Hybrid encryption: why combine classical and post-quantum cryptography

A developer has released Quipu, an open-source library that implements hybrid encryption by combining classical and post-quantum algorithms. The library uses X25519 with ML-KEM-1024 for key exchange and Ed25519 with ML-DSA-87 for signatures, targeting NIST security level 5. The developer notes that while the library composes standard primitives, it has not yet undergone an independent cryptographic audit.

When a new cryptographic algorithm appears, a tension shows up: classical algorithms such as X25519 or Ed25519 have resisted attacks for years, but are vulnerable to a future quantum computer; post-quantum ones such as ML-KEM or ML-DSA resist quantum attacks, but are newer and less tested. Hybrid encryption resolves the tension: use both at once . Combine a classical and a post-quantum algorithm so that the system only breaks if both fail simultaneously. A classical attacker would have to break the post-quantum algorithm; a quantum attacker would have to break the classical one and the post-quantum one. You gain security against the future without betting everything on a young algorithm. Key exchange encrypting for a recipient . You combine: The two resulting keys are mixed with a context-bound derivation function HKDF , so that neither one alone is enough. Digital signatures authenticity . You combine: The message is accepted only if both signatures verify — an AND combiner. There is a golden rule in cryptography, Kerckhoffs's principle : a system must be secure even if the attacker knows its entire design; security lives in the key , not in hiding the format. A good hybrid system uses public, audited primitives — XChaCha20-Poly1305 to encrypt, Argon2id to derive keys from passwords, HKDF to separate domains — and never invents its own cryptography . Quipu https://xiliux.com/blog/quipu-cifrado-multilenguaje-rust-python-node-go is a free library implementing exactly this approach for data at rest : hybrid X25519 + ML-KEM-1024 encryption, hybrid Ed25519 + ML-DSA-87 signatures, and only verified primitives underneath. It targets NIST security level 5 CNSA 2.0 and is open source, so anyone can review how it works. An honest note: Quipu composes standard primitives, but the composition has not yet passed an independentcryptographic audit. For real high-value secrets, that external review is the seal worth waiting for. The code is at github.com/isazajuancarlos/quipu https://github.com/isazajuancarlos/quipu , AGPL-3.0.