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diff --git a/third_party/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-29.txt b/third_party/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-29.txt new file mode 100644 index 00000000000..1c70b180451 --- /dev/null +++ b/third_party/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-29.txt @@ -0,0 +1,2013 @@ +NETWORK WORKING GROUP B. Tung +Internet-Draft USC Information Sciences Institute +Expires: April 22, 2006 L. Zhu + Microsoft Corporation + October 19, 2005 + + + Public Key Cryptography for Initial Authentication in Kerberos + draft-ietf-cat-kerberos-pk-init-29 + +Status of this Memo + + By submitting this Internet-Draft, each author represents that any + applicable patent or other IPR claims of which he or she is aware + have been or will be disclosed, and any of which he or she becomes + aware will be disclosed, in accordance with Section 6 of BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on April 22, 2006. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + This document describes protocol extensions (hereafter called PKINIT) + to the Kerberos protocol specification. These extensions provide a + method for integrating public key cryptography into the initial + authentication exchange, by using asymmetric-key signature and/or + encryption algorithms in pre-authentication data fields. + + + + + +Tung & Zhu Expires April 22, 2006 [Page 1] + +Internet-Draft PKINIT October 2005 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3.1. Definitions, Requirements, and Constants . . . . . . . . . 4 + 3.1.1. Required Algorithms . . . . . . . . . . . . . . . . . 4 + 3.1.2. Defined Message and Encryption Types . . . . . . . . . 5 + 3.1.3. Algorithm Identifiers . . . . . . . . . . . . . . . . 6 + 3.2. PKINIT Pre-authentication Syntax and Use . . . . . . . . . 7 + 3.2.1. Generation of Client Request . . . . . . . . . . . . . 7 + 3.2.2. Receipt of Client Request . . . . . . . . . . . . . . 10 + 3.2.3. Generation of KDC Reply . . . . . . . . . . . . . . . 14 + 3.2.4. Receipt of KDC Reply . . . . . . . . . . . . . . . . . 20 + 3.3. Interoperability Requirements . . . . . . . . . . . . . . 21 + 3.4. KDC Indication of PKINIT Support . . . . . . . . . . . . . 21 + 4. Security Considerations . . . . . . . . . . . . . . . . . . . 22 + 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 + 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 + 7.1. Normative References . . . . . . . . . . . . . . . . . . . 25 + 7.2. Informative References . . . . . . . . . . . . . . . . . . 26 + Appendix A. PKINIT ASN.1 Module . . . . . . . . . . . . . . . . . 26 + Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 32 + Appendix C. Miscellaneous Information about Microsoft Windows + PKINIT Implementations . . . . . . . . . . . . . . . 33 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 + Intellectual Property and Copyright Statements . . . . . . . . . . 36 + + + + + + + + + + + + + + + + + + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 2] + +Internet-Draft PKINIT October 2005 + + +1. Introduction + + A client typically authenticates itself to a service in Kerberos + using three distinct though related exchanges. First, the client + requests a ticket-granting ticket (TGT) from the Kerberos + authentication server (AS). Then, it uses the TGT to request a + service ticket from the Kerberos ticket-granting server (TGS). + Usually, the AS and TGS are integrated in a single device known as a + Kerberos Key Distribution Center, or KDC. Finally, the client uses + the service ticket to authenticate itself to the service. + + The advantage afforded by the TGT is that the client exposes his + long-term secrets only once. The TGT and its associated session key + can then be used for any subsequent service ticket requests. One + result of this is that all further authentication is independent of + the method by which the initial authentication was performed. + Consequently, initial authentication provides a convenient place to + integrate public-key cryptography into Kerberos authentication. + + As defined in [RFC4120], Kerberos authentication exchanges use + symmetric-key cryptography, in part for performance. One + disadvantage of using symmetric-key cryptography is that the keys + must be shared, so that before a client can authenticate itself, he + must already be registered with the KDC. + + Conversely, public-key cryptography (in conjunction with an + established Public Key Infrastructure) permits authentication without + prior registration with a KDC. Adding it to Kerberos allows the + widespread use of Kerberized applications by clients without + requiring them to register first with a KDC--a requirement that has + no inherent security benefit. + + As noted above, a convenient and efficient place to introduce public- + key cryptography into Kerberos is in the initial authentication + exchange. This document describes the methods and data formats for + integrating public-key cryptography into Kerberos initial + authentication. + + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + Both the AS and the TGS are referred to as the KDC. + + In this document, the encryption key used to encrypt the enc-part + + + +Tung & Zhu Expires April 22, 2006 [Page 3] + +Internet-Draft PKINIT October 2005 + + + field of the KDC-REP in the AS-REP [RFC4120] is referred to as the AS + reply key. + + +3. Extensions + + This section describes extensions to [RFC4120] for supporting the use + of public-key cryptography in the initial request for a ticket. + + Briefly, this document defines the following extensions to [RFC4120]: + + 1. The client indicates the use of public-key authentication by + including a special preauthenticator in the initial request. This + preauthenticator contains the client's public-key data and a + signature. + + 2. The KDC tests the client's request against its authentication + policy and trusted Certification Authorities (CAs). + + 3. If the request passes the verification tests, the KDC replies as + usual, but the reply is encrypted using either: + + a. a key generated through a Diffie-Hellman (DH) key exchange + [RFC2631] [IEEE1363] with the client, signed using the KDC's + signature key; or + + b. a symmetric encryption key, signed using the KDC's signature + key and encrypted using the client's public key. + + Any keying material required by the client to obtain the + encryption key for decrypting the KDC reply is returned in a pre- + authentication field accompanying the usual reply. + + 4. The client validates the KDC's signature, obtains the encryption + key, decrypts the reply, and then proceeds as usual. + + Section 3.1 of this document enumerates the required algorithms and + necessary extension message types. Section 3.2 describes the + extension messages in greater detail. + +3.1. Definitions, Requirements, and Constants + +3.1.1. Required Algorithms + + All PKINIT implementations MUST support the following algorithms: + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 4] + +Internet-Draft PKINIT October 2005 + + + o AS reply key enctype: aes128-cts-hmac-sha1-96 and aes256-cts-hmac- + sha1-96 [RFC3962]. + + o Signature algorithm: sha-1WithRSAEncryption [RFC3279]. + + o AS reply key delivery method: Diffie-Hellman key exchange + [RFC2631]. + + In addition, implementations of this specification MUST be capable of + processing the Extended Key Usage (EKU) extension and the id-pkinit- + san (as defined in Section 3.2.2) otherName of the Subject + Alternative Name (SAN) extension in X.509 certificates [RFC3280], if + present. + +3.1.2. Defined Message and Encryption Types + + PKINIT makes use of the following new pre-authentication types: + + PA_PK_AS_REQ 16 + PA_PK_AS_REP 17 + + PKINIT also makes use of the following new authorization data type: + + AD_INITIAL_VERIFIED_CAS 9 + + PKINIT introduces the following new error codes: + + KDC_ERR_CLIENT_NOT_TRUSTED 62 + KDC_ERR_INVALID_SIG 64 + KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED 65 + KDC_ERR_CANT_VERIFY_CERTIFICATE 70 + KDC_ERR_INVALID_CERTIFICATE 71 + KDC_ERR_REVOKED_CERTIFICATE 72 + KDC_ERR_REVOCATION_STATUS_UNKNOWN 73 + KDC_ERR_CLIENT_NAME_MISMATCH 75 + KDC_ERR_INCONSISTENT_KEY_PURPOSE 76 + + PKINIT uses the following typed data types for errors: + + TD_TRUSTED_CERTIFIERS 104 + TD_INVALID_CERTIFICATES 105 + TD_DH_PARAMETERS 