Keywords: public key, public-key encryption technology
Network Working Group G. Appenzeller
Request for Comments: 5408 Stanford University
Category: Informational L. Martin
Voltage Security
M. Schertler
Axway
January 2009
Identity-Based Encryption Architecture and Supporting Data Structures
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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Abstract
This document describes the security architecture required to
implement identity-based encryption, a public-key encryption
technology that uses a user's identity as a public key. It also
defines data structures that can be used to implement the technology.
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Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................3
2. Identity-Based Encryption .......................................3
2.1. Overview ...................................................3
2.2. Sending a Message That Is IBE-Encrypted ....................5
2.2.1. Sender Obtains Public Parameters ....................5
2.2.2. Construct and Send an IBE-Encrypted Message .........6
2.3. Receiving and Viewing an IBE-Encrypted Message .............6
2.3.1. Recipient Obtains Public Parameters .................7
2.3.2. Recipient Obtains IBE Private Key ...................8
2.3.3. Recipient Decrypts IBE-Encrypted Message ............8
3. Identity Format .................................................9
4. Public Parameter Lookup .........................................9
4.1. Request Method ............................................10
4.2. Parameter and Policy Format ...............................11
4.3. The application/ibe-pp-data MIME Type .....................14
5. Private Key Request Protocol ...................................15
5.1. Overview ..................................................15
5.2. Private Key Request .......................................15
5.3. Request Structure .........................................16
5.4. The application/ibe-key-request+xml MIME type .............17
5.5. Authentication ............................................18
5.6. Server Response Format ....................................18
5.6.1. The IBE100 responseCode ............................19
5.6.2. The IBE101 responseCode ............................20
5.6.3. The IBE201 responseCode ............................20
5.6.4. The IBE300 responseCode ............................21
5.6.5. The IBE301 responseCode ............................21
5.6.6. The IBE303 responseCode ............................21
5.6.7. The IBE304 responseCode ............................22
5.7. The application/ibe-pkg-reply+xml MIME type ...............22
6. ASN.1 Module ...................................................23
7. Security Considerations ........................................25
7.1. Attacks outside the Scope of This Document ................25
7.2. Attacks within the Scope of This Document .................26
7.2.1. Attacks on the Protocols Defined in This Document ..26
8. IANA Considerations ............................................27
8.1. Media Types ...............................................27
8.2. XML Namespace .............................................27
9. References .....................................................28
9.1. Normative References ......................................28
9.2. Informative References ....................................29
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1. Introduction
This document describes the security architecture required to
implement identity-based encryption, a public-key encryption
technology that uses a user's identity as a public key. It also
defines data structures that are required to implement the
technology. Objects used in this implementation are defined using
ASN.1 [ASN1] and XML [XML].
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEY].
2. Identity-Based Encryption
2.1. Overview
Identity-based encryption (IBE) is a public-key encryption technology
that allows a public key to be calculated from an identity and a set
of public mathematical parameters and that allows for the
corresponding private key to be calculated from an identity, a set of
public mathematical parameters, and a domain-wide secret value. An
IBE public key can be calculated by anyone who has the necessary
public parameters; a cryptographic secret is needed to calculate an
IBE private key, and the calculation can only be performed by a
trusted server that has this secret.
Calculation of both the public and private keys in an IBE system can
occur as needed, resulting in just-in-time creation of both public
and private keys. This contrasts with other public-key systems
[P1363], in which keys are generated randomly and distributed prior
to secure communication commencing, and in which private encryption
keys need to be securely archived to allow for their recovery if they
are lost or destroyed. The ability to calculate a recipient's public
key, in particular, eliminates the need for the sender and receiver
to interact with each other, either directly or through a proxy such
as a directory server, before sending secure messages.
A characteristic of IBE systems that differentiates them from other
server-based cryptographic systems is that once a set of public
parameters is fetched, encryption is possible with no further
communication with a server during the validity period of the public
parameters. Other server-based systems may require a connection to a
server for each encryption operation.
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This document describes an IBE-based messaging system, how the
components of such a system work together, and defines data
structures that support the operation of such a system. The server
components required for such a system are the following:
o A Public Parameter Server (PPS). IBE public parameters include
publicly-sharable cryptographic material, known as IBE public
parameters, and policy information for an associated PKG. A
PPS provides a well-known location for secure distribution of
IBE public parameters and policy information that describe the
operation of a PKG. Section 5 of this document describes the
protocol that a client uses to communicate with a PPS.
o A Private-key Generator (PKG). The PKG stores and uses
cryptographic material, known as a master secret, which is used
for generating a user's IBE private key. A PKG accepts an IBE
user's private key request, and after successfully
authenticating them in some way, returns their IBE private key.
Section 5 of this document describes the protocol that a client
uses to communicate with a PKG.
A logical architecture of such an IBE system would be to have a PKG
and PPS per name space, such as a DNS zone. The organization that
controls the DNS zone would also control the PKG and PPS and thus the
determination of which PKG or PPS to use when creating public and
private keys for the organization's members. In this case, the PPS
URI/IRI can be uniquely created from a user-friendly name for the
form of identity that the PPS supports. This architecture would make
it clear which set of public parameters to use and where to retrieve
them for a given identity (for example, an RFC 2821 address [SMTP]).
IBE-encrypted messages can use standard message formats, such as the
Cryptographic Message Syntax [CMS]. How to use IBE with the CMS to
encrypt email messages is defined in [IBECMS].
