the CA).
Adams & Farrell Standards Track [Page 48]
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Appendix B. PKI Management Message Profiles.
This appendix contains detailed profiles for those PKIMessages which
MUST be supported by conforming implementations (see Section 4).
Profiles for the PKIMessages used in the following PKI management
operations are provided:
- root CA key update
- information request/response
- cross-certification request/response (1-way)
- initial registration/certification
- basic authenticated scheme
- certificate request
- key update
<<Later versions of this document may extend the above to include
profiles for the operations listed below (along with other
operations, if desired).>>
- revocation request
- certificate publication
- CRL publication
B1. General Rules for interpretation of these profiles.
1. Where OPTIONAL or DEFAULT fields are not mentioned in individual
profiles, they SHOULD be absent from the relevant message (i.e., a
receiver can validly reject a message containing such fields as
being syntactically incorrect).
Mandatory fields are not mentioned if they have an obvious value
(e.g., pvno).
2. Where structures occur in more than one message, they are
separately profiled as appropriate.
3. The algorithmIdentifiers from PKIMessage structures are profiled
separately.
4. A "special" X.500 DN is called the "NULL-DN"; this means a DN
containing a zero-length SEQUENCE OF RelativeDistinguishedNames
(its DER encoding is then '3000'H).
5. Where a GeneralName is required for a field but no suitable
value is available (e.g., an end entity produces a request before
knowing its name) then the GeneralName is to be an X.500 NULL-DN
(i.e., the Name field of the CHOICE is to contain a NULL-DN).
This special value can be called a "NULL-GeneralName".
6. Where a profile omits to specify the value for a GeneralName
then the NULL-GeneralName value is to be present in the relevant
PKIMessage field. This occurs with the sender field of the
PKIHeader for some messages.
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RFC 2510 PKI Certificate Management Protocols March 1999
7. Where any ambiguity arises due to naming of fields, the profile
names these using a "dot" notation (e.g., "certTemplate.subject"
means the subject field within a field called certTemplate).
8. Where a "SEQUENCE OF types" is part of a message, a zero-based
array notation is used to describe fields within the SEQUENCE OF
(e.g., crm[0].certReq.certTemplate.subject refers to a
subfield of the first CertReqMsg contained in a request message).
9. All PKI message exchanges in Sections B7-B10 require a PKIConfirm
message to be sent by the initiating entity. This message is not
included in some of the profiles given since its body is NULL and
its header contents are clear from the context. Any authenticated
means can be used for the protectionAlg (e.g., password-based MAC,
if shared secret information is known, or signature).
B2. Algorithm Use Profile
The following table contains definitions of algorithm uses within PKI
management protocols.
The columns in the table are:
Name: an identifier used for message profiles
Use: description of where and for what the algorithm is used
Mandatory: an AlgorithmIdentifier which MUST be supported by
conforming implementations
Others: alternatives to the mandatory AlgorithmIdentifier
Name Use Mandatory Others
MSG_SIG_ALG Protection of PKI DSA/SHA-1 RSA/MD5...
messages using signature
MSG_MAC_ALG protection of PKI PasswordBasedMac HMAC,
messages using MACing X9.9...
SYM_PENC_ALG symmetric encryption of 3-DES (3-key- RC5,
an end entity's private EDE, CBC mode) CAST-128...
key where symmetric
key is distributed
out-of-band
PROT_ENC_ALG asymmetric algorithm D-H RSA
used for encryption of
(symmetric keys for
encryption of) private
keys transported in
PKIMessages
PROT_SYM_ALG symmetric encryption 3-DES (3-key- RC5,
algorithm used for EDE, CBC mode) CAST-128...
encryption of private
key bits (a key of this
Adams & Farrell Standards Track [Page 50]
RFC 2510 PKI Certificate Management Protocols March 1999
type is encrypted using
PROT_ENC_ALG)
Mandatory AlgorithmIdentifiers and Specifications:
DSA/SHA-1:
AlgId: {1 2 840 10040 4 3};
NIST, FIPS PUB 186: Digital Signature Standard, 1994;
Public Modulus size: 1024 bits.
PasswordBasedMac:
{1 2 840 113533 7 66 13}, with SHA-1 {1 3 14 3 2 26} as the owf
parameter and HMAC-SHA1 {1 3 6 1 5 5 8 1 2} as the mac parameter;
(this specification), along with
NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995;
H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing for Message
Authentication", Internet Request for Comments 2104, February 1997.
3-DES:
{1 2 840 113549 3 7};
(used in RSA's BSAFE and in S/MIME).