109 + + PKINIT defines the following encryption types, for use in the etype + field of the AS-REQ [RFC4120] message to indicate acceptance of the + corresponding algorithms that can used by Cryptographic Message + Syntax (CMS) [RFC3852] messages in the reply: + + + + +Tung & Zhu Expires April 22, 2006 [Page 5] + +Internet-Draft PKINIT October 2005 + + + dsaWithSHA1-CmsOID 9 + -- Indicates that the client supports dsaWithSHA1 + md5WithRSAEncryption-CmsOID 10 + -- Indicates that the client supports md5WithRSAEncryption + sha1WithRSAEncryption-CmsOID 11 + -- Indicates that the client supports sha1WithRSAEncryption + rc2CBC-EnvOID 12 + -- Indicates that the client supports rc2CBC + rsaEncryption-EnvOID 13 + -- Indicates that the client supports + -- rsaEncryption (PKCS1 v2.1) + id-RSAES-OAEP-EnvOID 14 + -- Indicates that the client supports + -- id-RSAES-OAEP (PKCS1 v2.1) + des-ede3-cbc-EnvOID 15 + -- Indicates that the client supports des-ede3-cbc + + The ASN.1 module for all structures defined in this document (plus + IMPORT statements for all imported structures) is given in + Appendix A. + + All structures defined in or imported into this document MUST be + encoded using Distinguished Encoding Rules (DER) [X680] [X690] + (unless otherwise noted). All data structures carried in OCTET + STRINGs must be encoded according to the rules specified in + corresponding specifications. + + Interoperability note: Some implementations may not be able to decode + wrapped CMS objects encoded with BER but not DER; specifically, they + may not be able to decode infinite length encodings. To maximize + interoperability, implementers SHOULD encode CMS objects used in + PKINIT with DER. + +3.1.3. Algorithm Identifiers + + PKINIT does not define, but does make use of, the following algorithm + identifiers. + + PKINIT uses the following algorithm identifier(s) for Diffie-Hellman + key agreement [RFC3279]: + + dhpublicnumber (Modular Exponential Diffie-Hellman [RFC2631]) + + PKINIT uses the following signature algorithm identifiers [RFC3279]: + + sha-1WithRSAEncryption (RSA with SHA1) + md5WithRSAEncryption (RSA with MD5) + id-dsa-with-sha1 (DSA with SHA1) + + + +Tung & Zhu Expires April 22, 2006 [Page 6] + +Internet-Draft PKINIT October 2005 + + + PKINIT uses the following encryption algorithm identifiers [RFC3447] + for encrypting the temporary key with a public key: + + rsaEncryption (PKCS1 v2.1) + id-RSAES-OAEP (PKCS1 v2.1) + + PKINIT uses the following algorithm identifiers [RFC3370] [RFC3565] + for encrypting the AS reply key with the temporary key: + + des-ede3-cbc (three-key 3DES, CBC mode) + rc2-cbc (RC2, CBC mode) + id-aes256-CBC (AES-256, CBC mode) + +3.2. PKINIT Pre-authentication Syntax and Use + + This section defines the syntax and use of the various pre- + authentication fields employed by PKINIT. + +3.2.1. Generation of Client Request + + The initial authentication request (AS-REQ) is sent as per [RFC4120]; + in addition, a pre-authentication data element, whose padata-type is + PA_PK_AS_REQ and whose padata-value contains the DER encoding of the + type PA-PK-AS-REQ, is included. + + PA-PK-AS-REQ ::= SEQUENCE { + signedAuthPack [0] IMPLICIT OCTET STRING, + -- Contains a CMS type ContentInfo encoded + -- according to [RFC3852]. + -- The contentType field of the type ContentInfo + -- is id-signedData (1.2.840.113549.1.7.2), + -- and the content field is a SignedData. + -- The eContentType field for the type SignedData is + -- id-pkinit-authData (1.3.6.1.5.2.3.1), and the + -- eContent field contains the DER encoding of the + -- type AuthPack. + -- AuthPack is defined below. + trustedCertifiers [1] SEQUENCE OF + ExternalPrincipalIdentifier OPTIONAL, + -- A list of CAs, trusted by the client, that can + -- be used to certify the KDC. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + -- The information contained in the + -- trustedCertifiers SHOULD be used by the KDC as + -- hints to guide its selection of an appropriate + -- certificate chain to return to the client. + kdcPkId [2] IMPLICIT OCTET STRING + + + +Tung & Zhu Expires April 22, 2006 [Page 7] + +Internet-Draft PKINIT October 2005 + + + OPTIONAL, + -- Contains a CMS type SignerIdentifier encoded + -- according to [RFC3852]. + -- Identifies, if present, a particular KDC + -- public key that the client already has. + ... + } + + DHNonce ::= OCTET STRING + + ExternalPrincipalIdentifier ::= SEQUENCE { + subjectName [0] IMPLICIT OCTET STRING OPTIONAL, + -- Contains a PKIX type Name encoded according to + -- [RFC3280]. + -- Identifies the certificate subject by the + -- distinguished subject name. + -- REQUIRED when there is a distinguished subject + -- name present in the certificate. + issuerAndSerialNumber [1] IMPLICIT OCTET STRING OPTIONAL, + -- Contains a CMS type IssuerAndSerialNumber encoded + -- according to [RFC3852]. + -- Identifies a certificate of the subject. + -- REQUIRED for TD-INVALID-CERTIFICATES and + -- TD-TRUSTED-CERTIFIERS. + subjectKeyIdentifier [2] IMPLICIT OCTET STRING OPTIONAL, + -- Identifies the subject's public key by a key + -- identifier. When an X.509 certificate is + -- referenced, this key identifier matches the X.509 + -- subjectKeyIdentifier extension value. When other + -- certificate formats are referenced, the documents + -- that specify the certificate format and their use + -- with the CMS must include details on matching the + -- key identifier to the appropriate certificate + -- field. + -- RECOMMENDED for TD-TRUSTED-CERTIFIERS. + ... + } + + AuthPack ::= SEQUENCE { + pkAuthenticator [0] PKAuthenticator, + clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL, + -- Type SubjectPublicKeyInfo is defined in + -- [RFC3280]. + -- Specifies Diffie-Hellman domain parameters + -- and the client's public key value [IEEE1363]. + -- The DH public key value is encoded as a BIT + -- STRING according to [RFC3279]. + -- This field is present only if the client wishes + + + +Tung & Zhu Expires April 22, 2006 [Page 8] + +Internet-Draft PKINIT October 2005 + + + -- to use the Diffie-Hellman key agreement method. + supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier + OPTIONAL, + -- Type AlgorithmIdentifier is defined in + -- [RFC3280]. + -- List of CMS encryption types supported by the + -- client in order of (decreasing) preference. + clientDHNonce [3] DHNonce OPTIONAL, + -- Present only if the client indicates that it + -- wishes to reuse DH keys or to allow the KDC to + -- do so (see Section 3.2.3.1). + ... + } + + PKAuthenticator ::= SEQUENCE { + cusec [0] INTEGER (0..999999), + ctime [1] KerberosTime, + -- cusec and ctime are used as in [RFC4120], for + -- replay prevention. + nonce [2] INTEGER (0..4294967295), + -- Chosen randomly; This nonce does not need to + -- match with the nonce in the KDC-REQ-BODY. + paChecksum [3] OCTET STRING, + -- Contains the SHA1 checksum, performed over + -- KDC-REQ-BODY. + ... + } + + The ContentInfo [RFC3852] structure for the signedAuthPack field is + filled out as follows: + + 1. The contentType field of the type ContentInfo is id-signedData + (as defined in [RFC3852]), and the content field is a SignedData + (as defined in [RFC3852]). + + 2. The eContentType field for the type SignedData is id-pkinit- + authData: { iso(1) org(3) dod(6) internet(1) security(5) + kerberosv5(2) pkinit(3) authData(1) }. + + 3. The eContent field for the type SignedData contains the DER + encoding of the type AuthPack. + + 4. The signerInfos field of the type SignedData contains a single + signerInfo, which contains the signature over the type AuthPack. + + 5. The certificates field of the type SignedData contains + certificates intended to facilitate certification path + construction, so that the KDC can verify the signature over the + + + +Tung & Zhu Expires April 22, 2006 [Page 9] + +Internet-Draft PKINIT October 2005 + + + type AuthPack. For path validation, these certificates SHOULD be + sufficient to construct at least one certification path from the + client certificate to one trust anchor acceptable by the KDC + [CAPATH]. The client MUST be capable of including such a set of + certificates if configured to do so. The certificates field MUST + NOT contain "root" CA certificates. + + 6. The client's Diffie-Hellman public value (clientPublicValue) is + included if and only if the client wishes to use the Diffie- + Hellman key agreement method. The