Abstract

Abstract
Peer-to-Peer networks are extensively used for largescale file sharing. As more information flows through these networks, people are becoming increasingly concerned about their privacy. Traditional P2P file sharing systems provide performance and scalability at the cost of requiring peers to publicly advertise what they download. Several P2P privacyenhancing systems have been proposed but they still require peers to advertise, either fully or partially, what they download. Lacking alternatives, users have adopted anonymity systems for P2P file sharing, misunderstanding the privacy guarantees provided by such systems, in particular when relaying traffic of insecure applications such as BitTorrent. Our goal is to prevent any malicious peer(s) from ascertaining users' content interests so that plausible deniability always applies. We propose a novel P2P file sharing model, Mistrustful P2P, that (1) supports file sharing over open and untrustworthy P2P networks, (2) requires no trust between users by avoiding the advertisement of what peers download or miss, and (3) still ensures deterministic protection of user's interests against attacks of size up to a configured privacy protection level. We hope that our model can pave the ground for a new generation of privacyenhancing systems that take advantage of the new possibilities it introduces. We validate Mistrustful P2P through simulation, and demonstrate its feasibility.

Abstract
Language designers usually need to implement parsers and printers. Despite being two intimately related programs, in practice they are often designed separately, and then need to be revised and kept consistent as the language evolves. It will be more convenient if the parser and printer can be unified and developed in one single program, with their consistency guaranteed automatically. Furthermore, in certain scenarios (like showing compiler optimisation results to the programmer), it is desirable to have a more powerful reflective printer that, when an abstract syntax tree corresponding to a piece of program text is modified, can reflect the modification to the program text while preserving layouts, comments, and syntactic sugar. To address these needs, we propose a domain-specific language BIYACC, whose programs denote both a parser and a reflective printer for an unambiguous context-free grammar. BIYACC is based on the theory of bidirectional transformations, which helps to guarantee by construction that the pairs of parsers and reflective printers generated by BIYACC are consistent. We show that BIYACC is capable of facilitating many tasks such as Pombrio and Krishnamurthi's "resugaring", simple refactoring, and language evolution.

Abstract

Abstract

Abstract