PKIX Working Group S. Farrell
INTERNET-DRAFT Baltimore Technologies
Expires in six months R. Housley
SPYRUS
March
May 2000
An Internet Attribute Certificate
Profile for Authorization
<draft-ietf-pkix-ac509prof-02.txt>
<draft-ietf-pkix-ac509prof-03.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of [RFC2026].
Internet-Drafts are working documents of the Internet Engineering
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progress."
The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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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.
Table of Contents
Status of this Memo..............................................1
Abstract.........................................................1 Memo.............................................1
Abstract........................................................1
Table of Contents................................................1 Contents...............................................2
1. Introduction.................................................3
1.1 Delegation and AC chains...............................4
1.2 Attribute Certificate Distribution ("push" vs "pull")..4
1.3 Document Structure.....................................6 Structure.....................................5
2. Terminology..................................................7 Terminology..................................................6
3. Requirements.................................................8 Requirements.................................................7
4. The AC Profile...............................................9 Attribute Certificate Profile................................8
4.1 X.509 Attribute Certificate Definition.................9 Definition.................8
4.2 Profile of Standard Fields............................11 Fields............................10
4.2.1 Version.........................................11 Version.........................................10
4.2.2 Holder..........................................11 Holder..........................................10
4.2.3 Issuer..........................................12 Issuer..........................................11
4.2.4 Signature.......................................12
4.2.5 Serial Number...................................13 Number...................................12
4.2.6 Validity Period.................................13 Period.................................12
4.2.7 Attributes......................................13
4.2.8 Issuer Unique Identifier........................14 Identifier........................13
4.2.9 Extensions......................................14 Extensions......................................13
4.3 Extensions............................................14
4.3.1 Audit Identity..................................14
4.3.2 AC Targeting....................................15
4.3.3 Authority Key Identifier........................16
4.3.4 Authority Information Access....................17 Access....................16
4.3.5 CRL Distribution Points.........................17 Points.........................16
4.3.6 No Revocation Available.........................17
4.4 Attribute Types.......................................18 Types.......................................17
4.4.1 Service Authentication Information..............18
4.4.2 Access Identity.................................19 Identity.................................18
4.4.3 Charging Identity...............................19 Identity...............................18
4.4.4 Group...........................................19
4.4.5 Role............................................19
4.4.6 Clearance.......................................20 Clearance.......................................19
4.5 Profile of AC Issuer's issuer's PKC............................21
5. Attribute Certificate Validation............................22
6. Revocation..................................................23
7. Optional Features...........................................24
7.1 Attribute Encryption..................................24
7.2 Proxying..............................................25
7.3 Use of ObjectDigestInfo...............................26
7.4 AA Controls...........................................27
8. Security Considerations.....................................29
9. References..................................................30 References..................................................31
Author's Addresses..............................................31 Addresses.............................................32
Full Copyright Statement........................................31 Statement.......................................32
Appendix B: A: Object Identifiers..................................32 Identifiers.................................33
Appendix B: "Compilable" ASN.1 Module...........................33 Module.......................................34
1. Introduction
The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
in this document are to be interpreted as described in [RFC2119].
A server makes an access control decision when a client requests
access to a resource offered by that server. The server must ensure
that the client is authorized to access that resource. The server
decision is based on the access control policy, the context of the
request, and the identity and authorizations of the client. The
access control policy and the context of the request are readily
available to the server. Certificates may be used to provide
identity and authorization information about the client.
Similar access control decisions are made in other network
environments, such as a store-and-forward electronic mail
environment. That is, access control decisions are not limited to
client-server protocol environments.
X.509 public key certificates (PKCs) [X.509-97], [X.509-DAM],
[PKIXPROF] [X.509-97, X.509-DAM, PKIXPROF]
bind an identity and a public key. The identity may be used to
support identity-based access control decisions after the client
proves that it has access to the private key that corresponds to the
public key contained in the PKC. The public key is used to validate
digital signatures or cryptographic key management operations.
However, not all access control decisions are identity-
based. Rule-based, identity-based. Rule-
based, role-based, and rank-based access control decisions require
additional information. For example, information about a client's
ability to pay for a resource access may be more important than the
client's identity. Authorization information to support such access
control decisions 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 this authorization
information from the PKC. Yet, this authorization information also
needs to be protected in a fashion similar to a PKC. An attribute
certificate (AC) AC provides
this protection, and protection; it is simply a digitally signed (or certified) set
of attributes.
An AC is a structure similar to a PKC; the main difference being
that it the AC contains no public key. An AC may contain attributes
that specify group membership, role, security clearance, and or other
access control information associated with the AC holder. The syntax
for the AC is defined in Recommendation X.509 (making X.509, making the term
"X.509 certificate" ambiguous). ambiguous. This document specifies a profile of
the X.509 AC suitable for use with authorization information within
Internet protocols.
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. For example, one way
in which the linkage between the request and the AC can be achieved
is if the AC has a "pointer" reference to a PKC for the requester and that PKC
has been used to authenticate the access request.
As there is often confusion about the difference between
Some people constantly confuse PKCs and
ACs, an ACs. An analogy may help. 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 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.
