Re: Subliminal Channels

Steganography, the art of hiding a secret message inside of an openly readable one, can be thought of as a subliminal channel. In the prisoner example, the prisoners could have pre-arranged that, say, every 10th character in the typed messages they exchange would be used to spell out a secret message. Or perhaps word or sentence lengths or spacings could send a message. In general, in any system where there is ambiguity, more than one way of expressing a valid message, there is a subliminal channel. Since DSS signatures are apparently not unique for a given message (unlike, say, RSA signatures as specified in the PKCS standards), they have such a channel. Hal