Thesis Proposal


"Anonymous Accounting for Decentralized Systems"

Chris Erway

Thursday, November 5, 2009 at 3:00 P.M.

Lubrano Conference Room (CIT 4th floor)

Peer-to-peer systems have been proposed for a wide variety of applications, such as file-sharing, distributed storage, and distributed computation. These systems seek the benefits of a decentralized design---chiefly, the ability of a system to self-scale as new participants join. In a peer-to-peer system, participants are motivated to contribute resources that offset the added workload they generate. Additionally, decentralization offers improved fault- tolerance and user privacy, because no central authority is responsible for orchestrating or recording peer interactions.

However, these beneficial system properties are at risk from selfish participants. While many peer-to-peer systems, such as BitTorrent and Samsara, provide incentive mechanisms for encouraging participation, past work has shown that these mechanisms can be gamed by selfish peers that consume resources while providing little or none in return. For example, the pairwise reputation scheme used by BitTorrent applies only in the short term of a single download; new peers must be boostrapped by altruistic service.

A currency-based accounting system provides fungible, long-term incentives for participation that persist beyond the limited scale of a single download or pairwise interaction. However, currency raises a number of privacy and systems concerns arising from the infrastructure required of such a system. For example, a centralized bank must be provided that checks and counts currency, which presents a potential performance bottleneck and privacy concern. We show how the privacy of peer interactions can be preserved through the use of anonymous, cryptographically secure electronic cash (e-cash).

This thesis aims to show that e-cash is a practical technique for ensuring fairness, robustness, and better long-term incentives in decentralized systems. It demonstrates how to build practical systems that anonymously account for three different resource types--- bandwidth, storage, and computation---through the application of protocols for cryptographic fair exchange and e-cash, and how to mitigate the cryptographic overhead involved in doing so. As a result, a currency-based file sharing and storage system will be demonstrated that uses e-cash to provide long-term, reliable service for users.

Host: John Jannotti