RFC 5755
An Internet Attribute Certificate Profile for Authorization
Internet Engineering Task Force (IETF) S. Farrell Request for Comments: 5755 Trinity College Dublin Obsoletes: 3281 R. Housley Category: Standards Track Vigil Security ISSN: 2070-1721 S. Turner IECA January 2010 An Internet Attribute Certificate Profile for AuthorizationAbstract
This specification defines a profile for the use of X.509 Attribute Certificates in Internet Protocols. Attribute certificates may be used in a wide range of applications and environments covering a broad spectrum of interoperability goals and a broader spectrum of operational and assurance requirements. The goal of this document is to establish a common baseline for generic applications requiring broad interoperability as well as limited special purpose requirements. The profile places emphasis on attribute certificate support for Internet electronic mail, IPsec, and WWW security applications. This document obsoletes RFC 3281. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5755.
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Table of Contents
1. Introduction ....................................................4 1.1. Requirements Terminology ...................................5 1.2. AC Path Delegation .........................................5 1.3. Attribute Certificate Distribution ("Push" vs. "Pull") .....6 1.4. Document Structure .........................................7 2. Terminology .....................................................7 3. Requirements ....................................................8 4. Attribute Certificate Profile ...................................9 4.1. X.509 Attribute Certificate Definition ....................10 4.2. Profile of Standard Fields ................................12 4.2.1. Version ............................................13 4.2.2. Holder .............................................13 4.2.3. Issuer .............................................14 4.2.4. Signature ..........................................14 4.2.5. Serial Number ......................................14 4.2.6. Validity Period ....................................15 4.2.7. Attributes .........................................15 4.2.8. Issuer Unique Identifier ...........................16 4.2.9. Extensions .........................................16 4.3. Extensions ................................................17 4.3.1. Audit Identity .....................................17 4.3.2. AC Targeting .......................................18 4.3.3. Authority Key Identifier ...........................19 4.3.4. Authority Information Access .......................19 4.3.5. CRL Distribution Points ............................20 4.3.6. No Revocation Available ............................20 4.4. Attribute Types ...........................................21 4.4.1. Service Authentication Information .................21 4.4.2. Access Identity ....................................22 4.4.3. Charging Identity ..................................23 4.4.4. Group ..............................................23 4.4.5. Role ...............................................23 4.4.6. Clearance ..........................................24 4.5. Profile of AC Issuer's PKC ................................26 5. Attribute Certificate Validation ...............................27 6. Revocation .....................................................28 7. Optional Features ..............................................29 7.1. Attribute Encryption ......................................29 7.2. Proxying ..................................................31 7.3. Use of ObjectDigestInfo ...................................32 7.4. AA Controls ...............................................33 8. Security Considerations ........................................35 9. IANA Considerations ............................................36
10. References ....................................................37 10.1. Reference Conventions ....................................37 10.2. Normative References .....................................37 10.3. Informative References ...................................38 Appendix A. Object Identifiers ....................................40 Appendix B. ASN.1 Module ..........................................41 Appendix C. Errata Report Submitted to RFC 3281 ...................47 Appendix D. Changes since RFC 3281 ................................481. Introduction
X.509 public key certificates (PKCs) [X.509-1997] [X.509-2000] [PKIXPROF] bind an identity and a public key. An attribute certificate (AC) is a structure similar to a PKC; the main difference being that the AC contains no public key. An AC may contain attributes that specify group membership, role, security clearance, or other authorization information associated with the AC holder. The syntax for the AC is defined in Recommendation X.509, making the term "X.509 certificate" ambiguous. Some people constantly confuse PKCs and ACs. An analogy may make the distinction clear. A PKC can be considered to be like a passport: it identifies the holder, tends to last for a long time, and should not be trivial to obtain. An AC is more like an entry visa: it is typically issued by a different authority and does not last for as long a time. As acquiring an entry visa typically requires presenting a passport, getting a visa can be a simpler process. Authorization information may be placed in a PKC extension or placed in a separate attribute certificate (AC). The placement of authorization information in PKCs is usually undesirable for two reasons. First, authorization information often does not have the same lifetime as the binding of the identity and the public key. When authorization information is placed in a PKC extension, the general result is the shortening of the PKC useful lifetime. Second, the PKC issuer is not usually authoritative for the authorization information. This results in additional steps for the PKC issuer to obtain authorization information from the authoritative source. For these reasons, it is often better to separate authorization information from the PKC. Yet, authorization information also needs to be bound to an identity. An AC provides this binding; it is simply a digitally signed (or certified) identity and set of attributes. An AC may be used with various security services, including access control, data origin authentication, and non-repudiation.
PKCs can provide an identity to access control decision functions. However, in many contexts, the identity is not the criterion that is used for access control decisions; rather, the role or group- membership of the accessor is the criterion used. Such access control schemes are called role-based access control. When making an access control decision based on an AC, an access control decision function may need to ensure that the appropriate AC holder is the entity that has requested access. One way in which the linkage between the request or identity and the AC can be achieved is the inclusion of a reference to a PKC within the AC and the use of the private key corresponding to the PKC for authentication within the access request. ACs may also be used in the context of a data origin authentication service and a non-repudiation service. In these contexts, the attributes contained in the AC provide additional information about the signing entity. This information can be used to make sure that the entity is authorized to sign the data. This kind of checking depends either on the context in which the data is exchanged or on the data that has been digitally signed. This document obsoletes [RFC3281]. Changes since [RFC3281] are listed in Appendix D.1.1. Requirements 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 [RFC2119].1.2. AC Path Delegation
The X.509 standard [X.509-2000] defines authorization as the "conveyance of privilege from one entity that holds such privilege, to another entity". An AC is one authorization mechanism. An ordered sequence of ACs could be used to verify the authenticity of a privilege asserter's privilege. In this way, chains or paths of ACs could be employed to delegate authorization. Since the administration and processing associated with such AC chains is complex and the use of ACs in the Internet today is quite limited, it is RECOMMENDED that implementations of this specification not use AC chains. Other (future) specifications may address the use of AC chains. This specification deals with the simple cases, where one authority issues all of the ACs for a particular set of attributes. However, this simplification does not preclude the use
of several different authorities, each of which manages a different set of attributes. For example, group membership may be included in one AC issued by one authority, and security clearance may be included in another AC issued by another authority. This means that conformant implementations are only REQUIRED to be able to process a single AC at a time. Processing of more than one AC, one after another, may be necessary. Note however, that validation of an AC MAY require validation of a chain of PKCs, as specified in [PKIXPROF].1.3. Attribute Certificate Distribution ("Push" vs. "Pull")
As discussed above, ACs provide a mechanism to securely provide authorization information to, for example, access control decision functions. However, there are a number of possible communication paths for ACs. In some environments, it is suitable for a client to "push" an AC to a server. This means that no new connections between the client and server are required. It also means that no search burden is imposed on servers, which improves performance and that the AC verifier is only presented with what it "needs to know". The "push" model is especially suitable in inter-domain cases where the client's rights should be assigned within the client's "home" domain. In other cases, it is more suitable for a client to simply authenticate to the server and for the server to request or "pull" the client's AC from an AC issuer or a repository. A major benefit of the "pull" model is that it can be implemented without changes to the client or to the client-server protocol. The "pull" model is especially suitable for inter-domain cases where the client's rights should be assigned within the server's domain, rather than within the client's domain. There are a number of possible exchanges involving three entities: the client, the server, and the AC issuer. In addition, a directory service or other repository for AC retrieval MAY be supported.
Figure 1 shows an abstract view of the exchanges that may involve ACs. This profile does not specify a protocol for these exchanges. +--------------+ | | Server Acquisition | AC issuer +<---------------------------+ | | | +--+-----------+ | ^ | | Client | | Acquisition | v v +--+-----------+ +--+------------+ | | AC "push" | | | Client +<------------------------| Server | | | (part of app. protocol) | | +--+-----------+ +--+------------+ ^ ^ | Client | Server | Lookup +--------------+ | Lookup | | | | +-------------->+ Repository +<--------+ | | +--------------+ Figure 1: AC Exchanges1.4. Document Structure
Section 2 defines some terminology. Section 3 specifies the requirements that this profile is intended to meet. Section 4 contains the profile of the X.509 AC. Section 5 specifies rules for AC validation. Section 6 specifies rules for AC revocation checks. Section 7 specifies optional features that MAY be supported; however, support for these features is not required for conformance to this profile. Finally, the appendices contain the list of object identifiers (OIDs) required to support this specification and an ASN.1 module.2. Terminology
For simplicity, we use the terms client and server in this specification. This is not intended to indicate that ACs are only to be used in client-server environments. For example, ACs may be used in the Secure/Multipurpose Internet Mail Extensions (S/MIME) v3.2 context, where the mail user agent would be both a "client" and a "server" in the sense the terms are used here.
