The Trinity (, 2007) spam classification system is based on a distributed hash table that is implemented using a structured peer-to-peer overlay. Such an overlay must be capable of processing hundreds of messages per second, and must be able to route messages to their destination even in the presence of failures and malicious peers that misroute packets or inject fraudulent routing information into the system. Typically there is tension between the requirements to route messages securely and efficiently in the overlay. We describe a secure and efficient routing extension that we developed within the I3 ( 2004) implementation of the Chord ( 2001) overlay. Secure routing is accomplished through several complementary approaches: First, peers in close proximity form overlapping groups that police themselves to identify and mitigate fraudulent routing information. Second, a form of random routing solves the problem of entire packet flows passing through a malicious peer. Third, a message authentication mechanism links each message to it sender, preventing spoofing. Fourth, each peer's identifier links the peer to its network address, and at the same time uniformly distributes the peers in the key-space. Lastly, we present our initial evaluation of the system, comprising a 255 peer overlay running on a local cluster. We describe our methodology and show that the overhead of our secure implementation is quite reasonable.
@cite_7 proposed several approaches to securing peer-to-peer overlays. They proposed to delegate assignment of keys to trusted certification authorities, that would ensure that the keys are chosen at random, and that each peer is bound to a unique key, with the peer's IP embedded in the key. To securely route messages, they proposed to use constrained routing tables, which contain keys from specific locations in the overlay. In our case Chord already constrains a key's location within the overlay, obviating the need for constrained routing tables. In fact, our self-policing and random routing mechanisms leverage this constraint.
@cite_7
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Structured peer-to-peer overlay networks provide a substrate for the construction of large-scale, decentralized applications, including distributed storage, group communication, and content distribution. These overlays are highly resilient; they can route messages correctly even when a large fraction of the nodes crash or the network partitions. But current overlays are not secure; even a small fraction of malicious nodes can prevent correct message delivery throughout the overlay. This problem is particularly serious in open peer-to-peer systems, where many diverse, autonomous parties without preexisting trust relationships wish to pool their resources. This paper studies attacks aimed at preventing correct message delivery in structured peer-to-peer overlays and presents defenses to these attacks. We describe and evaluate techniques that allow nodes to join the overlay, to maintain routing state, and to forward messages securely in the presence of malicious nodes.