Decentralized Review System

Online product review systems are a critical component of modern e-commerce, directly influencing consumer purchasing decisions. However, existing centralised review platforms are highly susceptible to manipulation, including fake review injection, seller-incentivised rating fraud, and unilateral deletion of legitimate negative feedback by platform administrators. This paper proposes ReviewChain, a decentralised, tamper-proof product review system built upon blockchain architecture to address these limitations. The proposed system implements SHA-256 cryptographic hashing via the browser-native SubtleCrypto API and a Proof-of-Work consensus mechanism to mine each review into an immutable block. Every block encodes the reviewer's pseudonymous wallet address, product metadata, review content, rating, timestamp, nonce, and the previous block's hash — forming a cryptographically linked chain. Any post-submission modification to a review invalidates the block's hash and breaks all subsequent chain links, making tampering instantly and mathematically detectable. For global decentralised storage and real-time synchronisation, the system integrates Gun.js — an open-source, serverless, peer-to-peer graph database — eliminating the need for any central server or database infrastructure. The application is deployed as a fully client-side web application, requiring no backend, accessible on any static hosting platform. Experimental results demonstrate that the system successfully detects all tamper attempts, synchronises review data across geographically distributed peers in real time, and maintains chain integrity under concurrent multi-user conditions. ReviewChain presents a viable, cost-free, and scalable alternative to centralised review platforms for trustworthy consumer feedback.