Diffie-Hellman domain + parameters [IEEE1363] for the client's public key are specified + in the algorithm field of the type SubjectPublicKeyInfo [RFC3279] + and the client's Diffie-Hellman public key value is mapped to a + subjectPublicKey (a BIT STRING) according to [RFC3279]. When + using the Diffie-Hellman key agreement method, implementations + MUST support Oakley 1024-bit Modular Exponential (MODP) well- + known group 2 [RFC2412] and Oakley 2048-bit MODP well-known group + 14 [RFC3526], and SHOULD support Oakley 4096-bit MODP well-known + group 16 [RFC3526]. + + The Diffie-Hellman field size should be chosen so as to provide + sufficient cryptographic security [RFC3766]. + + When MODP Diffie-Hellman is used, the exponents should have at + least twice as many bits as the symmetric keys that will be + derived from them [ODL99]. + + 7. The client may wish to reuse DH keys or to allow the KDC to do so + (see Section 3.2.3.1). If so, then the client includes the + clientDHNonce field. This nonce string needs to be as long as + the longest key length of the symmetric key types that the client + supports. This nonce MUST be chosen randomly. + + +3.2.2. Receipt of Client Request + + Upon receiving the client's request, the KDC validates it. This + section describes the steps that the KDC MUST (unless otherwise + noted) take in validating the request. + + The KDC verifies the client's signature in the signedAuthPack field + according to [RFC3852]. + + If, while validating the client's X.509 certificate [RFC3280], the + KDC cannot build a certification path to validate the client's + certificate, it sends back a KRB-ERROR [RFC4120] message with the + code KDC_ERR_CANT_VERIFY_CERTIFICATE. The accompanying e-data for + this error message is a TYPED-DATA (as defined in [RFC4120]) that + + + +Tung & Zhu Expires April 22, 2006 [Page 10] + +Internet-Draft PKINIT October 2005 + + + contains an element whose data-type is TD_TRUSTED_CERTIFIERS, and + whose data-value contains the DER encoding of the type TD-TRUSTED- + CERTIFIERS: + + TD-TRUSTED-CERTIFIERS ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Identifies a list of CAs trusted by the KDC. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + + Upon receiving this error message, the client SHOULD retry only if it + has a different set of certificates (from those of the previous + requests) that form a certification path (or a partial path) from one + of the trust anchors acceptable by the KDC to its own certificate. + + If, while processing the certification path, the KDC determines that + the signature on one of the certificates in the signedAuthPack field + is invalid, it returns a KRB-ERROR [RFC4120] message with the code + KDC_ERR_INVALID_CERTIFICATE. The accompanying e-data for this error + message is a TYPED-DATA that contains an element whose data-type is + TD_INVALID_CERTIFICATES, and whose data-value contains the DER + encoding of the type TD-INVALID-CERTIFICATES: + + TD-INVALID-CERTIFICATES ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Each ExternalPrincipalIdentifier identifies a + -- certificate (sent by the client) with an invalid + -- signature. + + If more than one X.509 certificate signature is invalid, the KDC MAY + include one IssuerAndSerialNumber per invalid signature within the + TD-INVALID-CERTIFICATES. + + The client's X.509 certificate is validated according to [RFC3280]. + + Based on local policy, the KDC may also check whether any X.509 + certificates in the certification path validating the client's + certificate have been revoked. If any of them have been revoked, the + KDC MUST return an error message with the code + KDC_ERR_REVOKED_CERTIFICATE; if the KDC attempts to determine the + revocation status but is unable to do so, it SHOULD return an error + message with the code KDC_ERR_REVOCATION_STATUS_UNKNOWN. The + certificate or certificates affected are identified exactly as for + the error code KDC_ERR_INVALID_CERTIFICATE (see above). + + Note that the TD_INVALID_CERTIFICATES error data is only used to + identify invalid certificates sent by the client in the request. + + + + +Tung & Zhu Expires April 22, 2006 [Page 11] + +Internet-Draft PKINIT October 2005 + + + The client's public key is then used to verify the signature. If the + signature fails to verify, the KDC MUST return an error message with + the code KDC_ERR_INVALID_SIG. There is no accompanying e-data for + this error message. + + In addition to validating the client's signature, the KDC MUST also + check that the client's public key used to verify the client's + signature is bound to the client's principal name as specified in the + AS-REQ as follows: + + 1. If the KDC has its own binding between either the client's + signature-verification public key or the client's certificate and + the client's Kerberos principal name, it uses that binding. + + 2. Otherwise, if the client's X.509 certificate contains a Subject + Alternative Name (SAN) extension carrying a KRB5PrincipalName + (defined below) in the otherName field of the type GeneralName + [RFC3280], it binds the client's X.509 certificate to that name. + + The type of the otherName field is AnotherName. The type-id field + of the type AnotherName is id-pkinit-san: + + id-pkinit-san OBJECT IDENTIFIER ::= + { iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2) + x509SanAN (2) } + + And the value field of the type AnotherName is a + KRB5PrincipalName. + + KRB5PrincipalName ::= SEQUENCE { + realm [0] Realm, + principalName [1] PrincipalName + } + + If the KDC does not have its own binding and there is no + KRB5PrincipalName name present in the client's X.509 certificate, or + if the Kerberos name in the request does not match the + KRB5PrincipalName in the client's X.509 certificate (including the + realm name), the KDC MUST return an error message with the code + KDC_ERR_CLIENT_NAME_MISMATCH. There is no accompanying e-data for + this error message. + + Even if the certification path is validated and the certificate is + mapped to the client's principal name, the KDC may decide not to + accept the client's certificate, depending on local policy. + + The KDC MAY require the presence of an Extended Key Usage (EKU) + KeyPurposeId [RFC3280] id-pkinit-KPClientAuth in the extensions field + + + +Tung & Zhu Expires April 22, 2006 [Page 12] + +Internet-Draft PKINIT October 2005 + + + of the client's X.509 certificate: + + id-pkinit-KPClientAuth OBJECT IDENTIFIER ::= + { iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2) + pkinit(3) keyPurposeClientAuth(4) } + -- PKINIT client authentication. + -- Key usage bits that MUST be consistent: + -- digitalSignature. + + If this EKU KeyPurposeId is required but it is not present or if the + client certificate is restricted not to be used for PKINIT client + authentication per Section 4.2.1.13 of [RFC3280], the KDC MUST return + an error message of the code KDC_ERR_INCONSISTENT_KEY_PURPOSE. There + is no accompanying e-data for this error message. KDCs implementing + this requirement SHOULD also accept the EKU KeyPurposeId id-ms-kp-sc- + logon (1.3.6.1.4.1.311.20.2.2) as meeting the requirement, as there + are a large number of X.509 client certificates deployed for use with + PKINIT which have this EKU. + + As a matter of local policy, the KDC MAY decide to reject requests on + the basis of the absence or presence of other specific EKU OID's. + + If the client's public key is not accepted, the KDC returns an error + message with the code KDC_ERR_CLIENT_NOT_TRUSTED. + + The KDC MUST check the timestamp to ensure that the request is not a + replay, and that the time skew falls within acceptable limits. The + recommendations for clock skew times in [RFC4120] apply here. If the + check fails, the KDC MUST return error code KRB_AP_ERR_REPEAT or + KRB_AP_ERR_SKEW, respectively. + + If the clientPublicValue is filled in, indicating that the client + wishes to use the Diffie-Hellman key agreement method, the KDC SHOULD + check to see if the key parameters satisfy its policy. If they do + not, it MUST return an error message with the code + KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED. The accompanying e-data is a + TYPED-DATA that contains an element whose data-type is + TD_DH_PARAMETERS, and whose data-value contains the DER encoding of + the type TD-DH-PARAMETERS: + + TD-DH-PARAMETERS ::= SEQUENCE OF