compiler: emit Neo.Crypto.ECDsaVerify syscall instead of CHECKSIG

Also change the name of `VerifySignature` interop, to match
syscall's name. It also accepts arguments in different order.

pkg/compiler/analysis.go

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

pkg/compiler/codegen.go

@@ -1063,8 +1063,6 @@ func (c *codegen) convertBuiltin(expr *ast.CallExpr) {
 		emit.Opcode(c.prog.BinWriter, opcode.SHA256)
 	case "SHA1":
 		emit.Opcode(c.prog.BinWriter, opcode.SHA1)
-	case "VerifySignature":
-		emit.Opcode(c.prog.BinWriter, opcode.VERIFY)
 	case "AppCall":
 		numArgs := len(expr.Args) - 1
 		c.emitReverse(numArgs)

pkg/compiler/syscall.go

@@ -1,6 +1,9 @@
 package compiler
 
 var syscalls = map[string]map[string]string{
+	"crypto": {
+		"ECDsaVerify": "Neo.Crypto.ECDsaVerify",
+	},
 	"storage": {
 		"GetContext": "Neo.Storage.GetContext",
 		"Put":        "Neo.Storage.Put",

pkg/compiler/verify_test.go

@@ -5,24 +5,28 @@ import (
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+	"github.com/nspcc-dev/neo-go/pkg/vm"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+// In this test we only check that needed interop
+// is called with the provided arguments in the right order.
 func TestVerifyGood(t *testing.T) {
 	msg := []byte("test message")
 	pub, sig := signMessage(t, msg)
 	src := getVerifyProg(pub, sig, msg)
 
-	eval(t, src, true)
-}
+	v, p := vmAndCompileInterop(t, src)
+	p.interops[vm.InteropNameToID([]byte("Neo.Crypto.ECDsaVerify"))] = func(v *vm.VM) error {
+		assert.Equal(t, msg, v.Estack().Pop().Bytes())
+		assert.Equal(t, pub, v.Estack().Pop().Bytes())
+		assert.Equal(t, sig, v.Estack().Pop().Bytes())
+		v.Estack().PushVal(true)
+		return nil
+	}
 
-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)
+	require.NoError(t, v.Run())
 }
 
 func signMessage(t *testing.T, msg []byte) ([]byte, []byte) {
@@ -49,7 +53,7 @@ func getVerifyProg(pub, sig, msg []byte) string {
 			pub := ` + pubS + `
 			sig := ` + sigS + `
 			msg := ` + msgS + `
-			return crypto.VerifySignature(msg, sig, pub)
+			return crypto.ECDsaVerify(msg, pub, sig)
 		}
 	`
 }

pkg/interop/crypto/crypto.go

@@ -13,7 +13,7 @@ func SHA256(b []byte) []byte {
 	return nil
 }
 
-// VerifySignature checks that sig is msg's signature with pub.
-func VerifySignature(msg []byte, sig []byte, pub []byte) bool {
+// ECDsaVerify checks that sig is msg's signature with pub.
+func ECDsaVerify(msg []byte, pub []byte, sig []byte) bool {
 	return false
 }