Term Meaning
AA Attribute Authority, the entity that issues the AC,
synonymous in this specification with "AC issuer".
AC Attribute Certificate.
AC user Any entity that parses or processes an AC.
AC verifier Any entity that checks the validity of an AC and then
makes use of the result.
AC issuer The entity that signs the AC: synonymous in this
specification with "AA".
AC holder The entity indicated (perhaps indirectly) in the Holder
field of the AC.
Client The entity that is requesting the action for which
authorization checks are to be made.
Proxying In this specification, Proxying is used to mean the
situation where an application server acts as an
application client on behalf of a user. Proxying here
does not mean granting of authority.
PKC Public Key Certificate - uses the ASN.1 type
Certificate defined in X.509 and profiled in RFC 5280.
This (non-standard) acronym is used in order to avoid
confusion about the term "X.509 certificate".
Server The entity that requires that the authorization checks
are made.
3. Requirements
This AC profile meets the following requirements.
Time/Validity requirements:
1. Support for short-lived as well as long-lived ACs. Typical short-
lived validity periods might be measured in hours, as opposed to
months for PKCs. Short validity periods allow ACs to be useful
without a revocation mechanism.
Attribute Types:
2. Issuers of ACs should be able to define their own attribute types
for use within closed domains.
3. Some standard attribute types, which can be contained within ACs,
should be defined. Examples include "access identity", "group",
"role", "clearance", "audit identity", and "charging identity".
4. Standard attribute types should be defined in a manner that
permits an AC verifier to distinguish between uses of the same
attribute in different domains. For example, the "Administrators
group" as defined by "Baltimore" and the "Administrators group" as
defined by "SPYRUS" should be easily distinguished.
Targeting of ACs:
5. It should be possible to "target" an AC at one, or a small number
of, servers. This means that a trustworthy non-target server will
reject the AC for authorization decisions.
Push vs. Pull
6. ACs should be defined so that they can either be "pushed" by the
client to the server, or "pulled" by the server from a repository
or other network service, including an online AC issuer.
4. Attribute Certificate Profile
ACs may be used in a wide range of applications and environments
covering a broad spectrum of interoperability goals and a broader
spectrum of operational and assurance requirements. The goal of this
document is to establish a common baseline for generic applications
requiring broad interoperability and limited special purpose
requirements. In particular, the emphasis will be on supporting the
use of attribute certificates for informal Internet electronic mail,
IPsec, and WWW applications.
This section presents a profile for ACs that will foster
interoperability. This section also defines some private extensions
for the Internet community.
While the ISO/IEC/ITU documents use the 1993 (or later) version of
ASN.1, this document uses the 1988 ASN.1 syntax, as has been done for
PKCs [PKIXPROF]. The encoded certificates and extensions from either
ASN.1 version are bit-wise identical.
Where maximum lengths for fields are specified, these lengths refer to the DER encoding and do not include the ASN.1 tag or length fields. Conforming implementations MUST support the profile specified in this section.4.1. X.509 Attribute Certificate Definition
X.509 contains the definition of an AC given below. All types that are not defined in this document can be found in [PKIXPROF]. AttributeCertificate ::= SEQUENCE { acinfo AttributeCertificateInfo, signatureAlgorithm AlgorithmIdentifier, signatureValue BIT STRING } AttributeCertificateInfo ::= SEQUENCE { version AttCertVersion, -- version is v2 holder Holder, issuer AttCertIssuer, signature AlgorithmIdentifier, serialNumber CertificateSerialNumber, attrCertValidityPeriod AttCertValidityPeriod, attributes SEQUENCE OF Attribute, issuerUniqueID UniqueIdentifier OPTIONAL, extensions Extensions OPTIONAL } AttCertVersion ::= INTEGER { v2(1) } Holder ::= SEQUENCE { baseCertificateID [0] IssuerSerial OPTIONAL, -- the issuer and serial number of -- the holder's Public Key Certificate entityName [1] GeneralNames OPTIONAL, -- the name of the claimant or role objectDigestInfo [2] ObjectDigestInfo OPTIONAL -- used to directly authenticate the holder, -- for example, an executable }
ObjectDigestInfo ::= SEQUENCE {
digestedObjectType ENUMERATED {
publicKey (0),
publicKeyCert (1),
otherObjectTypes (2) },
-- otherObjectTypes MUST NOT
-- be used in this profile
otherObjectTypeID OBJECT IDENTIFIER OPTIONAL,
digestAlgorithm AlgorithmIdentifier,
objectDigest BIT STRING
}
AttCertIssuer ::= CHOICE {
v1Form GeneralNames, -- MUST NOT be used in this
-- profile
v2Form [0] V2Form -- v2 only
}
V2Form ::= SEQUENCE {
issuerName GeneralNames OPTIONAL,
baseCertificateID [0] IssuerSerial OPTIONAL,
objectDigestInfo [1] ObjectDigestInfo OPTIONAL
-- issuerName MUST be present in this profile
-- baseCertificateID and objectDigestInfo MUST NOT
-- be present in this profile
}
IssuerSerial ::= SEQUENCE {
issuer GeneralNames,
serial CertificateSerialNumber,
issuerUID UniqueIdentifier OPTIONAL
}
AttCertValidityPeriod ::= SEQUENCE {
notBeforeTime GeneralizedTime,
notAfterTime GeneralizedTime
}
Although the Attribute syntax is defined in [PKIXPROF], we repeat the definition here for convenience. Attribute ::= SEQUENCE { type AttributeType, values SET OF AttributeValue -- at least one value is required } AttributeType ::= OBJECT IDENTIFIER AttributeValue ::= ANY DEFINED BY AttributeType Implementers should note that the DER encoding (see [X.509-1988], [X.690]) of the SET OF values requires ordering of the encodings of the values. Though this issue arises with respect to distinguished names, and has to be handled by [PKIXPROF] implementations, it is much more significant in this context, since the inclusion of multiple values is much more common in ACs.4.2. Profile of Standard Fields
GeneralName offers great flexibility. To achieve interoperability, in spite of this flexibility, this profile imposes constraints on the use of GeneralName. Conforming implementations MUST be able to support the dNSName, directoryName, uniformResourceIdentifier, and iPAddress options. This is compatible with the GeneralName requirements in [PKIXPROF] (mainly in Section 4.2.1.6). Implementations SHOULD also support the SRVName, as defined in [X509-SRV]. Conforming implementations MUST NOT use the x400Address, ediPartyName, or registeredID options. Conforming implementations MAY use the otherName option to convey name forms defined in Internet Standards. For example, Kerberos [KRB] format names can be encoded into the otherName, using a Kerberos 5 principal name OID and a SEQUENCE of the Realm and the PrincipalName.
4.2.1. Version
The version field MUST have the value of v2. That is, the version field is present in the DER encoding. Note: This version (v2) is not backwards compatible with the previous attribute certificate definition (v1) from the 1997 X.509 standard [X.509-1997], but is compatible with the v2 definition from X.509 (2000) [X.509-2000].4.2.2. Holder
The Holder field is a SEQUENCE allowing three different (optional) syntaxes: baseCertificateID, entityName, and objectDigestInfo. Where only one option is present, the meaning of the Holder field is clear. However, where more than one option is used, there is a potential for confusion as to which option is "normative", which is a "hint", etc. Since the correct position is not clear from [X.509-2000], this specification RECOMMENDS that only one of the options be used in any given AC. For any environment where the AC is passed in an authenticated message or session and where the authentication is based on the use of an X.509 PKC, the Holder field SHOULD use the baseCertificateID. With the baseCertificateID option, the holder's PKC serialNumber and issuer MUST be identical to the AC Holder field. The PKC issuer MUST have a non-empty distinguished name that is to be present as the single value of the holder.baseCertificateID.issuer construct in the directoryName field. The AC holder.baseCertificateID.issuerUID field MUST only be used if the holder's PKC contains an issuerUniqueID field. If both the AC holder.baseCertificateID.issuerUID and the PKC issuerUniqueID fields are present, the same value MUST be present in both fields. Thus, the baseCertificateID is only usable with PKC profiles (like [PKIXPROF]) that mandate that the PKC issuer field contain a non-empty distinguished name value. Note: An empty distinguished name is a distinguished name where the SEQUENCE OF relative distinguished names is of zero length. In a DER encoding, this has the value '3000'H. If the Holder field uses the entityName option and the underlying authentication is based on a PKC, the entityName MUST be the same as the PKC subject field or one of the values of the PKC subjectAltName field extension (if present). Note that [PKIXPROF] mandates that the subjectAltName extension be present if the PKC subject is an empty
distinguished name. See the Security Considerations section, which mentions some name collision problems that may arise when using the entityName option. In any other case where the Holder field uses the entityName option, only one name SHOULD be present. Implementations conforming to this profile are not required to support the use of the objectDigest field. However, Section 7.3 specifies how this optional feature MAY be used. Any protocol conforming to this profile SHOULD specify which AC holder option is to be used and how this fits with the supported authentication schemes defined in that protocol.4.2.3. Issuer
ACs conforming to this profile MUST use the v2Form choice, which MUST contain one and only one GeneralName in the issuerName, which MUST contain a non-empty distinguished name in the directoryName field. This means that all AC issuers MUST have non-empty distinguished names. ACs conforming to this profile MUST omit the baseCertificateID and objectDigestInfo fields. Part of the reason for the use of the v2Form containing only an issuerName is that it means that the AC issuer does not have to know which PKC the AC verifier will use for it (the AC issuer). Using the baseCertificateID field to reference the AC issuer would mean that the AC verifier would have to trust the PKC that the AC issuer chose (for itself) at AC creation time.4.2.4. Signature
Contains the algorithm identifier used to validate the AC signature. This MUST be one of the signing algorithms defined in [PKIXALGS] or defined in any IETF-approved update to [PKIXALGS]. Conforming implementations MUST honor all MUST/SHOULD/MAY signing algorithm statements specified in [PKIXALGS] or IETF-approved updates to [PKIXALGS].4.2.5. Serial Number
For any conforming AC, the issuer/serialNumber pair MUST form a unique combination, even if ACs are very short-lived.
