18.11.1. "Can messages be scanned and checked for encryption?"
- If the encryption produces _markers_ or other indications,
then of course. "BEGIN PGP" is a pretty clear beacon. (Such
markers assists in decryption by the recipient, but are not
essential. "Stealth" versions of PGP and other encryption
programs--such as S-Tools for DOS--don't have such
markers.)
- If the encryption produces "random-looking" stuff, then
entropy measures and other statistical tests may or may not
be able detect such messages reliably. Depends on what non-
encrypted messages look like, and how the algorithm works.
+ Steganography:
- making messages look like normal ones
- tucking th ebits in with other random-like bits, such as
in the low-order bits of images or sound files
- The practical concern depends on one's local political
environment. In many countries, mere suspicion of using
crypto could put one in real danger.
By Tim May, see README
HTML by Jonathan Rochkind