Note that IBE algorithms are used only for encryption, so if digital
signatures are required, they will need to be provided by an
additional mechanism.
Section 3 of this document describes the identity format that all PPS
and PKG servers MUST support.
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2.2. Sending a Message That Is IBE-Encrypted
In order to send an encrypted message, an IBE user must perform the
following steps:
1. Obtain the recipient's public parameters
The public parameters of the recipient's system are needed to
perform IBE operations. Once a user obtains these public
parameters, he can perform IBE encryption operations. These
public parameters may be available at a PPS that is operated by
the user's organization, one that is operated by the sender's
organization, or by a different organization entirely.
2. Construct and send an IBE-encrypted message
In addition to the IBE public parameters, all that is needed to
construct an IBE-encrypted message is the recipient's identity,
the form of which is defined by the public parameters. When
this identity is the same as the identity that a message would
be addressed to, then no more information is needed from a user
to send them an encrypted message than is needed to send them
an unencrypted message. This is one of the major benefits of
an IBE-based secure messaging system. Examples of identities
are individual, group, or role identifiers.
2.2.1. Sender Obtains Public Parameters
The sender of a message obtains the IBE public parameters that he
needs from a PPS that is hosted at a well-known URI or IRI. The IBE
public parameters contain all of the information that the sender
needs to create an IBE-encrypted message except for the identity of
the recipient. Section 4 of this document describes the URI [URI] or
IRI [IRI] of a PPS, the format of IBE public parameters, and how to
obtain them from a PPS. The URI or IRI from which users obtain IBE
public parameters MUST be authenticated in some way. PPS servers
MUST support TLS 1.2 [TLS] to satisfy this requirement and SHOULD
support its successors. This step is shown below in Figure 1.
IBE Public Parameter Request
----------------------------->
Sender PPS
<-----------------------------
IBE Public Parameters
Figure 1: Requesting IBE Public Parameters
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The sender of an IBE-encrypted message selects the PPS and
corresponding PKG based on his local security policy. Different PPS
servers may provide public parameters that specify different IBE
algorithms or different key strengths, for example. Or, they may
require the use of PKG servers that require different levels of
authentication before granting IBE private keys.
2.2.2. Construct and Send an IBE-Encrypted Message
To IBE-encrypt a message, the sender chooses a content-encryption key
(CEK) and uses it to encrypt his message and then encrypts the CEK
with the recipient's IBE public key as described in [CMS]. This
operation is shown below in Figure 2. The document [IBCS] describes
the algorithms needed to implement two forms of IBE, and [IBECMS]
describes how to use the Cryptographic Message Syntax (CMS) to
encapsulate the encrypted message along with the IBE information that
the recipient needs to decrypt an email message.
CEK ----> Sender ----> IBE-encrypted CEK
^
|
|
Recipient's Identity
and IBE Public Parameters
Figure 2: Using an IBE Public-key Algorithm to Encrypt
2.3. Receiving and Viewing an IBE-Encrypted Message
In order to read an IBE-encrypted message, a recipient of such a
message parses it to find the URI or IRI he needs in order to obtain
the IBE public parameters that are required to perform IBE
calculations as well as to obtain a component of the identity that
was used to encrypt the message. Next, the recipient carries out the
following steps:
1. Obtain the IBE public parameters
An IBE system's public parameters allow it to uniquely create
public and private keys. The recipient of an IBE-encrypted
message can decrypt an IBE-encrypted message if he has both the
IBE public parameters and the necessary IBE private key. The
public parameters also provide the URI or IRI of the PKG where
the recipient of an IBE-encrypted message can obtain the IBE
private keys.
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2. Obtain the IBE private key from the PKG
To decrypt an IBE-encrypted message, in addition to the IBE
public parameters, the recipient needs to obtain the private
key that corresponds to the public key that the sender used.
The IBE private key is obtained after successfully
authenticating to a private key generator (PKG), a trusted
third party that calculates private keys for users. The
recipient then receives the IBE private key over a secure
connection.
3. Decrypt the IBE-encrypted Message
The IBE private key decrypts the CEK (see Section 2.3.3). The
CEK is then used to decrypt the encrypted message.
It may be useful for a PKG to allow users other than the intended
recipient to receive some IBE private keys. Giving a mail-filtering
appliance permission to obtain IBE private keys on behalf of users,
for example, can allow the appliance to decrypt and scan encrypted
messages for viruses or other malicious features.
2.3.1. Recipient Obtains Public Parameters
Before he can perform any IBE calculations related to the message
that he has received, the recipient of an IBE-encrypted message needs
to obtain the IBE public parameters that were used in the encryption
operation. This operation is shown below in Figure 3. Because the
use of the correct public parameters is vital to the overall security
of an IBE system, IBE public parameters MUST be transported to
recipients over a secure protocol. PPS servers MUST support TLS 1.2
[TLS] or its successors, using the latest version supported by both
parties, for transport of IBE public parameters. In addition, users
MUST verify that the subject name in the server certificate matches
the URI/IRI of the PPS. The comments in Section 2.2.1 also apply to
this operation.
