一种改进的门限代理签密协议

针对不可否认L-L-C-Z门限代理签密协议中存在的安全缺陷，提出了一个改进的门限代理签密协议.通过对L-L-C-Z门限代理签密协议的密码分析，利用接收方修改公钥的方法，计算出任意消息的有效伪造签密结果.利用类似于缩短的数字签名标准（SDSS）的安全技术，以及通过公钥验证签密结果的技术，给出一个新的改进协议.安全分析结果表明，与L-L-C-Z门限代理签密协议相比，该改进门限代理签密协议能够承受接收方公钥替换攻击.改进的门限代理签密协议利用接收方公钥而不是私钥来验证签密结果，其验证过程能向第三方公开.

Improvement of threshold proxy signcryption scheme

To overcome the existing lack of security existing in the non-repudiable threshold proxy signcryption L-L-C-Z protocol,an improved threshold proxy signcryption protocol was presented.The security performance of L-L-C-Z protocol was analyzed,and forged valid signcryption result was computed out by substituting receiptor's public key for any plaintext message.When secure technology similar to shortened version of digital signature standard(SDSS) scheme was exploited and the method of directly verifiable signcryption with public key was used,an improvement of threshold proxy signcryption protocol was proposed.Security analysis results show that compared with L-L-C-Z threshold proxy signcryption protocol,the improved threshold proxy signcryption protocol can withstand the public key substitution attack.Improved threshold proxy signcryption protocol utilize receiptor's public key but not private key to verify signcryption's result.The verification procedure can be publicly shown to the third party.