AC issuers MUST force the serialNumber to be a positive integer, that is, the sign bit in the DER encoding of the INTEGER value MUST be zero -- this can be done by adding a leading (leftmost) '00'H octet if necessary. This removes a potential ambiguity in mapping between a string of octets and an integer value. Given the uniqueness and timing requirements above, serial numbers can be expected to contain long integers. AC users MUST be able to handle serialNumber values longer than 4 octets. Conformant ACs MUST NOT contain serialNumber values longer than 20 octets. There is no requirement that the serial numbers used by any AC issuer follow any particular ordering. In particular, they need not be monotonically increasing with time. Each AC issuer MUST ensure that each AC that it issues contains a unique serial number.4.2.6. Validity Period
The attrCertValidityPeriod (a.k.a. validity) field specifies the period for which the AC issuer certifies that the binding between the holder and the attributes fields will be valid. The generalized time type, GeneralizedTime, is a standard ASN.1 type for variable precision representation of time. The GeneralizedTime field can optionally include a representation of the time differential between the local time zone and Greenwich Mean Time. For the purposes of this profile, GeneralizedTime values MUST be expressed in Coordinated universal time (UTC) (also known as Greenwich Mean Time or Zulu)) and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even when the number of seconds is zero. GeneralizedTime values MUST NOT include fractional seconds. (Note: this is the same as specified in [PKIXPROF], Section 4.1.2.5.2.) AC users MUST be able to handle an AC which, at the time of processing, has parts of its validity period or all its validity period in the past or in the future (a post-dated AC). This is valid for some applications, such as backup.4.2.7. Attributes
The attributes field gives information about the AC holder. When the AC is used for authorization, this will often contain a set of privileges.
The attributes field contains a SEQUENCE OF Attribute. Each Attribute contains the type of the attribute and a SET OF values. For a given AC, each AttributeType OBJECT IDENTIFIER in the sequence MUST be unique. That is, only one instance of each attribute can occur in a single AC, but each instance can be multi-valued. AC users MUST be able to handle multiple values for all attribute types. An AC MUST contain at least one attribute. That is, the SEQUENCE OF Attributes MUST NOT be of zero length. Some standard attribute types are defined in Section 4.4.4.2.8. Issuer Unique Identifier
This field MUST NOT be used unless it is also used in the AC issuer's PKC, in which case it MUST be used. Note that [PKIXPROF] states that this field SHOULD NOT be used by conforming certification authorities (CAs), but that applications SHOULD be able to parse PKCs containing the field.4.2.9. Extensions
The extensions field generally gives information about the AC as opposed to information about the AC holder. An AC that has no extensions conforms to the profile; however, Section 4.3 defines the extensions that MAY be used with this profile, and whether or not they may be marked critical. If any other critical extension is used, the AC does not conform to this profile. However, if any other non-critical extension is used, the AC does conform to this profile. The extensions defined for ACs provide methods for associating additional attributes with holders. This profile also allows communities to define private extensions to carry information unique to those communities. Each extension in an AC may be designated as critical or non-critical. An AC-using system MUST reject an AC if it encounters a critical extension it does not recognize; however, a non-critical extension may be ignored if it is not recognized. Section 4.3 presents recommended extensions used within Internet ACs and standard locations for information. Communities may elect to use additional extensions; however, caution should be exercised in adopting any critical extensions in ACs that might prevent use in a general context.
4.3. Extensions
4.3.1. Audit Identity
In some circumstances, it is required (e.g., by data protection/data privacy legislation) that audit trails not contain records that directly identify individuals. This circumstance may make the use of the AC Holder field unsuitable for use in audit trails. To allow for such cases, an AC MAY contain an audit identity extension. Ideally, it SHOULD be infeasible to derive the AC holder's identity from the audit identity value without the cooperation of the AC issuer. The value of the audit identity, along with the AC issuer/serial, SHOULD then be used for audit/logging purposes. If the value of the audit identity is suitably chosen, a server/service administrator can use audit trails to track the behavior of an AC holder without being able to identify the AC holder. The server/service administrator in combination with the AC issuer MUST be able to identify the AC holder in cases where misbehavior is detected. This means that the AC issuer MUST be able to determine the actual identity of the AC holder from the audit identity. Of course, auditing could be based on the AC issuer/serial pair; however, this method does not allow tracking of the same AC holder with multiple ACs. Thus, an audit identity is only useful if it lasts for longer than the typical AC lifetime. Auditing could also be based on the AC holder's PKC issuer/serial; however, this will often allow the server/service administrator to identify the AC holder. As the AC verifier might otherwise use the AC holder or some other identifying value for audit purposes, this extension MUST be critical when used. Protocols that use ACs will often expose the identity of the AC holder in the bits on-the-wire. In such cases, an opaque audit identity does not make use of the AC anonymous; it simply ensures that the ensuing audit trails do not contain identifying information.
The value of an audit identity MUST be longer than zero octets. The
value of an audit identity MUST NOT be longer than 20 octets.
name id-pe-ac-auditIdentity
OID { id-pe 4 }
syntax OCTET STRING
criticality MUST be TRUE
4.3.2. AC Targeting
To target an AC, the target information extension, imported from
[X.509-2000], MAY be used to specify a number of servers/services.
The intent is that the AC SHOULD only be usable at the specified
servers/services. An (honest) AC verifier who is not amongst the
named servers/services MUST reject the AC.
If this extension is not present, the AC is not targeted and may be
accepted by any server.
In this profile, the targeting information simply consists of a list
of named targets or groups.
The following syntax is used to represent the targeting information:
Targets ::= SEQUENCE OF Target
Target ::= CHOICE {
targetName [0] GeneralName,
targetGroup [1] GeneralName,
targetCert [2] TargetCert
}
TargetCert ::= SEQUENCE {
targetCertificate IssuerSerial,
targetName GeneralName OPTIONAL,
certDigestInfo ObjectDigestInfo OPTIONAL
}
The targetCert CHOICE within the Target structure is only present to
allow future compatibility with [X.509-2000] and MUST NOT be used.
The targets check passes if the current server (recipient) is one of
the targetName fields in the Targets SEQUENCE, or if the current
server is a member of one of the targetGroup fields in the Targets
SEQUENCE. In this case, the current server is said to "match" the
targeting extension.
How the membership of a target within a targetGroup is determined is not defined here. It is assumed that any given target "knows" the names of the targetGroups to which it belongs or can otherwise determine its membership. For example, the targetGroup specifies a DNS domain, and the AC verifier knows the DNS domain to which it belongs. For another example, the targetGroup specifies "PRINTERS", and the AC verifier knows whether or not it is a printer or print server. Note: [X.509-2000] defines the extension syntax as a "SEQUENCE OF Targets". Conforming AC issuer implementations MUST only produce one "Targets" element. Conforming AC users MUST be able to accept a "SEQUENCE OF Targets". If more than one Targets element is found in an AC, the extension MUST be treated as if all Target elements had been found within one Targets element. name id-ce-targetInformation OID { id-ce 55 } syntax SEQUENCE OF Targets criticality MUST be TRUE4.3.3. Authority Key Identifier
The authorityKeyIdentifier extension, as profiled in [PKIXPROF], MAY be used to assist the AC verifier in checking the signature of the AC. The [PKIXPROF] description should be read as if "CA" meant "AC issuer". As with PKCs, this extension SHOULD be included in ACs. Note: An AC, where the issuer field used the baseCertificateID CHOICE, would not need an authorityKeyIdentifier extension, as it is explicitly linked to the key in the referred certificate. However, as this profile states (in Section 4.2.3), ACs MUST use the v2Form with issuerName CHOICE, this duplication does not arise. name id-ce-authorityKeyIdentifier OID { id-ce 35 } syntax AuthorityKeyIdentifier criticality MUST be FALSE4.3.4. Authority Information Access
The authorityInfoAccess extension, as defined in [PKIXPROF], MAY be used to assist the AC verifier in checking the revocation status of the AC. Support for the id-ad-caIssuers accessMethod is OPTIONAL by this profile since AC chains are not expected.
