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author | Ken Raeburn <raeburn@mit.edu> | 2008-10-10 20:14:25 +0000 |
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committer | Ken Raeburn <raeburn@mit.edu> | 2008-10-10 20:14:25 +0000 |
commit | 7a03f1e6de24c6acf6e4d9ca1257c6dab2b0fa7c (patch) | |
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PKINIT specs, draft 9 and final standard
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diff --git a/doc/krb5-protocol/draft-ietf-cat-kerberos-pk-init-09.txt b/doc/krb5-protocol/draft-ietf-cat-kerberos-pk-init-09.txt new file mode 100644 index 0000000..748f089 --- /dev/null +++ b/doc/krb5-protocol/draft-ietf-cat-kerberos-pk-init-09.txt @@ -0,0 +1,908 @@ +INTERNET-DRAFT Brian Tung +draft-ietf-cat-kerberos-pk-init-09.txt Clifford Neuman +Updates: RFC 1510 ISI +expires December 1, 1999 Matthew Hur + CyberSafe Corporation + Ari Medvinsky + Excite + Sasha Medvinsky + General Instrument + John Wray + Iris Associates, Inc. + Jonathan Trostle + Cisco + + Public Key Cryptography for Initial Authentication in Kerberos + +0. Status Of This Memo + + This document is an Internet-Draft and is in full conformance with + all provisions of Section 10 of RFC 2026. 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. + + To learn the current status of any Internet-Draft, please check + the "1id-abstracts.txt" listing contained in the Internet-Drafts + Shadow Directories on ftp.ietf.org (US East Coast), + nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or + munnari.oz.au (Pacific Rim). + + The distribution of this memo is unlimited. It is filed as + draft-ietf-cat-kerberos-pk-init-09.txt, and expires December 1, + 1999. Please send comments to the authors. + +1. Abstract + + This document defines extensions (PKINIT) to the Kerberos protocol + specification (RFC 1510 [1]) to provide a method for using public + key cryptography during initial authentication. The methods + defined specify the ways in which preauthentication data fields and + error data fields in Kerberos messages are to be used to transport + public key data. + +2. Introduction + + The popularity of public key cryptography has produced a desire for + its support in Kerberos [2]. The advantages provided by public key + cryptography include simplified key management (from the Kerberos + perspective) and the ability to leverage existing and developing + public key certification infrastructures. + + Public key cryptography can be integrated into Kerberos in a number + of ways. One is to associate a key pair with each realm, which can + then be used to facilitate cross-realm authentication; this is the + topic of another draft proposal. Another way is to allow users with + public key certificates to use them in initial authentication. This + is the concern of the current document. + + PKINIT utilizes Diffie-Hellman keys in combination with digital + signature keys as the primary, required mechanism. It also allows + for the use of RSA keys. Note that PKINIT supports the use of + separate signature and encryption keys. + + PKINIT enables access to Kerberos-secured services based on initial + authentication utilizing public key cryptography. PKINIT utilizes + standard public key signature and encryption data formats within the + standard Kerberos messages. The basic mechanism is as follows: The + user sends a request to the KDC as before, except that if that user + is to use public key cryptography in the initial authentication + step, his certificate and a signature accompany the initial request + in the preauthentication fields. Upon receipt of this request, the + KDC verifies the certificate and issues a ticket granting ticket + (TGT) as before, except that the encPart from the AS-REP message + carrying the TGT is now encrypted utilizing either a Diffie-Hellman + derived key or the user's public key. This message is authenticated + utilizing the public key signature of the KDC. + + The PKINIT specification may also be used as a building block for + other specifications. PKCROSS [3] utilizes PKINIT for establishing + the inter-realm key and associated inter-realm policy to be applied + in issuing cross realm service tickets. As specified in [4], + anonymous Kerberos tickets can be issued by applying a NULL + signature in combination with Diffie-Hellman in the PKINIT exchange. + Additionally, the PKINIT specification may be used for direct peer + to peer authentication without contacting a central KDC. This + application of PKINIT is described in PKTAPP [5] and is based on + concepts introduced in [6, 7]. For direct client-to-server + authentication, the client uses PKINIT to authenticate to the end + server (instead of a central KDC), which then issues a ticket for + itself. This approach has an advantage over TLS [8] in that the + server does not need to save state (cache session keys). + Furthermore, an additional benefit is that Kerberos tickets can + facilitate delegation (see [9]). + +3. Proposed Extensions + + This section describes extensions to RFC 1510 for supporting the + use of public key cryptography in the initial request for a ticket + granting ticket (TGT). + + In summary, the following change to RFC 1510 is proposed: + + * Users may authenticate using either a public key pair or a + conventional (symmetric) key. If public key cryptography is + used, public key data is transported in preauthentication + data fields to help establish identity. The user presents + a public key certificate and obtains an