IBE Public Parameter Request
----------------------------->
Recipient PPS
<-----------------------------
IBE Public Parameters
Figure 3: Requesting IBE Public Parameters
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2.3.2. Recipient Obtains IBE Private Key
To obtain an IBE private key, the recipient of an IBE-encrypted
message provides the IBE public key used to encrypt the message and
their authentication credentials to a PKG and requests the private
key that corresponds to the IBE public key. Section 5 of this
document defines the protocol for communicating with a PKG as well as
a minimum interoperable way to authenticate to a PKG that all IBE
implementations MUST support. Because the security of IBE private
keys is vital to the overall security of an IBE system, IBE private
keys MUST be transported to recipients over a secure protocol. PKG
servers MUST support TLS 1.2 [TLS] or its successors, using the
latest version supported by both parties, for transport of IBE
private keys. This operation is shown below in Figure 4.
IBE Private Key Request
---------------------------->
Recipient PKG
<----------------------------
IBE Private Key
Figure 4: Obtaining an IBE Private Key
2.3.3. Recipient Decrypts IBE-Encrypted Message
After obtaining the necessary IBE private key, the recipient uses
that IBE private key and the corresponding IBE public parameters to
decrypt the CEK. This operation is shown below in Figure 5. He then
uses the CEK to decrypt the encrypted message content. An example of
how to do this with email messages is given in [IBECMS].
IBE-encrypted CEK ----> Recipient ----> CEK
^
|
|
IBE Private Key
and IBE Public Parameters
Figure 5: Using an IBE Public-Key Algorithm to Decrypt
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3. Identity Format
An IBEIdentityInfo type MUST be used to represent the identity of a
recipient. This is defined to be the following:
IBEIdentityInfo ::= SEQUENCE {
district IA5String,
serial INTEGER,
identityType OBJECT IDENTIFIER,
identityData OCTET STRING
}
An IBEIdentityInfo type is used to calculate public and private IBE
keys. Because of this, such a structure is typically DER-encoded
[DER].
The fields of an IBEIdentityInfo structure have the following
meanings.
The district is an IA5String that represents the URI [URI] or IRI
[IRI] where the recipient of an IBE-encrypted message can retrieve
the IBE public parameters needed to encrypt or decrypt a message
encrypted for this identity. Applications MUST support the method
described in Section 4 for doing this and MAY support other methods.
IRIs MUST be handled according to the procedures specified in Section
7.4 of [PKIX].
The serial is an INTEGER that defines a unique set of IBE public
parameters in the event that more than one set of parameters is used
by a single district.
identityType is an OBJECT IDENTIFIER that defines the format that the
identityData field is encoded with.
An example of a useful IBEIdentityInfo type is given in [IBECMS].
This example is tailored to the use of IBE in encrypting email.
Because the information that comprises an identity is very dependent
on the application, this document does not define an identityType
that all applications MUST support.
4. Public Parameter Lookup
This section specifies how a component of an IBE system can retrieve
the public parameters. A sending or receiving client MUST allow
configuration of these parameters manually, for example, through
editing a configuration file. However, for simplified configuration,
a client SHOULD also implement the public parameter URI/IRI request
method described in this document to fetch the public parameters
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based on a configured URI/IRI. This is especially useful for
federating between IBE systems. By specifying a single URI/IRI, a
client can be configured to fetch all the relevant parameters for a
remote PKG. These public parameters can then be used to encrypt
messages to recipients who authenticate to and retrieve private keys
from that PKG.
The following section outlines the URI/IRI request method to retrieve
a parameter block and describes the structure of the parameter block
itself. The technique for fetching IBE public parameters using the
process defined in this section is indicated by the OID uriPPSOID,
which is defined to be the following:
uriPPSOID OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840)
organization(1) identicrypt(114334)
pps-schemas(3) ic-schemas(1) pps-uri(1) version(1)
}
4.1. Request Method
The configuration URI/IRI SHOULD be an HTTPS URI [HTTP] and MAY
additionally support IRIs [IRI] for this purpose. To retrieve the
IBE public parameters, the client SHOULD use the HTTP GET method as
defined in [HTTP]. The request MUST happen over a secure protocol.
The requesting client MUST support TLS 1.2 [TLS] or its successors
and SHOULD use the latest version supported by both parties. When
requesting the URI/IRI, the client MUST only accept the system
parameter block if the server identity was verified successfully by
TLS 1.2 [TLS] or its successors.
A successful GET request returns in its body the base64 [B64]
encoding of the DER-encoded [DER] IBESysParams structure that is
described in the next section. This structure MUST be encoded as an
application/ibe-pp-data MIME type.
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4.2. Parameter and Policy Format
The IBE public parameters are a structure of the form
IBESysParams ::= SEQUENCE {
version INTEGER { v2(2) },
districtName IA5String,
districtSerial INTEGER,
validity ValidityPeriod,
ibePublicParameters IBEPublicParameters,
ibeIdentityType OBJECT IDENTIFIER,
ibeParamExtensions IBEParamExtensions OPTIONAL
}
The fields of an IBESysParams structure have the following meanings.
The version field specifies the version of the IBESysParams format.
For the format described in this document, this MUST be set to 2.
The districtName field is an IA5String that MUST be an encoding of an
URI [URI] or IRI [IRI]. IRIs MUST be handled according to the
procedures specified in Section 7.4 of [PKIX].
The districtSerial field is an integer that represents a unique set
of IBE public parameters that are available at the URI or IRI defined
by the districtName. If new parameters are published for a
districtName, the districtSerial MUST be increased to a number
greater than the previously-used districtSerial.
