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diff --git a/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-11.txt b/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-11.txt deleted file mode 100644 index 9b0e76ad..0000000 --- a/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-11.txt +++ /dev/null @@ -1,1059 +0,0 @@ -INTERNET-DRAFT Brian Tung -draft-ietf-cat-kerberos-pk-init-11.txt Clifford Neuman -Updates: RFC 1510 USC/ISI -expires September 15, 2000 Matthew Hur - CyberSafe Corporation - Ari Medvinsky - Keen.com, Inc. - Sasha Medvinsky - Motorola - 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-11.txt, and expires September 15, - 2000. 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 ephemeral-ephemeral Diffie-Hellman keys in - combination with digital signature keys as the primary, required - mechanism. It also allows for the use of RSA keys and/or (static) - Diffie-Hellman certificates. Note in particular 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 an AS-REQ message 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. - - Note that PKINIT does not require the use of certificates. A KDC - may store the public key of a principal as part of that principal's - record. In this scenario, the KDC is the trusted party that vouches - for the principal (as in a standard, non-cross realm, Kerberos - environment). Thus, for any principal, the KDC may maintain a - secret key, a public key, or both. - - 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 the X.500 name of a - certificate authority as a Realm. When such a name appears as - a realm it will be represented using the "other" form of the realm - name as specified in the naming constraints section of RFC1510. - For a realm derived from an X.500 name, NAMETYPE will have the value - X500-RFC2253. The full realm name will appear as follows: - - <nametype> + ":" + <string> - - where nametype is "X500-RFC2253" and string is the result of doing - an RFC2253 encoding of the distinguished name, i.e. - - "X500-RFC2253:" + RFC2253Encode(DistinguishedName) - - where DistinguishedName is an X.500 name, and RFC2253Encode is a - function returing a readable UTF encoding of an X.500 name, as - defined by RFC 2253 [14] (part of LDAPv3 [18]). - - 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, in cases where the KDC does not provide a specific - policy based mapping from the X.500 name or X.509 Version 3 - SubjectAltName extension in the user's certificate to a Kerberos - principal name, PKINIT requires the direct encoding of the X.500 - name as a PrincipalName. In this case, the name-type of the - principal name shall be set to KRB_NT-X500-PRINCIPAL. This new - name type is defined in RFC 1510 as: - - KRB_NT_X500_PRINCIPAL 6 - - The name-string shall be set as follows: - - RFC2253Encode(DistinguishedName) - - as described above. When this name type is used, the principal's - realm shall be set to the certificate authority's distinguished - name using the X500-RFC2253 realm name format described earlier in - this section - - 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 as a Kerberos name for - use in Kerberos structures, the name-string shall be encoded as a - single GeneralString. The name-type should be KRB_NT_X500_PRINCIPAL, - as noted above. All Kerberos names must conform to validity - requirements as given in RFC 1510. Note that name mapping may be - required or optional, based on policy. - - We also define the following similar ASN.1 structure: - - CertPrincipalName ::= SEQUENCE { - name-type[0] INTEGER, - name-string[1] SEQUENCE OF UTF8String - } - - When a Kerberos PrincipalName is to be placed within an X.509 data - structure, the CertPrincipalName structure is to be used, with the - name-string encoded as a single UTF8String. The name-type should be - as identified in the original PrincipalName structure. The mapping - between the GeneralString and UTF8String formats can be found in - [19]. - - The following rules relate to the the matching of PrincipalNames (or - corresponding CertPrincipalNames) with regard to the PKI name - constraints for CAs as laid out in RFC 2459 [15]. In order to be - regarded as a match (for permitted and excluded name trees), the - following must be satisfied. - - 1. If the constraint is given as a user plus realm name, or - as a user plus instance plus realm name (as specified in - RFC 1510), the realm name must be valid (see 2.a-d below) - and the match must be exact, byte for byte. - - 2. If the constraint is given only as a realm name, matching - depends on the type of the realm: - - a. If the realm contains a colon (':') before any equal - sign ('='), it is treated as a realm of type Other, - and must match exactly, byte for byte. - - b. Otherwise, if the realm contains an equal sign, it - is treated as an X.500 name. In order to match, every - component in the constraint MUST be in the principal - name, and have the same value. For example, 'C=US' - matches 'C=US/O=ISI' but not 'C=UK'. - - c. Otherwise, if the realm name conforms to rules regarding - the format of DNS