ordinary TGT that may + be used for subsequent authentication, with such + authentication using only conventional cryptography. + + Section 3.1 provides definitions to help specify message formats. + Section 3.2 describes the extensions for the initial authentication + method. + +3.1. Definitions + + The extensions involve new preauthentication fields; we introduce + the following preauthentication types: + + PA-PK-AS-REQ 14 + PA-PK-AS-REP 15 + + The extensions also involve new error types; we introduce the + following types: + + KDC_ERR_CLIENT_NOT_TRUSTED 62 + KDC_ERR_KDC_NOT_TRUSTED 63 + KDC_ERR_INVALID_SIG 64 + KDC_ERR_KEY_TOO_WEAK 65 + KDC_ERR_CERTIFICATE_MISMATCH 66 + KDC_ERR_CANT_VERIFY_CERTIFICATE 70 + KDC_ERR_INVALID_CERTIFICATE 71 + KDC_ERR_REVOKED_CERTIFICATE 72 + KDC_ERR_REVOCATION_STATUS_UNKNOWN 73 + KDC_ERR_REVOCATION_STATUS_UNAVAILABLE 74 + KDC_ERR_CLIENT_NAME_MISMATCH 75 + KDC_ERR_KDC_NAME_MISMATCH 76 + + We utilize the following typed data for errors: + + TD-PKINIT-CMS-CERTIFICATES 101 + TD-KRB-PRINCIPAL 102 + TD-KRB-REALM 103 + TD-TRUSTED-CERTIFIERS 104 + TD-CERTIFICATE-INDEX 105 + + We utilize the following encryption types (which map directly to + OIDs): + + dsaWithSHA1-CmsOID 9 + md5WithRSAEncryption-CmsOID 10 + sha1WithRSAEncryption-CmsOID 11 + rc2CBC-EnvOID 12 + rsaEncryption-EnvOID (PKCS#1 v1.5) 13 + rsaES-OAEP-ENV-OID (PKCS#1 v2.0) 14 + des-ede3-cbc-Env-OID 15 + + These mappings are provided so that a client may send the + appropriate enctypes in the AS-REQ message in order to indicate + support for the corresponding OIDs (for performing PKINIT). + + In many cases, PKINIT requires the encoding of an X.500 name as a + Realm. In these cases, the realm will be represented using a + different style, specified in RFC 1510 with the following example: + + NAMETYPE:rest/of.name=without-restrictions + + For a realm derived from an X.500 name, NAMETYPE will have the value + X500-RFC2253. The full realm name will appear as follows: + + X500-RFC2253:RFC2253Encode(DistinguishedName) + + where DistinguishedName is an X.500 name, and RFC2253Encode is a + readable UTF encoding of an X.500 name, as defined by + RFC 2253 [14] (part of LDAPv3). + + To ensure that this encoding is unique, we add the following rule + to those specified by RFC 2253: + + The order in which the attributes appear in the RFC 2253 + encoding must be the reverse of the order in the ASN.1 + encoding of the X.500 name that appears in the public key + certificate. The order of the relative distinguished names + (RDNs), as well as the order of the AttributeTypeAndValues + within each RDN, will be reversed. (This is despite the fact + that an RDN is defined as a SET of AttributeTypeAndValues, where + an order is normally not important.) + + Similarly, PKINIT may require the encoding of an X.500 name as a + PrincipalName. In these cases, the name-type of the principal name + shall be set to KRB_NT-X500-PRINCIPAL. This new name type is + defined as: + + KRB_NT_X500_PRINCIPAL 6 + + The name-string shall be set as follows: + + RFC2253Encode(DistinguishedName) + + as described above. + + RFC 1510 specifies the ASN.1 structure for PrincipalName as follows: + + PrincipalName ::= SEQUENCE { + name-type[0] INTEGER, + name-string[1] SEQUENCE OF GeneralString + } + + For the purposes of encoding an X.500 name within this structure, + the name-string shall be encoded as a single GeneralString. + + Note that name mapping may be required or optional based on + policy. + +3.1.1. Encryption and Key Formats + + In the exposition below, we use the terms public key and private + key generically. It should be understood that the term "public + key" may be used to refer to either a public encryption key or a + signature verification key, and that the term "private key" may be + used to refer to either a private decryption key or a signature + generation key. The fact that these are logically distinct does + not preclude the assignment of bitwise identical keys. + + In the case of Diffie-Hellman, the key shall be produced from the + agreed bit string as follows: + + * Truncate the bit string to the appropriate length. + * Rectify parity in each byte (if necessary) to obtain the key. + + For instance, in the case of a DES key, we take the first eight + bytes of the bit stream, and then adjust the least significant bit + of each byte to ensure that each byte has odd parity. + +3.1.2. Algorithm Identifiers + + PKINIT does not define, but does permit, the algorithm identifiers + listed below. + +3.1.2.1. Signature Algorithm Identifiers + + The following signature algorithm identifiers specified in [11] and + in [15] shall be used with PKINIT: + + id-dsa-with-sha1 (DSA with SHA1) + md5WithRSAEncryption (RSA with MD5) + sha-1WithRSAEncryption (RSA with SHA1) + +3.1.2.2 Diffie-Hellman Key Agreement Algorithm Identifier + + The following algorithm identifier shall be used within the + SubjectPublicKeyInfo data structure: dhpublicnumber + + This identifier and the associated algorithm parameters are + specified in RFC 2459 [15]. + +3.1.2.3. Algorithm Identifiers for RSA Encryption + + These algorithm identifiers are used inside the EnvelopedData data + structure, for encrypting the temporary key with a public key: + + rsaEncryption (RSA encryption, PKCS#1 v1.5) + id-RSAES-OAEP (RSA encryption, PKCS#1 v2.0) + + Both of the above RSA encryption schemes are specified in [16]. + Currently, only PKCS#1 v1.5 is specified by CMS [11], although the + CMS specification says that it will likely