Delegatability of an ID-based designated verifier signature scheme

In this paper we criticize the claimed security of an identity-based strong designated verifier signature (IBSDVS) scheme proposed recently based on bilinear pairings. In particular, we show that, contrary to the authorspsila claim, this scheme is delegatable if the computational Diffie-Hellman problem in the underlying group is intractable. We also explain why the claimed proof fails, in the hope that similar mistake is not repeated in future research.