[sllug-members]: Encrypted backup tapes

[Corey Edwards]

On Thu, 2007-01-11 at 12:24 -0700, M. Alton jensen wrote:
> I'm not sure if this is distro specific, but the defaults for gnupg on
> my desktop(SuSE) include compressing the item being encrypted.  I ran a
> simple test with a text file to confirm this and here are the results.
> 
> > du -sk test.txt*
> 328     test.txt
> 40      test.txt.gpg
> 40      test.txt.gz

A lot of encryption schemes, and I believe PGP is one of them, implement
a compression step before the encryption. The idea is to increase the
entropy. Plain text really isn't that random, whereas compression by
design removes redundancy and is thus more random. A friend of mine did
her master's thesis on the subject of measuring the randomness of
compression algorithms by running them through compression. A truly
random file would not compress at all and a well encrypted file should
be indistinguishable from randomness.

Corey