Des encryption produces wrong output

I have the following function:

Code:

---

public static void Des(byte[] key, byte[] inBuf, byte[] outBuf)
{
    if (key.Length != 8 || inBuf.Length != 8 || outBuf.Length != 8)
    {
        throw new Exception("Des: Buffer or key length incorrect.");
    }

    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    des.Key = key;
    des.Mode = CipherMode.ECB;

    ICryptoTransform encryptor = des.CreateEncryptor();

    byte[] tmpBuf = encryptor.TransformFinalBlock(inBuf, 0, 1);
    tmpBuf.CopyTo(outBuf, 0);
}

---

if I call it with some standard test data like so:

Code:

---

byte[] outBuf;
MyClass.Des(new byte[] { 0x58, 0x40, 0x23, 0x64, 0x1A, 0xBA, 0x61, 0x76 },
            new byte[] { 0x00, 0x4B, 0xD6, 0xEF, 0x09, 0x17, 0x60, 0x62 },
            out outBuf);

---

I do not get the expected output of

Code:

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{ 0x88, 0xBF, 0x0D, 0xB6, 0xD7, 0x0D, 0xEE, 0x56 }

---

instead I get

Code:

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{ 0xC6, 0x61, 0x8D, 0x63, 0x0B, 0x39, 0x31, 0xB0 }

---

am I doing something wrong?

I've even tried reversing the byte order of the test data, and I don't get the right result. I've tested the same data using C++ with CryptoPP on Linux, and I get the expected result, but I'm porting this code to run on .Net, and this is my main stoppage in the process at the moment.

In Line 14 of your first block of code you are telling it to only encrypt the first byte. Change that to an 8 since you are sending 8 bytes.

Strangely, changing the read length to 8 results in a byte array containing 16 elements. The 8 bytes expected in the OP's expected output, followed by an additional 8 bytes. I don't really understand it. However using TransformBlock rather than TransformFinalBlock seems to result in the desired result:

Code:

---

using System;
using System.Linq;
using System.Security.Cryptography;

namespace ConsoleApplication10
{
    class Program
    {
        static void Main(string[] args)
        {
            byte[] outBuf = test(new byte[] { 0x58, 0x40, 0x23, 0x64, 0x1A, 0xBA, 0x61, 0x76 },
                new byte[] { 0x00, 0x4B, 0xD6, 0xEF, 0x09, 0x17, 0x60, 0x62 });

            foreach (byte b in outBuf)
                Console.Write(String.Format("0x{0:X2}", b) + " ");

            Console.Read();
        }

        static byte[] test(byte[] key, byte[] data)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            des.Key = key;
            des.Mode = CipherMode.ECB;
            ICryptoTransform enc = des.CreateEncryptor();
            byte[] buf = new byte[1024];
            int size = enc.TransformBlock(data, 0, data.Length, buf, 0);
            return buf.Take(size).ToArray();
        }

    }
}

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it generates the correct output now, and I also found the reason for the 16 bytes: you have to set padding to None on the DESCryptoServiceProvider, and then you get exactly 8 bytes of output for 8 bytes of input.

You realize the weaknesses of ECB mode, right?

yes, and I also realize the weakness of DES, but this application only ever requires encrypting a single block at a time, so CBC would be pointless, and the proprietary smart card with which I'm interfacing doesn't give me the option of a different mode or encryption algorithm.