include PKCS#1 v2.0 in + the future. (PKCS#1 v2.0 addresses adaptive chosen ciphertext + vulnerability discovered in PKCS#1 v1.5.) + +3.1.2.4. Algorithm Identifiers for Encryption with Secret Keys + + These algorithm identifiers are used inside the EnvelopedData data + structure in the PKINIT Reply, for encrypting the reply key with the + temporary key: + des-ede3-cbc (3-key 3-DES, CBC mode) + rc2-cbc (RC2, CBC mode) + + The full definition of the above algorithm identifiers and their + corresponding parameters (an IV for block chaining) is provided in + the CMS specification [11]. + +3.2. Public Key Authentication + + Implementation of the changes in this section is REQUIRED for + compliance with PKINIT. + + It is assumed that all public keys are signed by some certification + authority (CA). The initial authentication request is sent as per + RFC 1510, except that a preauthentication field containing data + signed by the user's private key accompanies the request: + + PA-PK-AS-REQ ::= SEQUENCE { + -- PA TYPE 14 + signedAuthPack [0] SignedData + -- defined in CMS [11] + -- AuthPack (below) defines the data + -- that is signed + trustedCertifiers [1] SEQUENCE OF TrustedCas OPTIONAL, + -- CAs that the client trusts + kdcCert [2] IssuerAndSerialNumber OPTIONAL + -- as defined in CMS [11] + -- specifies a particular KDC + -- certificate if the client + -- already has it; + -- must be accompanied by + -- a single trustedCertifier + encryptionCert [3] IssuerAndSerialNumber OPTIONAL + -- For example, this may be the + -- client's Diffie-Hellman + -- certificate, or it may be the + -- client's RSA encryption + -- certificate. + } + + TrustedCas ::= CHOICE { + principalName [0] KerberosName, + -- as defined below + caName [1] Name + -- fully qualified X.500 name + -- as defined by X.509 + issuerAndSerial [2] IssuerAndSerialNumber OPTIONAL + -- Since a CA may have a number of + -- certificates, only one of which + -- a client trusts + } + + Usage of SignedData: + The SignedData data type is specified in the Cryptographic + Message Syntax, a product of the S/MIME working group of the IETF. + - The encapContentInfo field must contain the PKAuthenticator + and, optionally, the client's Diffie Hellman public value. + - The eContentType field shall contain the OID value for + id-data: iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs7(7) data(1) + - The eContent field is data of the type AuthPack (below). + - The signerInfos field contains the signature of AuthPack. + - The Certificates field, when non-empty, contains the client's + certificate chain. If present, the KDC uses the public key from + the client's certificate to verify the signature in the request. + Note that the client may pass different certificates that are used + for signing or for encrypting. Thus, the KDC may utilize a + different client certificate for signature verification than the + one it uses to encrypt the reply to the client. For example, the + client may place a Diffie-Hellman certificate in this field in + order to convey its static Diffie Hellman certificate to the KDC + enable static-ephemeral Diffie-Hellman mode for the reply. As + another example, the client may place an RSA encryption + certificate in this field. + + AuthPack ::= SEQUENCE { + pkAuthenticator [0] PKAuthenticator, + clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL + -- if client is using Diffie-Hellman + } + + PKAuthenticator ::= SEQUENCE { + kdcName [0] PrincipalName, + kdcRealm [1] Realm, + cusec [2] INTEGER, + -- for replay prevention + ctime [3] KerberosTime, + -- for replay prevention + nonce [4] INTEGER + } + + SubjectPublicKeyInfo ::= SEQUENCE { + algorithm AlgorithmIdentifier, + -- dhKeyAgreement + subjectPublicKey BIT STRING + -- for DH, equals + -- public exponent (INTEGER encoded + -- as payload of BIT STRING) + } -- as specified by the X.509 recommendation [10] + + AlgorithmIdentifier ::= SEQUENCE { + algorithm ALGORITHM.&id, + parameters ALGORITHM.&type + } -- as specified by the X.509 recommendation [10] + + If the client passes an issuer and serial number in the request, + the KDC is requested to use the referred-to certificate. If none + exists, then the KDC returns an error of type + KDC_ERR_CERTIFICATE_MISMATCH. It also returns this error if, on the + other hand, the client does not pass any trustedCertifiers, + believing that it has the KDC's certificate, but the KDC has more + than one certificate. The KDC should include information in the + KRB-ERROR message that indicates the KDC certificate(s) that a + client may utilize. This data is specified in the e-data, which + is defined in RFC 1510 revisions as a SEQUENCE of TypedData: + + TypedData ::= SEQUENCE { + data-type [0] INTEGER, + data-value [1] OCTET STRING, + } -- per Kerberos RFC 1510 revisions + + where: + data-type = TD-PKINIT-CMS-CERTIFICATES = 101 + data-value = CertificateSet // as specified by CMS [11] + + The PKAuthenticator carries information to foil replay attacks, + to bind the request and response. The PKAuthenticator is signed + with the private key corresponding to the public key in the + certificate found in userCert (or cached by the KDC). + + The trustedCertifiers field contains a list of certification + authorities trusted by the client, in the case that the client does + not possess the KDC's public key certificate. If the KDC has no + certificate signed by any of the trustedCertifiers, then it returns + an error of type KDC_ERR_KDC_NOT_TRUSTED. + + KDCs should try to (in order of