Abstract: By applying the concepts of double threshold technology to signcryption theory，a new double-threshold proxy signcryption scheme from bilinear pairings is proposed.In this new scheme，the first(k,n)threshold technology is adopted in the key sharing，the original signcrypter entrusts this key to n secretaries for escrow，at least k secretaries cooperate can recover the key.It greatly reduces the risk of key-compromise.The(t,m)threshold technology is adopted in the process of proxy signcryption，it gives the right of signcryption to entrust m proxy signcrypters sharing，no less than t proxy signcrypters with no right can receive the correct cipher text.To a great extent，it enhances the security.Analysis shows that the scheme is secure，and it is suitable for many applications in practice.

Key words: signcryption, secret sharing, bilinear parings, proxy signcryption, threshold scheme

摘要： 在签密理论中引入两重门限技术，构造一个新的基于双线性对的两重门限代理签密方案。在该方案中，把第一重(k,n)门限体制应用在密钥共享上，原始签密人把密钥委托给n个秘书来托管，至少k个秘书合作才能恢复此密钥，大大降低了密钥泄露的风险;将第二重(t,m)门限体制应用在代理签密过程中，把签密权委托给m个代签人共享，任何少于t个代理签密者勾结也不能得出正确的签密密文，在很大程度上增强了代理签密的安全性。理论分析表明，说明该方案是可证明安全的，适合实际应用。

关键词: 签密, 秘密共享, 双线性对, 代理签密, 门限方案