Network Working Group R. Housley Internet-Draft Vigil Security, LLC Intended status: Standards Track S. Ashmore Expires: October 22, 2009 National Security Agency C. Wallace Cygnacom Solutions April 20, 2009 Trust Anchor Format draft-ietf-pkix-ta-format-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 22, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the Housley, et al. Expires October 22, 2009 [Page 1] Internet-Draft TAF April 2009 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Housley, et al. Expires October 22, 2009 [Page 2] Internet-Draft TAF April 2009 Abstract This document describes a structure for representing trust anchor information. A trust anchor is an authoritative entity represented by a public key and associated data. The public key is used to verify digital signatures and the associated data is used to constrain the types of information or actions for which the trust anchor is authoritative. The structures defined in this document are intended to satisfy the format-related requirements defined in Trust Anchor Management Requirements. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Trust Anchor Information Syntax . . . . . . . . . . . . . . . 5 2.1. Version . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Public Key . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Key Identifier . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Trust Anchor Title . . . . . . . . . . . . . . . . . . . . 5 2.5. Certification Path Controls . . . . . . . . . . . . . . . 6 2.6. Extensions . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Trust Anchor List . . . . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Normative References . . . . . . . . . . . . . . . . . . . 13 6.2. Informative References . . . . . . . . . . . . . . . . . . 13 Appendix A. ASN.1 Modules . . . . . . . . . . . . . . . . . . . . 14 A.1. ASN.1 Module Using 1993 Syntax . . . . . . . . . . . . . . 14 A.2. ASN.1 Module Using 1988 Syntax . . . . . . . . . . . . . . 15 A.2.1. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Housley, et al. Expires October 22, 2009 [Page 3] Internet-Draft TAF April 2009 1. Introduction Trust anchors are widely used to verify digital signatures and validate certification paths [RFC5280][X.509]. They are required when validating certification paths. Though widely used, there is no standard format for representing trust anchor information. This document describes the TrustAnchorInfo structure. This structure is intended to satisfy the format-related requirements expressed in Trust Anchor Management Requirements [I-D.draft-ietf-pkix-ta-mgmt-reqs]. It can provide a more compact alternative to X.509 certificates for exchanging trust anchor information and provides a means of associating additional or alternative constraints with certificates without breaking the signature on the certificate. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Housley, et al. Expires October 22, 2009 [Page 4] Internet-Draft TAF April 2009 2. Trust Anchor Information Syntax This section describes the TrustAnchorInfo structure. TrustAnchorInfo ::= SEQUENCE { version TrustAnchorInfoVersion DEFAULT v1, pubKey SubjectPublicKeyInfo, keyId KeyIdentifier, taTitle TrustAnchorTitle OPTIONAL, certPath CertPathControls OPTIONAL, exts [1] EXPLICIT Extensions OPTIONAL } TrustAnchorInfoVersion ::= INTEGER { v1(1) } 2.1. Version version identifies the version of TrustAnchorInfo. 2.2. Public Key pubKey identifies the public key and algorithm associated with the trust anchor using the SubjectPublicKeyInfo structure. The SubjectPublicKeyInfo structure contains the algorithm identifier followed by the public key itself. The algorithm field is an AlgorithmIdentifier, which contains an object identifier and OPTIONAL parameters. The object identifier names the public key algorithm and indicates the syntax of the parameters, if present, as well as the format of the public key. The public key is encoded as a BIT STRING. 2.3. Key Identifier keyId contains the public key identifier of the trust anchor public key. 2.4. Trust Anchor Title TrustAnchorTitle ::= UTF8String (SIZE (1..64)) taTitle is OPTIONAL. When it is present, it provides a human readable name for the trust anchor. The text is encoded in UTF-8 [RFC3629], which accommodates most of the world's writing systems. Housley, et al. Expires October 22, 2009 [Page 5] Internet-Draft TAF April 2009 2.5. Certification Path Controls CertPathControls ::= SEQUENCE { taName Name, certificate [0] Certificate OPTIONAL, policySet [1] CertificatePolicies OPTIONAL, policyFlags [2] CertPolicyFlags OPTIONAL, nameConstr [3] NameConstraints OPTIONAL } certPath is OPTIONAL. When it is present, it provides the controls needed to initialize an X.509 certification path validation algorithm implementation (see Section 6 in [RFC5280]). When absent, the trust anchor cannot be used to validate the signature on an X.509 