Encrypt/Decrypt using Bouncy Castle in C#

Question

I am using the "BouncyCastle.Crypto.dll" for encrypt/decrypt a string in my app. I am using the following code from this blog:

1. I have a class BCEngine, exactly the same as the one given in the link mentioned above.

   public class BCEngine
   {
      private readonly Encoding _encoding;
      private readonly IBlockCipher _blockCipher;
      private PaddedBufferedBlockCipher _cipher;
      private IBlockCipherPadding _padding;
   
      public BCEngine(IBlockCipher blockCipher, Encoding encoding)
      {
         _blockCipher = blockCipher;
         _encoding = encoding;
      }
   
      public void SetPadding(IBlockCipherPadding padding)
      {
          if (padding != null)
            _padding = padding;
      }
   
      public string Encrypt(string plain, string key)
      {
          byte[] result = BouncyCastleCrypto(true, _encoding.GetBytes(plain), key);
          return Convert.ToBase64String(result);
      }
   
      public string Decrypt(string cipher, string key)
      {
         byte[] result = BouncyCastleCrypto(false, Convert.FromBase64String(cipher), key);
         return _encoding.GetString(result);
      }
   
      /// <summary>
      ///
      /// </summary>
      /// <param name="forEncrypt"></param>
      /// <param name="input"></param>
      /// <param name="key"></param>
      /// <returns></returns>
      /// <exception cref="CryptoException"></exception>
      private byte[] BouncyCastleCrypto(bool forEncrypt, byte[] input, string key)
      {
          try
          {
              _cipher = _padding == null ? new PaddedBufferedBlockCipher(_blockCipher) : new PaddedBufferedBlockCipher(_blockCipher, _padding);
              byte[] keyByte = _encoding.GetBytes(key);
              _cipher.Init(forEncrypt, new KeyParameter(keyByte));
              return _cipher.DoFinal(input);
          }
          catch (Org.BouncyCastle.Crypto.CryptoException ex)
          {
              throw new CryptoException(ex.Message);
          }
      }
   }
   

I am using an asp.net form in which i have written code as given below:

    public partial class EncryptionForm : System.Web.UI.Page
    {
      Encoding _encoding;
      IBlockCipherPadding _padding;
      string key = "DFGFRT";
       string textToBeEncrypted = "Original text. Please encrypt me.";
       string txtEncryptedText = string.empty;
       string txtDecryptedText = string.empty;

      protected void Page_Load(object sender, EventArgs e)
      {
          _encoding = Encoding.ASCII; 
          Pkcs7Padding pkcs = new Pkcs7Padding();
          _padding = pkcs;   
      }

      protected void btnEncrypt_Click(object sender, EventArgs e)
      {
          txtEncryptedText = AESEncryption(textToBeEncrypted, key, true);
      }

      protected void btnDecrypt_Click(object sender, EventArgs e)
      {
          txtDecryptedText = AESDecryption(txtEncryptedText.Text, key, true);
      }

      public string AESEncryption(string plain, string key, bool fips)
      {
          BCEngine bcEngine = new BCEngine(new AesEngine(), _encoding);
          bcEngine.SetPadding(_padding);
          return bcEngine.Encrypt(plain, key);
      }

      public string AESDecryption(string cipher, string key, bool fips)
      {
          BCEngine bcEngine = new BCEngine(new AesEngine(), _encoding);
          bcEngine.SetPadding(_padding);
          return bcEngine.Decrypt(cipher, key);
      }
    }

Not sure, but due to some reason, I get an exception when I call the btnEncrypt_Click

"Key length not 128/192/256 bits."

Can anybody please guide? I am a complete newbie to this. Thanks in Advance.

Answer 1

Your string key = "DFGFRT"; is not 128/192/256 bits.

DFGFRT is 6 characters, which is 6 (or 12?) bytes = 8*12 = 96 bits (at most).

To get a 128 bit key you need a 16 byte string, so I'd go on the safe side and use a 16 character string so it will be a 128 bit key if using single byte characters and 256 if using wide characters.

