Hybrid Encryption Combines Classical and Post-Quantum Algorithms for Stronger Security

Hybrid encryption addresses a key dilemma in modern cryptography: classical algorithms like X25519 and Ed25519 are well-tested but vulnerable to future quantum computers, while newer post-quantum algorithms like ML-KEM and ML-DSA lack the same track record. The hybrid approach combines both types so that a system is only compromised if both algorithms fail at the same time, offering protection against both current and future threats. For key exchange, classical X25519 and post-quantum ML-KEM-1024 outputs are blended using HKDF, while digital signatures require both Ed25519 and ML-DSA-87 to verify successfully. A open-source library called Quipu implements this hybrid model, targeting NIST security level 5 and using only established, audited primitives such as XChaCha20-Poly1305 and Argon2id. The developers caution that Quipu's composition of these primitives has not yet undergone an independent cryptographic audit, which they recommend before using it to protect high-value secrets.