names, it is considered a realm name of - type Domain. The constraint may be given as a realm - name 'FOO.BAR', which matches any PrincipalName within - the realm 'FOO.BAR' but not those in subrealms such as - 'CAR.FOO.BAR'. A constraint of the form '.FOO.BAR' - matches PrincipalNames in subrealms of the form - 'CAR.FOO.BAR' but not the realm 'FOO.BAR' itself. - - d. Otherwise, the realm name is invalid and does not match - under any conditions. - -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 for RSA - 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. - -3.2.1. Client Request - - Public keys may be signed by some certification authority (CA), or - they may be maintained by the KDC in which case the KDC is the - trusted authority. Note that the latter mode does not require the - use of certificates. - - 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, - -- This is a list of CAs that the - -- client trusts and that certify - -- KDCs. - kdcCert [2] IssuerAndSerialNumber OPTIONAL - -- As defined in CMS [11]; - -- specifies a particular KDC - -- certificate if the client - -- already has it. - 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 - -- 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 following describes how to fill in the fields of - this data: - - 1. The encapContentInfo field must contain the PKAuthenticator - and, optionally, the client's Diffie Hellman public value. - - a. The eContentType field shall contain the OID value for - pkdata: iso (1) org (3) dod (6) internet (1) security (5) - kerberosv5 (2) pkinit (3) pkdata (1) - - b. The eContent field is data of the type AuthPack (below). - - 2. The signerInfos field contains the signature of AuthPack. - - 3. 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 certificate - chains 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 to enable - static-ephemeral Diffie-Hellman mode for the reply; in this - case, the client does NOT place its public value in the - AuthPack (defined below). As another example, the client may - place an RSA encryption certificate in this field. However, - there must always be (at least) a signature certificate. - - AuthPack ::= SEQUENCE { - pkAuthenticator [0] PKAuthenticator, - clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL - -- if client is using Diffie-Hellman - -- (ephemeral-ephemeral only) - } - - PKAuthenticator ::= SEQUENCE { - kdcName [0] PrincipalName, - kdcRealm [1] Realm, - cusec [2] INTEGER, - -- for replay prevention as in RFC1510 - ctime [3] KerberosTime, - -- for replay prevention as in RFC1510 - 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, and - to bind the request and response. The PKAuthenticator is signed - with the client's signature key. - -3.2.2. KDC Response - - 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 while verifying a certificate chain the KDC determines that the - signature on one of the certificates in the CertificateSet from - the signedAuthPack 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 the index into the CertificateSet - ordered as sent by the client. - - 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 or not - available, then if required by policy, the KDC returns the - appropriate error of type KDC_ERR_REVOCATION_STATUS_UNKNOWN or - 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. One specific case of this is - the presence or absence of an Enhanced Key Usage (EKU) OID within - the certificate extensions. The rules regarding acceptability of - an EKU sequence (or the absence of any sequence) are a matter of - local policy. For the benefit of implementers, we define a PKINIT - EKU OID as the following: iso (1) org (3) dod (6) internet (1) - security (5) kerberosv5 (2) pkinit (3) pkekuoid (2). - - 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 as defined in 1510. - - 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 the SubjectAltName extention - and the local KDC policy defines a mapping from the - SubjectAltName to a Kerberos name, then use that name. - Else - 3. Use the name as represented in the certificate, mapping - 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 certifier that issued the user's certificate. - - Note that a principal name may be carried in the subject alt name - field of a certificate. This name may be mapped to a principal - record in a security database based on local policy, for example - the subject alt name may be kerberos/principal@realm format. In - this case the realm name is not that of the CA but that of the - local realm doing the mapping (or some realm name chosen by that - realm). - - 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 an 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 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. - - The KDC encrypts the reply not with the user's long-term key, but - with the Diffie Hellman derived key or a random key generated - for this particular response which is carried in the padata field of - the TGS-REP message. - - PA-PK-AS-REP ::= CHOICE { - -- PA TYPE 15 - dhSignedData [0] SignedData, - -- Defined in CMS and used only with - -- Diffie-Hellman key exchange (if the - -- client public value was present in the - -- request). - -- 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: - - When 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: - - 1. 