Network Working Group                                        M. Horowitz
<draft-ietf-cat-kerb-des3-hmac-sha1-00.txt>             Cygnus Solutions
Internet-Draft                                            November, 1996

           Triple DES with HMAC-SHA1 Kerberos Encryption Type

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   This document defines a new encryption type and a new checksum type
   for use with Kerberos V5 [RFC1510].  This encryption type is based on
   the Triple DES cryptosystem and the HMAC-SHA1 [Krawczyk96] message
   authentication algorithm.

   The des3-cbc-hmac-sha1 encryption type has been assigned the value 7.
   The hmac-sha1-des3 checksum type has been assigned the value 12.

Encryption Type des3-cbc-hmac-sha1

   EncryptedData using this type must be generated as described in
   [Horowitz96].  The encryption algorithm is Triple DES in Outer-CBC
   mode.  The keyed hash algorithm is HMAC-SHA1.  Unless otherwise
   specified, a zero IV must be used.  If the length of the input data
   is not a multiple of the block size, zero octets must be used to pad
   the plaintext to the next eight-octet boundary.  The counfounder must
   be eight random octets (one block).

Checksum Type hmac-sha1-des3

   Checksums using this type must be generated as described in
   [Horowitz96].  The keyed hash algorithm is HMAC-SHA1.

Horowitz                                                        [Page 1]

Internet Draft     Kerberos Triple DES with HMAC-SHA1     November, 1996

Common Requirements

   Where the Triple DES key is represented as an EncryptionKey, it shall
   be represented as three DES keys, with parity bits, concatenated
   together.  The key shall be represented with the most significant bit

   When keys are generated by the derivation function, a key length of
   168 bits shall be used.  The output bit string will be converted to a
   valid Triple DES key by inserting DES parity bits after every seventh

   Any implementation which implements either of the encryption or
   checksum types in this document must support both.

Security Considerations

   This entire document defines encryption and checksum types for use
   with Kerberos V5.


   [Horowitz96] Horowitz, M., "Key Derivation for Kerberos V5", draft-
      horowitz-kerb-key-derivation-00.txt, November 1996.
   [Krawczyk96] Krawczyk, H., Bellare, and M., Canetti, R., "HMAC:
      Keyed-Hashing for Message Authentication", draft-ietf-ipsec-hmac-
      md5-01.txt, August, 1996.
   [RFC1510] Kohl, J. and Neuman, C., "The Kerberos Network
      Authentication Service (V5)", RFC 1510, September 1993.

Author's Address

   Marc Horowitz
   Cygnus Solutions
   955 Massachusetts Avenue
   Cambridge, MA 02139

   Phone: +1 617 354 7688

Horowitz                                                        [Page 2]