Answer 2

Fairly simple, your key is "DFGFRT" which is 6 characters/bytes, which is 6 * 8 = 48 bits.

The encryption methods used needs a key of 128/192/256 bits in length, which equals to 16/24/32 characters/bytes.

Answer 3

public class AesGcm256 { private static readonly SecureRandom Random = new SecureRandom();

    // Pre-configured Encryption Parameters
    public static readonly int NonceBitSize = 128;
    public static readonly int MacBitSize = 128;
    public static readonly int KeyBitSize = 256;

    private AesGcm256() { }

    public static byte[] NewKey()
    {
        var key = new byte[KeyBitSize / 8];
        Random.NextBytes(key);
        return key;
    }

    public static byte[] NewIv()
    {
        var iv = new byte[NonceBitSize / 8];
        Random.NextBytes(iv);
        return iv;
    }

    public static Byte[] HexToByte(string hexStr)
    {
        byte[] bArray = new byte[hexStr.Length / 2];
        for (int i = 0; i < (hexStr.Length / 2); i++)
        {
            byte firstNibble = Byte.Parse(hexStr.Substring((2 * i), 1), System.Globalization.NumberStyles.HexNumber); // [x,y)
            byte secondNibble = Byte.Parse(hexStr.Substring((2 * i) + 1, 1), System.Globalization.NumberStyles.HexNumber);
            int finalByte = (secondNibble) | (firstNibble << 4); // bit-operations only with numbers, not bytes.
            bArray[i] = (byte)finalByte;
        }
        return bArray;
    }


    public static string toHex(byte[] data)
    {
        string hex = string.Empty;
        foreach (byte c in data)
        {
            hex += c.ToString("X2");
        }
        return hex;
    }


    public static string toHex(string asciiString)
    {
        string hex = string.Empty;
        foreach (char c in asciiString)
        {
            int tmp = c;
            hex += string.Format("{0:x2}", System.Convert.ToUInt32(tmp.ToString()));
        }
        return hex;
    }

    public static string encrypt(string PlainText, byte[] key, byte[] iv)
    {
        string sR = string.Empty;
        try
        {
            byte[] plainBytes = Encoding.UTF8.GetBytes(PlainText);

            GcmBlockCipher cipher = new GcmBlockCipher(new AesFastEngine());
            AeadParameters parameters = new AeadParameters(new KeyParameter(key), 128, iv, null);

            cipher.Init(true, parameters);

            byte[] encryptedBytes = new byte[cipher.GetOutputSize(plainBytes.Length)];
            Int32 retLen = cipher.ProcessBytes(plainBytes, 0, plainBytes.Length, encryptedBytes, 0);
            cipher.DoFinal(encryptedBytes, retLen);
            sR = Convert.ToBase64String(encryptedBytes, Base64FormattingOptions.None);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            Console.WriteLine(ex.StackTrace);
        }

        return sR;
    }


    public static string decrypt(string EncryptedText, byte[] key, byte[] iv)
    {
        string sR = string.Empty;
        try
        {
            byte[] encryptedBytes = Convert.FromBase64String(EncryptedText);

            GcmBlockCipher cipher = new GcmBlockCipher(new AesFastEngine());
            AeadParameters parameters = new AeadParameters(new KeyParameter(key), 128, iv, null);
            //ParametersWithIV parameters = new ParametersWithIV(new KeyParameter(key), iv);

            cipher.Init(false, parameters);
            byte[] plainBytes = new byte[cipher.GetOutputSize(encryptedBytes.Length)];
            Int32 retLen = cipher.ProcessBytes(encryptedBytes, 0, encryptedBytes.Length, plainBytes, 0);
            cipher.DoFinal(plainBytes, retLen);

            sR = Encoding.UTF8.GetString(plainBytes).TrimEnd("\r\n\0".ToCharArray());
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            Console.WriteLine(ex.StackTrace);
        }

        return sR;
    }

}