ftp.cc.uoc.gr
rfc5755
This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 3731, EID 4541
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 Authorization

Abstract

   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.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

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 ................................48

1.  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 Exchanges

1.4.  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 TRUE

4.3.3.  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 FALSE

4.3.4.  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-pe-authorityInfoAccess 
      OID            { id-pe 1 }

EID 4541 (Verified) is as follows:

Section: 4.3.4

Original Text:

      name           id-ce-authorityInfoAccess
      OID            { id-pe 1 }

Corrected Text:

      name           id-pe-authorityInfoAccess
      OID            { id-pe 1 }
Notes:
id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 } is defined in http://tools.ietf.org/html/rfc5280#section-4.2.2.1
syntax AuthorityInfoAccessSyntax criticality MUST be FALSE 4.3.5. 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 FALSE 4.3.6. 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 IetfAttrSyntax 4.4.4. 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 IetfAttrSyntax 4.4.5. 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 encryptedContentInfo identifies the content type carried within the ciphertext. In this case, the contentType field of encryptedContentInfo MUST contain id-ct- attrCertEncAttrs, which has the following value:
EID 3731 (Verified) is as follows:

Section: 7.1

Original Text:

   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:

Corrected Text:

   Within EnvelopedData, the encryptedContentInfo identifies the
   content type carried within the ciphertext.  In this case, the
   contentType field of encryptedContentInfo MUST contain id-ct-
   attrCertEncAttrs, which has the following value:
Notes:
The EnvelopedData structure has no "EncapsulatedContentInfo". It has a "EncryptedContentInfo":

EnvelopedData ::= SEQUENCE {
version CMSVersion,
originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
recipientInfos RecipientInfos,
encryptedContentInfo EncryptedContentInfo,
unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }

CMS objects that carry a "EncapsulatedContentInfo" are of type "SignedData":

SignedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT RevocationInfoChoices OPTIONAL,
signerInfos SignerInfos }

Source: RFC 5652 (unchanged at least since RFC 3852).
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. 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. 10.2. 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