Re: [Ietf-krb-wg] CF2 test vectors for DES and 3DES

[Jeffrey Hutzelman <[e-mail]>]

--On Thursday, April 30, 2009 04:31:31 PM -0400 Sam Hartman 
<[e-mail]> wrote:

> MIT assumes that DES random bit strings are 7 byte strings that are
> expanded with parity bits.  The RFC 3961 spec assumes that you take an
> eight byte string and do parity fix-up.

I think this is an API issue.  The 3961 random-to-key operation is defined 
in terms of an input bitstring of a particular size.  For single-DES, the 
last paragraph before 6.2.1 says...

   For generation of a key from a random bitstring, we start with a 56-
   bit string and, as with the string-to-key operation above, insert
   parity bits.  If the result is a weak or semi-weak key, we modify it
   by eXclusive-OR with the constant 0x00000000000000F0:

        des_random_to_key(bitstring) {
             return key_correction(add_parity_bits(bitstring));
        }


Thus, 3961 assumes you start with a 56-bit string.  Whether that string is 
represented as seven 8-bit bytes of keying material or as eight 7-bit bytes 
of keying material in 8-bit fields is an implementation matter.

-- Jeff
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