Subliminal channel

Privacy requirements. The only privacy requirement that has so far been considered is the invisibility of invisible signature schemes. (Recall that blind signature schemes and schemes without subliminal channels are not signature schemes in the sense of the minimal requirements.) One could also add normal confidentiality requirements with respect to outsiders. 

Invisibility, however, can only be defined with at least two different attacker entities, and the same holds for the absence of subliminal channels. 

Simm84 Gustavus J. Simmons The Prisoners Problem and the Subliminal Channel Crypto 83, Plenum Press, New York 1984, 51-67. 

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