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diff --git a/crypto/heimdal/doc/standardisation/draft-raeburn-cat-gssapi-krb5-3des-00.txt b/crypto/heimdal/doc/standardisation/draft-raeburn-cat-gssapi-krb5-3des-00.txt deleted file mode 100644 index 24325fd..0000000 --- a/crypto/heimdal/doc/standardisation/draft-raeburn-cat-gssapi-krb5-3des-00.txt +++ /dev/null @@ -1,281 +0,0 @@ -CAT Working Group K. Raeburn -Internet-draft MIT -Category: July 14, 2000 -Updates: RFC 1964 -Document: draft-raeburn-cat-gssapi-krb5-3des-00.txt - - Triple-DES Support for the Kerberos 5 GSSAPI Mechanism - -Status of this Memo - - This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of RFC2026 [RFC2026]. 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. - -1. Abstract - - The MIT Kerberos 5 release version 1.2 includes support for - triple-DES with key derivation [KrbRev]. Recent work by the EFF - [EFF] has demonstrated the vulnerability of single-DES mechanisms - to brute-force attacks by sufficiently motivated and well-funded - parties. - - The GSSAPI Kerberos 5 mechanism definition [GSSAPI-KRB5] - specifically enumerates encryption and checksum types, - independently of how such schemes may be used in Kerberos. In the - long run, a new Kerberos-based mechanism, which does not require - separately enumerating for the GSSAPI mechanism each of the - encryption types defined by Kerberos, appears to be a better - approach. Efforts to produce such a specification are under way. - - In the interest of providing increased security in the interim, - however, MIT is proposing adding support for triple-DES to the - existing mechanism, as described here. - -2. Conventions Used in this Document - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in - this document are to be interpreted as described in RFC 2119. - -3. New Algorithm Identifiers - - One new sealing algorithm is defined, for use in WRAP tokens: - - 02 00 - DES3-KD - - This algorithm uses triple-DES with key derivation, with a usage - value KG_USAGE_SEAL. Padding is still to 8-byte multiples, and the - IV for encrypting application data is zero. - - One new signing algorithm is defined, for use in MIC, Wrap, and - Delete tokens: - - 04 00 - HMAC SHA1 DES3-KD - - This algorithm generates an HMAC using SHA-1 and a derived DES3 key - with usage KG_USAGE_SIGN, as (ought to be described) in [KrbRev]. - - [XXX: The current [KrbRev] description refers to expired I-Ds from - Marc Horowitz. The text in [KrbRev] may be inadequate to produce - an interoperable implementation.] - - The checksum size for this algorithm is 20 octets. See section 5.3 - below for the use of checksum lengths of other than eight bytes. - -4. Key Derivation - - For purposes of key derivation, we add three new usage values to the - list defined in [KrbRev]; one for signing messages, one for - sealing messages, and one for encrypting sequence numbers: - - #define KG_USAGE_SEAL 22 - #define KG_USAGE_SIGN 23 - #define KG_USAGE_SEQ 24 - -5. Adjustments to Previous Definitions - -5.1. Quality of Protection - - The GSSAPI specification [GSSAPI] says that a zero QOP value - indicates the "default". The original specification for the - Kerberos 5 mechanism says that a zero QOP value (or a QOP value - with the appropriate bits clear) means DES encryption. - - Rather than continue to force the use of plain DES when the - application doesn't use mechanism-specific QOP values, the better - choice appears to be to redefine the DES QOP value as some non-zero - value, and define a triple-DES value as well. Then a zero value - continues to imply the default, which would be triple-DES - protection when given a triple-DES session key. - - Our values are: - - GSS_KRB5_INTEG_C_QOP_HMAC_SHA1 0x0004 - /* SHA-1 checksum encrypted with key derivation */ - - GSS_KRB5_CONF_C_QOP_DES 0x0100 - /* plain DES encryption */ - GSS_KRB5_CONF_C_QOP_DES3_KD 0x0200 - /* triple-DES with key derivation */ - - Rather than open the question of whether to specify means for - deriving a key of one type given a key of another type, and the - security implications of whether to generate a long key from a - shorter one, our implementation will simply return an error if the - QOP value specified does not correspond to the session key type. - - [Implementation note: MIT's code does not implement QoP, and - returns an error for any non-zero QoP value.] - -5.2. MIC Sequence Number Encryption - - The sequence numbers are encrypted in the context key (as defined - in [GSSAPI-KRB5] -- this will be either the Kerberos session key or - asubkey provided by the context initiator), using whatever - encryption system is designated by the type of that context key. - The IV is formed from the first N bytes of the SGN_CKSUM field, - where N is the number of bytes needed for the IV. (With all - algorithms described here and in [GSSAPI-KRB5], the checksum is at - least as large as the IV.) - -5.3. Message Layout - - Both MIC and Wrap tokens, as defined