ML-KEM vs RSA: Quantum-Resistant Security Comparison

The comparison between ML-KEM and RSA highlights the fundamental shift needed in cryptographic approaches to address quantum threats.

RSA Cryptography: The Classical Approach

RSA (Rivest-Shamir-Adleman) has been a cornerstone of modern cryptography since the 1970s. Its security relies on the computational difficulty of factoring large composite numbers into their prime factors. The larger the key size, the more computationally intensive it becomes to factor the number using classical computers.

RSA serves dual purposes in modern systems: key exchange (RSA-KEM) and digital signatures (RSA-PSS). Despite its age, RSA remains widely deployed in TLS connections, SSH, PGP, and many other security protocols. However, its reliance on integer factorization makes it vulnerable to Shor's algorithm on quantum computers.

ML-KEM: The Lattice-Based Alternative

ML-KEM (Module-Lattice-based Key Encapsulation Mechanism) is based on the Module Learning With Errors (M-LWE) problem in lattice-based cryptography. It represents a fundamentally different mathematical approach compared to RSA, relying on the difficulty of solving certain problems in high-dimensional lattices.

ML-KEM, standardized as part of NIST's post-quantum cryptography initiative (specifically Kyber), offers key encapsulation functionality to replace RSA-based key exchange. The algorithm has been designed to resist attacks from both classical and quantum computers, addressing the vulnerabilities inherent in RSA.

Quantum Resistance Comparison

RSA's security completely collapses in the presence of sufficiently powerful quantum computers running Shor's algorithm. A quantum computer with enough logical qubits could factor RSA keys in polynomial time, rendering the encryption useless.

ML-KEM, on the other hand, is designed to be resistant to quantum attacks. The underlying lattice problems that ML-KEM relies on are not known to be efficiently solvable by quantum algorithms. While quantum computers might improve the constants involved in solving these problems, they don't reduce the exponential complexity as Shor's algorithm does for factoring.

Performance and Implementation Differences

RSA typically offers smaller signature sizes and well-understood performance characteristics. However, key generation in RSA can be computationally expensive, and the algorithm generally requires larger key sizes to maintain security as computing power increases.

ML-KEM generally provides faster key generation and encryption/decryption operations compared to RSA. However, ML-KEM keys and ciphertexts are typically larger than RSA equivalents. For example, Kyber768 has a public key size of about 1,184 bytes compared to a 256-byte public key for NIST P-256 ECC.

Migration Path from RSA to ML-KEM

Organizations looking to migrate from RSA to ML-KEM need to consider several factors, including system compatibility, performance impacts, and the availability of libraries supporting the new algorithms. The transition often involves a hybrid approach initially.

During the transition period, systems may implement both RSA and ML-KEM in parallel, allowing for gradual migration while maintaining compatibility with systems that haven't yet adopted post-quantum algorithms. This hybrid approach provides protection against both current classical attacks and future quantum attacks. Ethereum verifies ECDSA on-chain; no wallet makes on-chain sigs quantum-safe; BMIC protects vault/backups/device-handoff.

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