compiler: implement ECDSA signature verification

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

pkg/compiler/analysis.go

@@ -14,6 +14,7 @@ var (
 	builtinFuncs = []string{
 		"len", "append", "SHA256",
 		"SHA1", "Hash256", "Hash160",
+		"VerifySignature",
 		"FromAddress", "Equals",
 	}
 )

pkg/compiler/codegen.go

@@ -666,6 +666,8 @@ func (c *codegen) convertBuiltin(expr *ast.CallExpr) {
 		emitOpcode(c.prog.BinWriter, opcode.HASH256)
 	case "Hash160":
 		emitOpcode(c.prog.BinWriter, opcode.HASH160)
+	case "VerifySignature":
+		emitOpcode(c.prog.BinWriter, opcode.VERIFY)
 	case "Equals":
 		emitOpcode(c.prog.BinWriter, opcode.EQUAL)
 	case "FromAddress":

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)
+		}
+	`
+}

pkg/interop/crypto/crypto.go

@@ -22,3 +22,8 @@ func Hash160(b []byte) []byte {
 func Hash256(b []byte) []byte {
 	return nil
 }
+
+// VerifySignature checks that sig is msg's signature with pub.
+func VerifySignature(msg []byte, sig []byte, pub []byte) bool {
+	return false
+}