1.1 Delegation and AC chains
The X.509 standard [X.509-DAM] defines delegation authorization as "Conveyance the
"conveyance of privilege from one entity that holds such privilege,
to another entity". It
further defines a delegation path as "An An AC is one authorization mechanism.
An ordered sequence of
certificates which, together with authentication of a privilege
asserter's identity can ACs could be processed used to verify the authenticity
of a privilege asserter's privilege". It then goes on to define various
mechanisms for use in delegation cases involving "chains" privilege. In this way, chains or paths of ACs.
ACs could be employed to delegate authorization.
As the administration and processing associated with such AC chains
is potentially much more complex than use of one AC issued by a single AC, authority, and
as the use of ACs in the Internet is today in its infancy, is quite limited, this
specification does not address such NOT RECOMMEND the use of AC chains. Other
(future) specifications may address the use of AC chains.
This means that conformant implementations are only REQUIRED to be
able to "handle" a single AC at a time. Note however, that
validation of that AC MAY require validation of a full PKC chain, chain of PKCs, as
specified in [PKIXPROF].
1.2 Attribute Certificate Distribution ("push" vs "pull")
As discussed above, ACs provide a mechanism to securely provide
authorization information to access control decision functions.
However, there are a number of possible communication paths that an
AC may take. 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.
In other cases, it is more suitable for a client simply to
authenticate to the server and for the server to request ("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. It is also more
suitable for some inter-domain cases where the client's rights
should be assigned within the server's domain, rather than within
the client's "home" domain.
There are a number of possible exchanges that can occur and involving three
entities involved (client, server entities:
the client, the server, and the AC issuer). issuer. In addition the
use of 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 protocol for these exchanges.
+--------------+
| | Server Acquisition
| AC Issuer issuer +----------------------------+
| | |
+--+-----------+ |
| |
| Client |
| Acquisition |
| |
+--+-----------+ +--+------------+
| | AC "push" | |
| Client +-------------------------+ Server |
| | (part of app. protocol) | |
+--+-----------+ +--+------------+
| |
| Client | Server
| Lookup +--------------+ | Lookup
| | | |
+---------------+ Repository +---------+
| |
+--------------+
Figure 1: AC Exchanges
1.3 Document Structure
The remainder of the document is structured as follows:- follows:
Section 2 defines some terminology terminology; Section 3 specifies the
requirements that this profile is to meet meet; Section 4 contains the
profile of the X.509 AC AC; Section 5 specifies rules for AC validation
validation; Section 6 specifies rules for AC revocation checks checks;
Section 7 specifies optional features which MAY be supported but for
which support is not required for conformance to this profile profile; and
Appendices contain the list of OIDs required to support this
specification and a "compilable" 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, e.g. environments. For example, ACs may be used
in the S/MIME v3 context, where the mail user agent would, by turns, 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 which 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 which 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 type ASN.1
Certificate defined in X.509 and profiled in RFC
2459. This (non-standard) acronym is used in order
to avoid confusion about the term "X.509
certificate".
Server the entity which requires that the authorization
checks are made
3. Requirements
This Attribute Certificate AC profile meets the following requirements.
Time/Validity requirements:
1. Support for short-lived or as well as long-lived ACs is required.
Typical validity periods might be measured in hours, as opposed
to months for X.509 public key certificates. PKCs. Short validity periods mean that allow ACs can 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 should be defined which can be
contained within ACs, for example ACs. examples include "access identity",
"group", "role", "clearance", "audit identity", and "charging id" etc.
id".
4. Standard attribute types should be defined so in a manner that it is
possible for
permits an AC verifier to distinguish between e.g. 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. SPYRUS should be easily
distinguished.
Targeting of ACs:
5. It should be possible to "target" an AC. This means that a
given AC may be "targeted" at one, or a small
number of,
servers in the sense servers. This means that a trustworthy non- target 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 (which may be an online AC
issuer).
4. The AC Profile Attribute certificates 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 attribute certificates 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; as has been done for PKCs [PKIXPROF], this document uses the 1988 ASN.1 syntax, as has been done
for PKCs [PKIXPROF]. However, the encoded certificate and standard
extensions are equivalent.
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 Attribute Certificate AC given below. Types 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 DEFAULT v1,
holder Holder,
issuer AttCertIssuer,
signature AlgorithmIdentifier,
serialNumber CertificateSerialNumber,
attrCertValidityPeriod AttCertValidityPeriod,
attributes SEQUENCE OF Attribute,
issuerUniqueID UniqueIdentifier OPTIONAL,
extensions Extensions OPTIONAL
}
AttCertVersion ::= INTEGER {v1(0), { v1(0), 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
-- if present, version must be v2
}
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 {
oldForm
v1Form GeneralNames,
newForm -- v1 or v2
v2Form [0] V2Form -- v2 only
}
V2Form ::= SEQUENCE {
issuerName GeneralNames OPTIONAL,
baseCertificateId
baseCertificateID [0] IssuerSerial OPTIONAL,
objectDigestInfo [1] ObjectDigestInfo OPTIONAL
--at
-- at least one of issuerName, baseCertificateId or -- baseCertificateID
-- or objectDigestInfo must MUST be present --
-- if newForm is used, version must be v2--
}
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
Implementers should note that the DER encoding (DER is defined in
[X.208-88]) 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, its 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
For all GeneralName fields in this profile the otherName, otherName (except as
noted below), x400Address, ediPartyName and registeredID options
MUST NOT be used
unless otherwise specified (e.g. as in the description of targeting
extension). used. The use of Kerberos [KRB] format names, encoded
into the otherName, SHOULD however, be supported using the
krb5PrincipalName OID and the KerberosName syntax as defined in
[PKINIT].