D-H:
AlgId: {1 2 840 10046 2 1};
ANSI X9.42;
Public Modulus Size: 1024 bits.
DHParameter ::= SEQUENCE {
prime INTEGER, -- p
base INTEGER -- g
}
B3. "Self-signed" certificates
Profile of how a Certificate structure may be "self-signed". These
structures are used for distribution of "root" CA public keys. This
can occur in one of three ways (see Section 2.4 above for a
description of the use of these structures):
Type Function
newWithNew a true "self-signed" certificate; the contained public
key MUST be usable to verify the signature (though this
provides only integrity and no authentication whatsoever)
oldWithNew previous root CA public key signed with new private key
newWithOld new root CA public key signed with previous private key
Adams & Farrell Standards Track [Page 51]
RFC 2510 PKI Certificate Management Protocols March 1999
<<Such certificates (including relevant extensions) must contain
"sensible" values for all fields. For example, when present
subjectAltName MUST be identical to issuerAltName, and when present
keyIdentifiers must contain appropriate values, et cetera.>>
B4. Proof of Possession Profile
POP fields for use (in signature field of pop field of
ProofOfPossession structure) when proving possession of a private
signing key which corresponds to a public verification key for which
a certificate has been requested.
Field Value Comment
algorithmIdentifier MSG_SIG_ALG only signature protection is
allowed for this proof
signature present bits calculated using MSG_SIG_ALG
<<Proof of possession of a private decryption key which corresponds
to a public encryption key for which a certificate has been requested
does not use this profile; instead the method given in protectionAlg
for PKIConfirm in Section B8 is used.>>
Not every CA/RA will do Proof-of-Possession (of signing key,
decryption key, or key agreement key) in the PKIX-CMP in-band
certification request protocol (how POP is done MAY ultimately be a
policy issue which is made explicit for any given CA in its
publicized Policy OID and Certification Practice Statement).
However, this specification MANDATES that CA/RA entities MUST do POP
(by some means) as part of the certification process. All end
entities MUST be prepared to provide POP (i.e., these components of
the PKIX-CMP protocol MUST be supported).
B5. Root CA Key Update
A root CA updates its key pair. It then produces a CA key update
announcement message which can be made available (via one of the
transport mechanisms) to the relevant end entities. A PKIConfirm
message is NOT REQUIRED from the end entities.
ckuann message:
Field Value Comment
sender CA name responding CA name
body ckuann(CAKeyUpdAnnContent)
oldWithNew present see Section B3 above
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RFC 2510 PKI Certificate Management Protocols March 1999
newWithOld present see Section B3 above
newWithNew present see Section B3 above
extraCerts optionally present can be used to "publish"
certificates (e.g.,
certificates signed using
the new private key)
B6. PKI Information request/response
The end entity sends general message to the PKI requesting details
which will be required for later PKI management operations. RA/CA
responds with general response. If an RA generates the response then
it will simply forward the equivalent message which it previously
received from the CA, with the possible addition of the certificates
to the extraCerts fields of the PKIMessage. A PKIConfirm message is
NOT REQUIRED from the end entity.
Message Flows:
Step# End entity PKI
1 format genm
2 -> genm ->
3 handle genm
4 produce genp
5 <- genp <-
6 handle genp
genm:
Field Value
recipient CA name
-- the name of the CA as contained in issuerAltName extensions or
-- issuer fields within certificates
protectionAlg MSG_MAC_ALG or MSG_SIG_ALG
-- any authenticated protection alg.
SenderKID present if required
-- must be present if required for verification of message protection
freeText any valid value
body genr (GenReqContent)
GenMsgContent empty SEQUENCE
-- all relevant information requested
protection present
-- bits calculated using MSG_MAC_ALG or MSG_SIG_ALG
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genp:
Field Value
sender CA name
-- name of the CA which produced the message
protectionAlg MSG_MAC_ALG or MSG_SIG_ALG
-- any authenticated protection alg.
senderKID present if required
-- must be present if required for verification of message protection
body genp (GenRepContent)
CAProtEncCert present (object identifier one
of PROT_ENC_ALG), with relevant
value
-- to be used if end entity needs to encrypt information for the CA
-- (e.g., private key for recovery purposes)
SignKeyPairTypes present, with relevant value
-- the set of signature algorithm identifiers which this CA will
-- certify for subject public keys
EncKeyPairTypes present, with relevant value
-- the set of encryption/key agreement algorithm identifiers which
-- this CA will certify for subject public keys
PreferredSymmAlg present (object identifier one
of PROT_SYM_ALG) , with relevant
value
-- the symmetric algorithm which this CA expects to be used in later
-- PKI messages (for encryption)
CAKeyUpdateInfo optionally present, with
relevant value
-- the CA MAY provide information about a relevant root CA key pair
-- using this field (note that this does not imply that the responding
-- CA is the root CA in question)
CurrentCRL optionally present, with relevant value
-- the CA MAY provide a copy of a complete CRL (i.e., fullest possible
-- one)
protection present
-- bits calculated using MSG_MAC_ALG or MSG_SIG_ALG
extraCerts optionally present
-- can be used to send some certificates to the end entity. An RA MAY
-- add its certificate here.
