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diff --git a/doc/rfc/rfc1964.txt b/doc/rfc/rfc1964.txt new file mode 100644 index 0000000..f2960b9 --- /dev/null +++ b/doc/rfc/rfc1964.txt @@ -0,0 +1,1123 @@ + + + + + + +Network Working Group J. Linn +Request for Comments: 1964 OpenVision Technologies +Category: Standards Track June 1996 + + + The Kerberos Version 5 GSS-API Mechanism + +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. + +ABSTRACT + + This specification defines protocols, procedures, and conventions to + be employed by peers implementing the Generic Security Service + Application Program Interface (as specified in RFCs 1508 and 1509) + when using Kerberos Version 5 technology (as specified in RFC 1510). + +ACKNOWLEDGMENTS + + Much of the material in this memo is based on working documents + drafted by John Wray of Digital Equipment Corporation and on + discussions, implementation activities, and interoperability testing + involving Marc Horowitz, Ted Ts'o, and John Wray. Particular thanks + are due to each of these individuals for their contributions towards + development and availability of GSS-API support within the Kerberos + Version 5 code base. + +1. Token Formats + + This section discusses protocol-visible characteristics of the GSS- + API mechanism to be implemented atop Kerberos V5 security technology + per RFC-1508 and RFC-1510; it defines elements of protocol for + interoperability and is independent of language bindings per RFC- + 1509. + + Tokens transferred between GSS-API peers (for security context + management and per-message protection purposes) are defined. The + data elements exchanged between a GSS-API endpoint implementation and + the Kerberos KDC are not specific to GSS-API usage and are therefore + defined within RFC-1510 rather than within this specification. + + + + + + +Linn Standards Track [Page 1] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + To support ongoing experimentation, testing, and evolution of the + specification, the Kerberos V5 GSS-API mechanism as defined in this + and any successor memos will be identified with the following Object + Identifier, as defined in RFC-1510, until the specification is + advanced to the level of Proposed Standard RFC: + + {iso(1), org(3), dod(5), internet(1), security(5), kerberosv5(2)} + + Upon advancement to the level of Proposed Standard RFC, the Kerberos + V5 GSS-API mechanism will be identified by an Object Identifier + having the value: + + {iso(1) member-body(2) United States(840) mit(113554) infosys(1) + gssapi(2) krb5(2)} + +1.1. Context Establishment Tokens + + Per RFC-1508, Appendix B, the initial context establishment token + will be enclosed within framing as follows: + + InitialContextToken ::= + [APPLICATION 0] IMPLICIT SEQUENCE { + thisMech MechType + -- MechType is OBJECT IDENTIFIER + -- representing "Kerberos V5" + innerContextToken ANY DEFINED BY thisMech + -- contents mechanism-specific; + -- ASN.1 usage within innerContextToken + -- is not required + } + + The innerContextToken of the initial context token will consist of a + Kerberos V5 KRB_AP_REQ message, preceded by a two-byte token-id + (TOK_ID) field, which shall contain the value 01 00. + + The above GSS-API framing shall be applied to all tokens emitted by + the Kerberos V5 GSS-API mechanism, including KRB_AP_REP, KRB_ERROR, + context-deletion, and per-message tokens, not just to the initial + token in a context establishment sequence. While not required by + RFC-1508, this enables implementations to perform enhanced error- + checking. The innerContextToken field of context establishment tokens + for the Kerberos V5 GSS-API mechanism will contain a Kerberos message + (KRB_AP_REQ, KRB_AP_REP or KRB_ERROR), preceded by a 2-byte TOK_ID + field containing 01 00 for KRB_AP_REQ messages, 02 00 for KRB_AP_REP + messages and 03 00 for KRB_ERROR messages. + + + + + + +Linn Standards Track [Page 2] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + +1.1.1. Initial Token + + Relevant KRB_AP_REQ syntax (from RFC-1510) is as follows: + + AP-REQ ::= [APPLICATION 14] SEQUENCE { + pvno [0] INTEGER, -- indicates Version 5 + msg-type [1] INTEGER, -- indicates KRB_AP_REQ + ap-options[2] APOptions, + ticket[3] Ticket, + authenticator[4] EncryptedData + } + + APOptions ::= BIT STRING { + reserved (0), + use-session-key (1), + mutual-required (2) + } + + Ticket ::= [APPLICATION 1] SEQUENCE { + tkt-vno [0] INTEGER, -- indicates Version 5 + realm [1] Realm, + sname [2] PrincipalName, + enc-part [3] EncryptedData + } + + -- Encrypted part of ticket + EncTicketPart ::= [APPLICATION 3] SEQUENCE { + flags[0] TicketFlags, + key[1] EncryptionKey, + crealm[2] Realm, + cname[3] PrincipalName, + transited[4] TransitedEncoding, + authtime[5] KerberosTime, + starttime[6] KerberosTime OPTIONAL, + endtime[7] KerberosTime, + renew-till[8] KerberosTime OPTIONAL, + caddr[9] HostAddresses OPTIONAL, + authorization-data[10] AuthorizationData OPTIONAL + } + + -- Unencrypted authenticator + Authenticator ::= [APPLICATION 2] SEQUENCE { + authenticator-vno[0] INTEGER, + crealm[1] Realm, + cname[2] PrincipalName, + cksum[3] Checksum OPTIONAL, + cusec[4] INTEGER, + ctime[5] KerberosTime, + + + +Linn Standards Track [Page 3] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + