Abstract:

At Crypto 2000，Boneh and Naor first introduced  the timed commitment scheme , whose commitments are secure against parallel attacks while ensuring the possibility of forced opening. There are many important applications for the timed commitment scheme, such as fair exchange protocol, fair multiparty secure computation and fair multiparty coinflipping. However, the plain BonehNaor's construction is very expensive, it needs a lot of computation and bandwidth in each commitment.  In the paper, based on Pedersen commitment scheme, generalized BlumBlumShub assumption and master timelines techniques, we construct an efficient timed commitment scheme. The master timeline of new scheme is generated in the setup step, and can be reused. Compared to BonehNaor’s construction, we lower the session costs of existing timed applications. Furthermore, our commitment scheme has another important property: homomorphism.

Key words: timed commitment;commitment scheme;homomorphism