On delegatability of designated verifier signature schemes.

Lipmaa et al. introduced a new security notion of designated verifier signature schemes, non-delegatability: neither a signer nor a designated verifier can delegate the signing rights to any third party without revealing their secret keys. In this paper, we classify designated verifier signature schemes into three types and then discuss delegatability of existing designated verifier signature schemes, strong designated verifier signature schemes and universal designated verifier signature schemes, and open research issues. [ABSTRACT FROM AUTHOR]