Provably Secure Convertible Undeniable Signatures with Unambiguity

This paper shows some efficient and provably-secure convertible undeniable signature schemes (with both selective conversion and all conversion), in the standard model and discrete logarithm setting. They further satisfy unambiguity, which is traditionally required for anonymous signatures. Briefly, unambiguity means that it is hard to generate a (message, signature) pair which is valid for two different public-keys. In other words, our schemes can be viewed as anonymous signature schemes as well as convertible undeniable signature schemes. Besides other applications, we show that such schemes are very suitable for anonymous auction.