A forward-secure digital signature scheme using precious signatures for renewing the signing-key

摘要

Several digital signature schemes such as Forward-Secure Digital Signatures and Key-Insulated Signature Schemes have been proposed in order to realize the resistance to the physical attacks. The Forward-Secure Digital Signature provides a solution for the problem of the damage of signing-key exposure by evolving the signing-key for each divided period. If the key-evolution is one-way, it is shown that the adversary cannot forge any signature which was generated in previous periods even if he could steal a signing-key in the current period by physical attacks. Also, the Key-Insulated Signature Scheme is a signature scheme with the aim of solving the problem of damage of key exposure. In this scheme, a signing-key is updating by the use of a secure external device, such as smart cards, storing “master-key." Therefore, under the assumption that the master-key is kept secure, it is shown that even the adversary who can successfully steal a current signing-key cannot forge any signature which is generated in other periods. In this paper, we propose a new digital singnature scheme based on Forward-Secure Digital Signatures. Our scheme meets the same security requirement which the Key-Insulated Signature Scheme achieves without a secure external device, since our scheme uses the record of previously issued signatures instead of the master-key in order to renew the signing-key. Another advantage of our scheme includes the use of the record of previously issued signatures for the evidence to prove an illegal signature.