Contract Signing Protocol Research Articles

Atomic electronic contract protocol based on convertible signature

A new class of atomicity, namely contract atomicity is presented. A new technical strategy based on convertible signature and two-phase commitment is proposed for implementing atomicity of electronic contract protocol. A new atomic contract signing protocol is given nut by using ElGamal-like convertible undeniable signature and commitment of conversion key, and another new atomic contract signing protocol is brought forward by using RSA-based convertible undeniable signature scheme and commitment of conversion key. These two new protocols are proved to be of atomicity, fairness, privacy, non-repudiation.

Contract signing, optimism, and advantage

A contract signing protocol lets two parties exchange digital signatures on a pre-agreed text. Optimistic contract signing protocols enable the signers to do so without invoking a trusted third party. However, an adjudicating third party remains available should one or both signers seek timely resolution. We analyze optimistic contract signing protocols using a game-theoretic approach and prove a fundamental impossibility result: in any fair, optimistic, timely protocol, an optimistic player yields an advantage to the opponent. The proof relies on a careful characterization of optimistic play that postpones communication to the third party.

Finite-state analysis of two contract signing protocols

Optimistic contract signing protocols allow two parties to commit to a previously agreed upon contract, relying on a third party to abort or confirm the contract if needed. These protocols are relatively subtle, since there may be interactions between the subprotocols used for normal signing without the third party, aborting the protocol through the third party, or requesting confirmation from the third party. With the help of Murϕ , a finite-state verification tool, we analyze two related contract signing protocols: the optimistic contract signing protocol of Asokan, Shoup, and Waidner, and the abuse-free contract signing protocol of Garay, Jakobsson, and MacKenzie. For the first protocol, we discover that a malicious participant can produce inconsistent versions of the contract or mount a replay attack. For the second protocol, we discover that negligence or corruption of the trusted third party may allow abuse or unfairness. In this case, contrary to the intent of the protocol, the cheated party is not able to hold the third party accountable. We present and analyze modifications to the protocols that avoid these problems and discuss the basic challenges involved in formal analysis of fair exchange protocols.