Pretty Good Privacy (PGP) is one of the most prominent cryptographic standards offering end-to-end encryption for email messages and other sensitive information exchange. PGP allows to verify the identity of the correspondent in information exchange as well as the information integrity. PGP implements asymmetric encryption with certificates shared through a network of PGP key servers. In this paper, we propose a new PGP management framework with the key servers infrastructure implemented using blockchain technology. Our approach offers fast propagation of certificate revocation among PGP key servers and elimination of man-in-the-middle risks. It also grants users the required access control to update their own PGP certificates, which is not the case with the current PGP key servers. A prototype has been implemented using Ethereum blockchain and an open source key server, named Hockeypuck. Finally, we evaluated the prototype with extensive experiments. Our results show that our solution is practical and it could be integrated with the existing public PGP key servers infrastructure.

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Bluetooth MANETs, which consist of Bluetooth-enabled terminals, are a prospective methodology for mobile ad hoc networks (MANETs). Since Bluetooth is a connection-oriented and a low-power-consumption communication method, terminals must execute time-consuming connection establishment procedures in advance. We have to solve the following two problems for Bluetooth MANETs: (1) since terminals move within fields, terminals must establish their connection within a limited time. In addition, (2) since Bluetooth has a shorter range than other technologies, established connections are easily disrupted. In order to solve problem (1), a low-latency connection establishment method has been proposed. However, there is no countermeasure for problem (2). Therefore, the possibility of rapid re-establishment for connections ought to be investigated. In this paper, we have proposed a new adaptive connection-establishment timeout configuration method for environments with control packet loss. Our proposed method employs an adjustment mechanism for control packet loss. We have also implemented our proposed method on Raspberry Pi in order to evaluate our proposed method. To design our proposed method, we have conducted preliminary experiments to investigate the effects on varied connection-establishment timeouts. As a result, we have found that the minimum connection-establishment timeout is 2 seconds. At the same time, we have found that connection establishment failure rates increased as connection-establishment timeouts became shorter than 2 seconds. Especially, when connection-establishment timeouts were less than 2 seconds, the latency of the connection establishment became extremely long. This is due to the presence of a race condition between the processing time of control packets and the connection-establishment timeouts. From these results, we have set an adjustable interval of connection-establishment timeouts between 2 to 5 seconds. 5 seconds is the native default value of Bluetooth’s connection-establishment time-out. We have also conducted experiments of our proposed method in varying packet loss rate scenarios, and have confirmed the effectiveness of our proposed method.

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In recent years, the demand for multimedia services that can handle voice and/or videos on mobile terminals has increased. Many handover algorithms have been proposed for switching the connection between different networks while maintaining QoE (Quality of Experience), which is a metric that is a measure of users’ satisfaction when using a certain service or application. The QoE-driven VHO algorithm is one of such algorithms using a prediction model of QoE for movies streamed over wireless networks. Since the algorithm may not provide an acceptable level of quality when network performance temporarily decreases, the authors also proposed an algorithm (hereinafter referred to as the “previous algorithm”) to improve the problem. However, since these algorithms cannot predict QoE of candidate networks before switching, the connection may be switched to a network with much lower QoE. In order to solve the problem, this paper proposes a new handover algorithm for video communications by sharing communication quality information of access points between terminals. In this algorithm, each mobile terminal creates a list specifying the communication quality of the connected access point and shares it with other terminals. The simulation results show that terminals in the proposed method can connect to the access points with better QoE for longer durations than the QoE-driven VHO algorithm and the previous algorithm.

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