compiler: implement ECDSA signature verification

Add VerifySignature interop for signature verification.
It is converted to VERIFY opcode.

pkg/compiler/verify_test.go

@@ -0,0 +1,55 @@
+package compiler_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/crypto/keys"
+	"github.com/stretchr/testify/require"
+)
+
+func TestVerifyGood(t *testing.T) {
+	msg := []byte("test message")
+	pub, sig := signMessage(t, msg)
+	src := getVerifyProg(pub, sig, msg)
+
+	eval(t, src, true)
+}
+
+func TestVerifyBad(t *testing.T) {
+	msg := []byte("test message")
+	pub, sig := signMessage(t, msg)
+	sig[0] = ^sig[0]
+	src := getVerifyProg(pub, sig, msg)
+
+	eval(t, src, false)
+}
+
+func signMessage(t *testing.T, msg []byte) ([]byte, []byte) {
+	key, err := keys.NewPrivateKey()
+	require.NoError(t, err)
+
+	sig := key.Sign(msg)
+	pub := key.PublicKey().Bytes()
+
+	return pub, sig
+}
+
+func getVerifyProg(pub, sig, msg []byte) string {
+	pubS := fmt.Sprintf("%#v", pub)
+	sigS := fmt.Sprintf("%#v", sig)
+	msgS := fmt.Sprintf("%#v", msg)
+
+	return `
+		package hello
+
+		import "github.com/CityOfZion/neo-go/pkg/interop/crypto"
+
+		func Main() bool {
+			pub := ` + pubS + `
+			sig := ` + sigS + `
+			msg := ` + msgS + `
+			return crypto.VerifySignature(msg, sig, pub)
+		}
+	`
+}