Generate shared secret using elliptic-curve Diffie-Hellman function
Description
Curve25519 is a Diffie-Hellman function suitable for a wide variety of
applications.
Given a user's 32-byte secret key, Curve25519 computes the user's 32-byte
public key. Given the user's 32-byte secret key and another user's 32-byte
public key, Curve25519 computes a 32-byte secret shared by the two users. This
secret can then be used to authenticate and encrypt messages between the two
users.