The following accessMethod is used to indicate that revocation status checking is provided for this AC, using the Online Certificate Status Protocol (OCSP) defined in [OCSP]: id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 } The accessLocation MUST contain a URI, and the URI MUST contain an HTTP URL [HTTP-URL] that specifies the location of an OCSP responder. The AC issuer MUST, of course, maintain an OCSP responder at this location. name id-ce-authorityInfoAccess OID { id-pe 1 } syntax AuthorityInfoAccessSyntax criticality MUST be FALSE4.3.5. CRL Distribution Points
The crlDistributionPoints extension, as profiled in [PKIXPROF], MAY be used to assist the AC verifier in checking the revocation status of the AC. See Section 6 for details on revocation. If the crlDistributionPoints extension is present, then exactly one distribution point MUST be present. The crlDistributionPoints extension MUST use the DistributionPointName option, which MUST contain a fullName, which MUST contain a single name form. That name MUST contain either a distinguished name or a URI. The URI MUST be either an HTTP URL [HTTP-URL] or a Lightweight Directory Access Protocol (LDAP) URL [LDAP-URL]. name id-ce-cRLDistributionPoints OID { id-ce 31 } syntax CRLDistributionPoints criticality MUST be FALSE4.3.6. No Revocation Available
The noRevAvail extension, defined in [X.509-2000], allows an AC issuer to indicate that no revocation information will be made available for this AC. This extension MUST be non-critical. An AC verifier that does not understand this extension might be able to find a revocation list from the AC issuer, but the revocation list will never include an entry for the AC.
name id-ce-noRevAvail
OID { id-ce 56 }
syntax NULL (i.e., '0500'H is the DER encoding)
criticality MUST be FALSE
4.4. Attribute Types
Some of the attribute types defined below make use of the
IetfAttrSyntax type, also defined below. The reasons for using this
type are:
1. It allows a separation between the AC issuer and the attribute
policy authority. This is useful for situations where a single
policy authority (e.g., an organization) allocates attribute
values, but where multiple AC issuers are deployed for performance
or other reasons.
2. The syntaxes allowed for values are restricted to OCTET STRING,
OBJECT IDENTIFIER, and UTF8String, which significantly reduces the
complexity associated with matching more general syntaxes. All
multi-valued attributes using this syntax are restricted so that
each value MUST use the same choice of value syntax. For example,
AC issuers must not use one value with an oid and a second value
with a string.
IetfAttrSyntax ::= SEQUENCE {
policyAuthority [0] GeneralNames OPTIONAL,
values SEQUENCE OF CHOICE {
octets OCTET STRING,
oid OBJECT IDENTIFIER,
string UTF8String
}
}
In the descriptions below, each attribute type is either tagged
"Multiple Allowed" or "One Attribute value only; multiple values
within the IetfAttrSyntax". This refers to the SET OF
AttributeValues; the AttributeType still only occurs once, as
specified in Section 4.2.7.
4.4.1. Service Authentication Information
The SvceAuthInfo attribute identifies the AC holder to the
server/service by a name, and the attribute MAY include optional
service specific authentication information. Typically, this will
contain a username/password pair for a "legacy" application.
This attribute provides information that can be presented by the AC verifier to be interpreted and authenticated by a separate application within the target system. Note that this is a different use to that intended for the accessIdentity attribute in 4.4.2 below. This attribute type will typically be encrypted when the authInfo field contains sensitive information, such as a password (see Section 7.1). name id-aca-authenticationInfo OID { id-aca 1 } syntax SvceAuthInfo values Multiple allowed SvceAuthInfo ::= SEQUENCE { service GeneralName, ident GeneralName, authInfo OCTET STRING OPTIONAL }4.4.2. Access Identity
The accessIdentity attribute identifies the AC holder to the server/service. For this attribute the authInfo field MUST NOT be present. This attribute is intended to be used to provide information about the AC holder, that can be used by the AC verifier (or a larger system of which the AC verifier is a component) to authorize the actions of the AC holder within the AC verifier's system. Note that this is a different use to that intended for the svceAuthInfo attribute described in 4.4.1 above. name id-aca-accessIdentity OID { id-aca 2 } syntax SvceAuthInfo values Multiple allowed
4.4.3. Charging Identity
The chargingIdentity attribute identifies the AC holder for charging purposes. In general, the charging identity will be different from other identities of the holder. For example, the holder's company may be charged for service. name id-aca-chargingIdentity OID { id-aca 3 } syntax IetfAttrSyntax values One Attribute value only; multiple values within the IetfAttrSyntax4.4.4. Group
The group attribute carries information about group memberships of the AC holder. name id-aca-group OID { id-aca 4 } syntax IetfAttrSyntax values One Attribute value only; multiple values within the IetfAttrSyntax4.4.5. Role
The role attribute, specified in [X.509-2000], carries information about role allocations of the AC holder. The syntax used for this attribute is: RoleSyntax ::= SEQUENCE { roleAuthority [0] GeneralNames OPTIONAL, roleName [1] GeneralName } The roleAuthority field MAY be used to specify the issuing authority for the role specification certificate. There is no requirement that a role specification certificate necessarily exists for the roleAuthority. This differs from [X.500-2000], where the roleAuthority field is assumed to name the issuer of a role specification certificate. For example, to distinguish the administrator role as defined by "Baltimore" from that defined by "SPYRUS", one could put the value "urn:administrator" in the roleName field and the value "Baltimore" or "SPYRUS" in the roleAuthority field.
The roleName field MUST be present, and roleName MUST use the
uniformResourceIdentifier CHOICE of the GeneralName.
name id-at-role
OID { id-at 72 }
syntax RoleSyntax
values Multiple allowed
4.4.6. Clearance
The clearance attribute, specified in [X.501-1993], carries clearance
(associated with security labeling) information about the AC holder.
The policyId field is used to identify the security policy to which
the clearance relates. The policyId indicates the semantics of the
classList and securityCategories fields.
This specification includes the classList field exactly as it is
specified in [X.501-1993]. Additional security classification
values, and their position in the classification hierarchy, may be
defined by a security policy as a local matter or by bilateral
agreement. The basic security classification hierarchy is, in
ascending order: unmarked, unclassified, restricted, confidential,
secret, and top-secret.
An organization can develop its own security policy that defines
security classification values and their meanings. However, the BIT
STRING positions 0 through 5 are reserved for the basic security
classification hierarchy.
If present, the SecurityCategory field provides further authorization
information. The security policy identified by the policyId field
indicates the syntaxes that are allowed to be present in the
securityCategories SET. An OBJECT IDENTIFIER identifies each of the
allowed syntaxes. When one of these syntaxes is present in the
securityCategories SET, the OBJECT IDENTIFIER associated with that
syntax is carried in the SecurityCategory.type field.
The object identifier for the clearance attribute from [RFC3281] is:
id-at-clearance OBJECT IDENTIFIER ::= {
joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5)
clearance (55) }
The associated syntax was originally (and erroneously) defined in [RFC3281] as: Clearance ::= SEQUENCE { policyId [0] OBJECT IDENTIFIER, classList [1] ClassList DEFAULT {unclassified}, securityCategories [2] SET OF SecurityCategory OPTIONAL } But, it was later corrected (to restore conformance with [X.509-1997]) to: Clearance ::= SEQUENCE { policyId OBJECT IDENTIFIER, classList ClassList DEFAULT {unclassified}, securityCategories SET OF SecurityCategory OPTIONAL } The object identifier for the clearance attribute from [X.509-1997] is: id-at-clearance OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) attributeType(4) clearance (55) } The associated syntax is as follows: Clearance ::= SEQUENCE { policyId OBJECT IDENTIFIER, classList ClassList DEFAULT {unclassified}, securityCategories SET OF SecurityCategory OPTIONAL } Implementations MUST support the clearance attribute as defined in [X.501-1997]. Implementations SHOULD support decoding the clearance syntax from [RFC3281] and the errata report against it (see Appendix C). Implementations MUST NOT output the clearance attribute as defined in [RFC3281]. ClassList ::= BIT STRING { unmarked (0), unclassified (1), restricted (2), confidential (3), secret (4), topSecret (5) }
SecurityCategory ::= SEQUENCE {
type [0] OBJECT IDENTIFIER,
value [1] EXPLICIT ANY DEFINED BY type
}
-- Note that in [RFC3281], the SecurityCategory syntax was as
-- follows:
--
-- SecurityCategory ::= SEQUENCE {
-- type [0] IMPLICIT OBJECT IDENTIFIER,
-- value [1] ANY DEFINED BY type
-- }
--
-- The removal of the IMPLICIT from the type line and the
-- addition of the EXPLICIT to the value line result in
-- no changes to the encodings.
