In the decentralized token system ZUZ, users can define their own token-based currencies which accrue reputation from publicly observable actions recorded on a transparent, universally accessible ledger. We design, implement, and evalaute the cost of privacy-preserving versions of the ZUZ system for both the UTXO- and account-based models. In the UTXO-based model, we extend the Zerocash protocol to support anonymous transfers over origin, destination, and value for a multi-token system with negligible overhead over Zerocash transactions. In the account-based model, we design a privacy-preserving Ethereum smart contract which represents the ledger state more concisely, while still achieving anonymous transfers over destination and value. Our preliminary results show that transaction times scale linearly in the size of the sender's wallet and anonymity ring. Finally, we introduce a novel primitive which formalizes the notion of reputation with respect to a public ledger. This provides a starting point for how to address the conflict between the reputation of users and the anonymity of transfers in a privacy-preserving ledger.

57 pages

Thesis Committee:
Seth Copen Goldstein (Chair)
Elaine Shi

Srinivasan Seshan, Head, Computer Science Department
Martial Hebert, Dean, School of Computer Science

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