Path: utzoo!utgpu!water!watmath!clyde!rutgers!mcnc!ecsvax!hes
From: hes@ecsvax.UUCP (Henry Schaffer)
Newsgroups: sci.crypt
Subject: Re: how do you tell encrytped data from random data?
Summary: character distribution of compressed data is smooth
Message-ID: <4403@ecsvax.UUCP>
Date: 10 Jan 88 02:22:25 GMT
References: <660@bucket.UUCP> <6992@brl-smoke.ARPA> <1499@osiris.UUCP>
Organization: NC State Univ.
Lines: 14


These days it is quite common to compress text (and other files too.)
The various compressions schemes such as Huffman encoding and Lempel-
Ziv-Welch tend to even out (smooth out) the character distribution
(i.e., they hope to maximize the information transmitted per character,
or per byte).  If this file is then encrypted, the smoothness may
end up in the encrypted data.  

Conversly, random data need not have a smooth character distribution.
(It is common to confuse "random" with "equi-probable".  However, even
though most examples given in courses of "random" are "equi-probable
there is no necessary connection.)

--henry schaffer  n c state univ