Solutions to Key Exposure Problem in Ring Signature

In this paper, we suggest solutions to the key exposure problem in ring signature. In particular, we propose the first forward secure ring signature scheme and the first key-insulated ring signature schemes. Both constructions allow a (t, n)-threshold setting. That is, even t secret keys are compromised, the validity of all forward secure ring signatures generated in the past is still preserved. In the other way, the compromise of up to all secret keys does not allow any adversary to generate a valid key-insulated ring signature for the remaining time periods. All our proposed schemes are proven secure in the random oracle model.