A directed signature is a type of signature with restricted verification ability.Directed signatures allow only a designated verifier to check the validity of the signature issued to him,and at the time of trouble or if necessary,any third party can verify the signature with the help of the signer or the designated verifier.Directed signature schemes are widely used in situations where the receiver's privacy should be protected.Proxy signatures allow an entity to delegate its signing capability to another entity in such a way that the latter can sign message on behalf of the former when the former is not available.Proxy signature schemes have found numerous practical applications such as distributed systems and mobile agent applications.In this paper,we firstly define the notion of the directed proxy signature by combining the proxy signature and directed signature.Then,we formalize its security model and present a concrete scheme in the standard model.Finally,we use the techniques from provable security to show that the proposed scheme is unforgeable under the gap Diffie-Hellman assumption,and invisible under the decisional Diffie-Hellman assumption.
针对现实中代理签密的安全问题,提出一种基于Gu等(GU K,JIA W J,JIANG C L.Efficient identitybased proxy signature in the standard model.The Computer Journal,2013:bxt132)代理签名的标准模型下可证安全的基于身份代理签密方案。代理签密允许原始签密者授权签密能力给代理签密者,后者能够代表前者生成密文。该方案通过结合基于身份签密和代理签名,既保持了基于身份签密的优点,又具有代理签名的功能。分析表明,基于DiffieHellman问题假设下,所提方案满足机密性性和不可伪造性。与已知方案相比,代理密钥生成算法和代理签密算法中各需要2个对运算和1个对运算,方案效率更高。
