Recent years have witnessed a slew of coding techniques custom designed for networked storage systems. Network coding inspired regenerating codes are the most prolifically studied among these new age storage centric codes. A lot of effort has been invested in understanding the fundamental achievable trade-offs of storage and bandwidth usage to maintain redundancy in presence of different models of failures, showcasing the efficacy of regenerating codes with respect to traditional erasure coding techniques. For practical usability in open and adversarial environments, as is typical in peer-to-peer systems, we need however not only resilience against erasures, but also from (adversarial) errors. In this paper, we study the resilience of generalized regenerating codes (supporting multi-repairs, using collaboration among newcomers) in the presence of two classes of Byzantine nodes, relatively benign selfish (non-cooperating) nodes, as well as under more active, malicious polluting nodes. We give upper bounds on the resilience capacity of regenerating codes, and show that the advantages of collaborative repair can turn to be detrimental in the presence of Byzantine nodes. We further exhibit that system mechanisms can be combined with regenerating codes to mitigate the effect of rogue nodes.
We study data integrity verification in peer-to-peer media streaming for content distribution. Challenges include the timing constraint of streaming as well as the untrustworthiness of peers. We show the inadequacy of existing data integrity verification protocols, and propose Block-Oriented Probabilistic verification (BOPV), an efficient protocol utilizing message digest and probabilistic verification. We then propose Tree-based Forward Digest Protocol (TFDP) to further reduce the communication overhead. A comprehensive comparison is presented by comparing the performance of existing protocols and our protocols, with respect to overhead, security assurance level, and packet loss tolerance. Finally, experimental results are presented to evaluate the performance of our protocols. RSS (really simple syndication) based feeds have become the defacto mechanism of web based publish subscribe. Peer-to-Peer delivery of such feeds can not only alleviate the load at the content server, but also reduce the dissemination latency. However, due to openness of P2P system, malicious peers can join the network as easily as normal peers do. Such malicious peers may pretend to relay but actually not, and thus deny service, or even disseminate counterfeit updates, rendering a Peer-to-Peer mechanism not only useless, but even harmful (e.g. by false updates). We propose overlay independent randomized strategies to mitigate these ill-effects of malicious peers at a marginal overhead, thus enjoying the benefits of Peer-to-Peer dissemination, along with the assurance of content integrity in RSS like web-based publish-subscribe applications without altering currently deployed server infrastructure. We conduct analysis of performance of our proposal by modeling behavior of the system and validating the same with simulation. Results show that our proposal is effective, robust and scalable. 