Two Digital Signature Schemes With Forward Security

This paper is comprised of two main study issues. The first one is studying how to imply forward security into normal proxy signature algorithms to enhance the security of the algorithms. The new scheme improves the normal proxy signature scheme, proposes a new delegation called forward-secure delegation and gives a forward-secure proxy signature scheme. It protects the revoked proxy singer, making the prior proxy signatures easily verified. This new scheme divides the validity time of a key pair of the original signer into time periods. At the end of each time period, the original signer derives a new secret key from the current one in an one-way fashion and updates the according proxies. So compromise of the current key does not enable the adversary to forge proxies in the past periods. Therefore, the prior proxy signatures are protected. Security of the proposed scheme relies on the Strong-RSA assumption.Another issue is studying how to imply forward-security into normal aggregate signature algorithms to satisfy some wireless sensor network. The property of forward security applied into normal aggregate signature schemes can offer overall integrity of the signed messages, while aggregate signatures have their own advantages of storage / communication efficiency. This newly notion first advanced by Di Ma called forward secure sequential aggregate (FssAgg) signature and it can widely used in application of wireless sensor network. But it just realized schemes of sign-ONE-message per time period, which cannot suffice real-time requirement. In this paper, we proposed a modified scheme derived from FssAgg signature scheme and called it as forward-secure aggregation of signatures (short for FSA). This newly scheme separates the sign-and-aggregate algorithm into two dependent algorithms and signs messages noboundary per time period. It can be useful in some scenario in wireless sensor network, supplying real-time and better concurrency. Meanwhile, it can be proved secure based on the intractability of co-CDH problem.