Path: utzoo!mnetor!uunet!portal!cup.portal.com!truett
From: truett@cup.portal.com
Newsgroups: sci.crypt
Subject: Re: how do you tell encrytped data from
Message-ID: <2558@cup.portal.com>
Date: 18 Jan 88 09:14:24 GMT
References: <660@bucket.UUCP> <3600002@osiris.cso.uiuc.edu> <2415@cup.portal.com> <7107@brl-smoke.ARPA>
Organization: The Portal System (TM)
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XPortal-User-Id: 1.1001.2190


The idea that the set of possible plaintext messages is small relative to the
set of possible messages is not always valid.  How about the encryption of
binary object codes or the vectorized files of the plans of a classified
mechanical device?  A good cryptographer must assume that any possible message
has a chance of eventually appearing for encryption.

So long as the encryption process is one-to-one between the spaces of possible
plaintext messages and cyphertext messages, then "nonrandom" (whatever that
means!) messages are encrypted into "rnadom" messages just as often as the
"random" ones are encrypted into "nonrandom" ones.  What *is* rare, so long as
the nonrandom messages are a smaller space than the space of all messages, is
the event in which a "nonrandom" message is encrypted into a "nonrandom"
message.  There are exceptions:  remember what the Germans thought of Navajo?

Truett Lee Smith, Sunnyvale, CA
UUCP:  truett@cup.portal.com