TVES: Threshold Verifiably Encrypted Signature and Its Applications

Verifiably Encrypted Signature (VES) is useful to enable fair exchange in online contract signing. This cryptographic primitive introduces the adjudicator, a trusted third party, to keep the signature a secret but verifiable. The ordinary signature can be revealed at a later stage. In this paper, we propose Threshold Verifiably Encrypted Signature (TVES), which applies threshold cryptography to both signer and adjudicator parties to decentralize the adjudicator’s power and achieve better fairness in multiparty contract signing where participants do not trust each other. We give TVES’s definition and security notions, then present a concrete construction from bilinear pairings based on BLS short signature scheme and analyze its security and performance. We also show a practical application of TVES in the multiparty contract signing and exchange scenario.