subkey[6] EncryptionKey OPTIONAL, + seq-number[7] INTEGER OPTIONAL, + authorization-data[8] AuthorizationData OPTIONAL + } + + For purposes of this specification, the authenticator shall include + the optional sequence number, and the checksum field shall be used to + convey channel binding, service flags, and optional delegation + information. The checksum will have a type of 0x8003 (a value being + registered within the Kerberos protocol specification), and a value + field of at least 24 bytes in length. The length of the value field + is extended beyond 24 bytes if and only if an optional facility to + carry a Kerberos-defined KRB_CRED message for delegation purposes is + supported by an implementation and active on a context. When + delegation is active, a TGT with its FORWARDABLE flag set will be + transferred within the KRB_CRED message. + + The checksum value field's format is as follows: + + Byte Name Description + 0..3 Lgth Number of bytes in Bnd field; + Currently contains hex 10 00 00 00 + (16, represented in little-endian form) + 4..19 Bnd MD5 hash of channel bindings, taken over all non-null + components of bindings, in order of declaration. + Integer fields within channel bindings are represented + in little-endian order for the purposes of the MD5 + calculation. + 20..23 Flags Bit vector of context-establishment flags, + with values consistent with RFC-1509, p. 41: + GSS_C_DELEG_FLAG: 1 + GSS_C_MUTUAL_FLAG: 2 + GSS_C_REPLAY_FLAG: 4 + GSS_C_SEQUENCE_FLAG: 8 + GSS_C_CONF_FLAG: 16 + GSS_C_INTEG_FLAG: 32 + The resulting bit vector is encoded into bytes 20..23 + in little-endian form. + 24..25 DlgOpt The Delegation Option identifier (=1) [optional] + 26..27 Dlgth The length of the Deleg field. [optional] + 28..n Deleg A KRB_CRED message (n = Dlgth + 29) [optional] + + In computing the contents of the "Bnd" field, the following detailed + points apply: + + (1) Each integer field shall be formatted into four bytes, using + little-endian byte ordering, for purposes of MD5 hash + computation. + + + +Linn Standards Track [Page 4] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + (2) All input length fields within gss_buffer_desc elements of a + gss_channel_bindings_struct, even those which are zero-valued, + shall be included in the hash calculation; the value elements of + gss_buffer_desc elements shall be dereferenced, and the + resulting data shall be included within the hash computation, + only for the case of gss_buffer_desc elements having non-zero + length specifiers. + + (3) If the caller passes the value GSS_C_NO_BINDINGS instead of + a valid channel bindings structure, the Bnd field shall be set + to 16 zero-valued bytes. + + In the initial Kerberos V5 GSS-API mechanism token (KRB_AP_REQ token) + from initiator to target, the GSS_C_DELEG_FLAG, GSS_C_MUTUAL_FLAG, + GSS_C_REPLAY_FLAG, and GSS_C_SEQUENCE_FLAG values shall each be set + as the logical AND of the initiator's corresponding request flag to + GSS_Init_sec_context() and a Boolean indicator of whether that + optional service is available to GSS_Init_sec_context()'s caller. + GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG, for which no corresponding + context-level input indicator flags to GSS_Init_sec_context() exist, + shall each be set to indicate whether their respective per-message + protection services are available for use on the context being + established. + + When input source address channel binding values are provided by a + caller (i.e., unless the input argument is GSS_C_NO_BINDINGS or the + source address specifier value within the input structure is + GSS_C_NULL_ADDRTYPE), and the corresponding token received from the + context's peer bears address restrictions, it is recommended that an + implementation of the Kerberos V5 GSS-API mechanism should check that + the source address as provided by the caller matches that in the + received token, and should return the GSS_S_BAD_BINDINGS major_status + value if a mismatch is detected. Note: discussion is ongoing about + the strength of recommendation to be made in this area, and on the + circumstances under which such a recommendation should be applicable; + implementors are therefore advised that changes on this matter may be + included in subsequent versions of this specification. + +1.1.2. Response Tokens + + A context establishment sequence based on the Kerberos V5 mechanism + will perform one-way authentication (without confirmation or any + return token from target to initiator in response to the initiator's + KRB_AP_REQ) if the mutual_req bit is not set in the application's + call to GSS_Init_sec_context(). Applications requiring confirmation + that their authentication was successful should request mutual + authentication, resulting in a "mutual-required" indication within + KRB_AP_REQ APoptions and the setting of the mutual_req bit in the + + + +Linn Standards Track [Page 5] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + flags field of the authenticator checksum. In response to such a + request, the context target will reply to the initiator with a token + containing either a KRB_AP_REP or KRB_ERROR, completing the mutual + context establishment exchange. + + Relevant KRB_AP_REP syntax is as follows: + + AP-REP ::= [APPLICATION 15] SEQUENCE { + pvno [0] INTEGER, -- represents