X25519 writes a shared key to |out_shared_key| that is calculated from the given private key and the peer's public value. It returns one on success and zero on error.
X25519_keypair sets |out_public_value| and |out_private_key| to a freshly generated, public/private key pair.
X25519.
Curve25519.
Curve25519 is an elliptic curve.