Secure Evidence Management Through TDAG-Based Digital Twin Architecture: A Smart Locker System for Tamper-Evident Chain of Custody

Digital evidence carriers such as phones, laptops, and storage devices require an unbroken chain of custody to ensure forensic integrity, yet current systems rely on manual tracking that may compromise integrity and security. Existing solutions lack integrated monitoring and resource management capabilities essential for guaranteeing reliable evidence handling. This paper proposes a comprehensive distributed architecture that unites physical smart lockers containing evidence with their digital twin representations through a Transaction-based DAG (TDAG).The TDAG ensures tamper-proof logging and synchronisation and forms the foundation for the digital twin layer that applies multi-dimensional optimisation using weighted cost functions for resource allocation, state prediction matrices, and PID-controlled environmental regulation. The architecture implements multi-layered security combining AES-256 encryption for evidence data, HMAC-SHA384 for node integrity verification, and ECDSA signatures with SECP384R1 curves for authentication. Role-based access control and comprehensive audit logging enforce full custody tracking and unbroken chain-of-custody assurance. Validation of the architecture’s foundation demonstrates scalability across 1,056 nodes and 140 evidence chains, with condition logs accounting for 74.43% of nodes while maintaining a resource-efficient 0.65 MB footprint.