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Unfairness of a protocol for certified delivery.

Juan Tapiador, Almudena Alcaide

Published Jan 1, 2005• 0 citations
OpenAlex

Abstract

Recently, Nenadić et al. (2004) proposed the RSA-CEGD protocol for certified delivery of e-goods. This is a relatively complex scheme based on verifiable and recoverable encrypted signatures (VRES) to guarantee properties such as strong fairness and non-repudiation, among others. In this paper, we demonstrate how this protocol cannot achieve fairness by presenting a severe attack and also pointing out some other weaknesses. Keywords: Cryptographic protocols; Fair exchange; Non-repudiation; 1

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Recently, Nenadić et al. (2004) proposed the RSA-CEGD protocol for certified delivery of e-goods. This is a relatively complex scheme based on verifiable and recoverable encrypted signatures (VRES) to guarantee properties such as strong fairness and non-repudiation, among others. In this paper, we demonstrate how this protocol cannot achieve fairness by presenting a severe attack and also pointing out some other weaknesses. Keywords: Cryptographic protocols; Fair exchange; Non-repudiation; 1
Nenadic etc(2004,2005) proposed RSA-CEGD protocol for certified e-goods delivery to guarantee strong fairness with the help of transparent Semi-Trust Third Party. Alcaide, Juan, etc(2005) pointed out it is vulnerable for replay attack and the NRO message can be abused. In this paper, we illustrate the STTP can not verify the message submitted by initiator which results in unfairness. In order to implement the Certified E-Good Delivery, this paper, first, defines the policy of Non-Repudiation messages, second, proposes a fixed protocol without changing the structure of the RSA-CEGD protocol. In the fixed protocol, the validity of the parameters, used to recover decryption key, can be checked by TTP and timestamps are added in messages to ensure the timeliness. Also in the fixed protocol, the messages composed the NRO and NRR satisfy the policy defined in this paper. At the same time, timeliness, fairness and non-repudiation of original and receipt are satisfied.
In 2005, A. Nenadic N. Zhang and Q. Shi proposed a new cryptographic primitive, called Verifiable and Recoverable Encryption of Signature VRES. Based on RSA-based VRES, they presented two variant protocols RSA-CEMD1 and RSA-CEMD2 for certified e-mail delivery with RSA receipts. They claimed that the protocols provided strong fairness to ensure that the recipient receives the e-mail if and only if the sender receives the receipt. Later, N. Zhang, Q. Shi, M. Merabti, and R. Askwith presented a practical and efficient fair document exchange protocol based on a verifiable and recoverable encryption of keys that is somewhat similar to the VRES. In this paper, we find that the VRES scheme is universal forgeable. Anyone can generate the false VRES for any message without the knowledge of any private key of the sender, the recipient and the TTP. It follows that the two variant protocols RSA-CEMD1, RSA-CEMD2 are all insecure. Meanwhile, we show that the document exchange protocol is not fair since the verifiable and recoverable encryption of keys is not recoverable.
This paper presents an efficient security protocol for certified e-goods delivery with the following features: (1) ensures strong fairness, (2) ensures non-repudiation of origin and non-repudiation of receipt, (3) allows the receiver of an e-goods to verify, during the protocol execution, that the e-goods he is about to receive is the one he is signing the receipt for, (4) does not require the active involvement of a fully trusted third party, but rather an off-line and transparent semi-trusted third party (STTP) only in cases of unfair behaviour by any party, and (5) provides confidentiality protection for the exchanged items from the STTP.
In this paper we present two variant protocols DSA-CEMD1 and DSA-CEMD2 for certified e-mail delivery with DSA receipts. The protocols are based on a cryptographic primitive called Verifiable and Recoverable Encryption of a Signature (VRES) and are capable of achieving non-repudiation and strong fairness security properties. The novel design of the VRES primitive allows efficiency improvements in comparison with the related certified e-mail delivery protocols based on similar primitives. The protocols employ the services of an off-line and invisible trusted third party (TTP) only in case of dispute. In DSA-CEMD1 the content of the e-mail message is not revealed to the TTP during possible recovery and this is achieved at the cost of some additional cryptographic operations. In DSA-CEMD2 the confidentiality of the message is not protected from the TTP, but the protocol is slightly more efficient.
Abstract:- An efficient and secure protocol in certified e-mail delivery is proposed in this paper. With the widespread use of public Internet, communication via electronic mail (e-mail) becomes a convenience application instead of traditional manuscript letter. People can easily append his/her digital signature to the e-mail in order to achieve the goal of non-repudiation of origin. However, the evidence of receipt still relies on the willingness of the recipient in the standard e-mail service. Hence, the recipient has no responsible for the received e-mail. In this paper, we present an efficient and secure protocol in fair certified e-mail delivery (CEMD). Our protocol efficiently provides non-repudiation of origin and receipt in the fair manner. In other words, the sender can obtain the irrefutable receipt if and only if the recipient gets the certified e-mail from the sender, otherwise, neither of them. Moreover, the proposed CEMD is efficiently in sending the other mails to the same recipient by using the pre-computation function. As the evaluations of computational cost and communication overhead, our protocol is cost-effective and efficient than other relevant protocols.