AlgorithmIdentifier + -- Each AlgorithmIdentifier specifies a set of + -- Diffie-Hellman domain parameters [IEEE1363]. + -- This list is in decreasing preference order. + + TD-DH-PARAMETERS contains a list of Diffie-Hellman domain parameters + that the KDC supports in decreasing preference order, from which the + client SHOULD pick one to retry the request. + + + +Tung & Zhu Expires April 22, 2006 [Page 13] + +Internet-Draft PKINIT October 2005 + + + If the client included a kdcPkId field in the PA-PK-AS-REQ and the + KDC does not possess the corresponding key, the KDC MUST ignore the + kdcPkId field as if the client did not include one. + + If there is a supportedCMSTypes field in the AuthPack, the KDC must + check to see if it supports any of the listed types. If it supports + more than one of the types, the KDC SHOULD use the one listed first. + If it does not support any of them, it MUST return an error message + with the code KDC_ERR_ETYPE_NOSUPP [RFC4120]. + +3.2.3. Generation of KDC Reply + + Assuming that the client's request has been properly validated, the + KDC proceeds as per [RFC4120], except as follows. + + The KDC MUST set the initial flag and include an authorization data + element of ad-type [RFC4120] AD_INITIAL_VERIFIED_CAS in the issued + ticket. The ad-data [RFC4120] field contains the DER encoding of the + type AD-INITIAL-VERIFIED-CAS: + + AD-INITIAL-VERIFIED-CAS ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Identifies the certification path based on which + -- the client certificate was validated. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + + The AS wraps any AD-INITIAL-VERIFIED-CAS data in AD-IF-RELEVANT + containers if the list of CAs satisfies the AS' realm's local policy + (this corresponds to the TRANSITED-POLICY-CHECKED ticket flag + [RFC4120]). Furthermore, any TGS MUST copy such authorization data + from tickets used within a PA-TGS-REQ of the TGS-REQ into the + resulting ticket. If the list of CAs satisfies the local KDC's + realm's policy, the TGS MAY wrap the data into the AD-IF-RELEVANT + container, otherwise it MAY unwrap the authorization data out of the + AD-IF-RELEVANT container. + + Application servers that understand this authorization data type + SHOULD apply local policy to determine whether a given ticket bearing + such a type *not* contained within an AD-IF-RELEVANT container is + acceptable. (This corresponds to the AP server checking the + transited field when the TRANSITED-POLICY-CHECKED flag has not been + set [RFC4120].) If such a data type is contained within an AD-IF- + RELEVANT container, AP servers MAY apply local policy to determine + whether the authorization data is acceptable. + + A pre-authentication data element, whose padata-type is PA_PK_AS_REP + and whose padata-value contains the DER encoding of the type PA-PK- + + + +Tung & Zhu Expires April 22, 2006 [Page 14] + +Internet-Draft PKINIT October 2005 + + + AS-REP (defined below), is included in the AS-REP [RFC4120]. + + PA-PK-AS-REP ::= CHOICE { + dhInfo [0] DHRepInfo, + -- Selected when Diffie-Hellman key exchange is + -- used. + encKeyPack [1] IMPLICIT OCTET STRING, + -- Selected when public key encryption is used. + -- Contains a CMS type ContentInfo encoded + -- according to [RFC3852]. + -- The contentType field of the type ContentInfo is + -- id-envelopedData (1.2.840.113549.1.7.3). + -- The content field is an EnvelopedData. + -- The contentType field for the type EnvelopedData + -- is id-signedData (1.2.840.113549.1.7.2). + -- The eContentType field for the inner type + -- SignedData (when unencrypted) is + -- id-pkinit-rkeyData (1.3.6.1.5.2.3.3) and the + -- eContent field contains the DER encoding of the + -- type ReplyKeyPack. + -- ReplyKeyPack is defined in Section 3.2.3.2. + ... + } + + DHRepInfo ::= SEQUENCE { + dhSignedData [0] IMPLICIT OCTET STRING, + -- Contains a CMS type ContentInfo encoded according + -- to [RFC3852]. + -- The contentType field of the type ContentInfo is + -- id-signedData (1.2.840.113549.1.7.2), and the + -- content field is a SignedData. + -- The eContentType field for the type SignedData is + -- id-pkinit-DHKeyData (1.3.6.1.5.2.3.2), and the + -- eContent field contains the DER encoding of the + -- type KDCDHKeyInfo. + -- KDCDHKeyInfo is defined below. + serverDHNonce [1] DHNonce OPTIONAL + -- Present if and only if dhKeyExpiration is + -- present in the KDCDHKeyInfo. + } + + KDCDHKeyInfo ::= SEQUENCE { + subjectPublicKey [0] BIT STRING, + -- KDC's DH public key. + -- The DH public key value is encoded as a BIT + -- STRING according to [RFC3279]. + nonce [1] INTEGER (0..4294967295), + -- Contains the nonce in the PKAuthenticator of the + + + +Tung & Zhu Expires April 22, 2006 [Page 15] + +Internet-Draft PKINIT October 2005 + + + -- request if DH keys are NOT reused, + -- 0 otherwise. + dhKeyExpiration [2] KerberosTime OPTIONAL, + -- Expiration time for KDC's key pair, + -- present if and only if DH keys are reused. If + -- this field is omitted then the serverDHNonce + -- field MUST also be omitted. See Section 3.2.3.1. + ... + } + + The content of the AS-REP is otherwise unchanged from [RFC4120]. The + KDC encrypts the reply as usual, but not with the client's long-term + key. Instead, it encrypts it with either a shared key derived from a + Diffie-Hellman exchange, or a generated encryption key. The contents + of the PA-PK-AS-REP indicate which key delivery method is used. + + In addition, the lifetime of the ticket returned by the KDC MUST NOT + exceed that of the client's public-private key pair. The ticket + lifetime, however, can be shorter than that of the client's public- + private key pair. For the implementations of this specification, the + lifetime of the client's public-private key pair is the validity + period in X.509 certificates [RFC3280], unless configured otherwise. + +3.2.3.1. Using Diffie-Hellman Key Exchange + + In this case, the PA-PK-AS-REP contains a DHRepInfo structure. + + The ContentInfo [RFC3852] structure for the dhSignedData field is + filled in as follows: + + 1. The contentType field of the type ContentInfo is id-signedData + (as defined in [RFC3852]), and the content field is a SignedData + (as defined in [RFC3852]). + + 2. The eContentType field for the type SignedData is the OID value + for id-pkinit-DHKeyData: { iso(1) org(3) dod(6) internet(1) + security(5) kerberosv5(2) pkinit(3) DHKeyData(2) }. + + 3. The eContent field for the type SignedData contains the DER + encoding of the type KDCDHKeyInfo. + + 4. The signerInfos field of the type SignedData contains a single + signerInfo, which contains the signature over the type + KDCDHKeyInfo. + + 5. The certificates field of the type SignedData contains + certificates intended to facilitate certification path + construction, so that the client can verify the KDC's signature + + + +Tung & Zhu Expires April 22, 2006 [Page 16] + +Internet-Draft PKINIT October 2005 + + + over the type KDCDHKeyInfo. The information contained in the + trustedCertifiers in the request SHOULD be used by the KDC as + hints to guide its selection of an appropriate certificate chain + to return to the client. This field may only. be left empty if + the KDC public key specified by the kdcPkId field in the PA-PK- + AS-REQ was used for signing. Otherwise, for path validation, + these certificates SHOULD be sufficient to construct at least one + certification path from the KDC certificate to one trust anchor + acceptable by the client [CAPATH]. The KDC MUST be capable of + including such a set of certificates if configured to do so. The + certificates field MUST NOT contain "root" CA certificates. + + 6. If the client included the clientDHNonce field, then the KDC may + choose to reuse its DH keys (see Section 3.2.3.1). If the server + reuses DH keys then it MUST include an expiration time in the + dhKeyExpiration field. Past the point of the expiration time, + the signature over the type DHRepInfo is considered expired/ + invalid. When the server reuses DH keys then it MUST include a + serverDHNonce at least as long as the length of keys for the + symmetric encryption system used to encrypt the AS reply. Note + that including the serverDHNonce changes how the client and + server calculate the key to use to encrypt the reply; see below + for details. The KDC SHOULD NOT reuse DH keys unless the + clientDHNonce field is present in the request. + + The