A Universal Forgery on Araki et al.'s Convertible Limited Verifier Signature Scheme

The digital signature provides the function of integration, authentication, and non-repudiation for the signing message. In ordinary digital signature schemes, anyone can verify the signatures with signer’s public key. However it is not necessary for anyone to be convinced a justification of signer’s dishonorable message such as a bill. It is enough for a receiver only to prove a justification of the signature if the signer does not execute a contract. The undeniable signature schemes [2] [3] and the limited verifier signature scheme[1] can solve this problem. There exists a message such as official documents which will be first treated as limited verifier signatures but after a few years as ordinary digital signatures. So the limited verifier signature scheme should be convertible. In 1999, Araki et al. [1] proposed a convertible limited verifier signature scheme. In this paper, we show that Araki et al.’s scheme is universally forgeable, that is, any one can forge a valid signature of a user UA on an arbitrary message.