[14312] in Cypherpunks
Compress before encrypting? (Was Re: NSA Helped Yeltsin...)
daemon@ATHENA.MIT.EDU (Martin Janzen)
Fri May 27 16:47:19 1994
From: Martin Janzen <janzen@idacom.hp.com>
To: cypherpunks@toad.com
Date: Fri, 27 May 94 14:43:02 MDT
In-Reply-To: <m0q76Cl-0003paC@jpplap>; from "Jay Prime Positive" at May 27, 94 11:00 am
Jay Prime Positive writes:
>[...]
>If you suspect that some of the non DOD/NSA cyphers might be broken,
>but you are not ready to employ one-time-pads, then you should
>threshold you mesages into N parts so that all N are needed to recover
>the original. Then encrypt each part under a different cypher.
>
>Perhaps IDEA, and 3DES would be apropriate. This will not increase
>the size of your messages very much since you compress before
>encrypting -- don't you?
Most compression programs add a characteristic signature to the beginning
of the compressed output file. If a cryptanalyst guesses that you may
be compressing before encrypting, wouldn't this make his job easier?
To me, this sounds as though you're adding a known bit of "plaintext" to
the start of each message.
If you're encrypting files that you wish to store securely you could just
clip off the signature, I suppose. But this would be unsuitable for sending
messages, because your compression program is now incompatible with everyone
else's.
Or am I missing something?
--
Martin Janzen janzen@idacom.hp.com