AS reply key is derived as follows: + + 1. Both the KDC and the client calculate the shared secret value as + follows: + + a) When MODP Diffie-Hellman is used, let DHSharedSecret be the + shared secret value. DHSharedSecret is the value ZZ as + described in Section 2.1.1 of [RFC2631]. + + DHSharedSecret is first padded with leading zeros such that the + size of DHSharedSecret in octets is the same as that of the + modulus, then represented as a string of octets in big-endian + order. + + Implementation note: Both the client and the KDC can cache the + triple (ya, yb, DHSharedSecret), where ya is the client's public + key and yb is the KDC's public key. If both ya and yb are the + same in a later exchange, the cached DHSharedSecret can be used. + + + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 17] + +Internet-Draft PKINIT October 2005 + + + 2. Let K be the key-generation seed length [RFC3961] of the AS reply + key whose enctype is selected according to [RFC4120]. + + 3. Define the function octetstring2key() as follows: + + octetstring2key(x) == random-to-key(K-truncate( + SHA1(0x00 | x) | + SHA1(0x01 | x) | + SHA1(0x02 | x) | + ... + )) + + where x is an octet string; | is the concatenation operator; 0x00, + 0x01, 0x02, etc., are each represented as a single octet; random- + to-key() is an operation that generates a protocol key from a + bitstring of length K; and K-truncate truncates its input to the + first K bits. Both K and random-to-key() are as defined in the + kcrypto profile [RFC3961] for the enctype of the AS reply key. + + 4. When DH keys are reused, let n_c be the clientDHNonce, and n_k be + the serverDHNonce; otherwise, let both n_c and n_k be empty octet + strings. + + 5. The AS reply key k is: + + k = octetstring2key(DHSharedSecret | n_c | n_k) + +3.2.3.2. Using Public Key Encryption + + In this case, the PA-PK-AS-REP contains a ContentInfo structure + wrapped in an OCTET STRING. The AS reply key is encrypted in the + encKeyPack field, which contains data of type ReplyKeyPack: + + + + + + + + + + + + + + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 18] + +Internet-Draft PKINIT October 2005 + + + ReplyKeyPack ::= SEQUENCE { + replyKey [0] EncryptionKey, + -- Contains the session key used to encrypt the + -- enc-part field in the AS-REP. + asChecksum [1] Checksum, + -- Contains the checksum of the AS-REQ + -- corresponding to the containing AS-REP. + -- The checksum is performed over the type AS-REQ. + -- The protocol key [RFC3961] of the checksum is the + -- replyKey and the key usage number is 6. + -- If the replyKey's enctype is "newer" [RFC4120] + -- [RFC4121], the checksum is the required + -- checksum operation [RFC3961] for that enctype. + -- The client MUST verify this checksum upon receipt + -- of the AS-REP. + ... + } + + The ContentInfo [RFC3852] structure for the encKeyPack field is + filled in as follows: + + 1. The contentType field of the type ContentInfo is id-envelopedData + (as defined in [RFC3852]), and the content field is an + EnvelopedData (as defined in [RFC3852]). + + 2. The contentType field for the type EnvelopedData is id- + signedData: { iso (1) member-body (2) us (840) rsadsi (113549) + pkcs (1) pkcs7 (7) signedData (2) }. + + 3. The eContentType field for the inner type SignedData (when + decrypted from the encryptedContent field for the type + EnvelopedData) is id-pkinit-rkeyData: { iso(1) org(3) dod(6) + internet(1) security(5) kerberosv5(2) pkinit(3) rkeyData(3) }. + + 4. The eContent field for the inner type SignedData contains the DER + encoding of the type ReplyKeyPack. + + 5. The signerInfos field of the inner type SignedData contains a + single signerInfo, which contains the signature over the type + ReplyKeyPack. + + 6. The certificates field of the inner type SignedData contains + certificates intended to facilitate certification path + construction, so that the client can verify the KDC's signature + over the type ReplyKeyPack. The information contained in the + trustedCertifiers in the request SHOULD be used by the KDC as + hints to guide its selection of an appropriate certificate chain + to return to the client. This field may only be left empty if + + + +Tung & Zhu Expires April 22, 2006 [Page 19] + +Internet-Draft PKINIT October 2005 + + + the KDC public key specified by the kdcPkId field in the PA-PK- + AS-REQ was used for signing. Otherwise, for path validation, + these certificates SHOULD be sufficient to construct at least one + certification path from the KDC certificate to one trust anchor + acceptable by the client [CAPATH]. The KDC MUST be capable of + including such a set of certificates if configured to do so. The + certificates field MUST NOT contain "root" CA certificates. + + 7. The recipientInfos field of the type EnvelopedData is a SET which + MUST contain exactly one member of type KeyTransRecipientInfo. + The encryptedKey of this member contains the temporary key which + is encrypted using the client's public key. + + 8. The unprotectedAttrs or originatorInfo fields of the type + EnvelopedData MAY be present. + + Implementations of this RSA encryption key delivery method are + RECOMMENDED to support for RSA keys at least 2048 bits in size. + +3.2.4. Receipt of KDC Reply + + Upon receipt of the KDC's reply, the client proceeds as follows. If + the PA-PK-AS-REP contains the dhSignedData field, the client derives + the AS reply key using the same procedure used by the KDC as defined + in Section 3.2.3.1. Otherwise, the message contains the encKeyPack + field, and the client decrypts and extracts the temporary key in the + encryptedKey field of the member KeyTransRecipientInfo, and then uses + that as the AS reply key. + + If the public key encryption method is used, the client MUST verify + the asChecksum contained in the ReplyKeyPack. + + In either case, the client MUST verify the signature in the + SignedData according to [RFC3852]. The KDC's X.509 certificate MUST + be validated according to [RFC3280]. In addition, unless the client + can otherwise verify that the public key used to verify the KDC's + signature is bound to the KDC of the target realm, the KDC's X.509 + certificate MUST contain a Subject Alternative Name extension + [RFC3280] carrying an AnotherName whose type-id is id-pkinit-san (as + defined in Section 3.2.2) and whose value is a KRB5PrincipalName that + matches the name of the TGS of the target realm (as defined in + Section 7.3 of [RFC4120]). + + Unless the client knows by some other means that the KDC certificate + is intended for a Kerberos KDC, the client MUST require that the KDC + certificate contains the EKU KeyPurposeId [RFC3280] id-pkinit-KPKdc: + + + + + +Tung & Zhu Expires April 22, 2006 [Page 20] + +Internet-Draft PKINIT October 2005 + + + id-pkinit-KPKdc OBJECT IDENTIFIER ::= + { iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2) + pkinit(3) keyPurposeKdc(5) } + -- Signing KDC responses. + -- Key usage bits that MUST be consistent: + -- digitalSignature. + + If the KDC certificate contains the Kerberos TGS name encoded as an + id-pkinit-san SAN, this certificate is certified by the issuing CA as + a KDC certificate, therefore the id-pkinit-KPKdc EKU is not required. + + If all applicable checks are satisfied, the client then decrypts the + enc-part field of the KDC-REP in the AS-REP using the AS reply key, + and then proceeds as described in [RFC4120]. + + Implementation note: CAs issuing KDC certificates SHOULD place all + "short" and "fully-qualified" Kerberos realm names of the KDC (one + per GeneralName [RFC3280]) into the KDC certificate to allow maximum + flexibility. + +3.3. Interoperability Requirements + + The client MUST be capable of sending a set of certificates + sufficient to allow the KDC to construct a certification path for the + client's certificate, if the correct set of certificates is provided + through configuration or policy. + + If the client sends all the X.509 certificates on a certification + path to a trust anchor acceptable by the KDC, and the KDC can not + verify the client's public key otherwise, the KDC MUST be able to + process path validation for the client's certificate based on the + certificates in the request. + + The KDC MUST be capable of sending a set of certificates sufficient + to allow the client to construct a certification path for the KDC's + certificate, if the correct set of