preference): + 1. Use the KDC certificate identified by the serialNumber included + in the client's request. + 2. Use a certificate issued to the KDC by the client's CA (if in the + middle of a CA key roll-over, use the KDC cert issued under same + CA key as user cert used to verify request). + 3. Use a certificate issued to the KDC by one of the client's + trustedCertifier(s); + If the KDC is unable to comply with any of these options, then the + KDC returns an error message of type KDC_ERR_KDC_NOT_TRUSTED to the + client. + + Upon receipt of the AS_REQ with PA-PK-AS-REQ pre-authentication + type, the KDC attempts to verify the user's certificate chain + (userCert), if one is provided in the request. This is done by + verifying the certification path against the KDC's policy of + legitimate certifiers. This may be based on a certification + hierarchy, or it may be simply a list of recognized certifiers in a + system like PGP. + + If the client's certificate chain contains no certificate signed by + a CA trusted by the KDC, then the KDC sends back an error message + of type KDC_ERR_CANT_VERIFY_CERTIFICATE. The accompanying e-data + is a SEQUENCE of one TypedData (with type TD-TRUSTED-CERTIFIERS=104) + whose data-value is an OCTET STRING which is the DER encoding of + + TrustedCertifiers ::= SEQUENCE OF PrincipalName + -- X.500 name encoded as a principal name + -- see Section 3.1 + + If the signature on one of the certificates in the client's chain + fails verification, then the KDC returns an error of type + KDC_ERR_INVALID_CERTIFICATE. The accompanying e-data is a SEQUENCE + of one TypedData (with type TD-CERTIFICATE-INDEX=105) whose + data-value is an OCTET STRING which is the DER encoding of + + CertificateIndex ::= INTEGER + -- 0 = 1st certificate, + -- (in order of encoding) + -- 1 = 2nd certificate, etc + + The KDC may also check whether any of the certificates in the + client's chain has been revoked. If one of the certificates has + been revoked, then the KDC returns an error of type + KDC_ERR_REVOKED_CERTIFICATE; if such a query reveals that the + certificate's revocation status is unknown, the KDC returns an + error of type KDC_ERR_REVOCATION_STATUS_UNKNOWN; if the revocation + status is unavailable, the KDC returns an error of type + KDC_ERR_REVOCATION_STATUS_UNAVAILABLE. In any of these three + cases, the affected certificate is identified by the accompanying + e-data, which contains a CertificateIndex as described for + KDC_ERR_INVALID_CERTIFICATE. + + If the certificate chain can be verified, but the name of the + client in the certificate does not match the client's name in the + request, then the KDC returns an error of type + KDC_ERR_CLIENT_NAME_MISMATCH. There is no accompanying e-data + field in this case. + + Finally, if the certificate chain is verified, but the KDC's name + or realm as given in the PKAuthenticator does not match the KDC's + actual principal name, then the KDC returns an error of type + KDC_ERR_KDC_NAME_MISMATCH. The accompanying e-data field is again + a SEQUENCE of one TypedData (with type TD-KRB-PRINCIPAL=102 or + TD-KRB-REALM=103 as appropriate) whose data-value is an OCTET + STRING whose data-value is the DER encoding of a PrincipalName or + Realm as defined in RFC 1510 revisions. + + Even if all succeeds, the KDC may--for policy reasons--decide not + to trust the client. In this case, the KDC returns an error message + of type KDC_ERR_CLIENT_NOT_TRUSTED. + + If a trust relationship exists, the KDC then verifies the client's + signature on AuthPack. If that fails, the KDC returns an error + message of type KDC_ERR_INVALID_SIG. Otherwise, the KDC uses the + timestamp (ctime and cusec) in the PKAuthenticator to assure that + the request is not a replay. The KDC also verifies that its name + is specified in the PKAuthenticator. + + If the clientPublicValue field is filled in, indicating that the + client wishes to use Diffie-Hellman key agreement, then the KDC + checks to see that the parameters satisfy its policy. If they do + not (e.g., the prime size is insufficient for the expected + encryption type), then the KDC sends back an error message of type + KDC_ERR_KEY_TOO_WEAK. Otherwise, it generates its own public and + private values for the response. + + The KDC also checks that the timestamp in the PKAuthenticator is + within the allowable window and that the principal name and realm + are correct. If the local (server) time and the client time in the + authenticator differ by more than the allowable clock skew, then the + KDC returns an error message of type KRB_AP_ERR_SKEW. + + Assuming no errors, the KDC replies as per RFC 1510, except as + follows. The user's name in the ticket is determined by the + following decision algorithm: + + 1. If the KDC has a mapping from the name in the certificate + to a Kerberos name, then use that name. + Else + 2. If the certificate contains a Kerberos name in an extension + field, and local KDC policy allows, then use that name. + Else + 3. Use the name as represented in the certificate, mapping + as necessary (e.g., as per RFC 2253 for X.500 names). In + this case the realm in the ticket shall be the name of the + certification authority that issued the user's certificate. + + The KDC encrypts the reply not with the user's long-term key, but + with a random key generated only for this particular response. This + random key is sealed in the preauthentication field: + + PA-PK-AS-REP ::= CHOICE { + -- PA TYPE 15 + dhSignedData [0] SignedData, + -- Defined