Game of Trust: How Trustworthy Does Your Blockchain Think You Are?
Petros Drineas, Rohit Nema, Rafail Ostrovsky, Vassilis Zikas
TL;DR
The paper addresses how a blockchain can distill the collective beliefs of its nodes into a rigorous reputation system for a subset of nodes. It introduces a two-part framework: (i) Information Extraction via a tailored Designated PageRank on a Reputation Graph, and (ii) Incentive Design via Trustworthy Reputation (TRep) games whose equilibria encode the ground-truth trust vector. The authors prove decodability results across perfect, hierarchical, and noisy information settings, showing that PageRank-based outputs recover relative trust and support equitable reward allocation in PoR/PoS blockchains. Theyalso provide a concrete instantiation with a concrete utility function based on Personalized PageRank, establish unique equilibria in key cases, and discuss bootstrapping and deployment within PoR/PoS protocols. The work offers a theory-grounded path to robust, scalable reputation mechanisms in blockchain and DeFi contexts, with broader applicability to generic graph-based reputation systems.
Abstract
We investigate how a blockchain can distill the collective belief of its nodes regarding the trustworthiness of a (sub)set of nodes into a {\em reputation system} that reflects the probability of correctly performing a task. To address this question, we introduce a framework that breaks it down into two sub-problems: 1. (Information Extraction): How can the system distill trust information from a function of the nodes' true beliefs? 2. (Incentive Design): How can we incentivize nodes to truthfully report such information? To tackle the first sub-problem, we adapt, in a non-trivial manner, the well-known PageRank algorithm to our problem. For the second, we define a new class of games, called Trustworthy Reputation games (TRep games), which aim to extract the collective beliefs on trust from the actions of rational participants. We then propose a concrete TRep game whose utility function leverages Personalized PageRank and can be instantiated through a straightforward blockchain rewards mechanism. Building on this, we show how the TRep game enables the design of a reputation system. Such systems can enhance the robustness, scalability, and efficiency of blockchain and DeFi solutions. For instance, we demonstrate how such a system can be used within a Proof-of-Reputation blockchain.