Kerberos V5 + msg-type [1] INTEGER, -- represents KRB_AP_REP + enc-part [2] EncryptedData + } + + EncAPRepPart ::= [APPLICATION 27] SEQUENCE { + ctime [0] KerberosTime, + cusec [1] INTEGER, + subkey [2] EncryptionKey OPTIONAL, + seq-number [3] INTEGER OPTIONAL + } + + The optional seq-number element within the AP-REP's EncAPRepPart + shall be included. + + The syntax of KRB_ERROR is as follows: + + KRB-ERROR ::= [APPLICATION 30] SEQUENCE { + pvno[0] INTEGER, + msg-type[1] INTEGER, + ctime[2] KerberosTime OPTIONAL, + cusec[3] INTEGER OPTIONAL, + stime[4] KerberosTime, + susec[5] INTEGER, + error-code[6] INTEGER, + crealm[7] Realm OPTIONAL, + cname[8] PrincipalName OPTIONAL, + realm[9] Realm, -- Correct realm + sname[10] PrincipalName, -- Correct name + e-text[11] GeneralString OPTIONAL, + e-data[12] OCTET STRING OPTIONAL + } + + Values to be transferred in the error-code field of a KRB-ERROR + message are defined in [RFC-1510], not in this specification. + + + + + + + + +Linn Standards Track [Page 6] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + +1.2. Per-Message and Context Deletion Tokens + + Three classes of tokens are defined in this section: "MIC" tokens, + emitted by calls to GSS_GetMIC() (formerly GSS_Sign()) and consumed + by calls to GSS_VerifyMIC() (formerly GSS_Verify()), "Wrap" tokens, + emitted by calls to GSS_Wrap() (formerly GSS_Seal()) and consumed by + calls to GSS_Unwrap() (formerly GSS_Unseal()), and context deletion + tokens, emitted by calls to GSS_Delete_sec_context() and consumed by + calls to GSS_Process_context_token(). Note: References to GSS-API + per-message routines in the remainder of this specification will be + based on those routines' newer recommended names rather than those + names' predecessors. + + Several variants of cryptographic keys are used in generation and + processing of per-message tokens: + + (1) context key: uses Kerberos session key (or subkey, if + present in authenticator emitted by context initiator) directly + + (2) confidentiality key: forms variant of context key by + exclusive-OR with the hexadecimal constant f0f0f0f0f0f0f0f0. + + (3) MD2.5 seed key: forms variant of context key by reversing + the bytes of the context key (i.e. if the original key is the + 8-byte sequence {aa, bb, cc, dd, ee, ff, gg, hh}, the seed key + will be {hh, gg, ff, ee, dd, cc, bb, aa}). + +1.2.1. Per-message Tokens - MIC + +Use of the GSS_GetMIC() call yields a token, separate from the user +data being protected, which can be used to verify the integrity of +that data as received. The token has the following format: + + Byte no Name Description + 0..1 TOK_ID Identification field. + Tokens emitted by GSS_GetMIC() contain + the hex value 01 01 in this field. + 2..3 SGN_ALG Integrity algorithm indicator. + 00 00 - DES MAC MD5 + 01 00 - MD2.5 + 02 00 - DES MAC + 4..7 Filler Contains ff ff ff ff + 8..15 SND_SEQ Sequence number field. + 16..23 SGN_CKSUM Checksum of "to-be-signed data", + calculated according to algorithm + specified in SGN_ALG field. + + + + + +Linn Standards Track [Page 7] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + GSS-API tokens must be encapsulated within the higher-level protocol + by the application; no embedded length field is necessary. + +1.2.1.1. Checksum + + Checksum calculation procedure (common to all algorithms): Checksums + are calculated over the data field, logically prepended by the first + 8 bytes of the plaintext packet header. The resulting value binds + the data to the packet type and signature algorithm identifier + fields. + + DES MAC MD5 algorithm: The checksum is formed by computing an MD5 + [RFC-1321] hash over the plaintext data, and then computing a DES-CBC + MAC on the 16-byte MD5 result. A standard 64-bit DES-CBC MAC is + computed per [FIPS-PUB-113], employing the context key and a zero IV. + The 8-byte result is stored in the SGN_CKSUM field. + + MD2.5 algorithm: The checksum is formed by first DES-CBC encrypting a + 16-byte zero-block, using a zero IV and a key formed by reversing the + bytes of the context key (i.e. if the original key is the 8-byte + sequence {aa, bb, cc, dd, ee, ff, gg, hh}, the checksum key will be + {hh, gg, ff, ee, dd, cc, bb, aa}). The resulting 16-byte value is + logically prepended to the to-be-signed data. A standard MD5 + checksum is calculated over the combined data, and the first 8 bytes + of the result are stored in the SGN_CKSUM field. Note 1: we refer to + this algorithm informally as "MD2.5" to connote the fact that it uses + half of the 128 bits generated by MD5; use of only a subset of the + MD5 bits is intended to protect against the prospect that data could + be postfixed to an existing message with corresponding modifications + being made to the checksum. Note 2: This algorithm is fairly novel + and has received more limited evaluation than that to which other + integrity algorithms have been subjected. An initial, limited + evaluation indicates that it may be significantly weaker than DES MAC + MD5. + + DES-MAC algorithm: A standard 64-bit DES-CBC MAC is computed on the + plaintext data per [FIPS-PUB-113], employing the context key and a + zero IV. Padding procedures to accomodate plaintext data lengths + which may not be integral multiples of 8 bytes are defined in [FIPS- + PUB-113]. The