fast des

[Eric Hughes <hughes@soda.berkeley.edu>]

> Compression will screw up character frequencies [...] enough to make
>automated detection of a successfully-broken encryption really darn
>hard.

The question is just how hard is "really darn hard"?

Compressed English text has characteristic patterns just as plain
English does.  The salient difference is that these patterns take
longer to emerge at the same confidence level.  The compressibility
limit is a limit not usually reached; the difference between that
limit and the actual compressed text will be non-zero.  This
difference manifests itself in patterns in the compressed text.

Some estimates of this size are necessary in order that the designer
have an assurance that automatic recognition of decrypted text is
difficult.

These concerns are largely obviated by using ciphers with longer key
lengths, of course.

Eric