-- This is the same as the original syntax, which was defined
-- using the MACRO construct, as follows:
-- SecurityCategory ::= SEQUENCE {
-- type [0] IMPLICIT SECURITY-CATEGORY,
-- value [1] ANY DEFINED BY type
-- }
--
-- SECURITY-CATEGORY MACRO ::=
-- BEGIN
-- TYPE NOTATION ::= type | empty
-- VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER)
-- END
name { id-at-clearance }
OID { joint-iso-ccitt(2) ds(5) attribute-type (4)
clearance (55) }
syntax Clearance -- imported from [X.501-1997]
values Multiple allowed
4.5. Profile of AC Issuer's PKC
The AC issuer's PKC MUST conform to [PKIXPROF], and the keyUsage
extension in the PKC MUST NOT explicitly indicate that the AC
issuer's public key cannot be used to validate a digital signature.
In order to avoid confusion regarding serial numbers and revocations,
an AC issuer MUST NOT also be a PKC Issuer. That is, an AC issuer cannot be a CA as well. So, the AC issuer's PKC MUST NOT have a basicConstraints extension with the cA boolean set to TRUE.5. Attribute Certificate Validation
This section describes a basic set of rules that all valid ACs MUST satisfy. Some additional checks are also described, which AC verifiers MAY choose to implement. To be valid, an AC MUST satisfy all of the following: 1. Where the holder uses a PKC to authenticate to the AC verifier, the AC holder's PKC MUST be found, and the entire certification path of that PKC MUST be verified in accordance with [PKIXPROF]. As noted in the Security Considerations section, if some other authentication scheme is used, AC verifiers need to be very careful mapping the identities (authenticated identity, holder field) involved. 2. The AC signature must be cryptographically correct, and the AC issuer's entire PKC certification path MUST be verified in accordance with [PKIXPROF]. 3. The AC issuer's PKC MUST also conform to the profile specified in Section 4.5 above. 4. The AC issuer MUST be directly trusted as an AC issuer (by configuration or otherwise). 5. The time for which the AC is being evaluated MUST be within the AC validity. If the evaluation time is equal to either notBeforeTime or notAfterTime, then the AC is timely and this check succeeds. Note that in some applications, the evaluation time MAY not be the same as the current time. 6. The AC targeting check MUST pass as specified in Section 4.3.2. 7. If the AC contains an unsupported critical extension, the AC MUST be rejected. Support for an extension in this context means: 1. The AC verifier MUST be able to parse the extension value. 2. Where the extension value causes the AC to be rejected, the AC verifier MUST reject the AC.
Additional Checks:
1. The AC MAY be rejected on the basis of further AC verifier
configuration. For example, an AC verifier may be configured to
reject ACs that contain or lack certain attributes.
2. If the AC verifier provides an interface that allows applications
to query the contents of the AC, then the AC verifier MAY filter
the attributes from the AC on the basis of configured information.
For example, an AC verifier might be configured not to return
certain attributes to certain servers.
6. Revocation
In many environments, the validity period of an AC is less than the
time required to issue and distribute revocation information.
Therefore, short-lived ACs typically do not require revocation
support. However, long-lived ACs and environments where ACs enable
high value transactions MAY require revocation support.
Two revocation schemes are defined, and the AC issuer should elect
the one that is best suited to the environment in which the AC will
be employed.
"Never revoke" scheme:
ACs may be marked so that the relying party understands that no
revocation status information will be made available. The
noRevAvail extension is defined in Section 4.3.6, and the
noRevAvail extension MUST be present in the AC to indicate use of
this scheme.
Where no noRevAvail is present, the AC issuer is implicitly
stating that revocation status checks are supported, and some
revocation method MUST be provided to allow AC verifiers to
establish the revocation status of the AC.
"Pointer in AC" scheme:
ACs may "point" to sources of revocation status information, using
either an authorityInfoAccess extension or a crlDistributionPoints
extension within the AC.
For AC users, the "never revoke" scheme MUST be supported, and the
"pointer in AC" scheme SHOULD be supported. If only the "never
revoke" scheme is supported, then all ACs that do not contain a
noRevAvail extension, MUST be rejected.
For AC issuers, the "never revoke" scheme MUST be supported. If all ACs that will ever be issued by that AC issuer contain a noRevAvail extension, the "pointer in AC" scheme need not be supported. If any AC can be issued that does not contain the noRevAvail extension, the "pointer in AC" scheme MUST be supported. An AC MUST NOT contain both a noRevAvail extension and a "pointer in AC". An AC verifier MAY use any source for AC revocation status information.7. Optional Features
This section specifies features that MAY be implemented. Conformance to this profile does NOT require support for these features; however, if these features are offered, they MUST be offered as described below.7.1. Attribute Encryption
AC attributes MAY need to be encrypted if the AC is carried in the clear within an application protocol or the AC contains sensitive information (e.g., username/password). When a set of attributes is to be encrypted within an AC, the Cryptographic Message Syntax, EnvelopedData structure [CMS] is used to carry the ciphertext and associated per-recipient keying information. This type of attribute encryption is targeted. Before the AC is signed, the attributes are encrypted for a set of predetermined recipients. Within EnvelopedData, the encapsulatedContentInfo identifies the content type carried within the ciphertext. In this case, the contentType field of encapsulatedContentInfo MUST contain id-ct- attrCertEncAttrs, which has the following value: attrCertEncAttrs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) id-smime(16) id-ct(1) 14 } The ciphertext is included in the AC as the value of an encAttrs attribute. Only one encAttrs attribute can be present in an AC; however, the encAttrs attribute MAY be multi-valued, and each of its values will contain an independent EnvelopedData.
Each value can contain a set of attributes (each possibly a multi-
valued attribute) encrypted for a set of predetermined recipients.
The cleartext that is encrypted has the type:
ACClearAttrs ::= SEQUENCE {
acIssuer GeneralName,
acSerial INTEGER,
attrs SEQUENCE OF Attribute
}
The DER encoding of the ACClearAttrs structure is used as the
encryptedContent field of the EnvelopedData. The DER encoding MUST
be embedded in an OCTET STRING.
The acIssuer and acSerial fields are present to prevent ciphertext
stealing. When an AC verifier has successfully decrypted an
encrypted attribute, it MUST then check that the AC issuer and
serialNumber fields contain the same values. This prevents a
malicious AC issuer from copying ciphertext from another AC (without
knowing its corresponding plaintext).
The procedure for an AC issuer when encrypting attributes is
illustrated by the following (any other procedure that gives the same
result MAY be used):
1. Identify the sets of attributes that are to be encrypted for each
set of recipients.
2. For each attribute set that is to be encrypted:
2.1. Create an EnvelopedData structure for the data for this set
of recipients.
2.2. Encode the ContentInfo containing the EnvelopedData as a
value of the encAttrs attribute.
2.3. Ensure the cleartext attributes are not present in the
to-be-signed AC.
3. Add the encAttrs (with its multiple values) to the AC.
Note that there may be more than one attribute of the same type (the
same OBJECT IDENTIFIER) after decryption. That is, an AC MAY contain
the same attribute type both in clear and in encrypted form (and
indeed several times if the different recipients are associated with
more than one EnvelopedData). For example, an AC could contain a
cleartext clearance attribute saying the holder is cleared to SECRET,
and, in addition, an encrypted clearance attribute whose value is
some higher clearance that's not allowed to be known everywhere. One
approach implementers may choose, would be to merge attribute values
following decryption in order to re-establish the "once only"
constraint.
name id-aca-encAttrs
OID { id-aca 6}
syntax ContentInfo
values Multiple Allowed
If an AC contains attributes apparently encrypted for the AC
verifier, then the decryption process failure MUST cause the AC to be
rejected.
7.2. Proxying
When a server acts as a client for another server on behalf of the AC
holder, the server MAY need to proxy an AC. Such proxying MAY have
to be done under the AC issuer's control, so that not every AC is
proxiable and so that a given proxiable AC can be proxied in a
targeted fashion. Support for chains of proxies (with more than one
intermediate server) MAY also be required. Note that this does not
involve a chain of ACs.
In order to meet this requirement, we define another extension,
ProxyInfo, similar to the targeting extension.
When this extension is present, the AC verifier MUST check that the
entity from which the AC was received was allowed to send it and that
the AC is allowed to be used by this verifier.
The proxying information is a list in which each item is a list of
targeting information. If the verifier and the sender of the AC are
both named in the same proxy list, the AC can then be accepted (the
exact rule is given below).
