crypto, crypto/ecies, crypto/secp256k1: libsecp256k1 scalar mult

thanks to Felix Lange (fjl) for help with design & impl

p2p/discover/node.go

@@ -210,7 +210,7 @@ func PubkeyID(pub *ecdsa.PublicKey) NodeID {
 // Pubkey returns the public key represented by the node ID.
 // It returns an error if the ID is not a point on the curve.
 func (id NodeID) Pubkey() (*ecdsa.PublicKey, error) {
-	p := &ecdsa.PublicKey{Curve: crypto.S256(), X: new(big.Int), Y: new(big.Int)}
+	p := &ecdsa.PublicKey{Curve: secp256k1.S256(), X: new(big.Int), Y: new(big.Int)}
 	half := len(id) / 2
 	p.X.SetBytes(id[:half])
 	p.Y.SetBytes(id[half:])