certificate. taName provides the X.500 distinguished name associated with the trust anchor, and this distinguished name is used to construct and validate an X.509 certification path. The name MUST NOT be an empty sequence. certificate provides an OPTIONAL X.509 certificate, which can be used in some environments to represent the trust anchor in certification path development and validation. If the certificate is present, the subject name in the certificate MUST exactly match the X.500 distinguished name provided in the taName field, the public key MUST exactly match the public key in the pubKey field and the subjectKeyIdentifier extension, if present, MUST exactly match the key identifier in the keyId field. The complete description of the syntax and semantics of the Certificate are provided in [RFC5280]. Constraints defined in the policySet, policyFlags, nameConstr and exts fields within TrustAnchorInfo replace values contained in a certificate or provide values for extensions not present in the certificate. Values defined in these TrustAnchorInfo fields are always enforced. Extensions included in a certificate are enforced only if there is no corresponding value in the TrustAnchorInfo. Correspondence between extensions within a certificate and TrustAnchorInfo fields is defined as follows: o an id-ce-certificatePolicies certificate extension corresponds to the CertPathControls.policySet field. o an id-ce-policyConstraints certificate extension corresponds to the CertPolicyFlags.inhibitPolicyMapping and CertPolicyFlags.requireExplicitPolicy fields. Housley, et al. Expires October 22, 2009 [Page 6] Internet-Draft TAF April 2009 o an id-ce-inhibitAnyPolicy certificate extension corresponds to the CertPolicyFlags.inhibitAnyPolicy field. o an id-ce-nameConstraints certificate extension corresponds to the CertPathControls.nameConstr field. o any other certificate extension corresponds to the same type of extension in the TrustAnchorInfo.exts field. CertificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation PolicyInformation ::= SEQUENCE { policyIdentifier CertPolicyId, policyQualifiers SEQUENCE SIZE (1..MAX) OF PolicyQualifierInfo OPTIONAL } CertPolicyId ::= OBJECT IDENTIFIER policySet is OPTIONAL. When present, it contains sequence of certificate policy identifiers to be provided as inputs to the certification path validation algorithm. When absent, the special value any-policy is provided as the input to the certification path validation algorithm. The complete description of the syntax and semantics of the CertificatePolicies are provided in [RFC5280], including the syntax for PolicyInformation. In this context, the OPTIONAL policyQualifiers structure MUST NOT be included. CertPolicyFlags ::= BIT STRING { inhibitPolicyMapping (0), requireExplicitPolicy (1), inhibitAnyPolicy (2) } policyFlags is OPTIONAL. When present, three Boolean values for input to the certification path validation algorithm are provided in a BIT STRING. When absent, the input to the certification path validation algorithm is { FALSE, FALSE, FALSE }, which represents the most liberal setting for these flags. The three bits are used as follows: inhibitPolicyMapping indicates if policy mapping is allowed in the certification path. When set to TRUE, policy mapping is not permitted. This value represents the initial-policy-mapping- inhibit input value to the certification path validation algorithm Housley, et al. Expires October 22, 2009 [Page 7] Internet-Draft TAF April 2009 described in section 6.1.1 of [RFC5280]. requireExplicitPolicy indicates if the certification path MUST be valid for at least one of the certificate policies in the policySet. When set to TRUE, all certificates in the certification path MUST contain an acceptable policy identifier in the certificate policies extension. This value represents the initial-explicit-policy input value to the certification path validation algorithm described in section 6.1.1 of [RFC5280]. An acceptable policy identifier is a member of the policySet or the identifier of a policy that is declared to be equivalent through policy mapping. This bit MUST be set to FALSE if policySet is absent. inhibitAnyPolicy indicates whether the special anyPolicy policy identifier, with the value { 2 5 29 32 0 }, is considered an explicit match for other certificate policies. This value represents the initial-any-policy-inhibit input value to the certification path validation algorithm described in section 6.1.1 of [RFC5280]. NameConstraints ::= SEQUENCE { permittedSubtrees [0] GeneralSubtrees OPTIONAL, excludedSubtrees [1] GeneralSubtrees OPTIONAL } GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree GeneralSubtree ::= SEQUENCE { base GeneralName, minimum [0] BaseDistance DEFAULT 0, maximum [1] BaseDistance OPTIONAL } BaseDistance ::= INTEGER (0..MAX) nameConstr is OPTIONAL. It has the same syntax and semantics as the Name Constraints