Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!PT.CS.CMU.EDU!NL.CS.CMU.EDU!mlm
From: mlm@NL.CS.CMU.EDU (Michael Mauldin)
Newsgroups: sci.crypt
Subject: Re: how do you tell encrytped data from random data?
Summary: artificially flat distributions
Message-ID: <688@PT.CS.CMU.EDU>
Date: 20 Jan 88 22:52:04 GMT
References: <660@bucket.UUCP> <275@sysco> <4454@ecsvax.UUCP>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 22

In article <275@sysco>, chapman@sco.COM (Brian Chapman Mx321) writes:
> Artificialy flat distributions mean that the data is
> either a fraud or the encryption method pads with extra
> characters.

The encryption algorithm might very easily generate purposefully "flat"
distributions by a variety of methods.  You could switch tables after
every block to shuffle "overused" bytes to less commonly used meanings.
You can even guarantee perfectly flat counts by not altering the
"meaning" of each byte.  This turns out to require extra bytes, since
once you make a decision that "I've used \035 enough, now", the
remaining bytes encode fewer bits.  Still, the result would be neither
fraudulent nor padded with extra characters (the extra bytes would be
"necessary").

If you got a really good encryption algorithm, this would be a
pointless add-on feature, but that doesn't mean that seomone else isn't
doing it.

Michael L. Mauldin (Fuzzy)		Department of Computer Science
ARPA: Michael.Mauldin@NL.CS.CMU.EDU	Carnegie-Mellon University
Phone: (412) 268-3065			Pittsburgh, PA  15213-3890