The increasing proliferation of Healthcare Internet of Things (H-IoT) devices has enabled real-time patient monitoring and seamless healthcare delivery. However, the sensitive nature of transmitted patient data presents major security and privacy risks, especially in resource-constrained environments. Traditional cryptographic solutions such as RSA and Diffie-Hellman (DH) are computationally intensive and unsuitable for low-power IoT devices. This paper proposes a lightweight and secure cryptographic framework that integrates Elliptic Curve Diffie-Hellman (ECDH) for efficient key exchange and Advanced Encryption Standard (AES) for symmetric data encryption. To further ensure tamper-proof storage and decentralized trust, we embed our solution within a fog-enabled blockchain infrastructure. The proposed model implements four core algorithms that cover secure patient data encryption, blockchain storage, authenticated access, and mutual device verification. Experimental evaluation in various configurations demonstrates significant performance improvements over existing models such as ASE in terms of reduced encryption and decryption time, enhanced authentication success rate, and lower packet error rates. Comparative analysis across fog and cloud environments confirms the system’s scalability and suitability for real-time, secure medical data exchange. This work contributes to a practical, modular, and energy efficient encryption model tailored for modern H-IoT ecosystems.