B7. Cross certification request/response (1-way)
Creation of a single cross-certificate (i.e., not two at once). The
requesting CA MAY choose who is responsible for publication of the
cross-certificate created by the responding CA through use of the
PKIPublicationInfo control.
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RFC 2510 PKI Certificate Management Protocols March 1999
Preconditions:
1. Responding CA can verify the origin of the request (possibly
requiring out-of-band means) before processing the request.
2. Requesting CA can authenticate the authenticity of the origin of
the response (possibly requiring out-of-band means) before
processing the response
Message Flows:
Step# Requesting CA Responding CA
1 format ccr
2 -> ccr ->
3 handle ccr
4 produce ccp
5 <- ccp <-
6 handle ccp
7 format conf
8 -> conf ->
9 handle conf
ccr:
Field Value
sender Requesting CA name
-- the name of the CA who produced the message
recipient Responding CA name
-- the name of the CA who is being asked to produce a certificate
messageTime time of production of message
-- current time at requesting CA
protectionAlg MSG_SIG_ALG
-- only signature protection is allowed for this request
senderKID present if required
-- must be present if required for verification of message protection
transactionID present
-- implementation-specific value, meaningful to requesting CA.
-- [If already in use at responding CA then a rejection message
-- MUST be produced by responding CA]
senderNonce present
-- 128 (pseudo-)random bits
freeText any valid value
body ccr (CertReqMessages)
only one CertReqMsg
allowed
-- if multiple cross certificates are required they MUST be packaged
-- in separate PKIMessages
certTemplate present
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RFC 2510 PKI Certificate Management Protocols March 1999
-- details follow
version v1 or v3
-- <<v3 STRONGLY RECOMMENDED>>
signingAlg present
-- the requesting CA must know in advance with which algorithm it
-- wishes the certificate to be signed
subject present
-- may be NULL-DN only if subjectAltNames extension value proposed
validity present
-- MUST be completely specified (i.e., both fields present)
issuer present
-- may be NULL-DN only if issuerAltNames extension value proposed
publicKey present
-- the key to be certified (which must be for a signing algorithm)
extensions optionally present
-- a requesting CA must propose values for all extensions which it
-- requires to be in the cross-certificate
POPOSigningKey present
-- see "Proof of possession profile" (Section B4)
protection present
-- bits calculated using MSG_SIG_ALG
extraCerts optionally present
-- MAY contain any additional certificates that requester wishes
-- to include
ccp:
Field Value
sender Responding CA name
-- the name of the CA who produced the message
recipient Requesting CA name
-- the name of the CA who asked for production of a certificate
messageTime time of production of message
-- current time at responding CA
protectionAlg MSG_SIG_ALG
-- only signature protection is allowed for this message
senderKID present if required
-- must be present if required for verification of message
-- protection
recipKID present if required
transactionID present
-- value from corresponding ccr message
senderNonce present
-- 128 (pseudo-)random bits
recipNonce present
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RFC 2510 PKI Certificate Management Protocols March 1999
-- senderNonce from corresponding ccr message
freeText any valid value
body ccp (CertRepMessage)
only one CertResponse allowed
-- if multiple cross certificates are required they MUST be packaged
-- in separate PKIMessages
response present
status present
PKIStatusInfo.status present
-- if PKIStatusInfo.status is one of:
-- granted, or
-- grantedWithMods,
-- then certifiedKeyPair MUST be present and failInfo MUST be absent
failInfo present depending on
PKIStatusInfo.status
-- if PKIStatusInfo.status is:
-- rejection
-- then certifiedKeyPair MUST be absent and failInfo MUST be present
-- and contain appropriate bit settings
certifiedKeyPair present depending on
PKIStatusInfo.status
certificate present depending on
certifiedKeyPair
-- content of actual certificate must be examined by requesting CA
-- before publication
protection present
-- bits calculated using MSG_SIG_ALG
extraCerts optionally present
-- MAY contain any additional certificates that responder wishes
-- to include
B8. Initial Registration/Certification (Basic Authenticated Scheme)
An (uninitialized) end entity requests a (first) certificate from a
CA. When the CA responds with a message containing a certificate, the
end entity replies with a confirmation. All messages are
authenticated.
