Deterministic Signatures, Subliminal channels and Hardware wallets

A subliminal channel in a signature scheme allows a signing party to send a covert message to an authorized receiver of signed messages without anyone else noticing it. One property of ECDSA, DSA and many similar digital signature schemes (such as Schnorr) is that they need to produce, for each signature generation, a fresh random data (hereafter designated as a value k). This value must never repeat, and it must be uniformly random. The need for a cryptographically secure source of randomness proves to be a hindrance to deployment of signature schemes in some architectures in which secure random number generation is challenging, in particular, embedded systems such as smartcards [taken from RFC6979].

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