Java DES encrypt, C# DES decrypt

Question

I received an encrypted string from Java, and I can see the Java encrypted source code. I wrote the decryption code in C#. But always report an error at "FlushFinalBlock". Error message: "System.Security.Cryptography.CryptographicException. Additional information: Incorrect data."

Can any body point out where the problem is in my C# code?

this is java code:

private static byte[] coderByDES(byte[] plainText, String key, int mode)
            throws InvalidKeyException, InvalidKeySpecException,
            NoSuchAlgorithmException, NoSuchPaddingException,
            BadPaddingException, IllegalBlockSizeException,
            UnsupportedEncodingException {
        SecureRandom sr = new SecureRandom();
        byte[] resultKey = makeKey(key);
        DESKeySpec desSpec = new DESKeySpec(resultKey);
        SecretKey secretKey = SecretKeyFactory.getInstance("DES").generateSecret(desSpec);
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(mode, secretKey, sr);
        return cipher.doFinal(plainText);
    }

private static byte[] makeKey(String key)
            throws UnsupportedEncodingException {
        byte[] keyByte = new byte[8];
        byte[] keyResult = key.getBytes("UTF-8");
        for (int i = 0; i < keyResult.length && i < keyByte.length; i++) {
            keyByte[i] = keyResult[i];
        }
        return keyByte;
    }


private static String byteArr2HexStr(byte[] arrB) {
        int iLen = arrB.length;

        StringBuilder sb = new StringBuilder(iLen * 2);
        for (int i = 0; i < iLen; i++) {
            int intTmp = arrB[i];

            while (intTmp < 0) {
                intTmp = intTmp + 256;
            }

            if (intTmp < 16) {
                sb.append("0");
            }
            sb.append(Integer.toString(intTmp, 16));
        }
        return sb.toString();
    }

this is C# code:

public static string DecryptForDES(string input, string key)
    {
        byte[] inputByteArray = HexStr2ByteArr(input);
        byte[] buffArray = null;
        using (DESCryptoServiceProvider des = new DESCryptoServiceProvider())
        {
            des.Key =  Encoding.UTF8.GetBytes(key); 
            des.IV =  Encoding.UTF8.GetBytes(key); 
            des.Mode = System.Security.Cryptography.CipherMode.ECB;
            des.Padding = PaddingMode.PKCS7;
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            using (CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(inputByteArray, 0, inputByteArray.Length);
                cs.FlushFinalBlock();//
                cs.Close();
            }
            buffArray = ms.ToArray();

            ms.Close();    
        }

        string str = string.Empty;
        if (buffArray != null)
        {
            str = Encoding.UTF8.GetString(buffArray);
        }
        return str;
    }



public static byte[] HexStr2ByteArr(string strIn)
    {
        byte[] arrB = Encoding.UTF8.GetBytes(strIn);
        int iLen = arrB.Length;

        byte[] arrOut = new byte[iLen / 2];
        byte[] arrTmp = new byte[2];
        for (int i = 0; i < iLen; i = i + 2)
        {
            string strTmp = Encoding.UTF8.GetString(arrB, i, 2);
            arrOut[i / 2] = (byte)Convert.ToInt32(strTmp, 16);
        }
        return arrOut;
    }

DES is an antique encryption algorithm (read the first paragraph of it's Wikipedia entry). The CPU in your PC's keyboard could probably crack it in less that a minute. Don't use DES for anything worth encrypting — Flydog57
– Flydog57, Commented Nov 10, 2018 at 16:47
@Flydog57 Can I have your keyboard? Oh, exaggerating a bit eh what? Yes, DES should not be used but it is not nearly that quick or easy to brute force. It took the EFF DES cracker about a day. — zaph
– zaph, Commented Nov 10, 2018 at 22:06

Topaco · Accepted Answer · 2018-11-10 23:04:54Z

Both, the Java encryption part and the C# decryption part work on my machine if the passwords match. Otherwise a System.Security.Cryptography.CryptographicException: 'Bad Data' is thrown. To get the password match replace in the C#-method DecryptForDES

 des.Key = Encoding.UTF8.GetBytes(key);

with

 des.Key = MakeKey(key);

with the C#-method:

 private static byte[] MakeKey(String key)
 {
     byte[] keyByte = new byte[8];
     byte[] keyResult = Encoding.UTF8.GetBytes(key); 
     for (int i = 0; i<keyResult.Length && i<keyByte.Length; i++) {
         keyByte[i] = keyResult[i];
     }
     return keyByte;
 }

corresponding to the Java-method makeKey(String key). Moreover, remove in the C#-method DecryptForDES

 des.IV = Encoding.UTF8.GetBytes(key);

since the ECB-mode doesn't use an IV.

In the following testcase

 coderByDES("This is a plain text that needs to be encrypted...", "This is the key used for encryption...", Cipher.ENCRYPT_MODE);

returns the byte-array

 a47b1b2c90fb3b7a0ab1f51f328ff55aae3c1eb7789c31c28346696a8b1f27c7413c14e68fe977d3235b5a6f63c07d7a95d912ff22f17ad6

and

 DecryptForDES("a47b1b2c90fb3b7a0ab1f51f328ff55aae3c1eb7789c31c28346696a8b1f27c7413c14e68fe977d3235b5a6f63c07d7a95d912ff22f17ad6", "This is the key used for encryption...");

returns the correct plain text.

By the way: As Flydog57 already stated DES is insecure (https://en.wikipedia.org/wiki/Data_Encryption_Standard). And also the ECB mode is not secure (https://crypto.stackexchange.com/questions/20941/why-shouldnt-i-use-ecb-encryption). Better choices are AES (https://en.wikipedia.org/wiki/Advanced_Encryption_Standard) with CBC or GCM mode (https://crypto.stackexchange.com/questions/2310/what-is-the-difference-between-cbc-and-gcm-mode).

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