The proliferation of dynamic and mobile internet of things (IoT) applications, including the internet of vehicles (IoV), internet of drones (IoD), and internet of gadgets (IoG), has introduced new challenges in secure and scalable public key management. This paper proposes LHBKM, a lightweight hierarchical blockchain-based public key management framework for interconnected mobile IoT supported by mobile edge computing (MEC) adopting a three-tier hierarchy to localize registration/verification at the edge while preserving global consistency via hierarchical anchoring. Key-registration transactions are authenticated using Boneh-Lynn-Shacham (BLS) signatures, while we comparatively evaluate three hash candidates: Ascon, BLAKE3, and Keccak (SHA3). Results show that BLAKE3 provides better overall efficiency, reducing computation time by 76.47% versus Keccak while also lowering communication and storage costs by 17.60% and 15.98%, respectively. Future work will explore the integration of deep reinforcement learning to enable intelligent key caching and long-term storage optimization. © 2026 IEEE.