The perl-Crypt-Curve25519 package
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.