Generic construction for convertible nominative signatures

Nominative signature is an useful cryptographic primitive to limit the publicly verifiable property of ordinary digital signature. In a nominative signature scheme, a nominator and a nominee jointly generate a signature in such a way that only the nominee can check the validity of the signature and further convince a third party of the fact. An extended concept, convertible nominative signature, equips the nominee with the additional ability to convert a nominative signature into a publicly verifiable one. In this paper, we propose a generic construction for convertible nominative signature. Our construction is based on selectively convertible undeniable signature and collision-resistant hash function. Next, we prove our construction is secure assuming the security of the underlying building blocks. Finally, we can apply our generic construction to obtain the first provable secure convertible nominative signature in the standard model.