Strong Proxy Signature and its Applications

Proxy signature is a signature scheme that an original signer delegates his/her signing capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. In this paper we show various attack scenarios against previous proxy signature schemes, which shows that proxy signature schemes should be designed very carefully. Based on these weaknesses, we provide new classifications of proxy signatures; strong vs. weak proxy signatures, designated vs. non-designated proxy signatures, and self-proxy signatures. We construct a simple and efficient strong non-designated proxy signature scheme and apply it to multi-proxy signature when plural delegations of multiple original signers exist. We also show that self-proxy signature can be applied to partially blind signatures.