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We present two efficient protocols which implement robust threshold RSA signature schemes, where the power to sign is shared by N players such that any subset of T or more signers can collaborate to produce a valid RSA signature on any given message, but no subset of fewer than T corrupted players can forge a signature. Our protocols are robust in the sense that the correct signature is computed even if up to T − 1 players behave in arbitrarily malicious way during the signature protocol. This in particular includes the cases of players that refuse to participate or that generate incorrect partial signatures. Our robust protocols achieve optimal resiliency as they can tolerate up to (N − 1)/2 faults, and their efficiency is comparable to the efficiency of the underlying threshold RSA signature scheme.

Robust threshold signature schemes have very important applications, since they provide increased …