An Electronic Contract Signing Protocol Using Fingerprint Biometrics

An Electronic Contract Signing Protocol Using Fingerprint Biometrics

Harkeerat Bedi, Li Yang, Joseph M. Kizza
DOI: 10.4018/978-1-4666-2919-6.ch029
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Fair exchange between a pair of parties can be defined as the fundamental concept of trade where none of the parties involved in the exchange have an unfair advantage over the other once the transaction completes. Fair exchange protocols are a group of protocols that provide means for accomplishing such fair exchanges. In this chapter we analyze one such protocol which offers means for fair contract signing, where two parties exchange their commitments over a pre-negotiated contract. We show that this protocol is not entirely fair and illustrate the possibilities of one party cheating by obtaining the other’s commitment and not providing theirs. We also analyze a revised version of this protocol which offers better fairness by handling many of the weaknesses. Both these protocols however fail to handle the possibilities of replay attacks where an intruder replays messages sent earlier from one party to the other. Our proposed protocol improves upon these protocols by addressing to the weaknesses which leads to such replay attacks. We implement a complete working system which provides fair contract signing along with properties like user authentication and efficient password management achieved by using a fingerprint based authentication system and features like confidentiality, data-integrity and non-repudiation accomplished through implementation of cryptographic algorithms based on elliptic curves.
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Fair Electronic Exchange

Fair electronic exchange can be demonstrated as e-commerce that takes place between two parties who are online and where exchange of goods and services is performed such that both parties either obtain what they expected or they obtain nothing at all. After an exchange is performed or aborted prematurely, none of the parties should have an unfair advantage over the other. If cheating takes place, where one party refuses to present their part of the exchange, other means for providing fairness should be available. These may include use of additional entities like a human judge or electronic ones that can comprehend the situation and act accordingly to provide fairness. Protocols that provide such facilities are known as fair exchange protocols. Such protocols can be used for the following purposes:

  • a.

    Certified E-Mail (CEM): where a user named Alice sends a message to a user named Bob and gets a receipt from him in return. Providing the quality of fairness would include Alice getting the receipt only when Bob gets the message or Bob getting the message only when Alice gets the receipt.

  • b.

    Electronic Contract Signing (ECS): where both Alice and Bob wish to sign a contract that has already been negotiated. This would involve Alice sending her commitment (digital signature) on the contract to Bob and him sending his commitment on the same in return. Providing fairness would involve Alice receiving Bob’s commitment only when her commitment is received by Bob and vice versa. This example demonstrates contract signing between two parties. However, various multi-party contract signing protocols also exist and have also been proposed in (Baum-Waidner, 2001; Ferrer-Gomila, Payeras-Capella, Huguet-Rotger, 2001; Garay & MacKenzie, 1999).

  • c.

    Online payment systems (OPS): where Alice is the seller and Bob is the buyer and payment is given in return of the item of value (Cox, Tygar & Sirbu, 1995).

In the ideal case, where both Alice and Bob are guaranteed to be honest and the communication channel is secure and provides resilience, fair exchange can be achieved trivially without the aid of any external fairness provider. The above described scenarios can thus be carried out as follows:

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