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ICPP Workshops on Collaboration and Mobile Computing

Improving fairness and privacy of Zhou-Gollmann's fair non-repudiation protocol

Kwangjo Kim, Sangjoon Park, Joonsang Baek

Published Jan 20, 2003• 25 citations
Publisher

Abstract

We deal with two claws of Zhou-Gollmann's fair non-repudiation protocol. Firstly, their protocol divides a message into 2 parts, i.e., a key K and a ciphertext C. Then, C is delivered to the recipient, while K is submitted to TTP (Trusted Third Party). If the originator doesn't submit K to TTP, then the protocol appears to have no dispute between the originator and the recipient. However the protocol depends on his action on whether the originator really submits K to TTP or not. We show that the originator can make the protocol unfair by using his advantageous position, and present how to improve the fairness of the protocol. Secondly, the protocol doesn't provide the message privacy. This means that additional protocols are required to transfer an important message in private. We propose an improved version of the protocol to guarantee the message privacy.

DOI
10.1109/icppw.1999.800053

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We deal with two claws of Zhou-Gollmann's fair non-repudiation protocol. Firstly, their protocol divides a message into 2 parts, i.e., a key K and a ciphertext C. Then, C is delivered to the recipient, while K is submitted to TTP (Trusted Third Party). If the originator doesn't submit K to TTP, then the protocol appears to have no dispute between the originator and the recipient. However the protocol depends on his action on whether the originator really submits K to TTP or not. We show that the originator can make the protocol unfair by using his advantageous position, and present how to improve the fairness of the protocol. Secondly, the protocol doesn't provide the message privacy. This means that additional protocols are required to transfer an important message in private. We propose an improved version of the protocol to guarantee the message privacy.
Zhou-Gollmann protocol is a fair non-repudiation protocol which is widely discussed in recent years.Kim found a flaw of this protocol on time-limited fairness.Aimming at this flaw,Kim gave an improved protocol,but the improved schema highly depended on synchronization of network clock.We analyzed Kim's protocol in detail and show that,without clock synchronization,Kim's improved protocol is also unfair.Then we proposed a new schema to improve it further.Without reducing the efficiency of the original protocol,our new method avoids depending on synchronization of the clock,and keeps fairness and non-repudiation of the protocol.
A non-repudiation protocol enables the fair exchange of an electronic message and an irrefutable digital receipt between two mistrusting parties over the Internet. That is, at the end of any execution instance of such a protocol, either both parties obtain their expected items or neither party does . In this paper, we first argue that it is really meaningful in practice to exploit generic fair non-repudiation protocols with transparent off-line trusted third party (TTP). Namely, in those protocols, each involved party could use any secure digital signature algorithm to produce non-repudiation evidences; and the issued evidences are the same regardless of whether the TTP is involved or not. Then, we present such a fair non-repudiation protocol to overcome some limitations and shortcomings in previous schemes. Technical discussions are provided to show that our protocol is not only secure but also the most efficient solution, compared with existing non-repudiation protocols. In addition, some potential extensions are also pointed out.
With the development of e-commence and other utilities on internet,a new security service——fair non-repudiation becomes more important and crucial.But,most current protocols depend on trusted third party(TTP),so a fair non-repudiation protocol without TTP is needed.But the existing fair protocols don't have equal security for message originator and receiver,and they can not assure the security of the message originator.In this paper,a new protocol is designed for the prior security of the originator,and a fair non-repudiation protocol without TTP based on entity's computing power is proposed to get rid of the dependence on TTP,to solve the security problems that exist when message originator and receiver's computing power are not equal.
Non-repudiation service is widely employed in information exchange and online transaction. It requires that its participants are unable to deny their involvement in specific protocol. At the same time, the service should keep fairness, which means that no one could take any advantages over the other one. Researchers have introduced a trusted third party (TTP) to realize these demands. Protocols are grouped into several categories according to the degree of TTP's involvement in protocols. Optimistic non-repudiation protocol is the most important method undoubtedly owe to its lower TTP's involvement. There are two questions. One is that whether it is possible to further decrease TTP's involvement or not. A computable optimistic non-repudiation protocol seems to be a good improvement. This is also our paper's basic protocol. The other question is about whether two types of finally evidences that produced by participants (here is Alice and Bob, and we denote this type evidences as the first type evidences) and TTP (or with the help of TTP, and we demote this type evidences as the second type evidences) are identical. If both types of evidences are not exactly the same, then it shows that TTP has taken part in process of protocol. Thus, it is certain that either participants behaved dishonest, or network went wrong. Participants' prestige will be negatively affected more or less. On the contrary, if two types of evidences are identical, then such feelings will be eliminated. This kind of TTP is called transparent TTP. In this paper, we have accomplished an optimistic non-repudiation protocol with the help of transparent TTP based on a computable non-repudiation protocol.
Non-repudiation is one of the most important premises to achieve electronic commerce while fairness is what people have been chasing during electronic transaction. Fair non-repudiation protocols resolve the question of non-repudiation during the course of transferring information in electronic commerce and make all communicating sides in equal positions. That is to say, the protocols are fair for all sides. In the present paper, a fair multi-party non-repudiation protocol based on a group encryption scheme is introduced. The flow of the protocol and its analysis are given in the paper. In the protocol, every side can not have advantages over other sides, because the advantages can result in great loss of other sides. The method that how to solve the dissension with this protocol is also given in the present paper. A trusted third party is used to generate non-repudiation evidence. With this method the number of exchanged messages is small. So this protocol can achieve non-repudiation service in an efficient and practical way.