Subliminal communication is easy using the DSA

Abstract

In I985, Simmons showed how to embed a subliminal channel in digital signatures created using the El Gamal signature scheme. This channel, though, had several shortcomings. In order for the subliminal receiver to be able to recover the subliminal message, it was necessary Tor him to know the transmitter’s secret key. This meant that the subliminal receiver had the capability to utter undetectable forgeries of the transmitter’s signature. Also, only a fraction of the number of messages that the channel could accommodate in principal could actually be communicated subliminally (φ(p-1) messages instead of p-1) and some of those that could be transmitted were computationally infeasible for the subliminal receiver to recover.