This scheme allows the end entity to request certification of a
locally-generated public key (typically a signature key). The end
entity MAY also choose to request the centralized generation and
certification of another key pair (typically an encryption key pair).
Certification may only be requested for one locally generated public
key (for more, use separate PKIMessages).
Adams & Farrell Standards Track [Page 57]
RFC 2510 PKI Certificate Management Protocols March 1999
The end entity MUST support proof-of-possession of the private key
associated with the locally-generated public key.
Preconditions:
1. The end entity can authenticate the CA's signature based on
out-of-band means
2. The end entity and the CA share a symmetric MACing key
Message flow:
Step# End entity PKI
1 format ir
2 -> ir ->
3 handle ir
4 format ip
5 <- ip <-
6 handle ip
7 format conf
8 -> conf ->
9 handle conf
For this profile, we mandate that the end entity MUST include all
(i.e., one or two) CertReqMsg in a single PKIMessage and that the PKI
(CA) MUST produce a single response PKIMessage which contains the
complete response (i.e., including the OPTIONAL second key pair, if
it was requested and if centralized key generation is supported). For
simplicity, we also mandate that this message MUST be the final one
(i.e., no use of "waiting" status value).
ir:
Field Value
recipient CA name
-- the name of the CA who is being asked to produce a certificate
protectionAlg MSG_MAC_ALG
-- only MAC protection is allowed for this request, based on
-- initial authentication key
senderKID referenceNum
-- the reference number which the CA has previously issued to
-- the end entity (together with the MACing key)
transactionID present
-- implementation-specific value, meaningful to end entity.
-- [If already in use at the CA then a rejection message MUST be
-- produced by the CA]
senderNonce present
-- 128 (pseudo-)random bits
freeText any valid value
Adams & Farrell Standards Track [Page 58]
RFC 2510 PKI Certificate Management Protocols March 1999
body ir (CertReqMessages)
only one or two CertReqMsg
are allowed
-- if more certificates are required requests MUST be packaged in
-- separate PKIMessages
CertReqMsg one or two present
-- see below for details, note: crm[0] means the first (which MUST
-- be present), crm[1] means the second (which is OPTIONAL, and used
-- to ask for a centrally-generated key)
crm[0].certReq. fixed value of zero
certReqId
-- this is the index of the template within the message
crm[0].certReq present
certTemplate
-- MUST include subject public key value, otherwise unconstrained
crm[0].pop... optionally present if public key
POPOSigningKey from crm[0].certReq.certTemplate is
a signing key
-- proof of possession MAY be required in this exchange (see Section
-- B4 for details)
crm[0].certReq. optionally present
controls.archiveOptions
-- the end entity MAY request that the locally-generated private key
-- be archived
crm[0].certReq. optionally present
controls.publicationInfo
-- the end entity MAY ask for publication of resulting cert.
crm[1].certReq fixed value of one
certReqId
-- the index of the template within the message
crm[1].certReq present
certTemplate
-- MUST NOT include actual public key bits, otherwise unconstrained
-- (e.g., the names need not be the same as in crm[0])
crm[0].certReq. present [object identifier MUST be PROT_ENC_ALG]
controls.protocolEncKey
-- if centralized key generation is supported by this CA, this
-- short-term asymmetric encryption key (generated by the end entity)
-- will be used by the CA to encrypt (a symmetric key used to encrypt)
-- a private key generated by the CA on behalf of the end entity
crm[1].certReq. optionally present
controls.archiveOptions
crm[1].certReq. optionally present
controls.publicationInfo
protection present
-- bits calculated using MSG_MAC_ALG
Adams & Farrell Standards Track [Page 59]
RFC 2510 PKI Certificate Management Protocols March 1999
ip:
Field Value
sender CA name
-- the name of the CA who produced the message
messageTime present
-- time at which CA produced message
protectionAlg MS_MAC_ALG
-- only MAC protection is allowed for this response
recipKID referenceNum
-- the reference number which the CA has previously issued to the
-- end entity (together with the MACing key)
transactionID present
-- value from corresponding ir message
senderNonce present
-- 128 (pseudo-)random bits
recipNonce present
-- value from senderNonce in corresponding ir message
freeText any valid value
body ir (CertRepMessage)
contains exactly one response
for each request
-- The PKI (CA) responds to either one or two requests as appropriate.
