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.
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