How to encapsulate and decapsulate a shared secret with ML-KEM-768 in Python

1from cryptography.hazmat.primitives.asymmetric import mlkem
2 
3# Receiver: a key pair; only the encapsulation (public) key is handed out
4private_key = mlkem.MLKEM768PrivateKey.generate()
5public_key = private_key.public_key()
6 
7# Sender: a fresh 32-byte shared secret and the ciphertext that carries it
8shared_secret, ciphertext = public_key.encapsulate()
9 
10# Receiver: the same secret from the ciphertext
11received = private_key.decapsulate(ciphertext)
12 
13print(f"encapsulation key {len(public_key.public_bytes_raw())} bytes, "
14      f"ciphertext {len(ciphertext)} bytes, shared secret {len(shared_secret)} bytes")
15print("shared secret agreed:", received == shared_secret)
16 

1from cryptography.hazmat.primitives import serialization
2from cryptography.hazmat.primitives.asymmetric import mlkem
3 
4# Keys in the standard containers, e.g. written by OpenSSL 3.5:
5# the encapsulation key as SPKI ("BEGIN PUBLIC KEY"), the decapsulation key as PKCS#8
6with open("openssl-pub.pem", "rb") as f:
7    encapsulation_key = serialization.load_pem_public_key(f.read())
8with open("seed.pem", "rb") as f:
9    decapsulation_key = serialization.load_pem_private_key(f.read(), password=None)
10 
11if not isinstance(encapsulation_key, mlkem.MLKEM768PublicKey):
12    raise TypeError(f"expected an ML-KEM-768 key, got {type(encapsulation_key).__name__}")
13if not isinstance(decapsulation_key, mlkem.MLKEM768PrivateKey):
14    raise TypeError(f"expected an ML-KEM-768 key, got {type(decapsulation_key).__name__}")
15