-- crc[0] denotes the first (always present); crc[1] denotes the
-- second (only present if the ir message contained two requests and
-- if the CA supports centralized key generation).
crc[0]. fixed value of zero
certReqId
-- MUST contain the response to the first request in the corresponding
-- ir message
crc[0].status. present, positive values allowed:
status "granted", "grantedWithMods"
negative values allowed:
"rejection"
crc[0].status. present if and only if
failInfo crc[0].status.status is "rejection"
crc[0]. present if and only if
certifiedKeyPair crc[0].status.status is
"granted" or "grantedWithMods"
certificate present unless end entity's public
key is an encryption key and POP
is done in this in-band exchange
encryptedCert present if and only if end entity's
public key is an encryption key and
POP done in this in-band exchange
publicationInfo optionally present
-- indicates where certificate has been published (present at
-- discretion of CA)
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RFC 2510 PKI Certificate Management Protocols March 1999
crc[1]. fixed value of one
certReqId
-- MUST contain the response to the second request in the
-- corresponding ir message
crc[1].status. present, positive values allowed:
status "granted", "grantedWithMods"
negative values allowed:
"rejection"
crc[1].status. present if and only if
failInfo crc[0].status.status is "rejection"
crc[1]. present if and only if
certifiedKeyPair crc[0].status.status is "granted"
or "grantedWithMods"
certificate present
privateKey present
publicationInfo optionally present
-- indicates where certificate has been published (present at
-- discretion of CA)
protection present
-- bits calculated using MSG_MAC_ALG
extraCerts optionally present
-- the CA MAY provide additional certificates to the end entity
conf:
Field Value
recipient CA name
-- the name of the CA who was asked to produce a certificate
transactionID present
-- value from corresponding ir and ip messages
senderNonce present
-- value from recipNonce in corresponding ip message
recipNonce present
-- value from senderNonce in corresponding ip message
protectionAlg MSG_MAC_ALG
-- only MAC protection is allowed for this message. The MAC is
-- based on the initial authentication key if only a signing key
-- pair has been sent in ir for certification, or if POP is not
-- done in this in-band exchange. Otherwise, the MAC is based on
-- a key derived from the symmetric key used to decrypt the
-- returned encryptedCert.
senderKID referenceNum
-- the reference number which the CA has previously issued to the
-- end entity (together with the MACing key)
body conf (PKIConfirmContent)
-- this is an ASN.1 NULL
protection present
-- bits calculated using MSG_MAC_ALG
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RFC 2510 PKI Certificate Management Protocols March 1999
B9. Certificate Request
An (initialized) end entity requests a certificate from a CA (for any
reason). When the CA responds with a message containing a
certificate, the end entity replies with a confirmation. All messages
are authenticated.
The profile for this exchange is identical to that given in Section
B8 with the following exceptions:
- protectionAlg may be MSG_MAC_ALG or MSG_SIG_ALG in request,
response, and confirm messages (the determination in the confirm
message being dependent upon POP considerations for key-
encipherment and key- agreement certificate requests);
- senderKID and recipKID are only present if required for message
verification;
- body is cr or cp;
- protocolEncKey is not present;
- protection bits are calculated according to the protectionAlg
field.
B10. Key Update Request
An (initialized) end entity requests a certificate from a CA (to
update the key pair and corresponding certificate that it already
possesses). When the CA responds with a message containing a
certificate, the end entity replies with a confirmation. All messages
are authenticated.
The profile for this exchange is identical to that given in Section
B8 with the following exceptions:
- protectionAlg may be MSG_MAC_ALG or MSG_SIG_ALG in request,
response, and confirm messages (the determination in the confirm
message being dependent upon POP considerations for key-
encipherment and key- agreement certificate requests);
- senderKID and recipKID are only present if required for message
verification;
- body is kur or kup;
- protection bits are calculated according to the protectionAlg
field.
