An Identity-Based Fair Contract Signing Protocol Constructed by the Confirmation Signature

Abstract

The contract signing protocol has been a mature technique developed in previous literature and adopts the fair exchange of signatures to achieve the purpose. However, two critical issues, practicality and efficiency, become bottlenecks in the studies of many previous proposed protocols. Since through using the bilinear pairings over elliptic curves, the identity-based cryptographic primitives can be constructed more efficiently and practically in the key generation stage, this paper aims to present an identity-based contract signing protocol from bilinear pairings. All parties, including the two signers and the trusted third party (TTP), have their own extended IDs to be used as the public keys and thus no certificate is needed so that the key management can be simplified. A new building block called the “identity-based confirmation signature” (IDCS), which makes the construction of contract signing protocol more flexible, will be introduced and its implementation details will also be stated. The fairness is achieved in the proposed protocol by adopting an offline TTP who participates in the signature exchange procedure only when a dispute occurs between the two signing parties. In that case, TTP converts IDCS into a universally verifiable signature for unlimited verification by everyone to resist the cheating of dishonest participants.