An optimistic fair e-commerce protocol for large e-goods

Suppose two entities that do not trust each other want to exchange some arbitrary data over a public channel. A fair exchange protocol ensures that both parties get what they want or neither gets anything. In this paper, a fair e-commerce protocol for large e-goods is proposed and implemented. The proposed protocol provides a method for the fair exchange of e-money for e-products, and a method for verifying the contents of the exchanged items. The protocol is optimistic and efficient such that when none of the parties tries to cheat, only three messages are sufficient. In case of disputes, three more messages are needed. Furthermore, the customer remains anonymous after the transaction; thus, no information about the customers' shopping habits can be gathered through the protocol. The implementation results show that the protocol is efficient and secure and that only a small number of cryptographic operations is sufficient

Design and development of crytographic fair exchange protocols

In this thesis, the problem of fair exchange on specific cases is addressed. The main idea of fair exchange is as follows: Two entities that do not trust each other want to exchange some arbitrary data over a communication network. Since they do not trust each other, neither party wants to transmit their own data before receiving the other entity's data. Even though either party could prove an unjust situation after termination of the protocol, if they are in different countries, solving disputes may require time and money due to the bureaucracy of international laws. In this thesis, a special application of fair exchange, a fair e-commerce protocol for large e-goods is designed and implemented. The proposed protocol provides a method for fair exchange of e-money to e-products, and a method for verifying the contents of the exchanged items. The presented protocol is efficient such that when none of the parties tries to cheat, only three messages are sufficient. In case of disputes, three more messages are needed. Furthermore, in most of the previously proposed protocols in the literature, e-goods are transferred multiple times among some entities. This situation is too costly when e-goods are large. In the presented protocol, e-goods are transferred only once. Another important property of the protocol is the anonymity of the customer; no information about the customers shopping habits can be gathered through the protocol. The implementation results show that the protocol is efficient and secure and that small number of cryptographic operations is sufficient. In addition to the fair e-commerce protocol, another special application of fair exchange, a fair multimedia exchange protocol using a different method is designed and implemented. This protocol is designed due to different requirements of different applications. In the fair multimedia exchange protocol, two entities want to exchange some multimedia files such as video or audio files. This protocol requires lower security and has a different a lower degree of fairness as compared to the fair e-commerce protocol. Fair multimedia exchange protocol uses a baby-step approach in which the probability of protocol completion is gradually increased over several cycles. In baby-step approach protocols, entities exchange pieces of the items, which they want to barter. At protocol completion, the complete items are formed by using the pieces exchanged

An alternative proof that exact inference problem in Bayesian belief networks is NP-hard

Exact inference problem in belief networks has been well studied in the literature and has various application areas. It is known that this problem and its approximation version are NP-hard. In this study, an alternative polynomial time transformation is provided from the well-known vertex cover problem. This new transformation may lead to new insights and polynomially solvable classes of the exact inference problem in Bayesian belief networks

SeFER: Secure, Flexible and Efficient Routing Protocol for Distributed Sensor Networks

Abstract – In this paper, we present a secure, flexible, and efficient routing protocol for sensor networks based on random key pre-distribution. Random key pre-distribution provides an easy way to manage the keys in a large-scale network without using public key cryptography, which is considered to be expensive. Our protocol aims to establish secure paths in a sensor network between a controller and a set of nodes where each node has been assigned a set of randomly chosen keys out of a key pool. A common model for sensor networks assumes a tree of sensor nodes delivering information to the controller according to an inquiry sent into the network. However, if we require the communication to be secure among the sensor nodes, such a tree cannot always be built efficiently. For example, when the nodes are assigned randomly chosen keys, many of them may not communicate directly since they do not often share a commo

SeFER: secure, flexible and efficient routing protocol for distributed sensor networks

In this paper, we present a secure, flexible, and efficient routing protocol for sensor networks based on random key pre-distribution. Random key predistribution provides an easy way to manage the keys in a large-scale network without using public key cryptography, which is considered to be expensive. Our protocol aims to establish secure paths in a sensor network between a controller and a set of nodes where each node has been assigned a set of randomly chosen keys out of a key pool. A common model for sensor networks assumes a tree of sensor nodes delivering information to the controller according to an inquiry sent into the network. However, if we require the communication to be secure among the sensor nodes, such a tree cannot always be built efficiently. For example, when the nodes are assigned randomly chosen keys, many of them may not communicate directly since they do not often share a common key. However, these two nodes may communicate .indirectly but securely over a multiple hop path where each pair of nodes on this path shares a common key. Our protocol bridges the gap between these two cases by -.providing the methods for nodes to securely share their keys and communicate directly so that the efficiency of communications is increased without jeopardizing the security. In this way, our protocol generates secure and efficient routes. We also provide simulation results for our protocol demonstrating that, for a small number of keys stored at each node, the average path length is smaller. However, the gains due to our protocol diminish as the number of available keys at each node increases since two nodes within communication range of each other are more likely to have a key in common