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Appendix C: "Compilable" ASN.1 Module using 1988 Syntax
PKIXCMP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-cmp(9)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
Certificate, CertificateList, Extensions, AlgorithmIdentifier
FROM PKIX1Explicit88 {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-explicit-88(1)}}
GeneralName, KeyIdentifier, ReasonFlags
FROM PKIX1Implicit88 {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-implicit-88(2)}
CertTemplate, PKIPublicationInfo, EncryptedValue, CertId,
CertReqMessages
FROM PKIXCRMF {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-crmf(5)}}
-- CertificationRequest
-- FROM PKCS10 {no standard ASN.1 module defined;
-- implementers need to create their own module to import
-- from, or directly include the PKCS10 syntax in this module}
-- Locally defined OIDs --
PKIMessage ::= SEQUENCE {
header PKIHeader,
body PKIBody,
protection [0] PKIProtection OPTIONAL,
extraCerts [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL
}
PKIHeader ::= SEQUENCE {
pvno INTEGER { ietf-version2 (1) },
sender GeneralName,
-- identifies the sender
recipient GeneralName,
Adams & Farrell Standards Track [Page 63]
RFC 2510 PKI Certificate Management Protocols March 1999
-- identifies the intended recipient
messageTime [0] GeneralizedTime OPTIONAL,
-- time of production of this message (used when sender
-- believes that the transport will be "suitable"; i.e.,
-- that the time will still be meaningful upon receipt)
protectionAlg [1] AlgorithmIdentifier OPTIONAL,
-- algorithm used for calculation of protection bits
senderKID [2] KeyIdentifier OPTIONAL,
recipKID [3] KeyIdentifier OPTIONAL,
-- to identify specific keys used for protection
transactionID [4] OCTET STRING OPTIONAL,
-- identifies the transaction; i.e., this will be the same in
-- corresponding request, response and confirmation messages
senderNonce [5] OCTET STRING OPTIONAL,
recipNonce [6] OCTET STRING OPTIONAL,
-- nonces used to provide replay protection, senderNonce
-- is inserted by the creator of this message; recipNonce
-- is a nonce previously inserted in a related message by
-- the intended recipient of this message
freeText [7] PKIFreeText OPTIONAL,
-- this may be used to indicate context-specific instructions
-- (this field is intended for human consumption)
generalInfo [8] SEQUENCE SIZE (1..MAX) OF
InfoTypeAndValue OPTIONAL
-- this may be used to convey context-specific information
-- (this field not primarily intended for human consumption)
}
PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
-- text encoded as UTF-8 String (note: each UTF8String SHOULD
-- include an RFC 1766 language tag to indicate the language
-- of the contained text)
PKIBody ::= CHOICE { -- message-specific body elements
ir [0] CertReqMessages, --Initialization Request
ip [1] CertRepMessage, --Initialization Response
cr [2] CertReqMessages, --Certification Request
cp [3] CertRepMessage, --Certification Response
p10cr [4] CertificationRequest, --imported from [PKCS10]
popdecc [5] POPODecKeyChallContent, --pop Challenge
popdecr [6] POPODecKeyRespContent, --pop Response
kur [7] CertReqMessages, --Key Update Request
kup [8] CertRepMessage, --Key Update Response
krr [9] CertReqMessages, --Key Recovery Request
krp [10] KeyRecRepContent, --Key Recovery Response
rr [11] RevReqContent, --Revocation Request
rp [12] RevRepContent, --Revocation Response
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RFC 2510 PKI Certificate Management Protocols March 1999
ccr [13] CertReqMessages, --Cross-Cert. Request
ccp [14] CertRepMessage, --Cross-Cert. Response
ckuann [15] CAKeyUpdAnnContent, --CA Key Update Ann.
cann [16] CertAnnContent, --Certificate Ann.
rann [17] RevAnnContent, --Revocation Ann.
crlann [18] CRLAnnContent, --CRL Announcement
conf [19] PKIConfirmContent, --Confirmation
nested [20] NestedMessageContent, --Nested Message
genm [21] GenMsgContent, --General Message
genp [22] GenRepContent, --General Response
error [23] ErrorMsgContent --Error Message
}
PKIProtection ::= BIT STRING
ProtectedPart ::= SEQUENCE {
header PKIHeader,
body PKIBody
}
PasswordBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 13}
PBMParameter ::= SEQUENCE {
salt OCTET STRING,
owf AlgorithmIdentifier,
-- AlgId for a One-Way Function (SHA-1 recommended)
iterationCount INTEGER,
-- number of times the OWF is applied
mac AlgorithmIdentifier
-- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
} -- or HMAC [RFC2104, RFC2202])
DHBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 30}
DHBMParameter ::= SEQUENCE {
owf AlgorithmIdentifier,
-- AlgId for a One-Way Function (SHA-1 recommended)
mac AlgorithmIdentifier
-- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
} -- or HMAC [RFC2104, RFC2202])
NestedMessageContent ::= PKIMessage
PKIStatus ::= INTEGER {
granted (0),
-- you got exactly what you asked for
grantedWithMods (1),
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RFC 2510 PKI Certificate Management Protocols March 1999
-- you got something like what you asked for; the
-- requester is responsible for ascertaining the differences
rejection (2),
-- you don't get it, more information elsewhere in the message
waiting (3),
-- the request body part has not yet been processed,
-- expect to hear more later
revocationWarning (4),
-- this message contains a warning that a revocation is
-- imminent
revocationNotification (5),
-- notification that a revocation has occurred
keyUpdateWarning (6)
-- update already done for the oldCertId specified in
-- CertReqMsg
}
PKIFailureInfo ::= BIT STRING {
-- since we can fail in more than one way!