The effect is that the AC holder can send the AC to any valid target,
which can then only proxy to targets that are in one of the same
proxy lists as itself.
The following data structure is used to represent the
targeting/proxying information:
ProxyInfo ::= SEQUENCE OF Targets
Targets is explained in Section 4.3.2. As in the case of targeting,
the targetCert CHOICE MUST NOT be used.
A proxy check succeeds if either one of the conditions below is met:
1. The identity of the sender, as established by the underlying
authentication service, matches the Holder field of the AC, and
the current server "matches" any one of the proxy sets. Recall
that "matches" is as defined Section 4.3.2.
2. The identity of the sender, as established by the underlying
authentication service, "matches" one of the proxy sets (call it
set "A"), and the current server is one of the targetName fields
in the set "A", or the current server is a member of one of the
targetGroup fields in set "A".
When an AC is proxied more than once, a number of targets will be on
the path from the original client, which is normally, but not always,
the AC holder. In such cases, prevention of AC "stealing" requires
that the AC verifier MUST check that all targets on the path are
members of the same proxy set. It is the responsibility of the AC-
using protocol to ensure that a trustworthy list of targets on the
path is available to the AC verifier.
name id-pe-ac-proxying
OID { id-pe 10 }
syntax ProxyInfo
criticality MUST be TRUE
7.3. Use of ObjectDigestInfo
In some environments, it may be required that the AC is not linked
either to an identity (via entityName) or to a PKC (via
baseCertificateID). The objectDigestInfo CHOICE in the Holder field
allows support for this requirement.
If the holder is identified with the objectDigestInfo field, then the
AC version field MUST contain v2 (the integer 1).
The idea is to link the AC to an object by placing a hash of that
object into the Holder field of the AC. For example, this allows
production of ACs that are linked to public keys rather than names.
It also allows production of ACs that contain privileges associated
with an executable object such as a Java class. However, this
profile only specifies how to use a hash over a public key or PKC.
That is, conformant ACs MUST NOT use the otherObjectTypes value for
the digestedObjectType.
To link an AC to a public key, the hash must be calculated over the representation of that public key, which would be present in a PKC, specifically, the input for the hash algorithm MUST be the DER encoding of a SubjectPublicKeyInfo representation of the key. Note: this includes the AlgorithmIdentifier as well as the BIT STRING. The rules given in [PKIXALGS] for encoding keys MUST be followed. In this case, the digestedObjectType MUST be publicKey and the otherObjectTypeID field MUST NOT be present. Note that if the public key value used as input to the hash function has been extracted from a PKC, it is possible that the SubjectPublicKeyInfo from that PKC is NOT the value that should be hashed. This can occur if Digital Signature Algorithm (DSA) Dss- parms are inherited as described in Section 2.3.2 of [PKIXALGS]. The correct input for hashing in this context will include the value of the parameters inherited from the CA's PKC, and thus may differ from the SubjectPublicKeyInfo present in the PKC. Implementations that support this feature MUST be able to handle the representations of public keys for the algorithms specified in Section 2.3 of [PKIXALGS]. In order to link an AC to a PKC via a digest, the digest MUST be calculated over the DER encoding of the entire PKC, including the signature value. In this case, the digestedObjectType MUST be publicKeyCert and the otherObjectTypeID field MUST NOT be present.7.4. AA Controls
During AC validation, a relying party has to answer the question: is this AC issuer trusted to issue ACs containing this attribute? The AAControls PKC extension MAY be used to help answer the question. The AAControls extension is intended to be used in CA and AC issuer PKCs. id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 } AAControls ::= SEQUENCE { pathLenConstraint INTEGER (0..MAX) OPTIONAL, permittedAttrs [0] AttrSpec OPTIONAL, excludedAttrs [1] AttrSpec OPTIONAL, permitUnSpecified BOOLEAN DEFAULT TRUE } AttrSpec::= SEQUENCE OF OBJECT IDENTIFIER
The AAControls extension is used as follows: The pathLenConstraint, if present, is interpreted as in [PKIXPROF]. It restricts the allowed distance between the AA CA (a CA directly trusted to include AAControls in its PKCs), and the AC issuer. The permittedAttrs field specifies a list of attribute types that any AC issuer below this AA CA is allowed to include in ACs. If this field is not present, it means that no attribute types are explicitly allowed. The excludedAttrs field specifies a list of attribute types that no AC issuer below this AA CA is allowed to include in ACs. If this field is not present, it means that no attribute types are explicitly disallowed. The permitUnSpecified field specifies how to handle attribute types that are not present in either the permittedAttrs or excludedAttrs fields. TRUE (the default) means that any unspecified attribute type is allowed in ACs; FALSE means that no unspecified attribute type is allowed. When AAControls are used, the following additional checks on an AA's PKC chain MUST all succeed for the AC to be valid: 1. Some CA on the AC's certificate path MUST be directly trusted to issue PKCs that precede the AC issuer in the certification path; call this CA the "AA CA". 2. All PKCs on the path from the AA CA, down to and including the AC issuer's PKC, MUST contain an AAControls extension; however, the PKC of the AA CA need not contain this extension. 3. Only those attributes in the AC that are allowed, according to all of the AAControls extension values in all of the PKCs from the AA CA to the AC issuer, may be used for authorization decisions; all other attributes MUST be ignored. This check MUST be applied to the list of attributes following attribute decryption, and the id- aca-encAttrs type MUST also be checked. name id-pe-aaControls OID { id-pe 6 } syntax AAControls criticality MAY be TRUE
8. Security Considerations
The protection afforded for private keys is a critical factor in maintaining security. Failure of AC issuers to protect their private keys will permit an attacker to masquerade as them, potentially generating false ACs or revocation status. Existence of bogus ACs and revocation status will undermine confidence in the system. If the compromise is detected, all ACs issued by the AC issuer MUST be revoked. Rebuilding after such a compromise will be problematic, so AC issuers are advised to implement a combination of strong technical measures (e.g., tamper-resistant cryptographic modules) and appropriate management procedures (e.g., separation of duties) to avoid such an incident. Loss of an AC issuer's private signing key may also be problematic. The AC issuer would not be able to produce revocation status or perform AC renewal. AC issuers are advised to maintain secure backup for signing keys. The security of the key backup procedures is a critical factor in avoiding key compromise. The availability and freshness of revocation status will affect the degree of assurance that should be placed in a long-lived AC. While long-lived ACs expire naturally, events may occur during its natural lifetime that negate the binding between the AC holder and the attributes. If revocation status is untimely or unavailable, the assurance associated with the binding is clearly reduced. The binding between an AC holder and attributes cannot be stronger than the cryptographic module implementation and algorithms used to generate the signature. Short key lengths or weak hash algorithms will limit the utility of an AC. AC issuers are encouraged to note advances in cryptology so they can employ strong cryptographic techniques. Inconsistent application of name comparison rules may result in acceptance of invalid targeted or proxied ACs, or rejection of valid ones. The X.500 series of specifications defines rules for comparing distinguished names. These rules require comparison of strings without regard to case, character set, multi-character white space substrings, or leading and trailing white space. This specification and [PKIXPROF] relaxes these requirements, requiring support for binary comparison at a minimum. AC issuers MUST encode the distinguished name in the AC holder.entityName field identically to the distinguished name in the holder's PKC. If different encodings are used, implementations of this specification may fail to recognize that the AC and PKC belong to the same entity.
If an attribute certificate is tied to the holder's PKC using the baseCertificateID component of the Holder field and the PKI in use includes a rogue CA with the same issuer name specified in the baseCertificateID component, this rogue CA could issue a PKC to a malicious party, using the same issuer name and serial number as the proper holder's PKC. Then the malicious party could use this PKC in conjunction with the AC. This scenario SHOULD be avoided by properly managing and configuring the PKI so that there cannot be two CAs with the same name. Another alternative is to tie ACs to PKCs using the publicKeyCert type in the ObjectDigestInfo field. Failing this, AC verifiers have to establish (using other means) that the potential collisions cannot actually occur, for example, the Certificate Practice Statements (CPSs) of the CAs involved may make it clear that no such name collisions can occur. Implementers MUST ensure that following validation of an AC, only attributes that the issuer is trusted to issue are used in authorization decisions. Other attributes, which MAY be present MUST be ignored. Given that the AAControls PKC extension is optional to implement, AC verifiers MUST be provided with this information by other means. Configuration information is a likely alternative means. This becomes very important if an AC verifier trusts more than one AC issuer. There is often a requirement to map between the authentication supplied by a particular security protocol (e.g., TLS, S/MIME) and the AC holder's identity. If the authentication uses PKCs, then this mapping is straightforward. However, it is envisaged that ACs will also be used in environments where the holder may be authenticated using other means. Implementers SHOULD be very careful in mapping the authenticated identity to the AC holder, especially when the authenticated identity does not come from a public key certificate as link between identity and AC may not be as "strong".9. IANA Considerations
Attributes and attribute certificate extensions are identified by object identifiers (OIDs). Many of the OIDs used in this document are copied from X.509 [X.509-2000]. Other OIDs were assigned from an arc delegated by the IANA to the PKIX working group. No further action by the IANA is necessary for this document or any anticipated updates.
