Add initial WhatsApp support (#711)

vendor/github.com/Rhymen/go-whatsapp/crypto/curve25519/curve.go

@@ -0,0 +1,44 @@
+/*
+In cryptography, Curve25519 is an elliptic curve offering 128 bits of security and designed for use with the elliptic
+curve Diffie–Hellman (ECDH) key agreement scheme. It is one of the fastest ECC curves and is not covered by any known
+patents. The reference implementation is public domain software. The original Curve25519 paper defined it
+as a Diffie–Hellman (DH) function.
+*/
+package curve25519
+
+import (
+	"crypto/rand"
+	"golang.org/x/crypto/curve25519"
+	"io"
+)
+
+/*
+GenerateKey generates a public private key pair using Curve25519.
+*/
+func GenerateKey() (privateKey *[32]byte, publicKey *[32]byte, err error) {
+	var pub, priv [32]byte
+
+	_, err = io.ReadFull(rand.Reader, priv[:])
+	if err != nil {
+		return nil, nil, err
+	}
+
+	priv[0] &= 248
+	priv[31] &= 127
+	priv[31] |= 64
+
+	curve25519.ScalarBaseMult(&pub, &priv)
+
+	return &priv, &pub, nil
+}
+
+/*
+GenerateSharedSecret generates the shared secret with a given public private key pair.
+*/
+func GenerateSharedSecret(priv, pub [32]byte) []byte {
+	var secret [32]byte
+
+	curve25519.ScalarMult(&secret, &priv, &pub)
+
+	return secret[:]
+}