This paper presents the Blockchain subsystem of SecureExam Chain, a multi-modal online examination proctoring platform that integrates deep-learning-based fraud detection with a tamper-resistant audit ledger. The blockchain layer is implemented on a private Ethereum network using Solidity smart contracts, deployed via the Hardhat development framework, and interfaces through MetaMask-authenticated browser sessions. Two purpose-built contracts govern the system: ExamSystemsol, which manages role-based identity, exam life cycle and fraud history; and FraudLog.sol, which provides gas-optimised, privacy-preserving, immutable log of AI-generated fraud events. We describe the full contract architecture, state variables, function signatures, access-control modifiers, event schema, cryptographic privacy scheme, and deployment pipeline. The design ensures that no personally identifiable information (PII) is stored on-chain; instead, keccak256 hashes serve as verifiable integrity anchors that any third-party auditor can confirm without exposing raw student data.