Partial Signatures and their Applications

We introduce Partial Signatures, where a signer, given a message, can compute a “stub” whichpreserves her anonymity, yet later she, but nobody else, can complete the stub to a full and verifiablesignature under her public key. We provide a formal definition requiring three properties, namelyanonymity, unambiguity and unforgeability. We provide schemes meeting our definition both withand without random oracles. Our schemes are surprisingly cheap in both bandwidth and computa-tion. We describe applications including anonymous bidding and betting.