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From: kaz@vision.crest.nt.com (Kaz Kylheku)
Subject: Re: Not intended for use in medical,
Date: 1997/05/09
Message-ID: <5l0cl9$q07@bcrkh13.bnr.ca>#1/1
X-Deja-AN: 240710250
References: <3.0.32.19970423164855.00746db8@mail.4dcomm.com>
 <dewar.863062734@merv> <5ktldo$2pp@bcrkh13.bnr.ca> <dewar.863148621@merv>
Organization: Prism Systems Inc.
Newsgroups: comp.lang.ada
Date: 1997-05-09T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <dewar.863148621@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:
>Kaz said
>
><<I can't think of a reasonable name to give to the two intermediate
>cipher blocks other than 'a' and 'b'>>
>
>Whenever you cannot think of a reasonable name to give to a variable, that
>is a priori suspicious, it suggests that the expression of the algorithm
>involving the variables is not as clear as it might be. Sure, short names

Of course not! This is encryption we are talking about. :)

>are appropriate sometime, but you should always be able to give a very
>clear description of a variable. Essentially this desription is an invariant
>that describes the meaning of the value of the variable
>
>"Intermediate value" is not a very useful invariant!

Hmm. I still can't come up with names. There isn't really an invariant that
governs 'a' and 'b'; their contents get scrambled by the encryption rounds,
according to the arbitrary S-boxes and other operations. The initial values are
also meaningless, because they are just arbitrary bits being encrypted. So 'a'
and 'b' they will have to stay. Note that other identifiers are quite
meaningful. The identifier ``piece'' refers to scheduled portions of the key
material. Likewise ``make_external_cblock'' is a clear reference to conversion
between a more efficient internal representation to a more convenient (to the
user) external representation. There was no problem in naming ``apply_sbox''
or ``mult_combine''. But ``a'' and ``b'' are just faceless victims that
have stuff done to them. :)