How do you implement Post-Quantum Cryptography key exchange using Python?

For a Python example, you can use ML-KEM-768 (the standardized version of Kyber) through the Open Quantum Safe liboqs-python bindings. ML-KEM is a key-encapsulation mechanism: one side creates a key pair, and the other uses the public key to produce a ciphertext and a shared secret. The recipient decapsulates that ciphertext to arrive at the same secret.

A minimal ML-KEM-768 exchange

Install the native liboqs library and its Python bindings following the project’s instructions. Then the exchange can be simulated like this:

import hmac
import oqs

# The recipient creates a public key and keeps the matching private key local.
with oqs.KeyEncapsulation("ML-KEM-768") as recipient:
    public_key = recipient.generate_keypair()

    # The sender encapsulates a secret using the recipient's public key.
    with oqs.KeyEncapsulation("ML-KEM-768") as sender:
        ciphertext, sender_secret = sender.encap_secret(public_key)

    # The recipient recovers the same secret from the ciphertext.
    recipient_secret = recipient.decap_secret(ciphertext)

    # Compare safely; in a real protocol, derive encryption keys from this secret.
    print("Shared secrets match:",
          hmac.compare_digest(sender_secret, recipient_secret))

In a real exchange, the sender transmits the ciphertext to the recipient; the public key must also reach the sender. The shared secret stays on each side and should not be sent over the network. Use HKDF with appropriate protocol context to derive application keys rather than using the raw secret directly.

What this example does not provide

This is an unauthenticated key establishment demo, not a complete secure channel. An attacker who can replace the public key could establish separate secrets with each party. Real protocols need authentication, transcript binding, and careful key derivation. For production traffic, prefer a maintained TLS implementation that supports hybrid post-quantum TLS, rather than assembling a protocol from this snippet.

The liboqs project is useful for experimentation, but its algorithms and Python API availability depend on the installed version. Check the project documentation and treat this example as a learning aid, not production-ready cryptographic code.