EllipticCurves X25519

[microshine]

Should we support X25519 named curve?
signal-protocol
OpenSSL

The Signal Protocol combines the Double Ratchet Algorithm, prekeys, and a triple Diffie–Hellman (3-DH) handshake,[4] and uses Curve25519, AES-256 and HMAC-SHA256 as primitives

[rmhrisk]

To do this we will need to switch to BorringSSL which is something I want to see us do anyway.