Danger

This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.

X25519 key exchange

X25519 is an elliptic curve Diffie-Hellman key exchange using Curve25519. It allows two parties to jointly agree on a shared secret using an insecure channel.

Exchange Algorithm

For most applications the shared_key should be passed to a key derivation function.

>>> from cryptography.hazmat.backends import default_backend
>>> from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
>>> # Generate a private key for use in the exchange.
>>> private_key = X25519PrivateKey.generate()
>>> # In a real handshake the peer_public_key will be received from the
>>> # other party. For this example we'll generate another private key and
>>> # get a public key from that. Note that in a DH handshake both peers
>>> # must agree on a common set of parameters.
>>> peer_public_key = X25519PrivateKey.generate().public_key()
>>> shared_key = private_key.exchange(peer_public_key)
>>> # For the next handshake we MUST generate another private key.
>>> private_key_2 = X25519PrivateKey.generate()
>>> peer_public_key_2 = X25519PrivateKey.generate().public_key()
>>> shared_key_2 = private_key_2.exchange(peer_public_key_2)

Key interfaces

class cryptography.hazmat.primitives.asymmetric.x25519.X25519PrivateKey[source]

New in version 2.0.

classmethod generate()[source]

Generate an X25519 private key.

Returns:X25519PrivateKey
public_key()[source]
Returns:X25519PublicKey
exchange(peer_public_key)[source]
Parameters:peer_public_key (X25519PublicKey) – The public key for the peer.
Returns bytes:A shared key.
class cryptography.hazmat.primitives.asymmetric.x25519.X25519PublicKey[source]

New in version 2.0.

classmethod from_public_bytes(data)[source]
Parameters:data (bytes) – 32 byte public key.
Returns:X25519PublicKey
>>> from cryptography.hazmat.primitives.asymmetric import x25519
>>> private_key = x25519.X25519PrivateKey.generate()
>>> public_key = private_key.public_key()
>>> public_bytes = public_key.public_bytes()
>>> loaded_public_key = x25519.X25519PublicKey.from_public_bytes(public_bytes)
public_bytes()[source]
Returns bytes:The raw bytes of the public key.