CDR: Testing for encryption. (fwd)

[David Honig]

At 05:54 PM 2/21/01 -0600, Jim Choate wrote:
>
>There is NO algorithm which will determine if an arbitrary piece of text
>is encrypted by an arbitrary algorithm. You can tell, at least
>statistically if a particular piece of arbitrary text ISN'T a particular
>algorithm or language either. Again, not the same problem.

The problem is to find a reasonable way for a relay to refuse to forward
unencrypted messages.  So that participants don't accidentally reveal the
discussion.

*Not* to identify the language or cipher algorithm.  *Where* do you get
that idea?
(Rhetorical, I realize who I'm replying to..)

A general and reliable heuristic is to measure entropy.  This will of course
pass unencrypted compressed files (including possibly jpeg, mpeg, etc.).  A
more
reliable 'cheat' is to look for headers.  This can also enforce an
additional (and perhaps
unwanted) requirement that a certain tool is used.  But again, malicious
posters
will be able to spoof this.







.......
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