Article View: sci.crypt
Article #3967Re: how do you tell encrytped data from random data?
From: duncs home
Date: Wed, 20 Jan 1988 15:54
Date: Wed, 20 Jan 1988 15:54
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1206 bytes
In article <660@bucket.UUCP> leonard@bucket.UUCP (Leonard Erickson) writes:
> ...
>I know that transposition and *simple* substitution can be detected by
>letter frequency analysis. But is a "flat" distibution evidence of random
>data?
No. Consider this simple substitution cipher:
'a' = 'abcdefghijklmnopqrstuvwxyz'
'b' = 'bcdefghijklmnopqrstuvwxyza'
'c' = 'cdefghijklmnopqrstuvwxyzab'
...
'z' = 'zabcdefghijklmnopqrstuvwxy'
The frequency distribution of the letters will be absolutely flat, yet it
does contain a message. This shows that a flat distribution does not mean
absence of a message (and also that flat distribution, by itself, does not
guarantee a good cipher!)
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Path: arc1-ca.pugleaf.net!utzoo!mnetor!uunet!husc6!think!ames!amdahl!oliveb!sun!moria!dunc From: dunc%moria@Sun.COM (duncs home) Newsgroups: sci.crypt Subject: Re: how do you tell encrytped data from random data? Message-ID: <39394@sun.uucp> Date: 20 Jan 88 15:54:15 GMT References: <660@bucket.UUCP> Sender: news@sun.uucp Reply-To: dunc@sun.UUCP (duncs home) Organization: Sun Microsystems, Mountain View Lines: 18 Summary: Flat distribution does not imply random data.