10. References
10.1. Reference Conventions
[PKIXALGS] refers to [RFC3279], [RFC4055], [RFC5480], and [RFC5756].10.2. Normative References
[Err302] RFC Errata, Errata ID 302, RFC 3281, http://www.rfc-editor.org. [CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 5652, September 2009. [HTTP-URL] Housley, R. and P. Hoffman, "Internet X.509 Public Key Infrastructure Operational Protocols: FTP and HTTP", RFC 2585, May 1999. [LDAP-URL] Smith, M., Ed., and T. Howes, "Lightweight Directory Access Protocol (LDAP): Uniform Resource Locator", RFC 4516, June 2006. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, April 2002. [RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms and Identifiers for RSA Cryptography for use in the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 4055, June 2005. [RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk, "Elliptic Curve Cryptography Subject Public Key Information", RFC 5480, March 2009. [RFC5756] Turner, S. Brown, D., Yiu, K., Housley, R., and T. Polk, "Updates for RSAES-OAEP and RSASSA-PSS Algorithm Parameters", RFC 5756, January 2010. [PKIXPROF] 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.
[X509-SRV] Santesson, S., "Internet X.509 Public Key Infrastructure Subject Alternative Name for Expression of Service Name", RFC 4985, August 2007. [X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation. [X.690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER).10.3. Informative References
[KRB] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", RFC 4120, July 2005. [LDAP] Sermersheim, J., Ed., "Lightweight Directory Access Protocol (LDAP): The Protocol", RFC 4511, June 2006. [OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP", RFC 2560, June 1999. [RFC3281] Farrell, S. and R. Housley, "An Internet Attribute Certificate Profile for Authorization", RFC 3281, April 2002. [X.500-2000] ITU-T Recommendation X.500 (2000) | ISO/IEC 9594-1:2000, Information technology - Open Systems Interconnection - The Directory: Overview of concepts, models and services. [X.501-1993] ITU-T Recommendation X.501 (1993) | ISO/IEC 9594-2:1993, Information technology - Open Systems Interconnection - The Directory: Models. [X.501-1997] ITU-T Recommendation X.501 (1997) | ISO/IEC 9594-2:1997, Information technology - Open Systems Interconnection - The Directory: Models. [X.509-1988] CCITT Recommendation X.509: The Directory - Authentication Framework, 1988.
[X.509-1997] ITU-T Recommendation X.509: The Directory - Authentication Framework, 1997. [X.509-2000] ITU-T Recommendation X.509: The Directory - Public-Key and Attribute Certificate Frameworks, 2000.
Appendix A. Object Identifiers
This (normative) appendix lists the new object identifiers that are defined in this specification. Some of these are required only for support of optional features and are not required for conformance to this profile. This specification mandates support for OIDs that have arc elements with values that are less than 2^32, (i.e., they MUST be between 0 and 4,294,967,295 inclusive) and SHOULD be less than 2^31 (i.e., less than or equal to 2,147,483,647). This allows each arc element to be represented within a single 32-bit word. Implementations MUST also support OIDs where the length of the dotted decimal (see [LDAP], Section 4.1.2) string representation can be up to 100 bytes (inclusive). Implementations MUST be able to handle OIDs with up to 20 elements (inclusive). AAs SHOULD NOT issue ACs that contain OIDs that breach these requirements. The following OIDs are imported from [PKIXPROF]: id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) } id-mod OBJECT IDENTIFIER ::= { id-pkix 0 } id-pe OBJECT IDENTIFIER ::= { id-pkix 1 } id-ad OBJECT IDENTIFIER ::= { id-pkix 48 } id-at OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 4 } id-ce OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 29 } The following new ASN.1 module OID is defined: id-mod-attribute-cert OBJECT IDENTIFIER ::= { id-mod 12 } The following AC extension OIDs are defined: id-pe-ac-auditIdentity OBJECT IDENTIFIER ::= { id-pe 4 } id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 10 } id-ce-targetInformation OBJECT IDENTIFIER ::= { id-ce 55 } The following PKC extension OIDs are defined: id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 } The following attribute OIDs are defined: id-aca OBJECT IDENTIFIER ::= { id-pkix 10 } id-aca-authenticationInfo OBJECT IDENTIFIER ::= { id-aca 1 } id-aca-accessIdentity OBJECT IDENTIFIER ::= { id-aca 2 } id-aca-chargingIdentity OBJECT IDENTIFIER ::= { id-aca 3 } id-aca-group OBJECT IDENTIFIER ::= { id-aca 4 } id-aca-encAttrs OBJECT IDENTIFIER ::= { id-aca 6 }
id-at-role OBJECT IDENTIFIER ::= { id-at 72 }
id-at-clearance OBJECT IDENTIFIER ::= {
joint-iso-ccitt(2) ds(5) attributeType(4) clearance (55) }
id-at-clearance OBJECT IDENTIFIER ::= {
joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5)
clearance (55) }
As noted in Section 4.4.6, there are two OIDs for id-at-clearance.
Appendix B. ASN.1 Module
This appendix describes data objects used by conforming PKI
components in an "ASN.1-like" syntax [X.680]. This syntax is a
hybrid of the 1988 and 1993 ASN.1 syntaxes. The 1988 ASN.1 syntax is
augmented with 1993 UNIVERSAL Types UniversalString, BMPString, and
UTF8String.
The ASN.1 syntax does not permit the inclusion of type statements in
the ASN.1 module, and the 1993 ASN.1 standard does not permit use of
the new UNIVERSAL types in modules using the 1988 syntax. As a
result, this module does not conform to either version of the ASN.1
standard.
This appendix may be converted into 1988 ASN.1 by replacing the
definitions for the UNIVERSAL Types with the 1988 catch-all "ANY".
PKIXAttributeCertificate-2008 { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert-v2(61) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- IMPORTed module OIDs MAY change if [PKIXPROF] changes
-- PKIX Certificate Extensions
Attribute, AlgorithmIdentifier, CertificateSerialNumber,
Extensions, UniqueIdentifier, id-pkix, id-pe, id-kp, id-ad, id-at
FROM PKIX1Explicit88
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-88(18) }
GeneralName, GeneralNames, id-ce, AuthorityKeyIdentifier,
AuthorityInfoAccessSyntax, CRLDistributionPoint
FROM PKIX1Implicit88
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-implicit-88(19) }
ContentInfo
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
;
id-pe-ac-auditIdentity OBJECT IDENTIFIER ::= { id-pe 4 }
id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 }
id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 10 }
id-ce-targetInformation OBJECT IDENTIFIER ::= { id-ce 55 }
id-aca OBJECT IDENTIFIER ::= { id-pkix 10 }
id-aca-authenticationInfo OBJECT IDENTIFIER ::= { id-aca 1 }
id-aca-accessIdentity OBJECT IDENTIFIER ::= { id-aca 2 }
id-aca-chargingIdentity OBJECT IDENTIFIER ::= { id-aca 3 }
id-aca-group OBJECT IDENTIFIER ::= { id-aca 4 }
-- { id-aca 5 } is reserved
id-aca-encAttrs OBJECT IDENTIFIER ::= { id-aca 6 }
id-at-role OBJECT IDENTIFIER ::= { id-at 72}
id-at-clearance OBJECT IDENTIFIER ::= {
joint-iso-ccitt(2) ds(5) attributeType(4) clearance (55) }
-- Uncomment the following declaration and comment the above line if
-- using the id-at-clearance attribute as defined in [RFC3281]
-- id-at-clearance OBJECT IDENTIFIER ::= {
-- joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5)
-- clearance (55) }
-- Uncomment this if using a 1988 level ASN.1 compiler
-- UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
AttributeCertificate ::= SEQUENCE {
acinfo AttributeCertificateInfo,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING
}
AttributeCertificateInfo ::= SEQUENCE {
version AttCertVersion, -- version is v2
holder Holder,
issuer AttCertIssuer,
signature AlgorithmIdentifier,
serialNumber CertificateSerialNumber,
attrCertValidityPeriod AttCertValidityPeriod,
attributes SEQUENCE OF Attribute,
issuerUniqueID UniqueIdentifier OPTIONAL,
extensions Extensions OPTIONAL
}
AttCertVersion ::= INTEGER { v2(1) }
Holder ::= SEQUENCE {
baseCertificateID [0] IssuerSerial OPTIONAL,
-- the issuer and serial number of
-- the holder's Public Key Certificate
entityName [1] GeneralNames OPTIONAL,
-- the name of the claimant or role
objectDigestInfo [2] ObjectDigestInfo OPTIONAL
-- used to directly authenticate the
-- holder, for example, an executable
}
ObjectDigestInfo ::= SEQUENCE {
digestedObjectType ENUMERATED {
publicKey (0),
publicKeyCert (1),
otherObjectTypes (2) },
-- otherObjectTypes MUST NOT
-- MUST NOT be used in this profile
otherObjectTypeID OBJECT IDENTIFIER OPTIONAL,
digestAlgorithm AlgorithmIdentifier,
objectDigest BIT STRING
}
AttCertIssuer ::= CHOICE {
v1Form GeneralNames, -- MUST NOT be used in this
-- profile
v2Form [0] V2Form -- v2 only
}
V2Form ::= SEQUENCE {
issuerName GeneralNames OPTIONAL,
baseCertificateID [0] IssuerSerial OPTIONAL,
objectDigestInfo [1] ObjectDigestInfo OPTIONAL
-- issuerName MUST be present in this profile
-- baseCertificateID and objectDigestInfo MUST
-- NOT be present in this profile
}
IssuerSerial ::= SEQUENCE {
issuer GeneralNames,
serial CertificateSerialNumber,
issuerUID UniqueIdentifier OPTIONAL
}
AttCertValidityPeriod ::= SEQUENCE {
notBeforeTime GeneralizedTime,
notAfterTime GeneralizedTime
}
Targets ::= SEQUENCE OF Target
Target ::= CHOICE {
targetName [0] GeneralName,
targetGroup [1] GeneralName,
targetCert [2] TargetCert
}
TargetCert ::= SEQUENCE {
targetCertificate IssuerSerial,
targetName GeneralName OPTIONAL,
certDigestInfo ObjectDigestInfo OPTIONAL
}
IetfAttrSyntax ::= SEQUENCE {
policyAuthority [0] GeneralNames OPTIONAL,
values SEQUENCE OF CHOICE {
octets OCTET STRING,
oid OBJECT IDENTIFIER,
string UTF8String
}
}
SvceAuthInfo ::= SEQUENCE {
service GeneralName,
ident GeneralName,
authInfo OCTET STRING OPTIONAL
}
RoleSyntax ::= SEQUENCE {
roleAuthority [0] GeneralNames OPTIONAL,
roleName [1] GeneralName
}
Clearance ::= SEQUENCE {
policyId OBJECT IDENTIFIER,
classList ClassList DEFAULT {unclassified},
securityCategories SET OF SecurityCategory OPTIONAL
}
-- Uncomment the following lines to support deprecated clearance
-- syntax and comment out previous Clearance.