The validity field defines the lifetime of a specific instance of the
IBESysParams and is defined to be the following:
ValidityPeriod ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime
}
The values of notBefore and notAfter MUST be expressed in Greenwich
Mean Time (Zulu), MUST include seconds (i.e., times are always
YYYYMMDDHHMMSSZ), even where the number of seconds is equal to zero,
and MUST be expressed to the nearest second.
A client MUST verify that the date on which it uses the IBE public
parameters falls between the notBefore time and the notAfter time of
the IBE public parameters, and it MUST NOT use the parameters for IBE
encryption operations if they do not.
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IBE public parameters MUST be regenerated and republished whenever
the values of ibePublicParameters, ibeIdentityType, or
ibeParamExtensions change for a district. A client SHOULD refetch
the IBE public parameters at an application-configurable interval to
ensure that it has the most current version of the IBE public
parameters.
It is possible to create identities for use in IBE that have a time
component, as described in [IBECMS], for example. If such an
identity is used, the time component of the identity MUST fall
between the notBefore time and the notAfter times of the IBE public
parameters.
IBEPublicParameters is a structure containing public parameters that
correspond to IBE algorithms that the PKG supports. This structure
is defined to be following:
IBEPublicParameters ::= SEQUENCE (1..MAX) OF
IBEPublicParameter
IBEPublicParameter ::= SEQUENCE {
ibeAlgorithm OBJECT IDENTIFIER,
publicParameterData OCTET STRING
}
The ibeAlgorithm OID specifies an IBE algorithm. The OIDs for two
IBE algorithms (the Boneh-Franklin and Boneh-Boyen algorithms) and
their publicParameterData structures are defined in [IBCS].
The publicParameterData is a DER-encoded [DER] structure that
contains the actual cryptographic parameters. Its specific structure
depends on the algorithm.
The IBESysParams of a district MUST contain an OID that identifies at
least one algorithm and MAY contain OIDs that identify more than one
algorithm. It MUST NOT contain two or more IBEPublicParameter
entries with the same algorithm. A client that wants to use
IBESysParams can chose any of the algorithms specified in the
publicParameterData structure. A client MUST implement at least the
Boneh-Franklin algorithm [IBCS] and MAY implement the Boneh-Boyen
[IBCS] and other algorithms. If a client does not support any of the
supported algorithms, it MUST generate an error message and fail.
ibeIdentityType is an OID that defines the type of identities that
are used with this district. The OIDs and the required and optional
fields for each OID are application dependent. An example of this is
given in [IBECMS], which defines an identity format suitable for use
in encrypting email.
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IBEParamExtensions is a set of extensions that can be used to define
additional parameters that particular implementations may require.
This structure is defined as follows:
IBEParamExtensions ::= SEQUENCE OF IBEParamExtension
IBEParamExtension ::= SEQUENCE {
ibeParamExtensionOID OBJECT IDENTIFIER,
ibeParamExtensionValue OCTET STRING
}
The contents of the octet string ibeParamExtensionValue are defined
by the specific ibeParamExtensionOID. The IBEParamExtensions of a
district MAY have any number of extensions, including zero. One
example of extensions that have been used in practice is to provide a
URI where an encrypted message can be decrypted and viewed by users
of webmail systems. Another example is to provide commercial
branding information, so that a bank can provide a different user
interface for customers of different lines of business.
If a client receives public parameters that contain an extension that
it is unable to process, it MUST NOT use the values in the
IBESysParams structure for any cryptographic operations. Clients
MUST be able to process an IBESysParams structure that contains no
IBEParamExtensions.
The pkgURI OID that is defined below defines an IBEParamExtensions
structure that contains the URI or IRI of a Private Key Generator.
The presence of this OID in an IBEParamExtension indicates that
clients MUST use the protocol defined in Section 5 of this document
to obtain IBE private keys from the PKG and MUST do so using the
URI/IRI that is defined by the ibeParamExtensionValue in the
IBEParamExtension.
If the PKG is publicly-accessible, this extension SHOULD be present
to allow the automatic retrieval of private keys for recipients of
encrypted messages. For this extension, the ibeParamExtensionValue
OCTET STRING is an IA5String containing the URI [URI] or IRI [IRI] of
the PKG where IBE private keys can be obtained. IRIs MUST be handled
according to the procedures specified in Section 7.4 of [PKIX].
ibeParamExt OBJECT IDENTIFIER ::= {
ibcs ibcs3(3) parameter-extensions(2)
}
pkgURI OBJECT IDENTIFIER ::= { ibeParamExt pkgURI(1) }
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4.3. The application/ibe-pp-data MIME Type
The following summarizes the properties of the
application/ibe-pp-data MIME type.
MIME media type name: application
MIME subtype name: ibe-pp-data
Mandatory parameters: none
Optional parameters: none
Encoding considerations: This media type MUST be encoded as 7-bit
(US-ASCII text [ASCII]).
Security considerations: The data conveyed as this media type are the
public parameters needed for the operation of a cryptographic
system. To ensure that the parameters can be trusted, the request
for these parameters must take place over a secure protocol, such
as TLS 1.2 or its successors. To ensure the validity of the
server, the client MUST verify the server certificate and MUST
abort the parameter request if the verification of the server
certificate of the TLS connection fails. This media type contains
no active content and does not use compression.
Interoperability considerations: There are no known interoperability
considerations for this media type.
Applications that use this media type: Applications that implement
IBE in compliance with this specification will use this media
type. The most commonly used of these applications are encrypted
email and file encryption.
