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Re: 128 bit block ciphers

1998-06-29 17:17:34
At 02:38 PM 6/29/98 -0400, dontspam-tzeruch(_at_)ceddec(_dot_)com wrote:

   I spotted this a few months ago.  Technically the prefix should be the
   blocksize plus 2 and the text should be changed everywhere (including the
   long description of the reset) replacing 8 with Blocksize.  I have these
   as #defines in my implmentation but they are likely to become variables,
   so I was ready for this.

I'm willing to do this -- replacing 8 with Blocksize, and 10 with
Blocksize+2. It's an easy enough change that provides a lot of clarification.
   For that matter, what is the block size of a stream cipher?  (Applause
   with the sound of one hand clapping if you can answer correctly).  Or one
   that is a number of bits that is not divisible by 8? 

The blocksize of a stream cypher is 1/8 octet. Octet-level stream cyphers
(like RC4) can also be thought of as an 8-bit block cypher. Really.
   It would make sense to change the places that use "8" to Blocksize and
   "10" to Blocksize+2, and do stream ciphers without any CFB (but prefix it
   with either 4 or 10 bytes, the last pair being copies of the penultimate
   pair).  This mod will have to be in the next version of the spec.
I'm willing to do this.


Jon Callas                                  jon(_at_)pgp(_dot_)com
CTO, Total Network Security                 3965 Freedom Circle
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