certificates is provided through + configuration or policy. + + If the KDC sends all the X.509 certificates on a certification path + to a trust anchor acceptable by the client, and the client can not + verify the KDC's public key otherwise, the client MUST be able to + process path validation for the KDC's certificate based on the + certificates in the reply. + +3.4. KDC Indication of PKINIT Support + + If pre-authentication is required, but was not present in the + request, per [RFC4120] an error message with the code + + + +Tung & Zhu Expires April 22, 2006 [Page 21] + +Internet-Draft PKINIT October 2005 + + + KDC_ERR_PREAUTH_FAILED is returned and a METHOD-DATA object will be + stored in the e-data field of the KRB-ERROR message to specify which + pre-authentication mechanisms are acceptable. The KDC can then + indicate the support of PKINIT by including an empty element whose + padata-type is PA_PK_AS_REQ in that METHOD-DATA object. + + Otherwise if it is required by the KDC's local policy that the client + must be pre-authenticated using the pre-authentication mechanism + specified in this document, but no PKINIT pre-authentication was + present in the request, an error message with the code + KDC_ERR_PREAUTH_FAILED SHOULD be returned. + + KDCs MUST leave the padata-value field of the PA_PK_AS_REQ element in + the KRB-ERROR's METHOD-DATA empty (i.e., send a zero-length OCTET + STRING), and clients MUST ignore this and any other value. Future + extensions to this protocol may specify other data to send instead of + an empty OCTET STRING. + + +4. Security Considerations + + Kerberos error messages are not integrity protected, as a result, the + domain parameters sent by the KDC as TD-DH-PARAMETERS can be tampered + with by an attacker so that the set of domain parameters selected + could be either weaker or not mutually preferred. Local policy can + configure sets of domain parameters acceptable locally, or disallow + the negotiation of DH domain parameters. + + The symmetric reply key size and Diffie-Hellman field size or RSA + modulus size should be chosen so as to provide sufficient + cryptographic security [RFC3766]. + + When MODP Diffie-Hellman is used, the exponents should have at least + twice as many bits as the symmetric keys that will be derived from + them [ODL99]. + + PKINIT raises certain security considerations beyond those that can + be regulated strictly in protocol definitions. We will address them + in this section. + + PKINIT extends the cross-realm model to the public-key + infrastructure. Users of PKINIT must understand security policies + and procedures appropriate to the use of Public Key Infrastructures + [RFC3280]. + + In order to trust a KDC certificate that is certified by a CA as a + KDC certificate for a target realm (for example, by asserting the TGS + name of that Kerberos realm as an id-pkinit-san SAN and/or + + + +Tung & Zhu Expires April 22, 2006 [Page 22] + +Internet-Draft PKINIT October 2005 + + + restricting the certificate usage by using the id-pkinit-KPKdc EKU, + as described in Section 3.2.4), the client MUST verify that the KDC + certificate's issuing CA is authorized to issue KDC certificates for + that target realm. Otherwise, the binding between the KDC + certificate and the KDC of the target realm is not established. + + How to validate this authorization is a matter of local policy. A + way to achieve this is the configuration of specific sets of + intermediary CAs and trust anchors, one of which must be on the KDC + certificate's certification path [RFC3280]; and for each CA or trust + anchor the realms for which it is allowed to issue certificates. + + In addition, if any CA is trusted to issue KDC certificates can also + issue other kinds of certificates, then local policy must be able to + distinguish between them: for example, it could require that KDC + certificates contain the id-pkinit-KPKdc EKU or that the realm be + specified with the id-pkinit-san SAN. + + It is the responsibility of the PKI administrators for an + organization to ensure that KDC certificates are only issued to KDCs, + and that clients can ascertain this using their local policy. + + Standard Kerberos allows the possibility of interactions between + cryptosystems of varying strengths; this document adds interactions + with public-key cryptosystems to Kerberos. Some administrative + policies may allow the use of relatively weak public keys. Using + such keys to wrap data encrypted under stronger conventional + cryptosystems may be inappropriate. + + PKINIT requires keys for symmetric cryptosystems to be generated. + Some such systems contain "weak" keys. For recommendations regarding + these weak keys, see [RFC4120]. + + PKINIT allows the use of the same RSA key pair for encryption and + signing when doing RSA encryption based key delivery. This is not + recommended usage of RSA keys [RFC3447], by using DH based key + delivery this is avoided. + + Care should be taken in how certificates are chosen for the purposes + of authentication using PKINIT. Some local policies may require that + key escrow be used for certain certificate types. Deployers of + PKINIT should be aware of the implications of using certificates that + have escrowed keys for the purposes of authentication. Because + signing only certificates are normally not escrowed, by using DH + based key delivery this is avoided. + + PKINIT does not provide for a "return routability" test to prevent + attackers from mounting a denial-of-service attack on the KDC by + + + +Tung & Zhu Expires April 22, 2006 [Page 23] + +Internet-Draft PKINIT October 2005 + + + causing it to perform unnecessary and expensive public-key + operations. Strictly speaking, this is also true of standard + Kerberos, although the potential cost is not as great, because + standard Kerberos does not make use of public-key cryptography. By + using DH based key delivery and reusing DH keys, the necessary crypto + processing cost per request can be minimized. + + The syntax for the AD-INITIAL-VERIFIED-CAS authorization data does + permit empty SEQUENCEs to be encoded. Such empty sequences may only + be used if the KDC itself vouches for the user's certificate. + + +5. Acknowledgements + + The following people have made significant contributions to this + draft: Paul Leach, Stefan Santesson, Sam Hartman, Love Hornquist + Astrand, Ken Raeburn, Nicolas Williams, John Wray, Jonathan Trostle, + Tom Yu, Jeffrey Hutzelman, David Cross, Dan Simon, Karthik + Jaganathan, and Chaskiel M Grundman. + + Andre Scedrov, Aaron D. Jaggard, Iliano Cervesato, Joe-Kai Tsay and + Chris Walstad discovered a binding issue between the AS-REQ and AS- + REP in draft -26, the asChecksum field was added as the result. + + Special thanks to Clifford Neuman, Matthew Hur, Sasha Medvinsky and + Jonathan Trostle who wrote earlier versions of this document. + + The authors are indebted to the Kerberos working group chair Jeffrey + Hutzelman who kept track of various issues and was enormously helpful + during the creation of this document. + + Some of the ideas on which this document is based arose during + discussions over several years between members of the SAAG, the IETF + CAT working group, and the PSRG, regarding integration of Kerberos + and SPX. Some ideas have also been drawn from the DASS system. + These changes are by no means endorsed by these groups. This is an + attempt to revive some of the goals of those groups, and this + document approaches those goals primarily from the Kerberos + perspective. + + Lastly, comments from groups working on similar ideas in DCE have + been invaluable. + + +6. IANA Considerations + + This document has no actions for IANA. + + + + +Tung & Zhu Expires April 22, 2006 [Page 24] + +Internet-Draft PKINIT October 2005 + + +7. References + +7.1. Normative References + + [IEEE1363] + IEEE, "Standard Specifications for Public Key + Cryptography", IEEE 1363, 2000. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2412] Orman, H., "The OAKLEY Key Determination Protocol", + RFC 2412, November 1998. + + [RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method", + RFC 2631, June 1999. + + [RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and + Identifiers for the Internet X.509 Public Key + Infrastructure Certificate and Certificate Revocation List + (CRL) Profile", RFC 3279, April 2002. + + [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + [RFC3370] Housley, R., "Cryptographic Message Syntax (CMS) + Algorithms", RFC 3370, August 2002. + + [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography + Standards (PKCS) #1: RSA Cryptography Specifications + Version 2.1", RFC 3447, February 2003. + + [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + Diffie-Hellman groups for Internet Key Exchange (IKE)", + RFC 3526, May 2003. + + [RFC3565] Schaad, J., "Use of the Advanced Encryption Standard (AES) + Encryption Algorithm in Cryptographic Message Syntax + (CMS)", RFC 3565, July 2003. + + [RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For + Public Keys Used For Exchanging Symmetric Keys", BCP 86, + RFC 3766, April 2004. + + [RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", + RFC 3852, July 2004. + + + +Tung & Zhu Expires April 22, 2006 [Page 25] + +Internet-Draft PKINIT October 2005 + + + [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for + Kerberos 5", RFC 3961, February 2005. + + [RFC3962] Raeburn, K., "Advanced Encryption Standard (AES) + Encryption for Kerberos 5", RFC 3962, February 2005. + + [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The + Kerberos Network Authentication Service (V5)", RFC 4120, + July 2005. + + [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos + Version 5 Generic Security Service Application Program + Interface (GSS-API) Mechanism: Version 2", RFC 4121, + July 2005. + + [X.509-97] ITU-T Recommendation X.509: The Directory - Authentication + Framework, 1997. + + [X680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, + Information technology - Abstract Syntax Notation One + (ASN.1): Specification of basic notation. + + [X690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, + Information technology - ASN.1 encoding Rules: Specification + of Basic Encoding Rules (BER), Canonical Encoding Rules + (CER) and Distinguished Encoding Rules (DER). + +7.2. Informative References + + [CAPATH] RFC-Editor: To be replaced by RFC number for draft-ietf- + pkix-certpathbuild. Work in Progress. + + [LENSTRA] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key + Sizes", Journal of Cryptology 14 (2001) 255-293. + + [ODL99] Odlyzko, A., "Discrete logarithms: The past and the + future, Designs, Codes, and Cryptography (1999)". + + +Appendix A. PKINIT ASN.1 Module + + KerberosV5-PK-INIT-SPEC { + iso(1) identified-organization(3) dod(6) internet(1) + security(5) kerberosV5(2) modules(4) pkinit(5) + } DEFINITIONS EXPLICIT TAGS ::= BEGIN + + IMPORTS + + + +Tung & Zhu Expires April 22, 2006 [Page 26] + +Internet-Draft PKINIT October 2005 + + + SubjectPublicKeyInfo, AlgorithmIdentifier + FROM PKIX1Explicit88 { iso (1) + identified-organization (3) dod (6) internet (1) + security (5) mechanisms (5) pkix (7) id-mod (0) + id-pkix1-explicit (18) } + -- As defined in RFC 3280. + + KerberosTime, PrincipalName, Realm, EncryptionKey + FROM KerberosV5Spec2 { iso(1) identified-organization(3) + dod(6) internet(1) security(5) kerberosV5(2) + modules(4) krb5spec2(2) } ; + + id-pkinit OBJECT IDENTIFIER ::= + { iso (1) org (3) dod (6) internet (1) security (5) + kerberosv5 (2) pkinit (3) } + + id-pkinit-authData OBJECT IDENTIFIER ::= { id-pkinit 1 } + id-pkinit-DHKeyData OBJECT IDENTIFIER ::= { id-pkinit 2 } + id-pkinit-rkeyData OBJECT IDENTIFIER ::= { id-pkinit 3 } + id-pkinit-KPClientAuth OBJECT IDENTIFIER ::= { id-pkinit 4 } + id-pkinit-KPKdc OBJECT IDENTIFIER ::= { id-pkinit 5 } + + id-pkinit-san OBJECT IDENTIFIER ::= + { iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2) + x509SanAN (2) } + + pa-pk-as-req INTEGER ::= 16 + pa-pk-as-rep INTEGER ::= 17 + + ad-initial-verified-cas INTEGER ::= 9 + + td-trusted-certifiers INTEGER ::= 104 + td-invalid-certificates INTEGER ::= 105 + td-dh-parameters INTEGER ::= 109 + + PA-PK-AS-REQ ::= SEQUENCE { + signedAuthPack [0] IMPLICIT OCTET STRING, + -- Contains a CMS type ContentInfo encoded + -- according to [RFC3852]. + -- The contentType field of the type ContentInfo + -- is id-signedData (1.2.840.113549.1.7.2), + -- and the content field is a SignedData. + -- The eContentType field for the type SignedData is + -- id-pkinit-authData (1.3.6.1.5.2.3.1), and the + -- eContent field contains the DER encoding of the + -- type AuthPack. + -- AuthPack is defined below. + trustedCertifiers [1] SEQUENCE OF + + + +Tung & Zhu Expires April 22, 2006 [Page 27] + +Internet-Draft PKINIT October 2005 + + + ExternalPrincipalIdentifier OPTIONAL, + -- A list of CAs, trusted by the client, that can + -- be used to certify the KDC. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + -- The information contained in the + -- trustedCertifiers SHOULD be used by the KDC as + -- hints to guide its selection of an appropriate + -- certificate chain to return to the client. + kdcPkId [2] IMPLICIT OCTET STRING + OPTIONAL, + -- Contains a CMS type SignerIdentifier encoded + -- according to [RFC3852]. + -- Identifies, if present, a particular KDC + -- public key that the client already has. + ... + } + + DHNonce ::= OCTET STRING + + ExternalPrincipalIdentifier ::= SEQUENCE { + subjectName [0] IMPLICIT OCTET STRING OPTIONAL, + -- Contains a PKIX type Name encoded according to + -- [RFC3280]. + -- Identifies the certificate subject by the + -- distinguished subject name. + -- REQUIRED when there is a distinguished subject + -- name present in the certificate. + issuerAndSerialNumber [1] IMPLICIT OCTET STRING OPTIONAL, + -- Contains a CMS type IssuerAndSerialNumber encoded + -- according to [RFC3852]. + -- Identifies a certificate of the subject. + -- REQUIRED for TD-INVALID-CERTIFICATES and + -- TD-TRUSTED-CERTIFIERS. + subjectKeyIdentifier [2] IMPLICIT OCTET STRING OPTIONAL, + -- Identifies the subject's public key by a key + -- identifier. When an X.509 certificate is + -- referenced, this key identifier matches the X.509 + -- subjectKeyIdentifier extension value. When other + -- certificate formats are referenced, the documents + -- that specify the certificate format and their use + -- with the CMS must include details on matching the + -- key identifier to the appropriate certificate + -- field. + -- RECOMMENDED for TD-TRUSTED-CERTIFIERS. + ... + } + + + + +Tung & Zhu Expires April 22, 2006 [Page 28] + +Internet-Draft PKINIT October 2005 + + + AuthPack ::= SEQUENCE { + pkAuthenticator [0] PKAuthenticator, + clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL, + -- Type SubjectPublicKeyInfo is defined in + -- [RFC3280]. + -- Specifies Diffie-Hellman domain parameters + -- and the client's public key value [IEEE1363]. + -- The DH public key value is encoded as a BIT + -- STRING according to [RFC3279]. + -- This field is present only if the client wishes + -- to use the Diffie-Hellman key agreement method. + supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier + OPTIONAL, + -- Type AlgorithmIdentifier is defined in + -- [RFC3280]. + -- List of CMS encryption types supported by the + -- client in order of (decreasing) preference. + clientDHNonce [3] DHNonce OPTIONAL, + -- Present only if the client indicates that it + -- wishes to reuse DH keys or to allow the KDC to + -- do so. + ... + } + + PKAuthenticator ::= SEQUENCE { + cusec [0] INTEGER (0..999999), + ctime [1] KerberosTime, + -- cusec and ctime are used as in [RFC4120], for + -- replay prevention. + nonce [2] INTEGER (0..4294967295), + -- Chosen randomly; This nonce does not need to + -- match with the nonce in the KDC-REQ-BODY. + paChecksum [3] OCTET STRING, + -- Contains the SHA1 checksum, performed over + -- KDC-REQ-BODY. + ... + } + + TD-TRUSTED-CERTIFIERS ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Identifies a list of CAs trusted by the KDC. