In peer-to-peer systems, attrition attacks include both traditional, network-level denial of service attacks as well as application-level attacks in which malign peers conspire to waste loyal peers' resources. We describe several defenses for LOCKSS, a peer-to-peer digital preservation system, that help ensure that application-level attacks even from powerful adversaries are less effective than simple network-level attacks, and that network-level attacks must be intense, wide-spread, and prolonged to impair the system.
The protocol described here is derived from earlier work @cite_21 in which we covered the background of the LOCKSS system. That protocol used redundancy, rate limitation, effort balancing, bimodal behavior (polls must be won or lost by a landslide) and friend bias (soliciting some percentage of votes from peers on the friends list) to prevent powerful adversaries from modifying the content without detection, or discrediting the intrusion detection system with false alarms. To mitigate its vulnerability to attrition, in this work we reinforce these defenses using admission control, desynchronization, and redundancy, and restructure votes to support a block-based repair mechanism that penalizes free-riding. In this section we list work that describes the nature and types of denial of service attacks, as well as related work that applies defenses similar to ours.
@cite_21
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The LOCKSS project has developed and deployed in a world-wide test a peer-to-peer system for preserving access to journals and other archival information published on the Web. It consists of a large number of independent, low-cost, persistent web caches that cooperate to detect and repair damage to their content by voting in "opinion polls." Based on this experience, we present a design for and simulations of a novel protocol for voting in systems of this kind. It incorporates rate limitation and intrusion detection to ensure that even some very powerful adversaries attacking over many years have only a small probability of causing irrecoverable damage before being detected.