certificate extension [RFC5280], which includes a list of permitted names and a list of excluded names. The definition of GeneralName can be found in [RFC5280]. When it is present, constraints are provided on names (including alternative names) that might appear in subsequent X.509 certificates in a certification path. This field is used to set the initial-permitted-subtrees and initial-excluded-subtrees input values to the certification path validation algorithm described in section 6.1.1 of [RFC5280]. When this field is absent, the initial-permitted-subtrees variable is unbounded and the initial-excluded-subtrees variable is empty. Housley, et al. Expires October 22, 2009 [Page 8] Internet-Draft TAF April 2009 When the trust anchor is used to validate a certification path, CertPathControls provides limitations on certification paths that will successfully validate. An application that is validating a certification path SHOULD NOT ignore these limitations, but the application can impose additional limitations to ensure that the validated certification path is appropriate for the intended application context. As input to the certification path validation algorithm, an application MAY: o Provide a subset of the certification policies provided in the policySet; o Provide a TRUE value, if appropriate, for any of the flags in the policyFlags; o Provide a subset of the permitted names provided in the nameConstr; o Provide additional excluded names to the ones that are provided in the nameConstr 2.6. Extensions exts is OPTIONAL. When it is present, it can be used to associate additional information with the trust anchor using the standard Extensions structure. Extensions that are anticipated to be widely used have been included in the CertPathControls structure to avoid overhead associated with use of the Extensions structure. To avoid duplication with the CertPathControls field, the following types of extensions MUST NOT appear in the exts field and are ignored if they do appear: id-ce-certificatePolicies, id-ce-policyConstraints, id-ce- inhibitAnyPolicy or id-ce-nameConstraints. Housley, et al. Expires October 22, 2009 [Page 9] Internet-Draft TAF April 2009 3. Trust Anchor List TrustAnchorInfo allows for the representation of a single trust anchor. In many cases, it is convenient to represent a collection of trust anchors. The TrustAnchorList structure is defined for this purpose. TrustAnchorList is defined as a sequence of one or more TrustAnchorChoice objects. TrustAnchorChoice provides three options for representing a trust anchor. The certificate option allows for the use of a certificate with no additional associated constraints. The tbsCert option allows for associating constraints by removing a signature on a certificate and changing the extensions field. The taInfo option allows for use of the TrustAnchorInfo structure defined in this document. TrustAnchorList ::= SEQUENCE SIZE (1..MAX) OF TrustAnchorChoice TrustAnchorChoice ::= CHOICE { certificate Certificate, tbsCert [1] EXPLICIT TBSCertificate, taInfo [2] EXPLICIT TrustAnchorInfo } trust-anchor-list PKCS7-CONTENT-TYPE ::= { TrustAnchorList IDENTIFIED BY id-ct-trustAnchorList } The TrustAnchorList structure can be protected using the SignedData structured defined in the Cryptographic Message Syntax(CMS) [RFC3852]. The id-ct-trustAnchorList object identifier has been defined to represent TrustAnchorList payloads with CMS structures. Housley, et al. Expires October 22, 2009 [Page 10] Internet-Draft TAF April 2009 4. Security Considerations Compromise of a trust anchor private key permits unauthorized parties to masquerade as the trust anchor. Where TA-based constraints are enforced, the unauthorized holder of the trust anchor private key will be limited by the certification path controls associated with the trust anchor, as expressed in the certPath and exts fields. For example, name constraints in the trust anchor will determine the name space that will be accepted in certificates that are validated using the compromised trust anchor. The compromise of a Certification Authority's (CA's) private key leads to the same type of problems as the compromise of a trust anchor private key. The unauthorized holder of the CA private key will be limited by the certification path controls associated with the trust anchor, as expressed in the certPath field or as an extension. Usage of a certificate independent of the TrustAnchorInfo structure that envelopes it must be carefully managed to avoid violating constraints expressed in the TrustAnchorInfo. When enveloping a certificate in a TrustAnchorInfo structure, values included in the certificate should be evaluated to ensure there is no confusion or conflict with values in the TrustAnchorInfo structure. Housley, et al. Expires October 22, 2009 [Page 11] Internet-Draft TAF April 2009 5. IANA Considerations There are no IANA considerations. Please delete this section prior to RFC publication. Housley, et al. Expires October 22, 2009 [Page 12] Internet-Draft TAF April 2009 6. References 6.1. Normative References [I-D.ietf-pkix-new-asn1] Hoffman, P. and J. Schaad, "New ASN.1 Modules for PKIX", draft-ietf-pkix-new-asn1-05 (work in progress), April 2009. