Iranian Society of Cryptology The ISC International Journal of Information Security 2008-2045 Articles in Press 2026 02 22 Enhancing Kleptographic Backdoors in Hash-Based Deterministic Random Bit Generators 241269 10.22042/isecure.2026.241269 EN Sepehr Jafari Faculty of Computer Science and Engineering, Shahid Beheshti University, Tehran, Iran. Raziyeh Salarifard Faculty of Computer Science and Engineering, Shahid Beheshti University, Tehran, Iran. Journal Article Deterministic Random Bit Generators (DRBGs) are essential for cryptographic security but remain vulnerable to covert kleptographic attacks that implant backdoors to leak sensitive information. Despite being known for two decades, as demonstrated by incidents such as the Snowden revelations and Dual-EC, these attacks persist in modern protocols, including TLS and post-quantum systems. This paper introduces a novel kleptographic backdoor for hash-based DRBGs, utilising a dual-phase design: secret information is split across two complementary phases, each requiring the other for recovery. This design significantly increases the overall complexity compared with conventional methods. To enhance indistinguishability, we integrate randomness derived from the discrete logarithm problem, ensuring statistical conformity. By leveraging ElGamal encryption to ensure compatibility with our approach, we develop a highly covert backdoor. Rigorous validation via the NIST Statistical Test Suite (STS) and neural network-based anomaly detection confirms the backdoor passes all NIST tests while evading machine learning detection, maintaining statistical integrity and structural consistency.  https://www.isecure-journal.com/article_241269_cd5eb2ccf1186ca275fd357185d8fdc6.pdf