Motivated by the great success and adoption of Bitcoin, a number of cryptocurrencies such as Litecoin, Dogecoin, and Ethereum are becoming increasingly popular. Although existing blockchainbased cryptocurrency schemes can ensure reasonable security for transactions, they do not consider any notion of fairness. Fair exchange allows two players to exchange digital "items", such as digital signatures, over insecure networks fairly, so that either each player gets the other's item, or neither player does. Given that blockchain participants typically do not trust each other, enabling fairness in existing cryptocurrencies is an essential but insufficiently explored problem.In this paper, we explore the solution space for enabling the fair exchange of a cryptocurrency payment for a receipt. We identify the timeliness of an exchange as an important property especially when one of the parties involved in the exchange is resource-constrained. We introduce the notion of strong timeliness for a fair exchange protocol and propose two fair payment-for-receipt protocol instantiations that leverage functionality of the blockchain to achieve strong timeliness. We implement both and compare their security and efficiency.
In a mobile computing environment, it is desirable to protect information about the movements and activities of mobile entities from onlookers. Solutions to this problem of providing anonymity have to be developed with the constraints of mobile computing environments in mind. In this paper, it is argued that this issue merits investigation. A brief survey of the nature of anonymity provided in proposed or existing mobile computing environments is presented. It is argued further that achieving limited but practical anonymity using standard cryptographic techniques is feasible. Example solutions are presented.
Starting from the 5.0 Lollipop release all Android processes must be run inside confined SEAndroid access control domains. As a result, Android device manufacturers were compelled to develop SEAndroid expertise in order to create policies for their device-specific components. In this paper we analyse SEAndroid policies from a number of 5.0 Lollipop devices on the market, and identify patterns of common problems we found. We also suggest some practical tools that can improve policy design and analysis. We implemented the first of such tools, SEAL.
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