在本論文中,我們檢驗現有的金鑰絕緣簽章法,並且提出基於橢圓曲線密碼系統的金鑰絕緣的 簽密法(signcryption),簽密系統由Zheng在1997年提出,藉由同時進行簽章和加密來降低計算成本,其保留傳統先簽章 後加密的的機密性、完整性以及不可否認性,且計算成本遠遠低於傳統方法。我們藉由簽密法和橢圓曲線 密碼系統的結合提出之方案,同時降低了現有方法的計算成本和空間成本,並且保留了金鑰絕緣系統之所有特性。;Private key plays an important character in public key cryptosystem, if private key was exposed, the confidentiality of previous messages would not be guaranteed. With the progress of technology, almost everyone has his/her own mobile device such as cell phone. Signature or decryption are often performed on a mobile device operation in an environment where the private key is likely to be exposed by stealing the mobile device. It is easier to obtain the private key by stealing mobile device than to break the computational assumption on which the security the system is based. In order to reduce the damage of key exposure, Dodis proposed a new paradigm called key-insulation. In the key-insulation cryptosystem, the private key′s life time is divided into discrete time periods, and the private key will be updated by interacting with the "auxiliary device" which is placed in safety. It would only cause damage in time period $i$ if the private key exposed in time period $i$, it would not influence any other time periods. The computational cost and communication overhead in key-insulation signature schemes are higher than traditional signature scheme because of updating private key periodically.
Signcryption proposed by Zheng can simultaneously achieve both the function of signature and encryption in a logical step, and with more efficient in computational cost and communication overhead than traditional signature-then-encryption. In this thesis, we modified the exsisting key-insulation signature scheme and proposed a new key-insulation signcryption scheme based on elliptic curve with a cost significantly lower than that required by traditional "key-insulation signature-then-encryption" and remains all the properties in key-insulation cryptosystem.