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. - - 2. 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. - - 3. If the reply key is DES, N=64 bits, where some of the bits - are replaced with parity bits, according to FIPS PUB 74. - - 4. 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. - - 5. The encapContentInfo field must contain the KdcDHKeyInfo as - defined below. - - a. The eContentType field shall contain the OID value for - pkdata: iso (1) org (3) dod (6) internet (1) security (5) - kerberosv5 (2) pkinit (3) pkdata (1) - - b. The eContent field is data of the type KdcDHKeyInfo - (below). - - 6. 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). - - 7. 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 - } - - 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 a temporary key encrypted with the PKINIT - client's public key. It also contains a signed and encrypted - reply key. - - 1. The originatorInfo field is not required, since that - information may be presented in the signedData structure - that is encrypted within the encryptedContentInfo field. - - 2. The optional unprotectedAttrs field is not required for - PKINIT. - - 3. The recipientInfos field is a SET which must contain exactly - one member of the KeyTransRecipientInfo type for encryption - with an RSA public key. - - a. The encryptedKey field (in KeyTransRecipientInfo) - contains the temporary key which is encrypted with the - PKINIT client's public key. - - 4. The encryptedContentInfo field contains the signed and - encrypted reply key. - - a. 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) - - b. The encryptedContent field is encrypted data of the CMS - type signedData as specified below. - - i. The encapContentInfo field must contains the - ReplyKeyPack. - - * The eContentType field shall contain the OID value - for pkdata: iso (1) org (3) dod (6) internet (1) - security (5) kerberosv5 (2) pkinit (3) pkdata (1) - - * The eContent field is data of the type ReplyKeyPack - (below). - - ii. 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). - - iii. The signerInfos field is a SET that must contain at - least one member, since it contains the actual - signature. - - 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 equivalent to a separate Kerberos realm, the name - of each certifier in the certificate chain 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(s) must bind the public key(s) of the KDC to - a name derivable from the name of the realm for that KDC. X.509 - certificates shall contain the principal name of the KDC - (defined in section 8.2 of RFC 1510) 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] OtherName, - ... - } - - OtherName ::= SEQUENCE { - type-id OBJECT IDENTIFIER, - value [0] EXPLICIT ANY DEFINED BY type-id - } - - For the purpose of specifying a Kerberos principal name, the value - in OtherName shall be a KerberosName as defined in RFC 1510, but with - the PrincipalName replaced by CertPrincipalName as mentioned in - Section 3.1: - - KerberosName ::= SEQUENCE { - realm [0] Realm, - principalName [1] CertPrincipalName -- defined above - } - - This specific syntax is identified within subjectAltName by setting - the type-id in OtherName 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.) The KDC's certificate may be signed - directly by a CA, or there may be intermediaries if the server resides - within a large organization, or it may be unsigned if the client - indicates possession (and trust) of the KDC's certificate. - - 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. The client uses this - random key to decrypt the main reply, and subsequently proceeds as - described in RFC 1510. - -3.2.3. 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 the - limited capacity of self-signing their certificates, 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] Ari Medvinsky, M. Hur, Alexander Medvinsky, B. Clifford Neuman. - Public Key Utilizing Tickets for Application Servers (PKTAPP). - draft-ietf-cat-pktapp-02.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, approved for publication - as RFC. - - [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. - - [18] M. Wahl, T. Howes, S. Kille. Lightweight Directory Access - Protocol (v3), December 1997. Request for Comments 2251. - - [19] ITU-T (formerly CCITT) Information Processing Systems - Open - Systems Interconnection - Specification of Abstract Syntax Notation - One (ASN.1) Rec. X.680 ISO/IEC 8824-1 - -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 September 15, 2000. - -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 - Keen.com, Inc. - 150 Independence Drive - Menlo Park CA 94025 - Phone: +1 650 289 3134 - E-mail: ari@keen.com - - Sasha Medvinsky - Motorola - 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 |