This means that unless otherwise indicated,(e.g. for the role
attribute), conforming
Conforming implementations MUST be able to support the dNSName,
directoryName, uniformResourceIdentifier uniformResourceIdentifier, and iPAddress fields in
all cases where GeneralName is used. The MUST support This is compatible with the
GeneralName requirements for each of these fields are as specified in
[PKIXPROF], [PKIXPROF] (mainly in section 4.2.1.7).
4.2.1 Version
This
The version field MUST be the default value of v1, i.e. v1. That is, the
version field is not present in the DER encoding, except where when the
holder is identified using the optional objectDigestInfo field, as
specified in section 7.3.
4.2.2 Holder
For any environment where the AC is passed in an authenticated
message or session, session and where the authentication is based on the use
of an X.509 public key certificate (PKC), PKC, the holder field SHOULD use the baseCertificateID.
Note that this profile uses the field name "baseCertificateID"
everywhere, whereas [X.509-DAM] sometimes uses this, and sometimes
uses the field name "baseCertificateId" (i.e. ending with a
lowercase "d"). The use of different names causes programming
difficulties so developers may need to be aware of which ASN.1
module has been used (i.e. the [X.509-DAM] one, or the one from
Appendix B).
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 non-empty distinguished name which is to be present as the
single value of the holder.baseCertificateID.issuer construct in the
directoryName field. The holder.baseCertificateID.issuerUID field
MUST only be used if the holder's PKC contains an issuerUniqueID
field (in which case,
field. If both the holder.baseCertificateID.issuerUID and the
issuerUniqueID fields are present, then the same value MUST be
present in the
holder.baseCertificateID.issuerUID_field). both _fields. Thus, the baseCertificateID is only usable
with PKC profiles (like [PKIXPROF]) which mandate that the PKC
issuer field contain a non empty non-empty distinguished name value.
Note: An "empty" 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, then the entityName MUST be the
same as the PKC subject field, unless the PKC subject field contains
an empty distinguished name. In that case, If the PKC subject field contains an
empty distinguished name, then the entityName field MUST be
identical to one of the values of the PKC subjectAltName field
extension. Note that [PKIXPROF] mandates that the subjectAltNames
extension be present if the PKC subject is a non an empty distinguished
name.
In any other case where the holder field uses the entityName option option,
then 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 define defined in that protocol.
4.2.3 Issuer
ACs conforming to this profile MUST use the newForm.issuerName v1Form choice, which
MUST contain one and only one GeneralName, which MUST contain a non non-
empty distinguished name in the directoryName field. This means that
all AC issuers MUST have non empty non-empty distinguished names.
Part of the reason for the use of the issuerName v1Form field is that it allows
the AC verifier to be independent of the AC issuer's public key
infrastructure. Using the baseCertificateId baseCertificateID field to reference the
AC issuer would mean that the AC verifier would have such a
dependency.
4.2.4 Signature
Contains the algorithm identifier used to validate the AC signature.
This MUST be one of the following algorithms defined in [PKIXPROF]
section 7.2: md5WithRSAEncryption, id-dsa-with-sha1 or sha-
1WithRSAEncryption, 7.2 or ecdsa-with-SHA1 defined in [ECDSA] section
3.2. 3.2: md5WithRSAEncryption, id-dsa-
with-sha1, sha-1WithRSAEncryption, or ecdsa-with-SHA1.
id-dsa-with-sha1 MUST be supported by all AC users. The other
algorithms SHOULD be supported.
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 (one second is
the shortest possible validity due to the use of GeneralizedTime). 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 '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 32 bits. 4 octets. Conformant ACs MUST
NOT use 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, but they time. Each AC issuer MUST be unique for a
given ensure
that each AC issuer. that it issues contain a unique serial number.
4.2.6 Validity Period
The attrCertValidityPeriod (a.k.a. validity) field specifies the
period for which the AC issuer expects 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. Optionally, the 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 Greenwich Mean Time (Zulu) and MUST include seconds (i.e.,
times are YYYYMMDDHHMMSSZ), even where the number of seconds is
zero. GeneralizedTime values MUST NOT include fractional seconds.
(Note that the above
(Note: this is the same as specified in [PKIXPROF], section
4.1.2.5.2.)
Note that
AC users MUST be able to handle the case where an AC is
issued, which (at which, at the time of parsing),
processing, has its entire validity period in the future (a "post-dated" post-
dated AC). This is valid for some applications, e.g. 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 MAY contain a SET OF values. For a given AC AC, each attribute
type OID
AttributeType OBJECT IDENTIFIER in the sequence MUST be unique, that unique. That
is, only one instance of each attribute can occur in a single AC. All instances AC,
but each instance can
however, be multi-valued.
AC users MUST be able to handle multiple values for all attribute
types.
