package utils

import (
	"github.com/agl/ed25519/extra25519"
	"golang.org/x/crypto/curve25519"
	"golang.org/x/crypto/ed25519"
)

// EDH implements diffie hellman using curve25519 keys derived from ed25519 keys
// NOTE: This uses a 3rd party library extra25519 as the key conversion is not in the core golang lib
// as such this definitely needs further review.
func EDH(privateKey ed25519.PrivateKey, remotePublicKey ed25519.PublicKey) [32]byte {
	var privKeyBytes [64]byte
	var remotePubKeyBytes [32]byte
	copy(privKeyBytes[:], privateKey[:])
	copy(remotePubKeyBytes[:], remotePublicKey[:])
	var secret, curve25519priv, curve25519pub [32]byte
	extra25519.PrivateKeyToCurve25519(&curve25519priv, &privKeyBytes)
	extra25519.PublicKeyToCurve25519(&curve25519pub, &remotePubKeyBytes)
	curve25519.ScalarMult(&secret, &curve25519priv, &curve25519pub)
	return secret
}