Java TripleDES PKCS5Padding decryption to C# - bad data / padding error - encryption

Question

I'm trying to write the C# equivalent for the following Java code:
protected static final String DES_ECB_PKCS5PADDING = "DESede/ECB/PKCS5Padding";
public static String decryptValueDirect(String value, String key)
throws NoSuchAlgorithmException, NoSuchPaddingException,
GeneralSecurityException, IllegalBlockSizeException,
BadPaddingException {
byte[] bytes = Base64.decodeBase64(value);
Cipher cipher = Cipher.getInstance(DES_ECB_PKCS5PADDING);
cipher.init(Cipher.DECRYPT_MODE, convertSecretKey(key.getBytes()));
byte[] decryptedValue = cipher.doFinal(bytes);
String nstr = new String(decryptedValue);
return nstr;
}
protected static SecretKey convertSecretKey(byte[] encryptionKey) throws GeneralSecurityException {
if (encryptionKey == null || encryptionKey.length == 0)
throw new IllegalArgumentException("Encryption key must be specified");
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(TRIPLEDES);
KeySpec keySpec = new DESedeKeySpec(encryptionKey);
return keyFactory.generateSecret(keySpec);
}
The source text is a base64 encoded, then encrypted and then base64 encoded for transport on a rabbit queue. Our vendor who handles the encryption provided the above for decryption in Java, but has no idea about C#.
The only input on the encryption side is a key, a random string. We use the same string for encryption/decryption 012345678901234567890123456789 in our dev env. That is the only input, no salt, hashing (that i see) or pw iterations. The only requirement is that it is at least 24 chars long.
My C# code is below and a fiddle of my attempt is here.
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
public class Program
{
public static void Main()
{
//Message Data value
//We are using encrypted multibyte.
string myData = #"ROE8oYeV7B6faUsvfIx0Xe55vSs9IR5DlWGRbSM+lmKmLcaJsA13VudwWlAEYtLUD8+nMXShky0grSxsk0Z9cQe5V45XnAIfUhnyzI9a0jtMFC8XnIZ5dbclPO/V73QnieIZDkbNV5cPo3BM+l79ai96KB/gkF3xuerFPxvWejtPyWbOyO+FfNyFps4gAYDITsYIAEH39VP4eipmQ5zc18BA39lajQ3UaVewSxz7H+x3Ooe2SzJT/TQWRkioJSEFwexqzkHiLOQ0MOCIVD9xTWpLYnsL3LMwyF6H8f0PY4Fc57LVGhvUZ7dsB9NWUAnmG3uqbsonNFVhuXyvJTWNyFOHwFzOMx6XDLJJFHGZhaHg2VrescfnpUtonQY08RgojBngyJNRqK8URAvI3bqKq8Y7F/9HmEtMIIQe6KuuTmU=";
string myKey = "012345678901234567890123456789";//Development Env Key.
Console.WriteLine("Decrypt1:");
string s = Decrypt1(myData, myKey);
Console.ReadLine();
}
public static string Decrypt1(string value, string decryptionKey)
{
string decryptString = "";
TripleDESCryptoServiceProvider tDESalg = new TripleDESCryptoServiceProvider();
MD5CryptoServiceProvider hashMD5Provider = new MD5CryptoServiceProvider();
try
{
byte[] decodedData = Convert.FromBase64String(value);
tDESalg.Mode = CipherMode.ECB;
tDESalg.Padding = PaddingMode.PKCS7;//According to MS, same as PKCS5PADDING
byte[] Key = hashMD5Provider.ComputeHash(Encoding.UTF8.GetBytes(decryptionKey));
//byte[] IV = tDESalg.IV;
byte[] IV = new byte[tDESalg.BlockSize / 8]; //The size of the IV property must be the same as the BlockSize property divided by 8
var memoryStream = new MemoryStream(decodedData);
var cryptoStream = new CryptoStream(memoryStream, tDESalg.CreateDecryptor(Key, IV), CryptoStreamMode.Read);
var reader = new StreamReader(cryptoStream);
decryptString = reader.ReadToEnd();
byte[] decryptData = Convert.FromBase64String(decryptString);
}
catch (Exception e)
{
Console.WriteLine("A Cryptographic error occurred: {0}", e.Message + e.StackTrace);
return null;
}
return decryptString;
}
}
Searching seems to point to the same answer, the key, encoding, ... all must be the same. I just don't know what that would be the equivalent for the Java source provided. :) Any suggestions will be helpful.

Answer 1

MD5 has a 16-byte output, Triple DES (3DES) requires a 24-byte key. There is a key size mis-match.
The C# and Java key derivations are substantially different:
C#:
byte[] Key = hashMD5Provider.ComputeHash(Encoding.UTF8.GetBytes(decryptionKey));
returns 16-bytes.
Java:
SecretKeyFactory.getInstance(TRIPLEDES)
returns 24-bytes.
There is a key option (2TDEA) where a 16-byte key is used and the first 8-bytes will be duplicated to create the last 8-bytes. NIST has deprecated this option.
Some implementations will accept a 16-byte key and extend the key to 24-bytes and some will not. You should provide all 24-bytes to 3DES, do not rely on an implementation to create the 24-byte key.
Note: The question was updated so it is not clear that the the actual encrytpion key is derived.