result is an 8-byte value, which is stored in the + SGN_CKSUM field. Support for this algorithm may not be present in + all implementations. + +1.2.1.2. Sequence Number + + Sequence number field: The 8 byte plaintext sequence number field is + formed from the sender's four-byte sequence number as follows. If + the four bytes of the sender's sequence number are named s0, s1, s2 + + + +Linn Standards Track [Page 8] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + and s3 (from least to most significant), the plaintext sequence + number field is the 8 byte sequence: (s0, s1, s2, s3, di, di, di, + di), where 'di' is the direction-indicator (Hex 0 - sender is the + context initiator, Hex FF - sender is the context acceptor). The + field is then DES-CBC encrypted using the context key and an IV + formed from the first 8 bytes of the previously calculated SGN_CKSUM + field. After sending a GSS_GetMIC() or GSS_Wrap() token, the sender's + sequence number is incremented by one. + + The receiver of the token will first verify the SGN_CKSUM field. If + valid, the sequence number field may be decrypted and compared to the + expected sequence number. The repetition of the (effectively 1-bit) + direction indicator within the sequence number field provides + redundancy so that the receiver may verify that the decryption + succeeded. + + Since the checksum computation is used as an IV to the sequence + number decryption, attempts to splice a checksum and sequence number + from different messages will be detected. The direction indicator + will detect packets that have been maliciously reflected. + + The sequence number provides a basis for detection of replayed + tokens. Replay detection can be performed using state information + retained on received sequence numbers, interpreted in conjunction + with the security context on which they arrive. + + Provision of per-message replay and out-of-sequence detection + services is optional for implementations of the Kerberos V5 GSS-API + mechanism. Further, it is recommended that implementations of the + Kerberos V5 GSS-API mechanism which offer these services should honor + a caller's request that the services be disabled on a context. + Specifically, if replay_det_req_flag is input FALSE, replay_det_state + should be returned FALSE and the GSS_DUPLICATE_TOKEN and + GSS_OLD_TOKEN stati should not be indicated as a result of duplicate + detection when tokens are processed; if sequence_req_flag is input + FALSE, sequence_state should be returned FALSE and + GSS_DUPLICATE_TOKEN, GSS_OLD_TOKEN, and GSS_UNSEQ_TOKEN stati should + not be indicated as a result of out-of-sequence detection when tokens + are processed. + +1.2.2. Per-message Tokens - Wrap + + Use of the GSS_Wrap() call yields a token which encapsulates the + input user data (optionally encrypted) along with associated + integrity check quantities. The token emitted by GSS_Wrap() consists + of an integrity header whose format is identical to that emitted by + GSS_GetMIC() (except that the TOK_ID field contains the value 02 01), + followed by a body portion that contains either the plaintext data + + + +Linn Standards Track [Page 9] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + (if SEAL_ALG = ff ff) or encrypted data for any other supported value + of SEAL_ALG. Currently, only SEAL_ALG = 00 00 is supported, and + means that DES-CBC encryption is being used to protect the data. + + The GSS_Wrap() token has the following format: + + Byte no Name Description + 0..1 TOK_ID Identification field. + Tokens emitted by GSS_Wrap() contain + the hex value 02 01 in this field. + 2..3 SGN_ALG Checksum algorithm indicator. + 00 00 - DES MAC MD5 + 01 00 - MD2.5 + 02 00 - DES MAC + 4..5 SEAL_ALG ff ff - none + 00 00 - DES + 6..7 Filler Contains ff ff + 8..15 SND_SEQ Encrypted sequence number field. + 16..23 SGN_CKSUM Checksum of plaintext padded data, + calculated according to algorithm + specified in SGN_ALG field. + 24..last Data encrypted or plaintext padded data + + GSS-API tokens must be encapsulated within the higher-level protocol + by the application; no embedded length field is necessary. + +1.2.2.1. Checksum + + Checksum calculation procedure (common to all algorithms): Checksums + are calculated over the plaintext padded data field, logically + prepended by the first 8 bytes of the plaintext packet header. The + resulting signature binds the data to the packet type, protocol + version, and signature algorithm identifier fields. + + DES MAC MD5 algorithm: The checksum is formed by computing an MD5 + hash over the plaintext padded data, and then computing a DES-CBC MAC + on the 16-byte MD5 result. A standard 64-bit DES-CBC MAC is computed + per [FIPS-PUB-113], employing the context key and a zero IV. The 8- + byte result is stored in the SGN_CKSUM field. + + MD2.5 algorithm: The checksum is formed by first DES-CBC encrypting a + 16-byte zero-block, using a zero IV and a key formed by reversing the + bytes of the context key (i.e., if the original key is the 8-byte + sequence {aa, bb, cc, dd, ee, ff, gg, hh}, the checksum key will be + {hh, gg, ff, ee, dd, cc, bb, aa}). The resulting 16-byte value is + logically pre-pended to the "to-be-signed data". A standard MD5 + checksum is calculated over the combined data, and the first 8 