# Master’s Thesis Presentation • Cryptography, Security, and Privacy (CrySP) • FairBlock: Preventing Blockchain Front-running with Minimal Overheads

Thursday, July 28, 2022 — 4:00 PM to 5:00 PM EDT

## Please note: This master’s thesis presentation will take place online.

Peyman Momeni, Master’s candidate
David R. Cheriton School of Computer Science

Supervisor: Professor Sergey Gorbunov

While blockchain systems are quickly gaining popularity, front-running remains a major obstacle to fair exchange. Front-running is a family of strategies in which a malicious party manipulates the order of transactions such that a transaction $tx_2$ which is broadcasted in time $t_2$ executes before the transaction of victim $tx_1$ which is broadcasted earlier in time $t_1$ ($t_1 < t_2$). In this thesis, we show how to apply Identity-Based Encryption (IBE) to prevent front-running with minimal bandwidth overheads.

In our approach, to decrypt a block of $N$ transactions, the number of messages sent across the network only grows linearly with the size of decrypting committees, $S$. That is, to decrypt a set of $N$ transactions sequenced at a specific block, a committee only needs to exchange $S$ decryption shares (independent of $N$). In comparison, previous solutions are based on threshold decryption schemes, where each transaction in a block must be decrypted separately by the committee, resulting in bandwidth overhead of $N \times S$. Along the way, we present a model for fair block processing, explore technical challenges, and build prototype implementations. We show that on a sample of 1000 messages with 1000 validators our work saves 42.53 MB of bandwidth which is 99.6\% less compared with the standard threshold decryption paradigm.

To join this master’s thesis presentation on Zoom, please go to https://uwaterloo.zoom.us/j/95433503306.

Location
Online master’s thesis presentation
200 University Avenue West

Waterloo, ON N2L 3G1
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### September 2022

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