Research Of The Key-Insulated Scheme And Its Application

In the digital environment, the most important threat to the security of public-key scheme in practice is exposure of the secret key due to compromise of the underlying system. Key-insulated encryption (signature) schemes have been proposed to address this major shortcoming. In key-insulated schemes, the validity time of a public key is divided into time periods. The secret, key is evolved with the time period. All unexposed signatures are secure even if at most t time periods keys are exposed. The emphasis of this paper is on the research of the key-insulated scheme and its application.At first, this paper considers the usage of key insulation with threshold signature schemes. This means that even if more than the threshold number of players are compromised, some security remains: it is not possible to forge signature in any unexposed time periods. Then the concept of key-insulation is introduced into the multisignature scheme. This way enhances the security. The relationship between multi-grade proxy signature is discussed. The possibility of mutual conversion between multi-grade proxy signature schemes and key-insulated signature schemes are discussed. As a result, a new multi-grade proxy signature scheme is obtained.At the second, a new framework for protection against key exposure is suggested in chapter 3 . This scheme is strongly key insulated with optimal threshold. This means that regardless of the number of user stages that are compromised, signatures intended for any uncompromised stage remain secure. There is no threshold parameter in the picture, and since the total number of stages is not fixed, the key sizes and the costs of signing and verifying will not depend on the threshold or the total number of stages. With such a design, We take its realization further towards practice, an application can dynamically change its update frequency and yet can tolerate compromise of the maximum possible number.At last, aiming at the problem of the new key-insulated signature schemes, we give the modification to these schemes to improve the security.