No abstract

Hu and Huang proposed an identity-based proxy signature scheme with bilinear pairings. By this approach, the extra burden of verifying a public key with a certificate can be eliminated, and the length of a digital signature can be 160 bits only. Later, Park et al. pointed out that Hu and Huang's scheme suffers from one serious problem, privacy problem, such that a proxy key is generated by using a designated proxy signer's private key without his agreement. To solve this problem, Park et al. also proposed an improvement. With deep insight into Park et al.'s improvement, two drawbacks are found. First, a designated proxy signer may be fooled. Second, the verification of the proxy key in Park et al.'s scheme will never succeed. To preserve advantages and overcome drawbacks, an enhancement will be proposed in this paper.