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Path: utzoo!utcsri!outer
From: outer@utcsri.UUCP (Richard Outerbridge)
Newsgroups: net.crypt
Subject: Re: Initial permutation in DES
Message-ID: <3132@utcsri.UUCP>
Date: Fri, 18-Jul-86 19:27:39 EDT
Article-I.D.: utcsri.3132
Posted: Fri Jul 18 19:27:39 1986
Date-Received: Fri, 18-Jul-86 20:31:09 EDT
References: <167@zyx.UUCP>
Organization: CSRI, University of Toronto
Lines: 20

> 
> .... Is there some > form of standard for how to send the key, 
>
DEA keys are always treated as sixteen hex digits or eight 8-bit bytes
for purposes of transmission.  The 'parity bits' may indeed be used
as a simple checksum.  Why bother?  Keys are almost always accompanied by
checksums for far better snafu detection than the parity bits provide.
> 
> Secondly, the DES algorithm strikes me as a bit odd. As far as I
> can see the initial and final permutations serve no purpose > at all.
> (Other than to make life sour for people that are
>    trying to make fast software implementations :-)
>
Sorry to say, that is exactly why I think they're there.  There have been
various excuses proposed for them - parallel to serial conversion; mixing
up the bit frequencies of EBCDIC characters; or isolating the parity bits
of ASCII characters in one half of the message block - but no good reasons.
-- 
Richard Outerbridge	<outer@utcsri.UUCP>	 (416) 961-4757
Payload Deliveries:	N 43 39'36", W 79 23'42", Elev. 106.47m.