CBC-MAC算法似乎有6种变体。我一直在尝试匹配 PINPad 1000SE 上的 MAC 算法 [根据手册是 ISO 9797-1 算法 1]。
我从这里有了一个很好的开始。
我将算法编码如下：
public static byte[] CalculateMAC(this IPinPad pinpad, byte[] message, byte[] key)
{
//Divide the key with Key1[ first 64 bits] and key2 [last 64 bits]
var key1 = new byte[8];
Array.Copy(key, 0, key1, 0, 8);
var key2 = new byte[8];
Array.Copy(key, 8, key2, 0, 8); //64 bits
//divide the message into 8 bytes blocks
//pad the last block with "80" and "00","00","00" until it reaches 8 bytes
//if the message already can be divided by 8, then add
//another block "80 00 00 00 00 00 00 00"
Action<byte[], int> prepArray = (bArr, offset) =>
{
bArr[offset] = 0; //80
for (var i = offset + 1; i < bArr.Length; i++)
bArr[i] = 0;
};
var length = message.Length;
var mod = length > 8? length % 8: length - 8;
var newLength = length + ((mod < 0) ? -mod : (mod > 0) ? 8 - mod : 0);
//var newLength = length + ((mod < 0) ? -mod : (mod > 0) ? 8 - mod : 8);
Debug.Assert(newLength % 8 == 0);
var arr = new byte[newLength];
Array.Copy(message, 0, arr, 0, length);
//Encoding.ASCII.GetBytes(message, 0, length, arr, 0);
prepArray(arr, length);
//use initial vector {0,0,0,0,0,0,0,0}
var vector = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 };
//encrypt by DES CBC algorith with the first key KEY 1
var des = new DESCryptoServiceProvider { Mode = CipherMode.CBC };
var cryptor = des.CreateEncryptor(key1, vector);
var outputBuffer = new byte[arr.Length];
cryptor.TransformBlock(arr, 0, arr.Length, outputBuffer, 0);
//Decrypt the result by DES ECB with the second key KEY2 [Original suggestion]
//Now I'm Encrypting
var decOutputBuffer = new byte[outputBuffer.Length];
des.Mode = CipherMode.ECB;
var decryptor = des.CreateEncryptor(key2, vector);
//var decryptor = des.CreateDecryptor(key2, vector);
decryptor.TransformBlock(outputBuffer, 0, outputBuffer.Length, decOutputBuffer, 0);
//Encrypt the result by DES ECB with the first key KEY1
var finalOutputBuffer = new byte[decOutputBuffer.Length];
var cryptor2 = des.CreateEncryptor(key1, vector);
cryptor2.TransformBlock(decOutputBuffer, 0, decOutputBuffer.Length, finalOutputBuffer, 0);
//take the first 4 bytes as the MAC
var rval = new byte[4];
Array.Copy(finalOutputBuffer, 0, rval, 0, 4);
return rval;
}
然后我发现有 3 种填充方案，而让我开始的那个可能不一定是正确的。手册又来救我了。似乎该设备仅用 0 填充。也没有提到其他块，所以我做了以下更改：
Action<byte[], int> prepArray = (bArr, offset) =>
{
bArr[offset] = 0; ... }
没有额外的块（如果 mod 0 [可被 8 整除] 不改变数组长度）
var newLength = length + ((mod < 0) ? -mod : (mod > 0) ? 8 - mod : 0);
最初的建议希望我在第二步解密......但这里的 Valery 建议它一直加密。所以我将解密更改为加密。但我仍然无法获得必要的 MAC ......
手册说密钥“6AC292FAA1315B4D8234B3A3D7D5933A”[因为密钥应该是 16 个字节，我认为这里的密钥是十六进制字符串，所以我取了 6A、C2、92、FA 的字节值 ... new byte[] { 106, 194, 146, ...] 如果消息是 [0x1a + MENTERODOMETER 的字节数组]，MAC 应该是 7B,40,BA,95 [4 个字节]
有人可以帮忙吗？请？
由于 Pinpad 要求消息中的第一个字符是 0x1a...
public static byte[] CalculateAugmentedMAC(this IPinPad pinpad, string message, byte[] key)
{
var arr = new byte[message.Length + 1];
var source = Encoding.ASCII.GetBytes(message);
arr[0] = 0x1a; //ClearScreenIndicator
Array.Copy(source, 0, arr, 1, source.Length);
return CalculateMAC(pinpad, arr, key);
}
我用这个输入调用上面的代码：
var result = pad.CalculateAugmentedMAC("MENTERODOMETER", new byte[] { 106, 194, 146, 250, 161, 49, 91, 77, 130, 52, 179, 163, 215, 213, 147, 58 });