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852, July 2004. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [X.680] "ITU-T Recommendation X.680: Information Technology - Abstract Syntax Notation One", 1997. 6.2. Informative References [I-D.draft-ietf-pkix-ta-mgmt-reqs] Reddy, R. and C. Wallace, "Trust Anchor Management Requirements", draft-ietf-pkix-ta-mgmt-reqs-03 (work in progress). [X.509] "ITU-T Recommendation X.509 - The Directory - Authentication Framework", 2000. Housley, et al. Expires October 22, 2009 [Page 13] Internet-Draft TAF April 2009 Appendix A. ASN.1 Modules Appendix A.1 provides the normative ASN.1 definitions for the structures described in this specification using ASN.1 as defined in [X.680]. It includes definitions imported from [RFC5280] and [I-D.ietf-pkix-new-asn1]. A.1. ASN.1 Module Using 1993 Syntax TrustAnchorInfoModule { joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101) dod(2) infosec(1) modules(0) 33 } DEFINITIONS IMPLICIT TAGS ::= BEGIN IMPORTS Certificate, Name, SubjectPublicKeyInfo, TBSCertificate FROM PKIX1Explicit88 -- from [RFC5280] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) } CertificatePolicies, KeyIdentifier, NameConstraints FROM PKIX1Implicit88 -- [RFC5280] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) } Extensions FROM PKIX-CommonTypes -- from [I-D.ietf-pkix-new-asn1] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon(43) } ; TrustAnchorInfo ::= SEQUENCE { version TrustAnchorInfoVersion DEFAULT v1, pubKey SubjectPublicKeyInfo, keyId KeyIdentifier, taTitle TrustAnchorTitle OPTIONAL, certPath CertPathControls OPTIONAL, exts [1] EXPLICIT Extensions OPTIONAL } TrustAnchorInfoVersion ::= INTEGER { v1(1) } TrustAnchorTitle ::= UTF8String (SIZE (1..64)) CertPathControls ::= SEQUENCE { taName Name, Housley, et al. Expires October 22, 2009 [Page 14] Internet-Draft TAF April 2009 certificate [0] Certificate OPTIONAL, policySet [1] CertificatePolicies OPTIONAL, policyFlags [2] CertPolicyFlags OPTIONAL, nameConstr [3] NameConstraints OPTIONAL } CertPolicyFlags ::= BIT STRING { inhibitPolicyMapping (0), requireExplicitPolicy (1), inhibitAnyPolicy (2) } TrustAnchorList ::= SEQUENCE SIZE (1..MAX) OF TrustAnchorChoice TrustAnchorChoice ::= CHOICE { certificate Certificate, tbsCert [1] EXPLICIT TBSCertificate, taInfo [2] EXPLICIT TrustAnchorInfo } id-ct-trustAnchorList OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) id-smime(16) id-ct(1) 34 } END A.2. ASN.1 Module Using 1988 Syntax Appendix A.1 provides the normative ASN.1 definitions for the structures described in this specification using ASN.1 as defined in [X.680]. A.2.1. ASN.1 Module TrustAnchorInfoModule-88 { joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101) dod(2) infosec(1) modules(0) 33 } DEFINITIONS IMPLICIT TAGS ::= BEGIN IMPORTS Certificate, Name, Extensions, SubjectPublicKeyInfo, TBSCertificate FROM PKIX1Explicit88 -- from [RFC5280] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) } CertificatePolicies, KeyIdentifier, NameConstraints Housley, et al. Expires October 22, 2009 [Page 15] Internet-Draft TAF April 2009 FROM PKIX1Implicit88 -- [RFC5280] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) } ; TrustAnchorInfo ::= SEQUENCE { version TrustAnchorInfoVersion DEFAULT v1, pubKey SubjectPublicKeyInfo, keyId KeyIdentifier, taTitle TrustAnchorTitle OPTIONAL, certPath CertPathControls OPTIONAL, exts [1] EXPLICIT Extensions OPTIONAL } TrustAnchorInfoVersion ::= INTEGER { v1(1) } TrustAnchorTitle ::= UTF8String (SIZE (1..64)) CertPathControls ::= SEQUENCE { taName Name, certificate [0] Certificate OPTIONAL, policySet [1] CertificatePolicies OPTIONAL, policyFlags [2] CertPolicyFlags OPTIONAL, nameConstr [3] NameConstraints OPTIONAL } CertPolicyFlags ::= BIT STRING { inhibitPolicyMapping (0), requireExplicitPolicy (1), inhibitAnyPolicy (2) } TrustAnchorList ::= SEQUENCE SIZE (1..MAX) OF TrustAnchorChoice TrustAnchorChoice ::= CHOICE { certificate Certificate, tbsCert [1] EXPLICIT TBSCertificate, taInfo [2] EXPLICIT TrustAnchorInfo } id-ct-trustAnchorList OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) id-smime(16) id-ct(1) 34 } END Housley, et al. Expires October 22, 2009 [Page 16] Internet-Draft TAF April 2009 Authors' Addresses Russ Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 Email: housley@vigilsec.com Sam Ashmore National Security Agency Suite 6751 9800 Savage Road Fort Meade, MD 20755 Email: srashmo@radium.ncsc.mil Carl Wallace Cygnacom Solutions Suite 5200 7925 Jones Branch Drive McLean, VA 22102 Email: cwallace@cygnacom.com Housley, et al. Expires October 22, 2009 [Page 17]