Note that an
An AC MUST contain at least one attribute, that attribute. That is, the SEQUENCE OF
Attributes MUST NOT be of zero length.
Some standard attribute types are defined in section 4.5.
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" SHOULD NOT be used by conforming 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.
Section
An AC that has no extensions conforms to the profile; however,
section 4.3 defines the extensions that MAY be used with this
profile. An AC that has no extensions conforms to the profile. If any other critical extension is used, then the AC does
not conform to this profile. An AC that contains additional However, if any other non-critical
extensions still conforms.
extension is used, then 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
certificates 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, which might prevent use in
a general context.
4.3 Extensions. Extensions
4.3.1 Audit Identity
In some circumstances it is required (e.g. by data protection/data
privacy legislation) that audit trails do not contain records which
directly identify individuals. This circumstance may make the use of
the AC holder field of the AC unsuitable for use in audit trails.
In order to
To allow for such cases 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 except with without the co-operation of
the AC issuer.
The value of the audit identity plus along with the AC issuer/serial
SHOULD then be used for audit/logging purposes. If the value of the
audit identity is suitably chosen chosen, then 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 map
"backwards" from the audit identity to determine
the actual identity of the AC
holder. holder from the audit identity.
Of course, auditing could be based on the AC issuer/serial pair, pair;
however, this method doesn't allow tracking the same AC holder
across different with
multiple ACs. This means that Thus, an audit identity is only useful if it lasts for
longer than the typical AC lifetime - how
much longer is an issue for the AC issuer implementation. lifetime. Auditing could also be based on
the AC holder's PKC issuer/serial issuer/serial; however, this will often allow
the server/service administrator identify the AC holder.
As the AC verifier might otherwise use the AC subject 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" opaque audit
identity does not make use of the AC anonymous, it simply ensures
that the ensuing audit trails are "semi-anonymous". 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 MUST be TRUE
4.3.2 AC Targeting
In order to allow that
To target an AC is "targeted", , the target information
extension extension, imported from
[X.509-DAM], 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
servers/services. An (honest) AC verifier who is not amongst the
named servers/services MUST reject the AC.
If this extension is not present present, then 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,
targetCertificate
targetCert [2] TargetCert
}
TargetCert ::= SEQUENCE {
targetCertificate IssuerSerial,
targetDigest [3]
targetName GeneralName OPTIONAL,
certDigestInfo ObjectDigestInfo OPTIONAL
}
The targetCertificate and targetDigest fields are targetCert CHOICE is only present to allow future compatibility
with [X.509-DAM] and MUST NOT be used.
The targets check passes if the current server (recipient) is one of
the targetName fields in the targets part, or, Targets SEQUENCE, or if the current
server is a member of one of the targetGroup fields in the targets part. 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 targetGroup's targetGroups to which it belongs or can otherwise
determine its membership. For example, if the targetGroup were to be specifies a
DNS domain domain, and the AC verifier knows the DNS domain to which it
belongs. Another example would be where For another example, the targetGroup is
"PRINTERS" specifies "PRINTERS,"
and the AC verifier "knows" that it's knows whether or not it is a printer or print
server.
name id-pe-ac-targeting
<<will change this to id-ce-targetInformation from DAM if ISO can
change its syntax otherwise stick with the PKIX OID and live with
two different targeting extensions>>
OID { id-pe 5 id-ce 55 }
syntax Targets
criticality MUST be TRUE
4.3.3 Authority Key Identifier
The authorityKeyIdentifier extension extension, as profiled in [PKIXPROF] [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".
issuer." As with PKCs this extension SHOULD be included in ACs.
Note: An AC where the issuer field used the baseCertificateID choice 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) that ACs MUST use the
entityName choice,
v1Form CHOICE, this duplication does not arise here. arise.
name id-ce-authorityKeyIdentifier
OID { id-ce 35 }
syntax AuthorityKeyIdentifier
criticality MUST be FALSE
4.3.4 Authority Information Access
The authorityInformationAccess extension extension, as defined in [PKIXPROF] [PKIXPROF],
MAY be used to assist the AC verifier in checking the revocation
status of the AC. Note that support Support for the id-ad-caIssuers accessMethod defined in [PKIXPROF] is
NOT REQUIRED as in by this
profile, the profile since AC chains are not expected. The
authorityInformationAccess extension is only used for to support
revocation status checking. Conformant checking, therefore conformant ACs containing this
extension MUST contain exactly one AccessDescription.
The following accessMethod is used to indicate that revocation
status checking is provided for this AC, using the OCSP protocol
defined in [OCSP]:
id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }
The accessLocation must MUST contain a URI, this and theURI MUST contain an
HTTP
URL, specifying URL [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 FALSE
4.3.5 CRL Distribution Points
The crlDistributionPoints extension extension, as profiled in [PKIXPROF] [PKIXPROF], MAY
be used to assist the AC verifier in checking the revocation status
of the AC. See section 6 on revocation below for details.
Exactly details on revocation.
If the crlDistributionPoints extension is present, then exactly one
distribution point MUST be present, it 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 or a distinguished name. an LDAP URL [URL].
name id-ce-cRLDistributionPoints
OID { id-ce 31 }
syntax CRLDistPointsSyntax
criticality MUST be FALSE
4.3.6 No Revocation Available
This extension (imported from [X.509-DAM])
The noRevAvail extension, defined in [X.509-DAM], allows an AC
issuer to indicate that no revocation information will be made
available for this AC.