-- Clearance ::= SEQUENCE {
-- policyId [0] OBJECT IDENTIFIER,
-- classList [1] ClassList DEFAULT {unclassified},
-- securityCategories [2] SET OF SecurityCategory OPTIONAL
-- }
ClassList ::= BIT STRING {
unmarked (0),
unclassified (1),
restricted (2),
confidential (3),
secret (4),
topSecret (5)
}
SecurityCategory ::= SEQUENCE {
type [0] OBJECT IDENTIFIER,
value [1] EXPLICIT ANY DEFINED BY type
}
-- Note that in [RFC3281] the syntax for SecurityCategory was -- as follows: -- -- SecurityCategory ::= SEQUENCE { -- type [0] IMPLICIT OBJECT IDENTIFIER, -- value [1] ANY DEFINED BY type -- } -- -- The removal of the IMPLICIT from the type line and the -- addition of the EXPLICIT to the value line result in -- no changes to the encoding. AAControls ::= SEQUENCE { pathLenConstraint INTEGER (0..MAX) OPTIONAL, permittedAttrs [0] AttrSpec OPTIONAL, excludedAttrs [1] AttrSpec OPTIONAL, permitUnSpecified BOOLEAN DEFAULT TRUE } AttrSpec ::= SEQUENCE OF OBJECT IDENTIFIER ACClearAttrs ::= SEQUENCE { acIssuer GeneralName, acSerial INTEGER, attrs SEQUENCE OF Attribute } ProxyInfo ::= SEQUENCE OF Targets END
Appendix C. Errata Report Submitted to RFC 3281
The following is the errata report submitted against RFC 3281, posted online as [Err302]. Status: Verified Type: Technical Reported By: Stephen Farrell Date Reported: 2003-03-07 Section 4.4.6 says: Clearance ::= SEQUENCE { policyId [0] OBJECT IDENTIFIER, classList [1] ClassList DEFAULT {unclassified}, securityCategories [2] SET OF SecurityCategory OPTIONAL } It should say: Clearance ::= SEQUENCE { policyId OBJECT IDENTIFIER, classList ClassList DEFAULT {unclassified}, securityCategories SET OF SecurityCategory OPTIONAL } Notes: The differences in tagging arose due to an unnoticed technical corrigendum (TC-2) being applied to the X.501 document during preparation of RFC 3281. The X.501 format is the correct form and will be included in a future update of RFC 3281. Implementers SHOULD modify their decoding functions to accept either format and, even if claiming RFC 3281 conformance, SHOULD output the (correct) X.501 format pending the issuing of a corrected RFC at which point the incorrect RFC 3281 format will no longer be specified.
Appendix D. Changes since RFC 3281
1. Created a new Section 1.1 "Terminology", renumbered Sections 1.1-1.3 to 1.2-1.4, and moved first paragraph of Section 1 to Section 1.1. 2. In Section 1.2, rephrased first sentence in third paragraph. 3. In Section 2, replaced S/MIME v3 with S/MIME v3.2. 4. In Section 4.1, moved "," from the right of the ASN.1 comment to the left of the ASN.1 comment on the line describing version in the AttributeCertificateInfo structure. Replaced reference to X.208 with X.690. 5. In Section 4.2, replaced pointer to 4.2.1.7 of RFC 3280 with pointer to 4.2.1.6 of RFC 5280. Added requirement to support subject alternative name choice SRVName. 6. In Section 4.3.2, replaced "Confirming" with "Conforming". 7. In Section 4.3.4, replaced reference to RFC 1738, URL, with references to [HTTP-URL], "authorityInformationAccess" with "authorityInfoAccess", and "NOT REQUIRED" with "OPTIONAL." 8. In Section 4.3.5, replaced "HTTP or an LDAP" with "HTTP [HTTP-URL] or an LDAP [LDAP-URL]". Also, replaced "CRLDistPointsSyntax" with "CRLDistributionPoints". 9. In Section 4.4.6, added text to address having two OIDs for the same syntax and two syntaxes for one OID. 10. In Section 5, replaced "When the extension value SHOULD cause" with "When the extension value causes". 11. In Section 7.1, replaced text that described encapsulating encrypted attribute with corrected text. Clarified that attributes can appear more than once if they apply to different recipients. Reworded last paragraph to more clearly describe the failure case. 12. In Section 7.3, updated references to point to RFC 3279. 13. In Section 8, updated last paragraph to better explain why implementers need to be careful when mapping authenticated identities to the AC holder.
14. Updated References:
a) split references into informative/normative references
b) added reference to RFC 3281
c) replaced reference to X.501:1993 with X.501:1997
d) replaced reference to RFC 1510 with RFC 4120
e) replaced reference to RFC 1738 with RFC 4516 and 2585
f) replaced reference to RFC 2251 with RFC 4511
g) replaced reference to RFC 2459 with RFC 5280
h) replaced reference to RFC 2630 with RFC 5652
i) replaced reference to X.208-1988 with X.690
j) added reference to X.680
k) added reference to RFC 4985
l) expanded reference to RFC 3279 by adding RFC 5480 and RFC
4055, which update RFC 3279
m) deleted spurious reference to CMC, CMP, ESS, RFC 2026,
X.209-88, and X.501:1988.
15. In Appendix A, added second clearance attribute object
identifier.
16. Appendix B, updated ASN.1 with changes 3, 8, 9, and 11:
a) New OID for ASN.1 module.
b) Updated module OIDs for PKIX1Explicit88 and PKIX1Implicit88.
c) Added imports from PKIX1Implicit88 for AuthorityKeyIdentifier,
AuthorityInfoAccessSyntax, CRLDistributionPoint.
d) Added imports from CryptographicMessageSyntax2004 for
ContentInfo.
e) Added comments and commented out ASN.1 for old clearance
attribute syntax.
f) Added preamble to ASN.1, which is taken from Appendix A of RFC
5280.
17. Added Appendix C.
Authors' Addresses
Sean Turner IECA, Inc. 3057 Nutley Street, Suite 106 Fairfax, VA 22031 USA EMail: turners@ieca.com Russ Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA EMail: housley@vigilsec.com Stephen Farrell Distributed Systems Group Computer Science Department Trinity College Dublin Ireland EMail: stephen.farrell@cs.tcd.ie