As more business is conducted over the Internet, the fair-exchange problem is gaining greater importance. Fair exchange must be assured for applications such as e-commerce payment protocols, electronic contract signing, and certified e-mail delivery. A fair protocol allows two members participating in a contract to exchange digital signatures over the Internet in a fair way, so that either each person gets the other’s signature, or neither person does. In contract signing the property abuse-freeness is necessary. Abuse free means, if the protocol is not executed successfully, none of the two members involved in contract signing can show the validity of intermediate results to others. Here a contract-signing protocol in a multiple TTP scenario based on RSA digital signature is proposed. In this paper the security of the protocol, in case of any cheating occurs is also described. This digital signature exchange protocol is optimistic, means the third trusted party (TTP) is involved only in the situations where one person is cheating or the communication channel is interrupted, i.e., TTP is off-line.

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Fair-exchange protocols e-commerce RSA digital signatures security