This extension MUST be non-critical, on the basis that an non-critical. An AC verifier that does not
understand it can still this extension might be able to find a revocation list (for example),
from the AC issuer, but won't ever find 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 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, network
performance or other reasons.
2. The syntaxes allowed for values are restricted to OCTET STRING
OID STRING,
OBJECT IDENTIFIER, and UTF8String, which significantly reduces some of
the matching
complexities complexity associated with matching more general syntaxes.
All multi-
valued multi-valued attributes using this syntax are restricted so
that each value MUST use the same choice of value syntax, that is, it is syntax. For
example, AC issuers must not allowed that use one value use with an OID but that oid and a
second value
uses 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 tagged as either
"Multiple Allowed" or "One Attribute value only; multiple values
within the IetfAttrSyntax". This refers to the SET OF
AttributeValue, the AttributeType still only occurs once, as
specified in section 4.2.7.
4.4.1 Service Authentication Information
This
The SvceAuthInfo attribute type identifies the AC holder to the
server/service by a name 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 type will typically need to be encrypted if when the authInfo
field contains sensitive information (e.g. information, such as a password). password.
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
An access identity
The accessIdentity attribute identifies the AC holder to the
server/service. For this attribute the authInfo field MUST NOT be
present.
name id-aca-accessIdentity
OID { id-aca 2 }
syntax SvceAuthInfo
values: Multiple allowed
4.4.3 Charging Identity
This
The chargingIdentity attribute type identifies the AC holder for charging
purposes.
Note that, in In general, the charging identity will be different from
other identities of the holder, for holder. For example, when the holderĘs holder's company is to
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
This
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
This attribute (imported from [X.509-DAM])
The role attribute, specified in [X.509-DAM], 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 MUST NOT be used. The roleName field MUST be
present
present, and roleName MUST use the uniformResourceIdentifier field CHOICE
of the GeneralName.
name id-at-role
OID { id-aca 5 id-at 72 }
syntax RoleSyntax
values: Multiple allowed
4.4.6 Clearance
This attribute (imported from [X.501])
The clearance attribute, specified in [X.501-93], carries clearance (security
(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 is
specified in [X.501-93]. 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.
Clearance ::= SEQUENCE {
policyId OBJECT IDENTIFIER,
classList ClassList DEFAULT {unclassified},
securityCategories
SET OF SecurityCategory OPTIONAL
}
ClassList ::= BIT STRING {
unmarked (0),
unclassified (1),
restricted (2)
confidential (3),
secret (4),
topSecret (5)
}
SecurityCategory ::= SEQUENCE {
type [0] IMPLICIT OBJECT IDENTIFIER,
value [1] ANY DEFINED BY type
}
-- 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
The security category value above can uses the ASN.1 ANY construct.
Conformant ACs MUST only use UTF8String, OID and OCTET STRING
syntaxes for this value.
name { id-at-clearance }
OID { joint-iso-ccitt(2) ds(5) module(1) selected-
attribute-types(5)
selected-attribute-types(5) clearance (55) }
syntax Clearance - imported from [X.501] [X.501-93]
values Multiple allowed
4.5 Profile of AC Issuer's issuer's PKC
The AC Issuer's issuer's PKC MUST conform to [PKIXPROF] [PKIXPROF], and its the keyUsage
extension in the PKC MUST NOT explicitly indicate that the AC issuer can't sign.
issuer's public key cannot be used to validate a digital signature.
In order to avoid confusion (e.g. over regarding serial numbers or revocations) and
revocations, an AC issuer MUST NOT also be a PKC Issuer (i.e. it can't Issuer. That is,
an AC issuer cannot be a CA as
well), so well. So, the AC Issuer's issuer's PKC MUST
NOT have a basicConstraints extension with isACA the cA BOOLEAN set to
TRUE.
5. Attribute Certificate Validation
This section describes a basic set of rules that all "valid" 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. The AC signature must be cryptographically correct correct, and the AC
issuer's entire PKC certification path (including the AC issuer's
PKC) MUST be verified in
accordance with [PKIXPROF].
2. The AC issuer's PKC MUST also conform to the profile specified
in section 4.5 above.
3. The AC issuer MUST be directly trusted as an AC issuer (by
configuration or otherwise).
4. The time for which the AC is being evaluated MUST be within the
AC validity (if validity. If the evaluation time is equal to either
notBeforeTime or notAfterTime notAfterTime, then the AC is timely, i.e. timelyand this
check succeeds). succeeds. Note that in some applications, the evaluation
time MAY not be the same as the current time.
5. The AC targeting check MUST pass (see as specified in section 4.3.2 above) 4.3.2.
6. If the AC contains any "unsupported" a critical extensions extension that is not listed in
section 4.3, then the AC MUST be rejected.
"Support"
Support for an extension in this context means:
a. the
1. The AC verifier MUST be able to parse the extension value, and,
b. where value.
2. Where the extension value SHOULD cause 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
configuration. For example, an AC verifier may be configured to
reject ACs which contain or lack certain attribute types. 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, e.g. information. For example, an AC verifier might be
configured not to return certain attributes to certain targets. 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.
