Practical and efficient fair document exchange over networks

This paper presents a practical and efficient protocol to support a common Internet-based e-commerce activity—fair document exchange between two parties. This protocol incorporates a novel RSA-based method for the off-line recovery of a document decryption key of a party. The principal idea for such key recovery is based on a verifiable and recoverable encryption of the document decryption key. The verifiability of the encryption allows another party to verify the correctness of the encrypted key without actually knowing the original key, and the recoverability permits a designated third party to decrypt the encrypted key to recover the original key upon a legitimate request. Such verifiable and recoverable key encryption is essential for ensuring the fairness of the exchange. The protocol presented in this paper is more practical, cost-effective and efficient than other relevant protocols designed for fair document exchange.