Additional information: none
Person and email address for further information: Luther Martin,
martin@voltage.com.
Intended usage: COMMON
Author/Change controller: Luther Martin, martin@voltage.com.
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5. Private Key Request Protocol
5.1. Overview
When requesting a private key, a client has to transmit three
parameters:
1. The IBE algorithm for which the key is being requested
2. The identity for which it is requesting a key
3. Authentication credentials for the individual requesting the
key
The identity for which a client requests a key may not necessarily be
the same as the identity that the authentication credentials
validate. This may happen, for example, when a single user has
access to multiple aliases. For example, an email user may have
access to the keys that correspond to two different email addresses,
e.g., bob@example.com and bob.smith@example.com.
This section defines the protocol to request private keys, a minimum
user authentication method for interoperability, and how to pass
authentication credentials to the server. It assumes that a client
has already determined the URI/IRI of the PKG. This can be done from
information included in the IBE message format and the public
parameters of the IBE system.
The technique for fetching an IBE private key using the process
defined in this section is indicated by the OBJECT IDENTIFIER pkgURI,
which is defined to be the following:
ibcs OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840)
organization(1) identicrypt(114334) ibcs(1)
}
ibeParamExt OBJECT IDENTIFIER ::= {
ibcs ibcs3(3) parameter-extensions(2)
}
pkgURI OBJECT IDENTIFIER ::= { ibeParamExt pkgURI(1) }
5.2. Private Key Request
To request a private key, a client MUST perform a HTTP POST method as
defined in [HTTP]. The request MUST take place over a secure
protocol. The requesting client MUST support TLS 1.2 [TLS] or its
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successors, using the latest version supported by both the client and
the PKG. When requesting the URI/IRI, the client MUST verify the
server certificate [HTTPTLS], and it MUST abort the key request if
the server certificate verification of the TLS connection fails.
Doing so is critical to protect the authentication credentials and
the private key against man-in-the-middle attacks when it is
transmitted from the key server to the client.
5.3. Request Structure
The POST method contains in its body the following XML structure that
MUST be encoded as an application/ibe-key-request+xml MIME type:
<ibe:request xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:header>
<ibe:client version="clientID"/>
</ibe:header>
<ibe:body>
<ibe:keyRequest>
<ibe:algorithm>
algorithmOID
</ibe:algorithm>
<ibe:id>
ibeIdentityInfo
</ibe:id>
</ibe:keyRequest>
<ibe:authData>
ibeAuthData
</ibe:authData>
</ibe:body>
</ibe:request>
A <ibe:request> SHOULD include an <ibe:client> element in the
<ibe:header> part of a key request that contains an ASCII string that
identifies the client type and client version.
A key request MUST contain an <ibe:oid> element that contains the
base64 [B64] encoding of a DER-encoded [DER] object identifier that
identifies the algorithm for which a key is requested. OIDs for the
Boneh-Boyen (BB1) and Boneh-Franklin (BF) algorithms are listed in
[IBCS].
A key request MUST contain an <ibe:id> element that contains the
identity that the private key is being requested for. This identity
is the base64 [B64] encoding of a DER-encoded [DER] ASN.1 structure.
This structure defines a user's identity in a way appropriate for the
application. An example of such a structure that is appropriate for
use in encrypting email is defined in [IBECMS].
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A key request MAY contain an <ibe:authData> element. This element
contains authentication information that the PKG can use to determine
whether or not a request for a particular IBE private key should be
granted.
A client MAY include optional additional XML elements in the
<ibe:body> part of the key request. A PKG MUST be able to process
key requests that contain no such optional elements.
5.4. The application/ibe-key-request+xml MIME type
The following summarizes the properties of the
application/ibe-key-request+xml MIME type.
MIME media type name: application
MIME subtype name: ibe-key-request+xml
Mandatory parameters: none
Optional parameters: none
Encoding considerations: This media type MUST be encoded as US-ASCII
[ASCII].
Security considerations: The data conveyed in this media type may
contain authentication credentials. Because of this, its
confidentiality and integrity is extremely important. To ensure
this, the request for an IBE private key must take place over a
secure protocol, such as TLS 1.2 or its successors. To ensure the
validity of the server, the client MUST verify the server
certificate and MUST abort the key request if the verification of
the server certificate of the TLS connection fails. This media
type contains no active content and does not use compression.
Interoperability considerations: There are no known interoperability
considerations for this media type.
Applications that use this media type: Applications that implement
IBE in compliance with this specification will use this media
type. The most commonly used of these applications are encrypted
email and file encryption.
Additional information: none
Person and email address for further information: Luther Martin,
martin@voltage.com.
Appenzeller, et al. Informational [Page 17]
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Intended usage: COMMON
Author/Change controller: Luther Martin, martin@voltage.com.
5.5. Authentication
When a client requests a key from a PKG, the PKG MUST authenticate
the client before issuing the key. Authentication may either be done
through the key request structure or as part of the secure transport
protocol.
A client or server implementing the request protocol MUST support
HTTP Basic Auth [AUTH] and SHOULD also support HTTP Digest Auth
[AUTH]. Applications MAY also use other means of authentication that
are appropriate for the application. An email application, for
example, might rely on deployed email infrastructure for this.