The basic approach taken
Two revocation schemes are defined, and the AC issuer should elect
the one that is best suited to allow use of the following environment in which the AC
revocation related schemes. 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. A The
noRevAvail extension as is defined in section 4.3.6 above 4.3.6, and the
noRevAvail extension MUST be present in the AC to indicate this. use
of this scheme.
Where no noRevAvail is not present, then the AC issuer is
implicitly stating that revocation status checks are supported 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 be marked (like PKCs) to "point" to sources of revocation status information (using information,
using either an authorityInfoAccess extension or a
crlDistributionPoints extension in within the AC
itself). 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, will contain a
noRevAvail extension, then the "pointer in AC" scheme NEED NOT need not be
supported. If any AC can be issued that does not contain the
noRevAvail extension, then the "pointer in AC" scheme MUST be
supported.
All conformant ACs MUST contain exactly one of the noRevAvail,
authorityInformationAccess or crlDistributionPoints extensions. That
is, the crlDistributionPoints, authorityInformationAccess and
noRevAvail extensions are mutually exclusive for a single AC AC, and an
one AC MUST NOT contain more than one of these extensions. This
differs from the case with PKCs. PKCs, which permit both authorityInformationAccess and
crlDistributionPoints extensions within one PKC.
An AC verifier MAY any use other (e.g.
configured) sources source for AC revocation status
information.
7. Optional Features
This section specifies features that MAY be implemented. Conformance
to this specification profile does NOT require support for these features. features;
however, if these features are offered, they MUST be offered as
described below.
7.1 Attribute Encryption
Where an AC will be carried in clear within an application protocol
or where an AC contains some sensitive information (e.g. like a legacy
application username/password) username/password, then encryption of AC attributes MAY
be needed.
When a set of attributes are to be encrypted within an AC, the
cryptographic message syntax,
Cryptographic Message Syntax, EnvelopedData structure [CMS] is used
to carry the ciphertext(s) ciphertext and associated per-recipient keying
information.
This type of attribute encryption is targeted, which means that
before targeted. Before the AC is signed
signed, the attributes have been are encrypted for a set of predetermined
recipients.
The AC then contains the ciphertext(s) ciphertext inside its signed data. The
"enveloped-data"
EenvelopedData (id-envelopedData) ContentType is used used, and the
content field will contain the EnvelopedData type.
The set of ciphertexts ciphertext is included into in the AC as the value of an
encrypted attributes encAttrs
attribute. Only one encrypted attributes encAttrs attribute can be present in an AC - however it AC;
however, the encAttrs attribue MAY be multi-valued 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, i.e. the EnvelopedData. The DER encoding MUST
be embedded in an OCTET STRING.
The acIssuer and acSerial fields are present to prevent ciphertext
stealing - when
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 issuer's
AC into an AC issued by the malicious AC issuer. (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 which 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
EncryptedAttributes encAttrs attribute
2.3. Ensure the cleartext attribute(s) attributes are not present in the
to-be-signed AC
3. Add the EncryptedAttribute encAttrs (with its multiple values) to the AC
Note that the rule that each there may be more than one attribute of the same type (the OID) only occurs
once may not hold
same OBJECT IDENTIFIER) after decryption. That is, an AC MAY contain
the same attribute type both in clear and in encrypted form (and
indeed
more than once several times if the decryptor is a same recipient for is associated with more
than one EnvelopedData). One approach implementers may choose, would
be to merge attributes 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
verifier, then the decryption process MUST not fail - if fail. If decryption
fails
does fail, then the AC MUST be rejected.
7.2 Proxying
In some circumstances,
When a server needs to proxy an AC when it acts as a client (for for another server) server on behalf of the
AC holder. holder, the server MAY need to proxy an AC. Such proxying may 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) is MAY also sometimes 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 consists of a set of proxy information,
each of which is a set of targeting information. If the verifier and
the sender of the AC are both named in the same proxy set then the
AC can 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 which are in one of the same
"proxy sets"
proxy sets as itself.
The following data structure is used to represent the
targeting/proxying information.
ProxyInfo ::= SEQUENCE OF Targets
As in the case of targeting, the targetCertificate and targetDigest
fields 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, and the
current server "matches" any one of the proxy sets (where sets. Recall that
"matches" is as defined for the targeting check in section 4.3.2
above). 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, and the current server is one of the targetName fields
in the set "A", or, or the current server is a member of one of the
targetGroup fields in set "A".
Where
When an AC is proxied more than once 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 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 7 }
syntax ProxyInfo
criticality MUST be TRUE
7.3 Use of ObjectDigestInfo
In some environments 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 CHOICE in the holder field
allows support for this requirement.
If the holder is identified via with the objectDigestInfo field field, then
the AC version field MUST contain v2 (i.e. the (the integer 1).
The basic 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, or names.
It also allows production of ACs which contain privileges associated
with an executable object (e.g. such as a Java class). class. However, this
profile only specifies how to use a hash over a public key or PKC, that PKC.
That is, conformant ACs MUST NOT use the otherObjectTypes value for
the digestedObjectType.
