Post-Quantum Key Encapsulation Mechanisms: A Comparative Review of ML-KEM, BIKE, and HQC

Large-scale quantum computers will fundamentally compromise public-key cryptosystems based on integer factorization and the discrete logarithm problem. The National Institute of Standards and Technology (NIST) standardized ML-KEM (FIPS 203, August 2024) and selected HQC (March 2025) as a code-based backup Key Encapsulation Mechanism (KEM). This paper presents a structured comparative analysis of ML-KEM, BIKE (Bit Flipping Key Encapsulation), and HQC (Hamming Quasi-Cyclic) across six dimensions: mathematical foundations, key and ciphertext sizes, computational performance with explicit instruction-set architecture (ISA) attribution, quantitative security margins, side-channel resistance, and TLS 1.3 handshake overhead. A phased migration roadmap is also provided. ML-KEM delivers compact key material, formally proven Indistinguishability under Adaptive Chosen Ciphertext Attack (IND-CCA2) security, and balanced performance, making it the appropriate primary KEM for general deployment. HQC supplies a formally bounded Decryption Failure Rate (DFR) and mathematical independence from lattice assumptions, establishing it as a sound standardized backup. BIKE offers competitive encapsulation speed but relies on an empirically bounded, rather than formally proven, DFR, constituting a residual security gap that precluded its standardization.