For authentication methods that are not done by the transport
protocol, a client MAY include additional authentication information
in XML elements in the <ibe:authData> element of a key request. If a
client does not know how to authenticate to a server, the client MAY
send a key request without authentication information. If the key
server requires the client to authenticate externally, it MAY reply
with an IBE201 responseCode (as defined below) to redirect the client
to the correct authentication mechanism. After receiving an
authentication credential from this external mechanism, a client can
then use the credential to form a key request that contains the
additional authentication data.
5.6. Server Response Format
The key server replies to the HTTP request with an HTTP response. If
the response contains a client error or server error status code, the
client MUST abort the key request and fail.
If the PKG replies with an HTTP response that has a status code
indicating success, the body of the reply MUST contain the following
XML structure that MUST be encoded as an
application/ibe-pkg-reply+xml MIME type:
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="responseCode"/>
<ibe:body>
bodyTags
</ibe:body>
</ibe:response>
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The responseCode attribute contains an ASCII string that describes
the type of response from the key server. The list of currently-
defined responseCodes and their associated meanings is:
IBE100 KEY_FOLLOWS
IBE101 RESERVED
IBE201 FOLLOW_ENROLL_URI
IBE300 SYSTEM_ERROR
IBE301 INVALID_REQUEST
IBE303 CLIENT_OBSOLETE
IBE304 AUTHORIZATION DENIED
5.6.1. The IBE100 responseCode
If the key request was successful, the key server responds with a
responseCode of IBE100, and the <ibe:body> MUST contain a
<ibe:privateKey> element that contains a valid private key. An
example of this is shown below.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE100"/>
<ibe:body>
<ibe:privateKey>
privateKey
</ibe:privateKey>
</ibe:body>
</ibe:response>
The privateKey is the base64 [B64] encoding of the DER encoding [DER]
of the following structure:
IBEPrivateKeyReply ::= SEQUENCE {
pkgIdentity IBEIdentityInfo,
pgkAlgorithm OBJECT IDENTIFIER,
pkgKeyData OCTET STRING,
pkgOptions SEQUENCE SIZE (1..MAX) OF PKGOption
}
PKGOption ::= SEQUENCE {
optionID OBJECT IDENTIFIER,
optionValue OCTET STRING
}
The pkgIdentity is an IBEIdentityInfo structure that MUST be
identical to the IBEIdentityInfo structure that was sent in the key
request.
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The pkgAlgorithm is an OID that identifies the algorithm of the
returned private key. The OIDs for the BB1 and BF algorithms are
defined in [IBCS].
The pkgKeyData is a structure that contains the actual private key.
Private-key formats for the BB1 and BF algorithms are defined in
[IBCS].
A server MAY pass back additional information to a client in the
pkgOptions structure. A client that receives a IBEPrivateKeyReply
from a PKG that contains information in a pkgOptions structure that
it is unable process MUST NOT use the IBE private key in the
IBEPrivateKeyReply structure for any cryptographic operations. A
client MUST be able to process an IBEPrivateKeyReply that contains no
PKGOptions structure.
5.6.2. The IBE101 responseCode
The responseCode IBE101 is reserved to ensure interoperability with
earlier versions of the protocol described in this document. An
example of such a response is shown below. A response with the
IBE101 responseCode SHOULD contain no body. If information is
contained in the body of such a response, the client receiving the
response MUST discard any data that is contained in the body.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE101"/>
<ibe:body>
This message must be discarded by the recipient
</ibe:body
</ibe:response>
5.6.3. The IBE201 responseCode
A PKG MAY support authenticating users to external authentication
mechanisms. If this is the case, the server replies to the client
with responseCode IBE201 and the body of the response MUST contain a
<ibe:location> element that specifies the URI of the authentication
mechanism. An example of such a response is shown below.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE201"/>
<ibe:body>
<ibe:location
URI="http://www.example.com/enroll.asp"/>
</ibe:body>
</ibe:response>
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The client can now contact the URI returned in such a response using
the same mechanisms as defined in Section 5.2 to obtain an
authentication credential. Once the client has obtained the
credential from the authentication mechanism at this URI, it sends a
new key request to the PKG with the correct authentication
credentials contained in the request, placing the authentication
credential in the <ibe:authData> element of a key request as
described in Section 5.5.
5.6.4. The IBE300 responseCode
The IBE300 responseCode indicates that an internal server error has
occurred. Information that may help diagnose the error MAY be
included in the body of such a response. An example of such a
response is shown below. Upon receiving a IBE300 responseCode, the
client MUST abort the key request and discard any data that was
included in the body of the response.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE300"/>
<ibe:body>
Widget phlebotomy failure
</ibe:body>
</ibe:response>
5.6.5. The IBE301 responseCode
The IBE303 responseCode indicates that an invalid key request has
been received by the server. Information that may help diagnose the
error MAY be included in the body of such a response. An example of
such a response is shown below. Upon receiving an IBE301
responseCode, the client MUST abort the key request and discard any
data that was included in the body of the response.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE301"/>
<ibe:body>
Some additional stuff
</ibe:body>
</ibe:response>
5.6.6. The IBE303 responseCode
The IBE303 responseCode indicates that the server is unable to
correctly process the request because the version of the request is
no longer supported by the server. Information that may help
diagnose the error MAY be included in the body of such a response.
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An example of such a response is shown below. Upon receiving an
IBE303 responseCode, the client MUST abort the key request and
discard any data that was included in the body of the response.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE303"/>
<ibe:body>
Version 3.3 or later needed
</ibe:body>
</ibe:response>
5.6.7. The IBE304 responseCode
The IBE304 responseCode indicates that a valid key request has been
received by the server, but the authentication credentials provided
were invalid. Information that may help diagnose the error MAY be
included in the body of such a response. An example of such a
response is shown below. Upon receiving an IBE304 responseCode, the
client MUST abort the key request and discard any data that was
included in the body of the response.