In order to
To link an AC to a public key 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 [PKIXPROF] and [ECDSA] 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, then it is possible that the
SubjectPublicKeyInfo from that PKC is NOT the value which should be
hashed. This can occur if, e.g. if DSA Dss-parms are inherited as described
in section 7.3.3 of [PKIXPROF]. 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 which support this feature MUST be able to handle
the representations of public keys for the algorithms specified in
section 7.3 of [PKIXPROF] and those specified in [ECDSA]. In this
case the digestedObjectType MUST be publicKey and the
otherObjectTypeID field MUST NOT be present.
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 (i.e. PKC, including the
signature bits). 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 is
this AC issuer trusted to issue ACs containing this attribute?" attribute? The
AAControls PKC extension, intended to be used in CA and AC Issuer
PKCs, extension MAY be used to help answer the question.
Note that this
The AAControls extension is quite likely intended to change in future based
on experience with the use of ACs be used in the Internet. 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 AAControls extension is used as follows:
The pathLenConstraint, if present, is interpreted as in [PKIXPROF],
but now [PKIXPROF].
It restricts the allowed "distance" distance between the AA CA, (a CA directly
trusted to include AAControls in its PKCs), and the AC issuer.
The permittedAttrs field specifies a set 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 (though the permitUnSpecified field may open
things up). allowed.
The excludedAttrs field specifies a set of attribute types that no
AC issuer is allowed to include in ACs. If this field is not
present, it means that no attribute types are explicitly disallowed
(though the permitUnSpecified field may close things down). disallowed.
The permitUnSpecified field specifies how to handle attribute types
which 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.
Where aaControls
When AAControls are used then 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 ACs certificate path MUST be directly trusted to
issue PKCs which precede the AC issuer in the certification
path, call this CA the "AA CA".
2. All PKC's PKCs on the path from the AA CA down to and including the
AC issuer's PKC MUST contain an aaControls extension as defined
below (the PKC with AAControls extension; however,
the AA CA's as subject PKC need not contain this extension). extension.
3. Only those attributes in the AC which are allowed according to
all of the aaControls 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 (note that this ignored. This check
MUST be applied to the set of attributes following attribute decryption
decryption, and that in such cases the id-aca-encAttrs type MUST also be checked). checked.
name id-pe-aaControls
OID { id-pe 6 }
syntax AAControls
criticality MAY be TRUE
8. Security Considerations
The protection afforded 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 to 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 a 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 issuer's 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 which 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 AC, 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.
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 AA controls PKC extension is optional to
implement, this means that AC verifiers MUST be provided with the
required this information by
other means - e.g. by configuration. means. Configuration information is a likely alternative
means. This becomes very important if an AC verified 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 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.
9. References
[CMC] Myers, M., et al. "Certificate Management Messages over
CMS", draft-ietf-pkix-cmc-05.txt, July 1999.
[CMP] Adams, C., Farrell, S., "Internet X.509 Public Key
Infrastructure - Certificate Management Protocols",
RFC2510.
[CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630.
[ESS] Hoffman, P., "Enhanced Security Services for S/MIME",
RFC2634.
[ECDSA] D. Johnson, W. Polk, "Internet X.509 Public Key
Infrastructure Representation of Elliptic Curve Digital
Signature Algorithm (ECDSA) Keys and Signatures in
Internet X.509 Public Key Infrastructure Certificates"
draft-ietf-pkix-ipki-ecdsa-02.txt, October 1999.
[LDAP] Wahl, M., et al., "Lightweight Directory Access Protocol
(v3)", RFC 2251.
[ESS] Hoffman, P., "Enhanced Security Services for S/MIME",
RFC2634.
[KRB] Kohl, J., Neuman, C., "The Kerberos Network
Authentication Service (V5)", RFC 1510.
[LDAP] Wahl, M., et al., "Lightweight Directory Access Protocol
(v3)", RFC 2251.
[OCSP] Myers, M., et al., " X.509 Internet Public Key
Infrastructure - Online Certificate Status Protocol -
OCSP", RFC 2560.
[PKINIT] Tung, B., et al., "Public Key Cryptography for Initial
Authentication in Kerberos", draft-ietf-cat-kerberos-pk-
init-10.txt
[PKIXPROF] Housley, R., Ford, W., Polk, T, & Solo, D., "Internet
Public Key Infrastructure - X.509 Certificate and CRL
profile",RFC 2459.
[OCSP] Myers, M., et al., " X.509 Internet Public Key
Infrastructure - Online Certificate Status Protocol -
OCSP",
Profile", RFC 2560. 2459.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC 2026, BCP 9, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119.
[X.501] ITU-T Recommendation X.501 : Information Technology -
Open Systems Interconnection - The Directory: Models,
1993.
[URL] Berners-Lee, T., Masinter L., and M. McCahill., "Uniform
Resource Locators (URL)", RFC 1738.
[X.208-88] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.
[X.209-88] CCITT Recommendation X.209: Specification of Basic
Encoding Rules for Abstract Syntax Notation One (ASN.1).
1988.
[X.501-88] CCITT Recommendation X.501: The Directory - Models.
1988.
[X.501-93] ITU-T Recommendation X.501 : Information Technology -
Open Systems Interconnection - The Directory: Models,
1993.
[X.509-88] CCITT Recommendation X.509: The Directory -
Authentication Framework. 1988.