in CMS and used only with + -- Diffie-Helman key exchange + -- This choice MUST be supported + -- by compliant implementations. + encKeyPack [1] EnvelopedData, + -- Defined in CMS + -- The temporary key is encrypted + -- using the client public key + -- key + -- SignedReplyKeyPack, encrypted + -- with the temporary key, is also + -- included. + } + + Usage of SignedData: + If the Diffie-Hellman option is used, dhSignedData in PA-PK-AS-REP + provides authenticated Diffie-Hellman parameters of the KDC. The + reply key used to encrypt part of the KDC reply message is derived + from the Diffie-Hellman exchange: + - Both the KDC and the client calculate a secret value (g^ab mod p), + where a is the client's private exponent and b is the KDC's + private exponent. + - Both the KDC and the client take the first N bits of this secret + value and convert it into a reply key. N depends on the reply key + type. + - If the reply key is DES, N=64 bits, where some of the bits are + replaced with parity bits, according to FIPS PUB 74. + - If the reply key is (3-key) 3-DES, N=192 bits, where some of the + bits are replaced with parity bits, according to FIPS PUB 74. + - The encapContentInfo field must contain the KdcDHKeyInfo as + defined below. + - The eContentType field shall contain the OID value for + id-data: iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs7(7) data(1) + - The certificates field must contain the certificates necessary + for the client to establish trust in the KDC's certificate + based on the list of trusted certifiers sent by the client in + the PA-PK-AS-REQ. This field may be empty if the client did + not send to the KDC a list of trusted certifiers (the + trustedCertifiers field was empty, meaning that the client + already possesses the KDC's certificate). + - The signerInfos field is a SET that must contain at least one + member, since it contains the actual signature. + + Usage of EnvelopedData: + The EnvelopedData data type is specified in the Cryptographic + Message Syntax, a product of the S/MIME working group of the IETF. + It contains an temporary key encrypted with the PKINIT + client's public key. It also contains a signed and encrypted + reply key. + - The originatorInfo field is not required, since that information + may be presented in the signedData structure that is encrypted + within the encryptedContentInfo field. + - The optional unprotectedAttrs field is not required for PKINIT. + - The recipientInfos field is a SET which must contain exactly one + member of the KeyTransRecipientInfo type for encryption + with an RSA public key. + - The encryptedKey field (in KeyTransRecipientInfo) contains + the temporary key which is encrypted with the PKINIT client's + public key. + - The encryptedContentInfo field contains the signed and encrypted + reply key. + - The contentType field shall contain the OID value for + id-signedData: iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs7(7) signedData(2) + - The encryptedContent field is encrypted data of the CMS type + signedData as specified below. + - The encapContentInfo field must contains the ReplyKeyPack. + - The eContentType field shall contain the OID value for + id-data: iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs7(7) data(1) + - The eContent field is data of the type ReplyKeyPack (below). + - The certificates field must contain the certificates necessary + for the client to establish trust in the KDC's certificate + based on the list of trusted certifiers sent by the client in + the PA-PK-AS-REQ. This field may be empty if the client did + not send to the KDC a list of trusted certifiers (the + trustedCertifiers field was empty, meaning that the client + already possesses the KDC's certificate). + - The signerInfos field is a SET that must contain at least one + member, since it contains the actual signature. + + KdcDHKeyInfo ::= SEQUENCE { + -- used only when utilizing Diffie-Hellman + nonce [0] INTEGER, + -- binds responce to the request + subjectPublicKey [2] BIT STRING + -- Equals public exponent (g^a mod p) + -- INTEGER encoded as payload of + -- BIT STRING + } + + ReplyKeyPack ::= SEQUENCE { + -- not used for Diffie-Hellman + replyKey [0] EncryptionKey, + -- used to encrypt main reply + -- ENCTYPE is at least as strong as + -- ENCTYPE of session key + nonce [1] INTEGER, + -- binds response to the request + -- must be same as the nonce + -- passed in the PKAuthenticator + } + + + Since each certifier in the certification path of a user's + certificate is essentially a separate realm, the name of each + certifier must be added to the transited field of the ticket. The + format of these realm names is defined in Section 3.1 of this + document. If applicable, the transit-policy-checked flag should be + set in the issued ticket. + + The KDC's certificate must bind the public key to a name derivable + from the name of the realm for that KDC. X.509 certificates shall + contain the principal name of the KDC as the SubjectAltName version + 3 extension. Below is the definition of this version 3 extension, as + specified by the X.509 standard: + + subjectAltName EXTENSION ::= { + SYNTAX GeneralNames + IDENTIFIED BY id-ce-subjectAltName + } + + GeneralNames ::= SEQUENCE SIZE(1..MAX) OF GeneralName + + GeneralName ::= CHOICE { + otherName [0] INSTANCE OF OTHER-NAME, + ... + } + + OTHER-NAME ::= TYPE-IDENTIFIER + + In this definition, otherName is a name of any form defined as an + instance of the OTHER-NAME information object class. For