<ibe:response xmlns:ibe="urn:ietf:params:xml:ns:ibe">
<ibe:responseType value="IBE304"/>
<ibe:body>
Helpful error message
</ibe:body>
</ibe:response>
5.7. The application/ibe-pkg-reply+xml MIME type
The following summarizes the properties of the
application/ibe-pkg-reply+xml MIME type.
MIME media type name: application
MIME subtype name: ibe-pkg-reply+xml
Mandatory parameters: none
Optional parameters: none
Encoding considerations: This media type MUST be encoded as US-ASCII
[ASCII].
Security considerations: The data conveyed as this media type is an
IBE private key, so its confidentiality and integrity are
extremely important. To ensure this, the response from the server
that contains an IBE private key must take place over a secure
Appenzeller, et al. Informational [Page 22]
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protocol, such as TLS 1.2 or its successors. To ensure the
validity of the server, the client MUST verify the server
certificate and MUST abort the key request if the verification of
the server certificate of the TLS connection fails. This media
type contains no active content and does not use compression.
Interoperability considerations: There are no known interoperability
considerations for this media type.
Applications that use this media type: Applications that implement
IBE in compliance with this specification will use this media
type. The most commonly used of these applications are encrypted
email and file encryption.
Additional information: none
Person and email address for further information: Luther Martin,
martin@voltage.com.
Intended usage: COMMON
Author/Change controller: Luther Martin, martin@voltage.com.
6. ASN.1 Module
The following ASN.1 module summarizes the ASN.1 definitions discussed
in this document.
IBEARCH-module { joint-iso-itu-t(2) country(16) us(840)
organization(1) identicrypt(114334) ibcs(1) ibearch(5)
module(5) version(1)
}
DEFINITIONS IMPLICIT TAGS ::= BEGIN
IBESysParams ::= SEQUENCE {
version INTEGER { v2(2) },
districtName IA5String,
districtSerial INTEGER,
validity ValidityPeriod,
ibePublicParameters IBEPublicParameters,
ibeIdentityType OBJECT IDENTIFIER,
ibeParamExtensions IBEParamExtensions OPTIONAL
}
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ValidityPeriod ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime
}
IBEPublicParameters ::= SEQUENCE (1..MAX) OF
IBEPublicParameter
IBEPublicParameter ::= SEQUENCE {
ibeAlgorithm OBJECT IDENTIFIER,
publicParameterData OCTET STRING
}
IBEParamExtensions ::= SEQUENCE OF IBEParamExtension
IBEParamExtension ::= SEQUENCE {
ibeParamExtensionOID OBJECT IDENTIFIER,
ibeParamExtensionValue OCTET STRING
}
ibcs OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840)
organization(1) identicrypt(114334) ibcs(1)
}
ibeParamExt OBJECT IDENTIFIER ::= {
ibcs ibcs3(3) parameter-extensions(2)
}
pkgURI OBJECT IDENTIFIER ::= { ibeParamExt pkgURI(1) }
IBEPrivateKeyReply ::= SEQUENCE {
pkgIdentity IBEIdentityInfo,
pgkAlgorithm OBJECT IDENTIFIER,
pkgKeyData OCTET STRING,
pkgOptions SEQUENCE SIZE (1..MAX) OF PKGOption
}
PKGOption ::= SEQUENCE {
optionID OBJECT IDENTIFIER,
optionValue OCTET STRING
}
uriPPSOID OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840)
organization(1) identicrypt(114334)
pps-schemas(3) ic-schemas(1) pps-uri(1) version(1)
}
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IBEIdentityInfo ::= SEQUENCE {
district IA5String,
serial INTEGER,
identityType OBJECT IDENTIFIER,
identityData OCTET STRING
}
END
7. Security Considerations
7.1. Attacks outside the Scope of This Document
Attacks on the cryptographic algorithms that are used to implement
IBE are outside the scope of this document. Such attacks are
detailed in [IBCS], which defines parameters that give 80-bit,
112-bit, and 128-bit encryption strength. We assume that capable
administrators of an IBE system will select parameters that provide a
sufficient resistance to cryptanalytic attacks by adversaries.
Attacks that give an adversary the ability to access or change the
information on a PPS or PKG, especially the cryptographic material
(referred to in this document as the master secret), will defeat the
security of an IBE system. In particular, if the cryptographic
material is compromised, the adversary will have the ability to
recreate any user's private key and therefore decrypt all messages
protected with the corresponding public key. To address this
concern, it is highly RECOMMENDED that best practices for physical
and operational security for PPS and PKG servers be followed and that
these servers be configured (sometimes known as hardened) in
accordance with best current practices [NIST]. An IBE system SHOULD
be operated in an environment where illicit access is infeasible for
attackers to obtain.
Attacks that require administrative access or IBE-user-equivalent
access to machines used by either the client or the server components
defined in this document are also outside the scope of this document.
We also assume that all administrators of a system implementing the
protocols that are defined in this document are trustworthy and will
not abuse their authority to bypass the security provided by an IBE
system. Similarly, we assume that users of an IBE system will behave
responsibly, not sharing their authentication credentials with
others. Thus, attacks that require such assumptions are outside the
scope of this document.
