PAG: Private and Accountable Gossip

Abstract

Abstract-A large variety of content sharing applications rely, at least partially, on gossip-based dissemination protocols. However, these protocols are subject to various types of faults, among which selfish behaviours performed by nodes that benefit from the system without contributing their fair share to it. Accountability mechanisms (e.g., PeerReview, AVMs, FullReview), which require that nodes log their interactions with others and periodically inspect each others' logs are effective solutions to deter faults. However, these solutions require that nodes disclose the content of their logs, which may leak sensitive information about them. Building on a monitoring infrastructure and on homomorphic cryptographic procedures, we propose in this paper PAG, the first accountable and partially privacypreserving gossip protocol. We assess PAG theoretically using the ProVerif cryptographic protocol verifier and evaluate it experimentally using both a real deployment on a cluster of 48 machines and simulations. The performance evaluation of PAG, performed using a video live streaming application, shows that it is compatible with the visualisation of live video content on commodity Internet connections. Furthermore, PAG's bandwidth consumption inherits the desirable scalability properties of gossip when the number of users in the system grows.

Duck Attack on Accountable Distributed Systems

“…The duck attack is named after the duck test 1 and it can be summarized as follows: if you provide me the cryptographic digest H (m) of a message m, then it probably means that you know H (m) and the message m. Note that, this is outrightly false because concluding that you know m from the fact that you know H (m) is incorrect. We find this logical flaw in PAG [DMPQ16] and AcTinG [MDQ14a]. In a duck attack, the colluding nodes execute the protocol without exchanging the messages.…”

“…In Section 2, we discuss the threat model and colluding adversaries. We first demonstrate the power of the duck attack on PAG [DMPQ16] (Section 3). In Section 4, we also illustrate the duck attack on AcTinG a protocol which inherits the secure log system of PeerReview [HKD07].…”

“…PAG [DMPQ16] has been designed to provide accountability to fight both individual malicious nodes and malicious colluding nodes in gossip-based message dissemination schemes, where nodes periodically exchange data chunks with randomly chosen nodes [KMG03, BMM + 08]. In addition, it provides privacy guarantees for the messages provided by the nodes.…”

“…LiFTinG [GHK + 10] uses cross checking and statistical analysis. Finally, AcTinG [MDQ14a] and PAG [DMPQ16] rely on cryptography to ensure that nodes' actions are bound, nonrepudiable, tamper-evident and verifiable [YC04,YC05]. This last category of solutions is the focus of our work.…”

“…This last category of solutions is the focus of our work. We analyze the security provided by AcTinG [MDQ14a] and PAG [DMPQ16] and discover a new attack.…”