the purpose + of specifying a Kerberos principal name, INSTANCE OF OTHER-NAME will + be chosen and replaced by the type KerberosName: + + KerberosName ::= SEQUENCE { + realm [0] Realm, + -- as define in RFC 1510 + principalName [1] PrincipalName, + -- as define in RFC 1510 + } + + This specific syntax is identified within subjectAltName by setting + the OID id-ce-subjectAltName to krb5PrincipalName, where (from the + Kerberos specification) we have + + krb5 OBJECT IDENTIFIER ::= { iso (1) + org (3) + dod (6) + internet (1) + security (5) + kerberosv5 (2) } + + krb5PrincipalName OBJECT IDENTIFIER ::= { krb5 2 } + + This specification may also be used to specify a Kerberos name + within the user's certificate. + + If a non-KDC X.509 certificate contains the principal name within + the subjectAltName version 3 extension , that name may utilize + KerberosName as defined below, or, in the case of an S/MIME + certificate [17], may utilize the email address. If the KDC + is presented with as S/MIME certificate, then the email address + within subjectAltName will be interpreted as a principal and realm + separated by the "@" sign, or as a name that needs to be + canonicalized. If the resulting name does not correspond to a + registered principal name, then the principal name is formed as + defined in section 3.1. + + The client then extracts the random key used to encrypt the main + reply. This random key (in encPaReply) is encrypted with either the + client's public key or with a key derived from the DH values + exchanged between the client and the KDC. + +3.2.2. Required Algorithms + + Not all of the algorithms in the PKINIT protocol specification have + to be implemented in order to comply with the proposed standard. + Below is a list of the required algorithms: + + - Diffie-Hellman public/private key pairs + - utilizing Diffie-Hellman ephemeral-ephemeral mode + - SHA1 digest and DSA for signatures + - 3-key triple DES keys derived from the Diffie-Hellman Exchange + - 3-key triple DES Temporary and Reply keys + +4. Logistics and Policy + + This section describes a way to define the policy on the use of + PKINIT for each principal and request. + + The KDC is not required to contain a database record for users + who use public key authentication. However, if these users are + registered with the KDC, it is recommended that the database record + for these users be modified to an additional flag in the attributes + field to indicate that the user should authenticate using PKINIT. + If this flag is set and a request message does not contain the + PKINIT preauthentication field, then the KDC sends back as error of + type KDC_ERR_PREAUTH_REQUIRED indicating that a preauthentication + field of type PA-PK-AS-REQ must be included in the request. + +5. Security Considerations + + PKINIT raises a few security considerations, which we will address + in this section. + + First of all, PKINIT introduces a new trust model, where KDCs do not + (necessarily) certify the identity of those for whom they issue + tickets. PKINIT does allow KDCs to act as their own CAs, in order + to simplify key management, but one of the additional benefits is to + align Kerberos authentication with a global public key + infrastructure. Anyone using PKINIT in this way must be aware of + how the certification infrastructure they are linking to works. + + Secondly, PKINIT also introduces the possibility of interactions + between different cryptosystems, which may be of widely varying + strengths. Many systems, for instance, allow the use of 512-bit + public keys. Using such keys to wrap data encrypted under strong + conventional cryptosystems, such as triple-DES, is inappropriate; + it adds a weak link to a strong one at extra cost. Implementors + and administrators should take care to avoid such wasteful and + deceptive interactions. + + Lastly, PKINIT calls for randomly generated keys for conventional + cryptosystems. Many such systems contain systematically "weak" + keys. PKINIT implementations MUST avoid use of these keys, either + by discarding those keys when they are generated, or by fixing them + in some way (e.g., by XORing them with a given mask). These + precautions vary from system to system; it is not our intention to + give an explicit recipe for them here. + +6. Transport Issues + + Certificate chains can potentially grow quite large and span several + UDP packets; this in turn increases the probability that a Kerberos + message involving PKINIT extensions will be broken in transit. In + light of the possibility that the Kerberos specification will + require KDCs to accept requests using TCP as a transport mechanism, + we make the same recommendation with respect to the PKINIT + extensions as well. + +7. Bibliography + + [1] J. Kohl, C. Neuman. The Kerberos Network Authentication Service + (V5). Request for Comments 1510. + + [2] B.C. Neuman, Theodore Ts'o. Kerberos: An Authentication Service + for Computer Networks, IEEE Communications, 32(9):33-38. September + 1994. + + [3] B. Tung, T. Ryutov, C. Neuman, G. Tsudik, B. Sommerfeld, + A. Medvinsky, M. Hur. Public Key Cryptography for Cross-Realm + Authentication in Kerberos. + draft-ietf-cat-kerberos-pk-cross-04.txt + + [4] A. Medvinsky, J. Cargille, M. Hur. Anonymous Credentials in + Kerberos. + draft-ietf-cat-kerberos-anoncred-00.txt + + [5] A. Medvinsky, M. Hur, B. Clifford Neuman. Public Key Utilizing + Tickets for Application Servers (PKTAPP). + draft-ietf-cat-pktapp-00.txt + + [6] M. Sirbu, J. Chuang. Distributed