Strong Key-Insulated Signature Scheme Supporting Multi-Helpers in the Standard Model

Key-insulated signature is an important technique for protecting the signing secret keys. In key-insulated signature schemes, the security of the rest of the periods are unaffected even if a signing key of a time period is exposed. Parallel key-insulated signature schemes normally allow two helpers to help the signer update temporary private keys to strengthen the security. When two helper keys and any temporary private key are exposed simultaneously, the adversary can forge the correct signature of any time. In order to enhance the security of signature scheme, a new strong key-insulated signature scheme supporting n(n>2) helper devices is proposed. In the proposed scheme, if the user changes the frequency of updating temporary private keys to n times, the chance of exposing helper key still keeps the same as the original key-insulated system. As a result, it will not increase the chance of exposing the helper keys to insecure environment and will decrease the damage caused by key exposure. Finally, the scheme is proved secure based on the computation Diffie-Hellman assumption in the standard model.