An Enhanced Proxy Blind Signature with two Intractable Problems

A proxy blind signature scheme is combination of two signature schemes particularly proxy signature and blind signature. In this signature scheme the original signer delegate his/her signing authority to some other entity named proxy signer. The proxy signer signs the documents or messages, but he cannot be able to find any link between the blind signature and the identity of the signature requester. In the open literature the majority of the existing digital signature schemes were developed based on intractability of a single hard problem like integer factoring problem (IFP), discrete logarithm problem (DLP) or elliptic curve discrete logarithm problems (ECDLP). This paper analyzes Qi and Wang et al's scheme, which is based on multiple hard problems namely IFP and ECDLP. But their scheme has security weaknesses and cannot hold some of the basic properties of signature scheme. Improvements are suggested to overcome with these weaknesses, such that the proposed signature scheme satisfies the security standards of a proxy blind signature scheme. The security of the improved scheme is also analyzed, which shows that this signature scheme is more secure than that schemes based on single intractable problem.