add VerifyCryptogram function

globalplatform/crypto/crypto.go

@@ -1,6 +1,7 @@
 package crypto
 
 import (
+	"bytes"
 	"crypto/cipher"
 	"crypto/des"
 )
@@ -30,6 +31,35 @@ func DeriveKey(cardKey []byte, seq []byte, purpose []byte) ([]byte, error) {
 	return ciphertext, nil
 }
 
+func VerifyCryptogram(encKey, hostChallenge, cardChallenge, cardCryptogram []byte) (bool, error) {
+	data := make([]byte, 0)
+	data = append(data, hostChallenge...)
+	data = append(data, cardChallenge...)
+	paddedData := appendDESPadding(data)
+	calculated, err := mac3des(encKey, paddedData, nullBytes8)
+	if err != nil {
+		return false, err
+	}
+
+	return bytes.Equal(calculated, cardCryptogram), nil
+}
+
+func mac3des(key, data, iv []byte) ([]byte, error) {
+	key24 := resizeKey24(key)
+
+	block, err := des.NewTripleDESCipher(key24)
+	if err != nil {
+		return nil, err
+	}
+
+	ciphertext := make([]byte, 24)
+
+	mode := cipher.NewCBCEncrypter(block, iv)
+	mode.CryptBlocks(ciphertext, data)
+
+	return ciphertext[16:], nil
+}
+
 func resizeKey24(key []byte) []byte {
 	data := make([]byte, 24)
 	copy(data, key[0:16])

globalplatform/crypto/crypto_test.go

@@ -31,3 +31,24 @@ func TestAppendDESPadding(t *testing.T) {
 	expected := "AABB800000000000"
 	assert.Equal(t, expected, hexutils.BytesToHex(result))
 }
+
+func TestVerifyCryptogram(t *testing.T) {
+	encKey := hexutils.HexToBytes("16B5867FF50BE7239C2BF1245B83A362")
+	hostChallenge := hexutils.HexToBytes("32da078d7aac1cff")
+	cardChallenge := hexutils.HexToBytes("007284f64a7d6465")
+	cardCryptogram := hexutils.HexToBytes("05c4bb8a86014e22")
+
+	result, err := VerifyCryptogram(encKey, hostChallenge, cardChallenge, cardCryptogram)
+	assert.NoError(t, err)
+	assert.True(t, result)
+}
+
+func TestMac3des(t *testing.T) {
+	key := hexutils.HexToBytes("16B5867FF50BE7239C2BF1245B83A362")
+	data := hexutils.HexToBytes("32DA078D7AAC1CFF007284F64A7D64658000000000000000")
+	result, err := mac3des(key, data, nullBytes8)
+	assert.NoError(t, err)
+
+	expected := "05C4BB8A86014E22"
+	assert.Equal(t, expected, hexutils.BytesToHex(result))
+}