From: "David E. Smith" <dsmith@prairienet.org>
Date: Thu, 19 Sep 1996 14:31:18 +0800
To: sjohnson@packetengines.com
Subject: Re: a simple cypher scheme
Message-ID: <199609190415.XAA08538@bluestem.prairienet.org>
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To: sjohnson@packetengines.com, cypherpunks@toad.com
Date: Wed Sep 18 23:06:32 1996
>    i've been on cypherpunks for about a year a half now, and have
>  wacthed
> many interesting threads pass by but i've never posited anything.  what
>  has
> brought me out into the open is this : i work for an engineering firm
>  doing
> asic design, i use pgp ( as do all rational persons ), a co-worker here
>  has
> come up with a 'cypher' scheme that he would like to use to send code to
>  our
> clients.  the scheme is this : he would take the file of code and pad
>  all
> lines to the length of the longest line, he would then preform column
>  swaps,
> and then row swaps, to 'mix up' the file. the person receiving the file
> would then preform the opposite functions to recover the file.  it seems
>  so
> simple that it can't be good. i've convenced him to use pgp, but i
>  would
> like some input if possible on why his cypher scheme is not a good one.
> 
> thanx 
> 

Okay... well, in order to undo whatever was done (the column swaps
and row swaps, and the pads), the formula has to be transmitted.
Assuming that someone can intercept that as well as the alleged
cyphertext, it's no-good.  It's the whole "secure channel" issue.
(Also, some information would have to be attached to the file
containing the orignial end-of-lines for each line, or the padding
will be difficult to tell from the legitimate code.)

dave



- ----- David E. Smith, P O Box 324, Cape Girardeau MO USA 63702
dsmith@prairienet.org        http://www.prairienet.org/~dsmith
send mail with subject of "send pgp-key" for my PGP public key
"The world's at stake. Don't confuse me with details."
 -- Captain America, "Onslaught" ... famous last words

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