Energy-efficient cryptographic optimization for narrowband IoT security: Integrating blockchain and EP-CuMAC with ECM-SHA256

Narrowband Internet of Things (NB-IoT) continues to expand but faces challenges of cryptographic overhead and energy consumption. Security frameworks such as blockchain and Energy-Performance Cumulative Message Authentication Codes (EP-CuMAC) rely heavily on SHA-256, which is not optimized for energy-limited devices. This work unifies two complementary approaches-a hybrid blockchain-based NB-IoT framework and an EP-CuMAC-based framework-by engineering their cryptographic core with an Energy Complexity Model-optimized SHA-256 (ECM-SHA256). ECM applies parallel memory-bank mapping and block-level access optimization to reduce redundant power usage while preserving algorithmic integrity. Experimental evaluation on identical Intel DDR3 systems using pyRAPL shows energy savings of 2–13 % across blockchain (Unique ID Generation, Device Join, Transactions) and EP-CuMAC modules (Feedback, Prediction, Verification, Retransmission). The optimization leverages the Energy Complexity Model’s parallel memory-bank mapping of SHA-256, implemented on identical Intel DDR3 systems using pyRAPL for repeatable measurements. The results position ECM-SHA256 as a generalizable cryptographic optimization strategy for secure and sustainable NB-IoT deployments.