Abstract: To reduce the computational costs, XU Chungen proposed a certificateless proxy signature scheme without pairing; ZHANG Junrong proposed a certificateless proxy ring signature scheme that combined the advantages of the certificateless cryptosystem, the proxy signature and the ring signature. By the cryptanalysis, the paper points out that XU’s scheme has a seriously flaw in the proxy key generation algorithm, which results in an agent cannot generate a valid proxy signature; the ZHANG’s scheme has the original signer’s key compromise attack, the public key replacement attack and the anonymity defect. To address the above problems, two improved schemes are proposed to make up the deficiencies existed in the two signature schemes above, and their computing performance is better than their prototypes.

Key words: certificateless, proxy signature, ring signature, bilinear pairing, public key replacement attack

摘要： 为了降低计算开销，许春根提出一种无对运算的无证书代理签名方案；张俊茸提出一种无证书代理环签名方案，融合了无证书密码体制、代理签名和环签名的优点。分析指出，许春根方案的代理密钥产生算法存在严重缺陷，致使代理人无法进行有效签名；张俊茸方案存在原始签名人密钥泄露及仿冒授权攻击、公钥替换攻击和匿名性缺陷。针对上述问题，提出了改进方案，弥补了已有方案的安全缺陷，且计算性能较优。

关键词: 无证书, 代理签名, 环签名, 双线性对, 公钥替换攻击