A Secure Architecture for Immutable and Verifiable OTA Firmware Updates for IoT Devices using Blockchain

The rapid growth of Internet of Things (IoT) devices has intensified the need for secure and reliable over-the-air (OTA) firmware updates. Ensuring the confidentiality, integrity, and authenticity of firmware during updates is critical to prevent device compromise and maintain trust. However, existing systems still face challenges in providing fully secure OTA firmware updates. This paper proposes a blockchain enabled architecture that ensures immutable, verifiable, and confidential OTA firmware updates for IoT devices. The framework employs smart contracts to manage firmware metadata such as version, timestamp, and cumulative hash stored immutably on the blockchain, while the actual firmware binary is securely maintained in off chain cloud storage. To support lightweight verification on resource constrained devices, a chunk based cumulative hashing mechanism is introduced, where firmware is segmented into 100 byte blocks and aggregated using an XOR based hash computation. The system was implemented and tested on the Ethereum Sepolia testnet and validated on an ESP32 IoT board. Experimental results confirm secure update verification with minimal computational overhead. By integrating decentralized trust, tamper resistance, and efficient integrity validation, the proposed framework offers a scalable and transparent solution for secure OTA firmware management in IoT ecosystems.