Cryptanalysis of an Off-Line Electronic Cash Scheme Based on Proxy Blind Signature

摘要

Proxy bund signature is an important cryptographic primitive ana plays an essential role in construction of the electronic cash (e-cash). Recently, Tan (2001, An offline electronic cash scheme based on proxy blind signature. Comput. J., 54,505-512) proposed a new proxy blind signature scheme and applied it to electronic cash. The scheme was claimed as being provably secure under the Discrete Log assumption, DBDH assumption and Chosen-Target CDH assumption in the random oracle model. In this paper, we show that Tan's proxy blind signature scheme is insecure by demonstrating several attacks in which a malicious original signer can forge both valid proxy signature keys of arbitrary proxy signers and a proxy blind signature on an arbitrary message with respect to any proxy signer directly. We also discuss some weaknesses in the e-cash scheme proposed by Tan.