-- More codes may be added in the future if/when required.
badAlg (0),
-- unrecognized or unsupported Algorithm Identifier
badMessageCheck (1),
-- integrity check failed (e.g., signature did not verify)
badRequest (2),
-- transaction not permitted or supported
badTime (3),
-- messageTime was not sufficiently close to the system time,
-- as defined by local policy
badCertId (4),
-- no certificate could be found matching the provided criteria
badDataFormat (5),
-- the data submitted has the wrong format
wrongAuthority (6),
-- the authority indicated in the request is different from the
-- one creating the response token
incorrectData (7),
-- the requester's data is incorrect (for notary services)
missingTimeStamp (8),
-- when the timestamp is missing but should be there (by policy)
badPOP (9)
-- the proof-of-possession failed
}
PKIStatusInfo ::= SEQUENCE {
status PKIStatus,
statusString PKIFreeText OPTIONAL,
failInfo PKIFailureInfo OPTIONAL
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RFC 2510 PKI Certificate Management Protocols March 1999
}
OOBCert ::= Certificate
OOBCertHash ::= SEQUENCE {
hashAlg [0] AlgorithmIdentifier OPTIONAL,
certId [1] CertId OPTIONAL,
hashVal BIT STRING
-- hashVal is calculated over DER encoding of the
-- subjectPublicKey field of the corresponding cert.
}
POPODecKeyChallContent ::= SEQUENCE OF Challenge
-- One Challenge per encryption key certification request (in the
-- same order as these requests appear in CertReqMessages).
Challenge ::= SEQUENCE {
owf AlgorithmIdentifier OPTIONAL,
-- MUST be present in the first Challenge; MAY be omitted in any
-- subsequent Challenge in POPODecKeyChallContent (if omitted,
-- then the owf used in the immediately preceding Challenge is
-- to be used).
witness OCTET STRING,
-- the result of applying the one-way function (owf) to a
-- randomly-generated INTEGER, A. [Note that a different
-- INTEGER MUST be used for each Challenge.]
challenge OCTET STRING
-- the encryption (under the public key for which the cert.
-- request is being made) of Rand, where Rand is specified as
-- Rand ::= SEQUENCE {
-- int INTEGER,
-- - the randomly-generated INTEGER A (above)
-- sender GeneralName
-- - the sender's name (as included in PKIHeader)
-- }
}
POPODecKeyRespContent ::= SEQUENCE OF INTEGER
-- One INTEGER per encryption key certification request (in the
-- same order as these requests appear in CertReqMessages). The
-- retrieved INTEGER A (above) is returned to the sender of the
-- corresponding Challenge.
CertRepMessage ::= SEQUENCE {
caPubs [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL,
response SEQUENCE OF CertResponse
}
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CertResponse ::= SEQUENCE {
certReqId INTEGER,
-- to match this response with corresponding request (a value
-- of -1 is to be used if certReqId is not specified in the
-- corresponding request)
status PKIStatusInfo,
certifiedKeyPair CertifiedKeyPair OPTIONAL,
rspInfo OCTET STRING OPTIONAL
-- analogous to the id-regInfo-asciiPairs OCTET STRING defined
-- for regInfo in CertReqMsg [CRMF]
}
CertifiedKeyPair ::= SEQUENCE {
certOrEncCert CertOrEncCert,
privateKey [0] EncryptedValue OPTIONAL,
publicationInfo [1] PKIPublicationInfo OPTIONAL
}
CertOrEncCert ::= CHOICE {
certificate [0] Certificate,
encryptedCert [1] EncryptedValue
}
KeyRecRepContent ::= SEQUENCE {
status PKIStatusInfo,
newSigCert [0] Certificate OPTIONAL,
caCerts [1] SEQUENCE SIZE (1..MAX) OF
Certificate OPTIONAL,
keyPairHist [2] SEQUENCE SIZE (1..MAX) OF
CertifiedKeyPair OPTIONAL
}
RevReqContent ::= SEQUENCE OF RevDetails
RevDetails ::= SEQUENCE {
certDetails CertTemplate,
-- allows requester to specify as much as they can about
-- the cert. for which revocation is requested
-- (e.g., for cases in which serialNumber is not available)
revocationReason ReasonFlags OPTIONAL,
-- the reason that revocation is requested
badSinceDate GeneralizedTime OPTIONAL,
-- indicates best knowledge of sender
crlEntryDetails Extensions OPTIONAL
-- requested crlEntryExtensions
}
RevRepContent ::= SEQUENCE {
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status SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
-- in same order as was sent in RevReqContent
revCerts [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
-- IDs for which revocation was requested (same order as status)
crls [1] SEQUENCE SIZE (1..MAX) OF CertificateList OPTIONAL
-- the resulting CRLs (there may be more than one)
}
CAKeyUpdAnnContent ::= SEQUENCE {
oldWithNew Certificate, -- old pub signed with new priv
newWithOld Certificate, -- new pub signed with old priv
newWithNew Certificate -- new pub signed with new priv
}
CertAnnContent ::= Certificate
RevAnnContent ::= SEQUENCE {
status PKIStatus,
certId CertId,
willBeRevokedAt GeneralizedTime,
badSinceDate GeneralizedTime,
crlDetails Extensions OPTIONAL
-- extra CRL details(e.g., crl number, reason, location, etc.)
