On the Soundness of Restricted Universal Designated Verifier Signatures and Dedicated Signatures

In 2006, Huang, Susilo, Mu and Zhang proposed the concept of restricted universal designated verifier signatures while Klonowski, Kubiak, Kutylowski and Lauks proposed independently the dual primitive of dedicated signatures. In both notions, a signature holder can convince one or more verifiers of his knowledge of a digital signature, but cannot exploit this knowledge without being punished for that. In this paper, we state that a signature holder may generically provide a proof that it has a certain signature without being punished and that consequently both primitives cannot fulfill their alleged security goals. To demonstrate the feasibility of this claim, we propose the first non-interactive universal designated verifier proof of the possession of an Elgamal or a DSA signature in the random oracle model. This construction may be of independent interest.