bytes + of the result are stored in the SGN_CKSUM field. + + + +Linn Standards Track [Page 10] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + DES-MAC algorithm: A standard 64-bit DES-CBC MAC is computed on the + plaintext padded data per [FIPS-PUB-113], employing the context key + and a zero IV. The plaintext padded data is already assured to be an + integral multiple of 8 bytes; no additional padding is required or + applied in order to accomplish MAC calculation. The result is an 8- + byte value, which is stored in the SGN_CKSUM field. Support for this + lgorithm may not be present in all implementations. + +1.2.2.2. Sequence Number + + Sequence number field: The 8 byte plaintext sequence number field is + formed from the sender's four-byte sequence number as follows. If + the four bytes of the sender's sequence number are named s0, s1, s2 + and s3 (from least to most significant), the plaintext sequence + number field is the 8 byte sequence: (s0, s1, s2, s3, di, di, di, + di), where 'di' is the direction-indicator (Hex 0 - sender is the + context initiator, Hex FF - sender is the context acceptor). + + The field is then DES-CBC encrypted using the context key and an IV + formed from the first 8 bytes of the SEAL_CKSUM field. + + After sending a GSS_GetMIC() or GSS_Wrap() token, the sender's + sequence numbers are incremented by one. + +1.2.2.3. Padding + + Data padding: Before encryption and/or signature calculation, + plaintext data is padded to the next highest multiple of 8 bytes, by + appending between 1 and 8 bytes, the value of each such byte being + the total number of pad bytes. For example, given data of length 20 + bytes, four pad bytes will be appended, and each byte will contain + the hex value 04. An 8-byte random confounder is prepended to the + data, and signatures are calculated over the resulting padded + plaintext. + + After padding, the data is encrypted according to the algorithm + specified in the SEAL_ALG field. For SEAL_ALG=DES (the only non-null + algorithm currently supported), the data is encrypted using DES-CBC, + with an IV of zero. The key used is derived from the established + context key by XOR-ing the context key with the hexadecimal constant + f0f0f0f0f0f0f0f0. + +1.2.3. Context deletion token + + The token emitted by GSS_Delete_sec_context() is based on the packet + format for tokens emitted by GSS_GetMIC(). The context-deletion + token has the following format: + + + + +Linn Standards Track [Page 11] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + Byte no Name Description + 0..1 TOK_ID Identification field. + Tokens emitted by + GSS_Delete_sec_context() contain + the hex value 01 02 in this field. + 2..3 SGN_ALG Integrity algorithm indicator. + 00 00 - DES MAC MD5 + 01 00 - MD2.5 + 02 00 - DES MAC + 4..7 Filler Contains ff ff ff ff + 8..15 SND_SEQ Sequence number field. + 16..23 SGN_CKSUM Checksum of "to-be-signed data", + calculated according to algorithm + specified in SGN_ALG field. + + SGN_ALG and SND_SEQ will be calculated as for tokens emitted by + GSS_GetMIC(). The SGN_CKSUM will be calculated as for tokens emitted + by GSS_GetMIC(), except that the user-data component of the "to-be- + signed" data will be a zero-length string. + +2. Name Types and Object Identifiers + + This section discusses the name types which may be passed as input to + the Kerberos V5 GSS-API mechanism's GSS_Import_name() call, and their + associated identifier values. It defines interface elements in + support of portability, and assumes use of C language bindings per + RFC-1509. In addition to specifying OID values for name type + identifiers, symbolic names are included and recommended to GSS-API + implementors in the interests of convenience to callers. It is + understood that not all implementations of the Kerberos V5 GSS-API + mechanism need support all name types in this list, and that + additional name forms will likely be added to this list over time. + Further, the definitions of some or all name types may later migrate + to other, mechanism-independent, specifications. The occurrence of a + name type in this specification is specifically not intended to + suggest that the type may be supported only by an implementation of + the Kerberos V5 mechanism. In particular, the occurrence of the + string "_KRB5_" in the symbolic name strings constitutes a means to + unambiguously register the name strings, avoiding collision with + other documents; it is not meant to limit the name types' usage or + applicability. + + For purposes of clarification to GSS-API implementors, this section's + discussion of some name forms describes means through which those + forms can be supported with existing Kerberos technology. These + discussions are not intended to preclude alternative implementation + strategies for support of the name forms within Kerberos mechanisms + or mechanisms based on other technologies. To enhance application + + + +Linn Standards Track [Page 12] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + portability, implementors of mechanisms are encouraged to support + name forms as defined in this section, even if their mechanisms are + independent of Kerberos V5. + +2.1. Mandatory Name Forms + + This section discusses name forms which are to be supported by all + conformant