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + + TD-INVALID-CERTIFICATES ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Each ExternalPrincipalIdentifier identifies a + -- certificate (sent by the client) with an invalid + + + +Tung & Zhu Expires April 22, 2006 [Page 29] + +Internet-Draft PKINIT October 2005 + + + -- signature. + + KRB5PrincipalName ::= SEQUENCE { + realm [0] Realm, + principalName [1] PrincipalName + } + + AD-INITIAL-VERIFIED-CAS ::= SEQUENCE OF + ExternalPrincipalIdentifier + -- Identifies the certification path based on which + -- the client certificate was validated. + -- Each ExternalPrincipalIdentifier identifies a CA + -- or a CA certificate (thereby its public key). + + PA-PK-AS-REP ::= CHOICE { + dhInfo [0] DHRepInfo, + -- Selected when Diffie-Hellman key exchange is + -- used. + encKeyPack [1] IMPLICIT OCTET STRING, + -- Selected when public key encryption is used. + -- Contains a CMS type ContentInfo encoded + -- according to [RFC3852]. + -- The contentType field of the type ContentInfo is + -- id-envelopedData (1.2.840.113549.1.7.3). + -- The content field is an EnvelopedData. + -- The contentType field for the type EnvelopedData + -- is id-signedData (1.2.840.113549.1.7.2). + -- The eContentType field for the inner type + -- SignedData (when unencrypted) is + -- id-pkinit-rkeyData (1.3.6.1.5.2.3.3) and the + -- eContent field contains the DER encoding of the + -- type ReplyKeyPack. + -- ReplyKeyPack is defined below. + ... + } + + DHRepInfo ::= SEQUENCE { + dhSignedData [0] IMPLICIT OCTET STRING, + -- Contains a CMS type ContentInfo encoded according + -- to [RFC3852]. + -- The contentType field of the type ContentInfo is + -- id-signedData (1.2.840.113549.1.7.2), and the + -- content field is a SignedData. + -- The eContentType field for the type SignedData is + -- id-pkinit-DHKeyData (1.3.6.1.5.2.3.2), and the + -- eContent field contains the DER encoding of the + -- type KDCDHKeyInfo. + -- KDCDHKeyInfo is defined below. + + + +Tung & Zhu Expires April 22, 2006 [Page 30] + +Internet-Draft PKINIT October 2005 + + + serverDHNonce [1] DHNonce OPTIONAL + -- Present if and only if dhKeyExpiration is + -- present. + } + + KDCDHKeyInfo ::= SEQUENCE { + subjectPublicKey [0] BIT STRING, + -- KDC's DH public key. + -- The DH public key value is encoded as a BIT + -- STRING according to [RFC3279]. + nonce [1] INTEGER (0..4294967295), + -- Contains the nonce in the PKAuthenticator of the + -- request if DH keys are NOT reused, + -- 0 otherwise. + dhKeyExpiration [2] KerberosTime OPTIONAL, + -- Expiration time for KDC's key pair, + -- present if and only if DH keys are reused. If + -- this field is omitted then the serverDHNonce + -- field MUST also be omitted. + ... + } + + ReplyKeyPack ::= SEQUENCE { + replyKey [0] EncryptionKey, + -- Contains the session key used to encrypt the + -- enc-part field in the AS-REP. + asChecksum [1] Checksum, + -- Contains the checksum of the AS-REQ + -- corresponding to the containing AS-REP. + -- The checksum is performed over the type AS-REQ. + -- The protocol key [RFC3961] of the checksum is the + -- replyKey and the key usage number is 6. + -- If the replyKey's enctype is "newer" [RFC4120] + -- [RFC4121], the checksum is the required + -- checksum operation [RFC3961] for that enctype. + -- The client MUST verify this checksum upon receipt + -- of the AS-REP. + ... + } + + TD-DH-PARAMETERS ::= SEQUENCE OF AlgorithmIdentifier + -- Each AlgorithmIdentifier specifies a set of + -- Diffie-Hellman domain parameters [IEEE1363]. + -- This list is in decreasing preference order. + END + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 31] + +Internet-Draft PKINIT October 2005 + + +Appendix B. Test Vectors + + Function octetstring2key() is defined in Section 3.2.3.1. This + section describes a few sets of test vectors that would be useful for + implementers of octetstring2key(). + + + Set 1 + ===== + Input octet string x is: + + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + + Output of K-truncate() when the key size is 32 octets: + + 5e e5 0d 67 5c 80 9f e5 9e 4a 77 62 c5 4b 65 83 + 75 47 ea fb 15 9b d8 cd c7 5f fc a5 91 1e 4c 41 + + + Set 2: + ===== + Input octet string x is: + + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + + Output of K-truncate() when the key size is 32 octets: + + + +Tung & Zhu Expires April 22, 2006 [Page 32] + +Internet-Draft PKINIT October 2005 + + + ac f7 70 7c 08 97 3d df db 27 cd 36 14 42 cc fb + a3 55 c8 88 4c b4 72 f3 7d a6 36 d0 7d 56 78 7e + + + Set 3: + ====== + Input octet string x is: + + 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f + 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e + 0f 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d + 0e 0f 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c + 0d 0e 0f 10 00 01 02 03 04 05 06 07 08 09 0a 0b + 0c 0d 0e 0f 10 00 01 02 03 04 05 06 07 08 09 0a + 0b 0c 0d 0e 0f 10 00 01 02 03 04 05 06 07 08 09 + 0a 0b 0c 0d 0e 0f 10 00 01 02 03 04 05 06 07 08 + + Output of K-truncate() when the key size is 32 octets: + + c4 42 da 58 5f cb 80 e4 3b 47 94 6f 25 40 93 e3 + 73 29 d9 90 01 38 0d b7 83 71 db 3a cf 5c 79 7e + + + Set 4: + ===== + Input octet string x is: + + 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f + 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e + 0f 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d + 0e 0f 10 00 01 02 03 04 05 06 07 08 09 0a 0b 0c + 0d 0e 0f 10 00 01 02 03 04 05 06 07 08 + + Output of K-truncate() when the key size is 32 octets: + + 00 53 95 3b 84 c8 96 f4 eb 38 5c 3f 2e 75 1c 4a + 59 0e d6 ff ad ca 6f f6 4f 47 eb eb 8d 78 0f fc + + +Appendix C. Miscellaneous Information about Microsoft Windows PKINIT + Implementations + + Earlier revisions of the PKINIT I-D were implemented in various + releases of Microsoft Windows and deployed in fairly large numbers. + To enable the community to better interoperate with systems running + those releases, the following information may be useful. + + KDC certificates issued by Windows 2000 Enterprise CAs contain a + + + +Tung & Zhu Expires April 22, 2006 [Page 33] + +Internet-Draft PKINIT October 2005 + + + dNSName SAN with the DNS name of the host running the KDC, and the + id-kp-serverAuth EKU [RFC3280]. + + KDC certificates issued by Windows 2003 Enterprise CAs contain a + dNSName SAN with the DNS name of the host running the KDC, the id-kp- + serverAuth EKU and the id-ms-kp-sc-logon EKU. + + It is anticipated that the next release of Windows is already too far + along to allow it to support the issuing KDC certificates with id- + pkinit-san SAN as specified in this RFC. Instead, they will have a + dNSName SAN containing the domain name of the KDC and the intended + purpose of these KDC certificates be restricted by the presence of + the id-pkinit-KPKdc EKU and id-kp-serverAuth EKU. + + In addition to checking that the above are present in a KDC + certificate, Windows clients verify that the issuer of the KDC + certificate is one of a set of allowed issuers of such certificates, + so those wishing to issue KDC certificates need to configure their + Windows clients appropriately. + + Client certificates accepted by Windows 2000 and Windows 2003 Server + KDCs must contain an id-ms-san-sc-logon-upn (1.3.6.1.4.1.311.20.2.3) + SAN and the id-ms-kp-sc-logon EKU. The id-ms-san-sc-logon-upn SAN + contains a UTF8 encoded string whose value is that of the Directory + Service attribute UserPrincipalName of the client account object, and + the purpose of including the id-ms-san-sc-logon-upn SAN in the client + certificate is to validate the client mapping (in other words, the + client's public key is bound to the account that has this + UserPrincipalName value). + + It should be noted that all Microsoft Kerberos realm names are domain + style realm names and strictly in upper case. In addition, the + UserPrincipalName attribute is globally unique in Windows 2000 and + Windows 2003. + + + + + + + + + + + + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 34] + +Internet-Draft PKINIT October 2005 + + +Authors' Addresses + + Brian Tung + USC Information Sciences Institute + 4676 Admiralty Way Suite 1001 + Marina del Rey, CA 90292 + US + + Email: brian@isi.edu + + + Larry Zhu + Microsoft Corporation + One Microsoft Way + Redmond, WA 98052 + US + + Email: lzhu@microsoft.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Tung & Zhu Expires April 22, 2006 [Page 35] + +Internet-Draft PKINIT October 2005 + + +Intellectual Property Statement + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + +Disclaimer of Validity + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM 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. + + +Copyright Statement + + Copyright (C) The Internet Society (2005). This document is subject + to the rights, licenses and restrictions contained in BCP 78, and + except as set forth therein, the authors retain all their rights. + + +Acknowledgment + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + +Tung & Zhu Expires April 22, 2006 [Page 36] + + |