An Efficient IND-CCA2-Secure Certificateless Public Key Encryption Scheme with Cryptographic Reverse Firewalls

Lukman Umar Faruk (Department of Computer Engineering, Faculty of Engineering, Ahmadu Bello University Zaria, Kaduna state, Nigeria.)
Muhammad Bashir Abdulrazaq (Department of Computer Engineering at Ahmadu Bello University, Zaria, Nigeria)
Zainab Mukhtar Abubakar (Department of Computer Engineering at Ahmadu Bello University, Zaria, Nigeria)
Zahruddeen Haruna (Department of Computer Engineering, Faculty of Engineering, Ahmadu Bello University Zaria, Kaduna state, Nigeria)
A Umar (Department of Electrical and Electronics Engineering, Federal University of Transportation, Daura Katsina state, Nigeria)
Nafisa Shehu Usman (Department of Computer Engineering, Faculty of Engineering, Ahmadu Bello University Zaria, Kaduna state, Nigeria.)
Hassan Maharazu (Department of Electrical and Electronics Engineering, Federal University of Transportation, Daura Katsina state, Nigeria)

Vokasi UNESA Bulletin of Engineering, Technology and Applied Science
Vol. 3 No. 3 (2026): (In Progress)

Secure communication in Internet of Things (IoT), cloud computing, and peer-to-peer environments requires efficient cryptographic schemes resilient to advanced threats. Public Key Infrastructure (PKI) incurs certificate management overhead, while Identity-Based Encryption (IBE) introduces key escrow. Certificateless Public Key Encryption (CL-PKE) addresses these limitations, but existing constructions integrating Cryptographic Reverse Firewalls (CRFs) remain computationally expensive and lack IND-CCA2 security guarantees. This study develops an optimized CL-PKE-CRF scheme using a single-element public key, sender-side precomputation of pairing operations, and independent per-user randomization through a Key Derivation Function (KDF) at the Key Generation Center (KGC). The scheme was implemented using Charm-Crypto and evaluated over 1,000 iterations at 128-, 192-, and 256-bit security levels. Compared with the baseline, it reduced computational overhead by approximately 25% and communication costs by 33%, while subsequent encryption latency decreased by 76.6% for repeated operations. Simulated evaluations reported adversarial advantage below 0.004, 100% decryption correctness, and no observed information leakage across the tested compromise scenarios. A formal IND-CCA2 security reduction under the Computational Bilinear Diffie-Hellman (CBDH) assumption in the random oracle model is also presented. These findings demonstrate improved efficiency and resistance to exfiltration attacks, supporting secure communication in resource-constrained environments.