implementations of the Kerberos V5 GSS-API mechanism. + +2.1.1. Kerberos Principal Name Form + + This name form shall be represented by the Object Identifier {iso(1) + member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) + krb5(2) krb5_name(1)}. The recommended symbolic name for this type + is "GSS_KRB5_NT_PRINCIPAL_NAME". + + This name type corresponds to the single-string representation of a + Kerberos name. (Within the MIT Kerberos V5 implementation, such + names are parseable with the krb5_parse_name() function.) The + elements included within this name representation are as follows, + proceeding from the beginning of the string: + + (1) One or more principal name components; if more than one + principal name component is included, the components are + separated by `/`. Arbitrary octets may be included within + principal name components, with the following constraints and + special considerations: + + (1a) Any occurrence of the characters `@` or `/` within a + name component must be immediately preceded by the `\` + quoting character, to prevent interpretation as a component + or realm separator. + + (1b) The ASCII newline, tab, backspace, and null characters + may occur directly within the component or may be + represented, respectively, by `\n`, `\t`, `\b`, or `\0`. + + (1c) If the `\` quoting character occurs outside the contexts + described in (1a) and (1b) above, the following character is + interpreted literally. As a special case, this allows the + doubled representation `\\` to represent a single occurrence + of the quoting character. + + (1d) An occurrence of the `\` quoting character as the last + character of a component is illegal. + + + + + + +Linn Standards Track [Page 13] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + (2) Optionally, a `@` character, signifying that a realm name + immediately follows. If no realm name element is included, the + local realm name is assumed. The `/` , `:`, and null characters + may not occur within a realm name; the `@`, newline, tab, and + backspace characters may be included using the quoting + conventions described in (1a), (1b), and (1c) above. + +2.1.2. Host-Based Service Name Form + + This name form has been incorporated at the mechanism-independent + GSS-API level as of GSS-API, Version 2. This subsection retains the + Object Identifier and symbolic name assignments previously made at + the Kerberos V5 GSS-API mechanism level, and adopts the definition as + promoted to the mechanism-independent level. + + This name form shall be represented by the Object Identifier {iso(1) + member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) + generic(1) service_name(4)}. The previously recommended symbolic + name for this type is "GSS_KRB5_NT_HOSTBASED_SERVICE_NAME". The + currently preferred symbolic name for this type is + "GSS_C_NT_HOSTBASED_SERVICE". + + This name type is used to represent services associated with host + computers. This name form is constructed using two elements, + "service" and "hostname", as follows: + + service@hostname + + When a reference to a name of this type is resolved, the "hostname" + is canonicalized by attempting a DNS lookup and using the fully- + qualified domain name which is returned, or by using the "hostname" + as provided if the DNS lookup fails. The canonicalization operation + also maps the host's name into lower-case characters. + + The "hostname" element may be omitted. If no "@" separator is + included, the entire name is interpreted as the service specifier, + with the "hostname" defaulted to the canonicalized name of the local + host. + + Values for the "service" element will be registered with the IANA. + +2.1.3. Exported Name Object Form for Kerberos V5 Mechanism + + Support for this name form is not required for GSS-V1 + implementations, but will be required for use in conjunction with the + GSS_Export_name() call planned for GSS-API Version 2. Use of this + name form will be signified by a "GSS-API Exported Name Object" OID + value which will be defined at the mechanism-independent level for + + + +Linn Standards Track [Page 14] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + GSS-API Version 2. + + This name type represents a self-describing object, whose framing + structure will be defined at the mechanism-independent level for + GSS-API Version 2. When generated by the Kerberos V5 mechanism, the + Mechanism OID within the exportable name shall be that of the + Kerberos V5 mechanism. The name component within the exportable name + shall be a contiguous string with structure as defined for the + Kerberos Principal Name Form. + + In order to achieve a distinguished encoding for comparison purposes, + the following additional constraints are imposed on the export + operation: + + (1) all occurrences of the characters `@`, `/`, and `\` within + principal components or realm names shall be quoted with an + immediately-preceding `\`. + + (2) all occurrences of the null, backspace, tab, or newline + characters within principal components or realm names will be + represented, respectively, with `\0`, `\b`, `\t`, or `\n`. + + (3) the `\` quoting character shall not be emitted within an + exported name except to accomodate cases (1) and (2). + +2.2. Optional Name Forms + + This section discusses additional name