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7.2. Attacks within the Scope of This Document
Attacks within the scope of this document are those that allow an
adversary to:
o passively monitor information transmitted between users of an
IBE system and the PPS and PKG
o masquerade as a PPS or PKG
o perform a denial-of-service (DoS) attack on a PPS or PKG
o easily guess an IBE users authentication credential
7.2.1. Attacks on the Protocols Defined in This Document
All communications between users of an IBE system and the PPS or PKG
are protected using TLS 1.2 [TLS]. The IBE system defined in this
document provides no additional security protections for the
communications between IBE users and the PPS or PKG. Therefore, the
described IBE system is completely dependent on the TLS security
mechanisms for authentication of the PKG or PPS server and for
confidentiality and integrity of the communications. Should there be
a compromise of the TLS security mechanisms, the integrity of all
communications between an IBE user and the PPS or PKG will be
suspect.
The protocols defined in this document do not explicitly defend
against an attacker masquerading as a legitimate IBE PPS or PKG. The
protocols rely on the server authentication mechanism of TLS [TLS].
In addition to the TLS server authentication mechanism, IBE client
software can provide protection against this possibility by providing
user interface capabilities that allow users to visually determine
that a connection to PPS and PKG servers is legitimate. This
additional capability can help ensure that users cannot easily be
tricked into providing valid authorization credentials to an
attacker.
The protocols defined in this document are also vulnerable to attacks
against an IBE PPS or PKG. Denial-of-service attacks against either
component can result in users' being unable to encrypt or decrypt
using IBE, and users of an IBE system SHOULD take the appropriate
countermeasures [DOS, BGPDOS] that their use of IBE requires.
The IBE user authentication method selected by an IBE PKG SHOULD be
of sufficient strength to prevent attackers from easily guessing the
IBE user's authentication credentials through trial and error.
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8. IANA Considerations
8.1. Media Types
With this specification, IANA has registered three media types in the
standard registration tree. These are application/ibe-pp-data,
application/ibe-key-request+xml, and application/ibe-pkg-reply+xml.
The media type application/ibe-pp-data is defined in Section 4.3 of
this document. The media type application/ibe-key-request+xml is
defined in Section 5.4 of this document. The media type
application/ibe-pkg-reply+xml is defined in Section 5.7 of this
document.
8.2. XML Namespace
The IANA is requested to register the following namespace identifier:
urn:ietf:params:xml:ns:ibe
Registrant Contact:
Luther Martin
Voltage Security
1070 Arastradero Rd Suite 100
Palo Alto, CA 94304
Phone: +1 650 543 1280
Email: martin@voltage.com
XML:
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C/DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Identity-Based Encryption</title>
</head>
<body>
<h1>Namespace for Identity-Based Encryption</h1>
<h2>urn:ietf:params:xml:ns:ibe</h2>
<p>
<a href="http://www.rfc-editor.org/rfc/rfc5408.txt">RFC5408</a>.
</p>
</body>
</html>
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RFC 5408 IBE Architecture January 2009
9. References
9.1. Normative References
[ASCII] ISO/IEC 646:1991 - Information Technology - ISO 7-bit Coded
Character Set for Information Exchange.
[ASN1] ITU-T Recommendation X.680: Information Technology -
Abstract Syntax Notation One, 1997.
[AUTH] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[B64] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.
[DER] ITU-T Recommendation X.690: OSI Networking and System
Aspects: Abstract Syntax Notation One (ASN.1), July 2002.
[DOS] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
L., Leach, P., and T. Berners-Lee, "Hypertext Transfer
Protocol -- HTTP/1.1", RFC 2616, June 1999.
[HTTPTLS] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[IBCS] Boyen, X. and L. Martin, "Identity-Based Cryptography
Standard (IBCS) #1: Supersingular Curve Implementations of
the BF and BB1 Cryptosystems", RFC 5091, December 2007.
[IRI] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[KEY] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Appenzeller, et al. Informational [Page 28]
RFC 5408 IBE Architecture January 2009
[PKIX] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[XML] W3C, Extensible Markup Language (XML) 1.0 (Fourth Edition),
September 2006.
9.2. Informative References
[BGPDOS] Turk, D., "Configuring BGP to Block Denial-of-Service
Attacks", RFC 3882, September 2004.
[IBECMS] Martin, L. and M. Schertler, "Using the Boneh-Franklin
Identity-Based Encryption Algorithm with the Cryptographic
Message Syntax (CMS)", RFC 5409, January 2009.
[NIST] M. Souppaya, J. Wack and K. Kent, "Security Configuration
Checklist Program for IT Products - Guidance for Checklist
Users and Developers", NIST Special Publication SP 800-70,
May 2005.
[P1363] IEEE P1363, "Standard Specifications for Public-Key
Cryptography", 2001.
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RFC 5408 IBE Architecture January 2009
Authors' Addresses
Guido Appenzeller
Stanford University
Gates Building 3A
Stanford, CA 94305
Phone: +1 650 732 2273
EMail: appenz@cs.stanford.edu
Luther Martin
Voltage Security
1070 Arastradero Rd, Suite 100
Palo Alto, CA 94304
USA
Phone: +1 650 543 1280
EMail: martin@voltage.com
Mark Schertler
Axway
1600 Seaport Blvd, Suite 400
Redwood City, CA 94063
USA
Phone: +1 650 216 2039
EMail: mschertler@us.axway.com
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