Authentication in Kerberos + Using Public Key Cryptography. Symposium On Network and Distributed + System Security, 1997. + + [7] B. Cox, J.D. Tygar, M. Sirbu. NetBill Security and Transaction + Protocol. In Proceedings of the USENIX Workshop on Electronic + Commerce, July 1995. + + [8] T. Dierks, C. Allen. The TLS Protocol, Version 1.0 + Request for Comments 2246, January 1999. + + [9] B.C. Neuman, Proxy-Based Authorization and Accounting for + Distributed Systems. In Proceedings of the 13th International + Conference on Distributed Computing Systems, May 1993. + + [10] ITU-T (formerly CCITT) Information technology - Open Systems + Interconnection - The Directory: Authentication Framework + Recommendation X.509 ISO/IEC 9594-8 + + [11] R. Housley. Cryptographic Message Syntax. + draft-ietf-smime-cms-13.txt, April 1999. + + [12] PKCS #7: Cryptographic Message Syntax Standard, + An RSA Laboratories Technical Note Version 1.5 + Revised November 1, 1993 + + [13] R. Rivest, MIT Laboratory for Computer Science and RSA Data + Security, Inc. A Description of the RC2(r) Encryption Algorithm + March 1998. + Request for Comments 2268. + + [14] M. Wahl, S. Kille, T. Howes. Lightweight Directory Access + Protocol (v3): UTF-8 String Representation of Distinguished Names. + Request for Comments 2253. + + [15] R. Housley, W. Ford, W. Polk, D. Solo. Internet X.509 Public + Key Infrastructure, Certificate and CRL Profile, January 1999. + Request for Comments 2459. + + [16] B. Kaliski, J. Staddon. PKCS #1: RSA Cryptography + Specifications, October 1998. + Request for Comments 2437. + + [17] S. Dusse, P. Hoffman, B. Ramsdell, J. Weinstein. + S/MIME Version 2 Certificate Handling, March 1998. + Request for Comments 2312 + +8. Acknowledgements + + Some of the ideas on which this proposal 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 + proposal approaches those goals primarily from the Kerberos + perspective. Lastly, comments from groups working on similar ideas + in DCE have been invaluable. + +9. Expiration Date + + This draft expires December 1, 1999. + +10. Authors + + Brian Tung + Clifford Neuman + USC Information Sciences Institute + 4676 Admiralty Way Suite 1001 + Marina del Rey CA 90292-6695 + Phone: +1 310 822 1511 + E-mail: {brian, bcn}@isi.edu + + Matthew Hur + CyberSafe Corporation + 1605 NW Sammamish Road + Issaquah WA 98027-5378 + Phone: +1 425 391 6000 + E-mail: matt.hur@cybersafe.com + + Ari Medvinsky + Excite + 555 Broadway + Redwood City, CA 94063 + Phone +1 650 569 2119 + E-mail: amedvins@excitecorp.com + + Sasha Medvinsky + General Instrument + 6450 Sequence Drive + San Diego, CA 92121 + Phone +1 619 404 2825 + E-mail: smedvinsky@gi.com + + John Wray + Iris Associates, Inc. + 5 Technology Park Dr. + Westford, MA 01886 + E-mail: John_Wray@iris.com + + Jonathan Trostle + 170 W. Tasman Dr. + San Jose, CA 95134 + E-mail: jtrostle@cisco.com diff --git a/doc/krb5-protocol/rfc4557.txt b/doc/krb5-protocol/rfc4557.txt new file mode 100644 index 0000000..fe9a881 --- /dev/null +++ b/doc/krb5-protocol/rfc4557.txt @@ -0,0 +1,339 @@ + + + + + + +Network Working Group L. Zhu +Request for Comments: 4557 K. Jaganathan +Category: Standards Track Microsoft Corporation + N. Williams + Sun Microsystems + June 2006 + + + Online Certificate Status Protocol (OCSP) Support for + Public Key Cryptography for + Initial Authentication in Kerberos (PKINIT) + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document defines a mechanism to enable in-band transmission of + Online Certificate Status Protocol (OCSP) responses in the Kerberos + network authentication protocol. These responses are used to verify + the validity of the certificates used in Public Key Cryptography for + Initial Authentication in Kerberos (PKINIT), which is the Kerberos + Version 5 extension that provides for the use of public key + cryptography. + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. Message Definition ..............................................2 + 4. Security Considerations .........................................3 + 5. Acknowledgements ................................................4 + 6. References ......................................................4 + 6.1. Normative References .......................................4 + 6.2. Informative References .....................................4 + + + + + + + +Zhu, et al. Standards Track [Page 1] + +RFC 4557 OCSP Support for PKINIT June 2006 + + +1. Introduction + + Online Certificate Status Protocol (OCSP) [RFC2560] enables + applications to obtain timely information regarding the revocation + status of a certificate. Because OCSP responses are well bounded and + small in size, constrained clients may wish to use OCSP to check the + validity of the certificates for Kerberos Key Distribution Center + (KDC) in order to avoid transmission of large Certificate Revocation + Lists (CRLs) and therefore save bandwidth on constrained networks + [OCSP-PROFILE]. + + This document defines a pre-authentication type [RFC4120], where the + client and the KDC MAY piggyback OCSP responses for certificates used + in authentication exchanges, as defined in [RFC4556]. + + By using this OPTIONAL extension, PKINIT clients and the KDC can + maximize the reuse of cached OCSP responses. + +2. Conventions Used in This Document + + In this document, the key words "MUST", "MUST NOT", "REQUIRED", + "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", + and "OPTIONAL" are to be interpreted as described in [RFC2119]. + +3. Message Definition + + A pre-authentication type identifier is defined for this mechanism: + + PA-PK-OCSP-RESPONSE 18 + + The corresponding padata-value field [RFC4120] contains the DER [X60] + encoding of the following ASN.1 type: + + PKOcspData ::= SEQUENCE OF OcspResponse + -- If more than one OcspResponse is + -- included, the first OcspResponse + -- MUST contain the OCSP response + -- for the signer's certificate. + -- The signer refers to the client for + -- AS-REQ, and the KDC for the AS-REP, + -- respectively. + + OcspResponse ::= OCTET STRING + -- Contains a complete OCSP response, + -- as defined in [RFC2560]. + + The client MAY send OCSP responses for certificates used in PA-PK- + AS-REQ [RFC4556] via a PA-PK-OCSP-RESPONSE. + + + +Zhu, et al. Standards Track [Page 2] + +RFC 4557 OCSP Support for PKINIT June 2006 + + + The KDC that receives a PA-PK-OCSP-RESPONSE SHOULD send a PA-PK- + OCSP-RESPONSE containing OCSP responses for certificates used in the + KDC's PA-PK-AS-REP. The client can request a PA-PK-OCSP-RESPONSE by + using a PKOcspData containing an empty sequence. + + The KDC MAY send a PA-PK-OCSP-RESPONSE when it does not receive a + PA-PK-OCSP-RESPONSE from the client. + + The PA-PK-OCSP-RESPONSE sent by the KDC contains OCSP responses for + certificates used in PA-PK-AS-REP [RFC4556]. + + Note the lack of integrity protection for the empty or missing OCSP + response; lack of an expected OCSP response from the KDC for the + KDC's certificates SHOULD be treated as an error by the client, + unless it is configured otherwise. + + When using OCSP, the response is signed by the OCSP server, which is + trusted by the receiver. Depending on local policy, further + verification of the validity of the OCSP servers may be needed + + The client and the KDC SHOULD ignore invalid OCSP responses received + via this mechanism, and they MAY implement CRL processing logic as a + fall-back position, if the OCSP responses received via this mechanism + alone are not sufficient for the verification of certificate + validity. The client and/or the KDC MAY ignore a valid OCSP response + and perform its own revocation status verification independently. + +4. Security Considerations + + The pre-authentication data in this document do not actually + authenticate any principals, but are designed to be used in + conjunction with PKINIT. + + There is no binding between PA-PK-OCSP-RESPONSE pre-authentication + data and PKINIT pre-authentication data other than a given OCSP + response corresponding to a certificate used in a PKINIT pre- + authentication data element. Attacks involving removal or + replacement of PA-PK-OCSP-RESPONSE pre-authentication data elements + are, at worst, downgrade attacks, where a PKINIT client or KDC would + proceed without use of CRLs or OCSP for certificate validation, or + denial-of-service attacks, where a PKINIT client or KDC that cannot + validate the other's certificate without an accompanying OCSP + response might reject the AS exchange or might have to download very + large CRLs in order to continue. Kerberos V does not protect against + denial-of-service attacks; therefore, the denial-of-service aspect of + these attacks is acceptable. + + + + + +Zhu, et al. Standards Track [Page 3] + +RFC 4557 OCSP Support for PKINIT June 2006 + + + If a PKINIT client or KDC cannot validate certificates without the + aid of a valid PA-PK-OCSP-RESPONSE, then it SHOULD fail the AS + exchange, possibly according to local configuration. + +5. Acknowledgements + + This document was based on conversations among the authors, Jeffrey + Altman, Sam Hartman, Martin Rex, and other members of the Kerberos + working group. + +6. References + +6.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and + C. Adams, "X.509 Internet Public Key Infrastructure + Online Certificate Status Protocol - OCSP", RFC 2560, + June 1999. + + [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The + Kerberos Network Authentication Service (V5)", RFC + 4120, July 2005. + + [RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for + Initial Authentication in Kerberos (PKINIT)", RFC + 4556, June 2006. + + [X690] ASN.1 encoding rules: Specification of Basic Encoding + Rules (BER), Canonical Encoding Rules (CER) and + Distinguished Encoding Rules (DER), ITU-T + Recommendation X.690 (1997) | ISO/IEC International + Standard 8825-1:1998. + +6.2. Informative References + + [OCSP-PROFILE] Deacon, A. and R. Hurst, "Lightweight OCSP Profile for + High Volume Environments", Work in Progress, May 2006. + + + + + + + + + + + +Zhu, et al. Standards Track [Page 4] + +RFC 4557 OCSP Support for PKINIT June 2006 + + +Authors' Addresses + + Larry Zhu + Microsoft Corporation + One Microsoft Way + Redmond, WA 98052 + US + + EMail: lzhu@microsoft.com + + + Karthik Jaganathan + Microsoft Corporation + One Microsoft Way + Redmond, WA 98052 + US + + EMail: karthikj@microsoft.com + + + Nicolas Williams + Sun Microsystems + 5300 Riata Trace Ct + Austin, TX 78727 + US + + EMail: Nicolas.Williams@sun.com + + + + + + + + + + + + + + + + + + + + + + + + +Zhu, et al. Standards Track [Page 5] + +RFC 4557 OCSP Support for PKINIT June 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + 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. + + 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. + +Intellectual Property + + 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. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Zhu, et al. Standards Track [Page 6] + |