forms which may optionally be + supported by implementations of the Kerberos V5 GSS-API mechanism. + It is recognized that some of the name forms cited here are derived + from UNIX(tm) operating system platforms; some listed forms may be + irrelevant to non-UNIX platforms, and definition of additional forms + corresponding to such platforms may also be appropriate. It is also + recognized that OS-specific functions outside GSS-API are likely to + exist in order to perform translations among these forms, and that + GSS-API implementations supporting these forms may themselves be + layered atop such OS-specific functions. Inclusion of this support + within GSS-API implementations is intended as a convenience to + applications. + +2.2.1. User Name Form + + This name form shall be represented by the Object Identifier {iso(1) + member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) + generic(1) user_name(1)}. The recommended symbolic name for this + type is "GSS_KRB5_NT_USER_NAME". + + This name type is used to indicate a named user on a local system. + + + +Linn Standards Track [Page 15] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + Its interpretation is OS-specific. This name form is constructed as: + + username + + Assuming that users' principal names are the same as their local + operating system names, an implementation of GSS_Import_name() based + on Kerberos V5 technology can process names of this form by + postfixing an "@" sign and the name of the local realm. + +2.2.2. Machine UID Form + + This name form shall be represented by the Object Identifier {iso(1) + member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) + generic(1) machine_uid_name(2)}. The recommended symbolic name for + this type is "GSS_KRB5_NT_MACHINE_UID_NAME". + + This name type is used to indicate a numeric user identifier + corresponding to a user on a local system. Its interpretation is + OS-specific. The gss_buffer_desc representing a name of this type + should contain a locally-significant uid_t, represented in host byte + order. The GSS_Import_name() operation resolves this uid into a + username, which is then treated as the User Name Form. + +2.2.3. String UID Form + + This name form shall be represented by the Object Identifier {iso(1) + member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) + generic(1) string_uid_name(3)}. The recommended symbolic name for + this type is "GSS_KRB5_NT_STRING_UID_NAME". + + This name type is used to indicate a string of digits representing + the numeric user identifier of a user on a local system. Its + interpretation is OS-specific. This name type is similar to the + Machine UID Form, except that the buffer contains a string + representing the uid_t. + +3. Credentials Management + + The Kerberos V5 protocol uses different credentials (in the GSSAPI + sense) for initiating and accepting security contexts. Normal + clients receive a ticket-granting ticket (TGT) and an associated + session key at "login" time; the pair of a TGT and its corresponding + session key forms a credential which is suitable for initiating + security contexts. A ticket-granting ticket, its session key, and + any other (ticket, key) pairs obtained through use of the ticket- + granting-ticket, are typically stored in a Kerberos V5 credentials + cache, sometimes known as a ticket file. + + + + +Linn Standards Track [Page 16] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + The encryption key used by the Kerberos server to seal tickets for a + particular application service forms the credentials suitable for + accepting security contexts. These service keys are typically stored + in a Kerberos V5 key table, or srvtab file. In addition to their use + as accepting credentials, these service keys may also be used to + obtain initiating credentials for their service principal. + + The Kerberos V5 mechanism's credential handle may contain references + to either or both types of credentials. It is a local matter how the + Kerberos V5 mechanism implementation finds the appropriate Kerberos + V5 credentials cache or key table. + + However, when the Kerberos V5 mechanism attempts to obtain initiating + credentials for a service principal which are not available in a + credentials cache, and the key for that service principal is + available in a Kerberos V5 key table, the mechanism should use the + service key to obtain initiating credentials for that service. This + should be accomplished by requesting a ticket-granting-ticket from + the Kerberos Key Distribution Center (KDC), and decrypting the KDC's + reply using the service key. + +4. Parameter Definitions + + This section defines parameter values used by the Kerberos V5 GSS-API + mechanism. It defines interface elements in support of portability, + and assumes use of C language bindings per RFC-1509. + +4.1. Minor Status Codes + + This section recommends common symbolic names for minor_status values + to be returned by the Kerberos V5 GSS-API mechanism. Use of these + definitions will enable independent implementors to enhance + application portability across different implementations of the + mechanism defined in this specification. (In all cases, + implementations of GSS_Display_status() will enable callers to + convert minor_status indicators to text