From: "Thomas W. Strong, Jr." <strong+@cmu.edu>
Date: Fri, 21 May 93 18:20:18 PDT
To: cypherpunks@toad.com
Subject: Re: cypto + compression
In-Reply-To: <9305212138.AA12666@banff.procase.com>
Message-ID: <cfzJGlW00WB60vMs8q@andrew.cmu.edu>
MIME-Version: 1.0
Content-Type: text/plain


peb@PROCASE.COM writes:
> Compressing before encryption is vital--it makes brute force and plaintext
> attacks much more difficult.

Be careful doing that.  It's fine if you are using a compression
algorithm that is designed for use with encryption, but if you're just
using compress and you make that known, then an opponent just has to
look for the magic numbers and headers that compress puts in the front
of every file.  Instead of believing that strings like "the" will appear
somewhere, the opponent now knows exactly what the encrypted document
starts with.

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  Tom Strong              N3NBB              ts49+@andrew.cmu.edu