[X.509-97] ITU-T Recommendation X.509: The Directory -
Authentication Framework. 1997.
[X.509-DAM] ISO 9594-8 Information Technology - Open systems
Interconnection - The Directory: Authentication
Framework - Draft Amendment 1: Certificate Extensions,
October 1999.
Author's Addresses
Stephen Farrell, Farrell
Baltimore Technologies
61/62 Fitzwilliam Lane, Lane
Dublin 2, 2
IRELAND
tel: +353-1-647-3000
email: stephen.farrell@baltimore.ie
Russell Housley,
SPYRUS, Housley
SPYRUS
381 Elden Street, Street
Suite 1120, 1120
Herndon, VA 20170, 20170
USA
tel: +1-703-707-0696
email: housley@spyrus.com
Full Copyright Statement
Copyright (C) The Internet Society (date). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. In addition,
the ASN.1 module presented in Appendix B may be used in whole or in
part without inclusion of the copyright notice. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process shall be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. This
document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Appendix B: A: Object Identifiers
This (normative) appendix lists the new object identifiers which 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 which
have arc elements with values that are less than 2^28, i.e. 2^32, (i.e. they
MUST be between 0 and
268,435,455 inclusive. 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). AA's SHOULD NOT
issue ACs which 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-targeting
id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 5 7 }
id-pe-ac-proxying
id-ce-targetInformation OBJECT IDENTIFIER ::= { id-pe 7 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) module(1)
selected-attribute-types(5) clearance (55) }
Appendix B: "Compilable" ASN.1 Module
PKIXAttributeCertificate {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert(12)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- PKIX Certificate Extensions
Attribute, AlgorithmIdentifier, CertificateSerialNumber,
Extensions, UniqueIdentifier,
id-pkix, id-pe, id-kp, id-ad 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(1)}
GeneralName, GeneralNames GeneralNames, id-ce
FROM PKIX1Implicit88 {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5)
pkix(7) id-mod(0) id-pkix1-implicit-88(2)} ;
id-pe-ac-auditIdentity OBJECT IDENTIFIER ::= { id-pe 4 }
id-pe-ac-targeting
id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 5 6 }
id-pe-aaControls
id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 6 7 }
id-pe-ac-proxying
id-ce-targetInformation OBJECT IDENTIFIER ::= { id-pe 7 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) 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 DEFAULT v1,
holder Holder,
issuer AttCertIssuer,
signature AlgorithmIdentifier,
serialNumber CertificateSerialNumber,
attrCertValidityPeriod AttCertValidityPeriod,
attributes SEQUENCE OF Attribute,
issuerUniqueID UniqueIdentifier OPTIONAL,
extensions Extensions OPTIONAL
}
AttCertVersion ::= INTEGER {v1(0), 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
-- if present, version must be v2
}
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 {
oldForm
v1Form GeneralNames,
newForm -- v1 or v2
v2Form [0] V2Form -- v2 only
}
V2Form ::= SEQUENCE {
issuerName GeneralNames OPTIONAL,
baseCertificateId
baseCertificateID [0] IssuerSerial OPTIONAL,
objectDigestInfo [1] ObjectDigestInfo OPTIONAL
-- at least one of issuerName, baseCertificateId or -- baseCertificateID
-- or objectDigestInfo must be present --
-- if newForm is used, version must be v2--
}
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,
targetCertificate
targetCert [2] TargetCert
}
TargetCert ::= SEQUENCE {
targetCertificate IssuerSerial,
targetDigest [3]
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
}
ClassList ::= BIT STRING {
unmarked (0),
unclassified (1),
restricted (2),
confidential (3),
secret (4),
topSecret (5)
}
SecurityCategory ::= SEQUENCE {
type [0] IMPLICIT OBJECT IDENTIFIER,
value [1] ANY DEFINED BY type
}
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: Changes Change History
<<This Appendix to be deleted after last call>>
This appendix lists major changes since the previous revision.
Major changes since last revision:
Changes from -02 to -03
1. Many minor editorial changes
2. Changed OID max element arc text in app. A
3. Removed restriction on Clearance SecurityValue syntaxes to allow
support for various existing clearance schemes
4. Finalized alignment with 4th edition of X.509
Changes from -01 to -02
1. Re-Synchronized with X.509 DAM
2. Deleted AC chains concept
3. Moved AAControls to "optional features" section
4. Samples will be a separate draft
5. Revocation: now using X.509 DAM (noRevAvail) and standard 2459
mechanisms only
6. Deleted the special wildcard target "ALL"
Changes from -00 to -01
1. Re-structured conformance to profile + options as per Oslo
consensus
2. Moved acquisition protocol (LAAP)_to separate I-D
3. Removed restrictions entirely
4. Added new AC revocation options
5. Added optional support for use of objectDigestInfo for keys
6. Added optional support for chains of ACs
7. Changed some syntax:
Added UTF8String to IetfAttrSyntax value choice
Split target & proxy extensions, removed owner from proxyInfo
8. Allocated PKIX OIDs (note: check with repository before using
these, the PKIX arc is currently available at
http://www.imc.org/ietf-pkix/pkix-oid.asn)
9. Added compiled ASN.1 module