}
CRLAnnContent ::= SEQUENCE OF CertificateList
PKIConfirmContent ::= NULL
InfoTypeAndValue ::= SEQUENCE {
infoType OBJECT IDENTIFIER,
infoValue ANY DEFINED BY infoType OPTIONAL
}
-- Example InfoTypeAndValue contents include, but are not limited to:
-- { CAProtEncCert = {id-it 1}, Certificate }
-- { SignKeyPairTypes = {id-it 2}, SEQUENCE OF AlgorithmIdentifier }
-- { EncKeyPairTypes = {id-it 3}, SEQUENCE OF AlgorithmIdentifier }
-- { PreferredSymmAlg = {id-it 4}, AlgorithmIdentifier }
-- { CAKeyUpdateInfo = {id-it 5}, CAKeyUpdAnnContent }
-- { CurrentCRL = {id-it 6}, CertificateList }
-- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
-- This construct MAY also be used to define new PKIX Certificate
-- Management Protocol request and response messages, or general-
-- purpose (e.g., announcement) messages for future needs or for
-- specific environments.
GenMsgContent ::= SEQUENCE OF InfoTypeAndValue
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RFC 2510 PKI Certificate Management Protocols March 1999
-- May be sent by EE, RA, or CA (depending on message content).
-- The OPTIONAL infoValue parameter of InfoTypeAndValue will typically
-- be omitted for some of the examples given above. The receiver is
-- free to ignore any contained OBJ. IDs that it does not recognize.
-- If sent from EE to CA, the empty set indicates that the CA may send
-- any/all information that it wishes.
GenRepContent ::= SEQUENCE OF InfoTypeAndValue
-- The receiver is free to ignore any contained OBJ. IDs that it does
-- not recognize.
ErrorMsgContent ::= SEQUENCE {
pKIStatusInfo PKIStatusInfo,
errorCode INTEGER OPTIONAL,
-- implementation-specific error codes
errorDetails PKIFreeText OPTIONAL
-- implementation-specific error details
}
-- The following definition is provided for compatibility reasons with
-- 1988 and 1993 ASN.1 compilers which allow the use of UNIVERSAL class
-- tags (not a part of formal ASN.1); 1997 and subsequent compilers
-- SHOULD comment out this line.
UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
END
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Appendix D: Registration of MIME Type for Section 5
To: ietf-types@iana.org
Subject: Registration of MIME media type application/pkixcmp
MIME media type name: application
MIME subtype name: pkixcmp
Required parameters: -
Optional parameters: -
Encoding considerations:
Content may contain arbitrary octet values (the ASN.1 DER encoding of
a PKI message, as defined in the IETF PKIX Working Group
specifications). base64 encoding is required for MIME e-mail; no
encoding is necessary for HTTP.
Security considerations:
This MIME type may be used to transport Public-Key Infrastructure
(PKI) messages between PKI entities. These messages are defined by
the IETF PKIX Working Group and are used to establish and maintain an
Internet X.509 PKI. There is no requirement for specific security
mechanisms to be applied at this level if the PKI messages themselves
are protected as defined in the PKIX specifications.
Interoperability considerations: -
Published specification: this document
Applications which use this media type:
Applications using certificate management, operational, or ancillary
protocols (as defined by the IETF PKIX Working Group) to send PKI
messages via E-Mail or HTTP.
Additional information:
Magic number (s): -
File extension (s): ".PKI"
Macintosh File Type Code (s): -
Person and email address to contact for further information:
Carlisle Adams, cadams@entrust.com
Intended usage: COMMON
Author/Change controller: Carlisle Adams
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RFC 2510 PKI Certificate Management Protocols March 1999
Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Adams & Farrell Standards Track [Page 72]