Study Signature Key Isolation Polymerization

In order to solve the problem of key exposure in aggregate signatures, this thesis extends the key-insulated mechanism to aggregate signatures and proposes three different key-insulated aggregate signatures. The main work and contributions of the thesis are as follows:1. This paper gives the concept of key-insulated aggregate signatures, formalizes the definition of key-insulated aggregate signature schemes and provides the corresponding formal security model. Construct an efficient key-insulated aggregate signature scheme that meets the definition. Compared with forward-secure aggregate signatures, key-insulated aggregate signatures achieve a higher security level. The leakage of all users’temporary secret keys in some period will not compromise the security of all the remaining periods. Besides, our scheme allows efficient verification because the verification algorithm requires only three pairing operations. We prove the proposed scheme is security in the random oracle model.2. To further improve the security in aggregate signature system, we propose a parallel key-insulated aggregate signature scheme to solve the problem of helper key exposure in key-insulated aggregate signatures. The users in this scheme can perform frequent key updates without increasing the chances of helper key exposure, which improves the ability of the system defending key exposure. The proposed scheme satisfies key-insulated security, strong key-insulated security and security key-updates, and our scheme is high-efficiency in verifications. We prove the security of our scheme in the random oracle model under the Computation Diffie-Hellman assumption.3. A short (t, N) key-insulated aggregate signature scheme with specified verifier is proposed in this paper. The scheme satisfies key-insulated security and strong key-insulated security. Aggregate signatures in this scheme have the advantage of short length because of the individual signature is based on short signature. Only the specified verifier can verify the validity of the aggregate signature, others can not.