in [GSSAPI-KRB5], contain an - checksum field SGN_CKSUM. In [GSSAPI-KRB5], this field was - specified as being 8 bytes long. We now change this size to be - "defined by the checksum algorithm", and retroactively amend the - descriptions of all the checksum algorithms described in - [GSSAPI-KRB5] to explicitly specify 8-byte output. Application - data continues to immediately follow the checksum field in the Wrap - token. - - The revised message descriptions are thus: - - MIC: - - Byte no Name Description - 0..1 TOK_ID Identification field. - 2..3 SGN_ALG Integrity algorithm indicator. - 4..7 Filler Contains ff ff ff ff - 8..15 SND_SEQ Sequence number field. - 16..s+15 SGN_CKSUM Checksum of "to-be-signed data", - calculated according to algorithm - specified in SGN_ALG field. - - Wrap: - - 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. - 4..5 SEAL_ALG Sealing algorithm indicator. - 6..7 Filler Contains ff ff - 8..15 SND_SEQ Encrypted sequence number field. - 16..s+15 SGN_CKSUM Checksum of plaintext padded data, - calculated according to algorithm - specified in SGN_ALG field. - s+16..last Data encrypted or plaintext padded data - - Where "s" indicates the size of the checksum. - - As indicated above in section 2, we define the HMAC SHA1 DES3-KD - checksum algorithm to produce a 20-byte output, so encrypted data - begins at byte 36. - -6. Backwards Compatibility Considerations - - The context initiator SHOULD request of the KDC credentials using - session-key cryptosystem types supported by that implementation; if - the only types returned by the KDC are not supported by the - mechanism implementation, it MUST indicate a failure. This may - seem obvious, but early implementations of both Kerberos and the - GSSAPI Kerberos mechanism supported only DES keys, so the - cryptosystem compatibility question was easy to overlook. - - Under the current mechanism, no negotiation of algorithm types - occurs, so server-side (acceptor) implementations cannot request - that clients not use algorithm types not understood by the server. - However, administration of the server's Kerberos data has to be - done in communication with the KDC, and it is from the KDC that the - client will request credentials. The KDC could therefore be tasked - with limiting session keys for a given service to types actually - supported by the Kerberos and GSSAPI software on the server. - - This does have a drawback for cases where a service principal name - is used both for GSSAPI-based and non-GSSAPI-based communication, - if the GSSAPI implementation does not understand triple-DES but the - Kerberos implementation does. It means that triple-DES session - keys cannot be issued for that service principal, which keeps the - protection of non-GSSAPI services weaker than necessary. However, - in the most recent MIT releases thus far, while triple-DES support - has been present, it has required additional work to enable, so it - is not likely to be in use for many services. - - It would also be possible to have clients attempt to get single-DES - session keys before trying to get triple-DES session keys, and have - the KDC refuse to issue the single-DES keys only for the most - critical of services, for which single-DES protection is considered - inadequate. However, that would eliminate the possibility of - connecting with the more secure cryptosystem to any service that - can be accessed with the weaker cryptosystem. - - We have chosen to go with the former approach, putting the burden - on the KDC administration and gaining the best protection possible - for GSSAPI services, possibly at the cost of protection of - non-GSSAPI Kerberos services running earlier versions of the - software. - -6. Security Considerations - - Various tradeoffs arise regarding the mixing of new and old - software, or GSSAPI-based and non-GSSAPI Kerberos authentication. - They are discussed in section 5. - -7. References - - [EFF] Electronic Frontier Foundation, "Cracking DES: Secrets of - Encryption Research, Wiretap Politics, and Chip Design", O'Reilly & - Associates, Inc., May, 1998. - - [GSSAPI] Linn, J., "Generic Security Service Application Program - Interface Version 2, Update 1", RFC 2743, January, 2000. - - [GSSAPI-KRB5] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", - RFC 1964, June, 1996. - - [KrbRev] Neuman, C., Kohl, J., Ts'o, T., "The Kerberos Network - Authentication Service (V5)", - draft-ietf-cat-kerberos-revisions-05.txt, March 10, 2000. - - [RFC2026] Bradner, S., "The Internet Standards Process -- Revision - 3", RFC 2026, October, 1996. - -8. Author's Address - - Kenneth Raeburn - Massachusetts Institute of Technology - 77 Massachusetts Avenue - Cambridge, MA 02139 - -9. Full Copyright Statement - - Copyright (C) The Internet Society (2000). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph - are included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS 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." |
