Privatizing the Volume and Timing of Blockchain Transactions
Miller, Trevor John
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With current state-of-the-art privacy-preserving blockchain solutions, users can submit transactions to a blockchain while maintaining full anonymity and not leaking the contents of the transaction through cryptographic techniques like zero-knowledge proofs and homomorphic encryption. However, the architecture of a blockchain consists of a decentralized network where every network participant maintains their own local copy of the blockchain and updates it upon every added transaction. As a result, the volume of blockchain transactions and the timestamp of each blockchain transaction for an application is publicly available. This is problematic for applications with time-sensitive or volume-sensitive outcomes because users may want this information to be privatized, such as not leaking the lateness of student examinations. However, this is not possible with existing blockchain research. In this thesis, we propose a blockchain system for multi-party applications that does not leak any useful information from the volume and timing metadata of the application's transactions, including maintaining the privacy of a time-sensitive or volume-sensitive outcome. We achieve this by adding sufficient noise using indistinguishable decoy transactions such that an adversary cannot deduce which transactions actually impacted the outcome of the application. This is facilitated in a manner where anyone can publicly verify the application's execution to be correct, fair, and honest. We demonstrate and evaluate our approach by implementing a Dutch auction that supports decoy bid transactions on a private Ethereum blockchain network.
General Audience Abstract
Blockchains are distributed, append-only, digital ledgers whose current state is continuously agreed upon through the consensus of network participants and not by any centralized party. These characteristics make them unique for many applications because they enable the application to be facilitated and executed in a public, verifiable, decentralized, and tamper-proof manner. For example, Bitcoin, the most popular cryptocurrency, uses blockchains to continuously maintain a permanent, verifiable ledger of payment transactions. However, one downside of this public architecture is that the volume of transactions and the timestamp of each transaction can always be publicly observed (e.g. the timestamp of every Bitcoin payment is public). This is problematic for applications with time-sensitive or volume-sensitive outcomes because users may want this volume and timing information to be privatized, such as not leaking the lateness of student examinations which could have severe consequences like violating student privacy laws. But currently with state-of-the-art blockchain research, privatizing this information is not possible. In this thesis, we demonstrate our approach that enables these time-sensitive and volume-sensitive applications to be implemented on blockchains in a manner that can maintain the privacy of these time-sensitive or volume-sensitive outcomes without sacrificing the application's integrity or verifiability. We then demonstrate and evaluate our approach through implementing a Dutch auction that supports decoy bid transactions on a private blockchain network.
- Masters Theses