representations.) Each + implementation should make available, through include files or other + means, a facility to translate these symbolic names into the concrete + values which a particular GSS-API implementation uses to represent + the minor_status values specified in this section. + + It is recognized that this list may grow over time, and that the need + for additional minor_status codes specific to particular + implementations may arise. It is recommended, however, that + implementations should return a minor_status value as defined on a + mechanism-wide basis within this section when that code is accurately + representative of reportable status rather than using a separate, + implementation-defined code. + + + +Linn Standards Track [Page 17] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + +4.1.1. Non-Kerberos-specific codes + + GSS_KRB5_S_G_BAD_SERVICE_NAME + /* "No @ in SERVICE-NAME name string" */ + GSS_KRB5_S_G_BAD_STRING_UID + /* "STRING-UID-NAME contains nondigits" */ + GSS_KRB5_S_G_NOUSER + /* "UID does not resolve to username" */ + GSS_KRB5_S_G_VALIDATE_FAILED + /* "Validation error" */ + GSS_KRB5_S_G_BUFFER_ALLOC + /* "Couldn't allocate gss_buffer_t data" */ + GSS_KRB5_S_G_BAD_MSG_CTX + /* "Message context invalid" */ + GSS_KRB5_S_G_WRONG_SIZE + /* "Buffer is the wrong size" */ + GSS_KRB5_S_G_BAD_USAGE + /* "Credential usage type is unknown" */ + GSS_KRB5_S_G_UNKNOWN_QOP + /* "Unknown quality of protection specified" */ + +4.1.2. Kerberos-specific-codes + + GSS_KRB5_S_KG_CCACHE_NOMATCH + /* "Principal in credential cache does not match desired name" */ + GSS_KRB5_S_KG_KEYTAB_NOMATCH + /* "No principal in keytab matches desired name" */ + GSS_KRB5_S_KG_TGT_MISSING + /* "Credential cache has no TGT" */ + GSS_KRB5_S_KG_NO_SUBKEY + /* "Authenticator has no subkey" */ + GSS_KRB5_S_KG_CONTEXT_ESTABLISHED + /* "Context is already fully established" */ + GSS_KRB5_S_KG_BAD_SIGN_TYPE + /* "Unknown signature type in token" */ + GSS_KRB5_S_KG_BAD_LENGTH + /* "Invalid field length in token" */ + GSS_KRB5_S_KG_CTX_INCOMPLETE + /* "Attempt to use incomplete security context" */ + +4.2. Quality of Protection Values + + This section defines Quality of Protection (QOP) values to be used + with the Kerberos V5 GSS-API mechanism as input to GSS_Wrap() and + GSS_GetMIC() routines in order to select among alternate integrity + and confidentiality algorithms. Additional QOP values may be added in + future versions of this specification. Non-overlapping bit positions + are and will be employed in order that both integrity and + + + +Linn Standards Track [Page 18] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + + confidentiality QOP may be selected within a single parameter, via + inclusive-OR of the specified integrity and confidentiality values. + +4.2.1. Integrity Algorithms + + The following Quality of Protection (QOP) values are currently + defined for the Kerberos V5 GSS-API mechanism, and are used to select + among alternate integrity checking algorithms. + + GSS_KRB5_INTEG_C_QOP_MD5 (numeric value: 1) + /* Integrity using partial MD5 ("MD2.5") of plaintext */ + + GSS_KRB5_INTEG_C_QOP_DES_MD5 (numeric value: 2) + /* Integrity using DES MAC of MD5 of plaintext */ + + GSS_KRB5_INTEG_C_QOP_DES_MAC (numeric value: 3) + /* Integrity using DES MAC of plaintext */ + +4.2.2. Confidentiality Algorithms + + Only one confidentiality QOP value is currently defined for the + Kerberos V5 GSS-API mechanism: + + GSS_KRB5_CONF_C_QOP_DES (numeric value: 0) + /* Confidentiality with DES */ + + Note: confidentiality QOP should be indicated only by GSS-API calls + capable of providing confidentiality services. If non-zero + confidentiality QOP values are defined in future to represent + different algorithms, therefore, the bit positions containing those + values should be cleared before being returned by implementations of + GSS_GetMIC() and GSS_VerifyMIC(). + +4.3. Buffer Sizes + + All implementations of this specification shall be capable of + accepting buffers of at least 16 Kbytes as input to GSS_GetMIC(), + GSS_VerifyMIC(), and GSS_Wrap(), and shall be capable of accepting + the output_token generated by GSS_Wrap() for a 16 Kbyte input buffer + as input to GSS_Unwrap(). Support for larger buffer sizes is optional + but recommended. + + + + + + + + + + +Linn Standards Track [Page 19] + +RFC 1964 Kerberos Version 5 GSS-API June 1996 + + +5. Security Considerations + + Security issues are discussed throughout this memo. + +6. References + + + [RFC-1321]: Rivest, R., "The MD5 Message-Digest Algorithm", RFC + 1321, April 1992. + + [RFC-1508]: Linn, J., "Generic Security Service Application Program + Interface", RFC 1508, September 1993. + + [RFC-1509]: Wray, J., "Generic Security Service Application Program + Interface: C-bindings", RFC 1509, September 1993. + + [RFC-1510]: Kohl, J., and C. Neuman, "The Kerberos Network + Authentication Service (V5)", RFC 1510, September 1993. + + [FIPS-PUB-113]: National Bureau of Standards, Federal Information + Processing Standard 113, "Computer Data Authentication", May 1985. + +AUTHOR'S ADDRESS + + John Linn + OpenVision Technologies + One Main St. + Cambridge, MA 02142 USA + + Phone: +1 617.374.2245 + EMail: John.Linn@ov.com + + + + + + + + + + + + + + + + + + + + +Linn Standards Track [Page 20] + |