javax.crypto.IllegalBlockSizeException: Input length must be multiple of 8

[Jason Wylde]

Hi,
I'm using "DES/ECB/PKCS5Padding" getting the following error when decrypting my encrypted value.

javax.crypto.IllegalBlockSizeException: Input length must be multiple of 8 when decrypting with padded cipher

It fails on the line "byte[] ciphertext = cipher.doFinal( cleartext );". Any ideas what I'm missing ?

  



private static String encryptionScheme = "DES/ECB/PKCS5Padding";
private static String encryptionKey = "123456789012345678901234";
private KeySpec				keySpec;
private SecretKeyFactory	keyFactory;
private Cipher				cipher;

byte[] keyAsBytes = encryptionKey.getBytes( UNICODE_FORMAT );
keySpec = new DESKeySpec( keyAsBytes );

keyFactory = SecretKeyFactory.getInstance( "DES" );
cipher = Cipher.getInstance( encryptionScheme );

public String decrypt( String encryptedString ) throws EncryptionException
	{
		
		try
		{
			SecretKey key = keyFactory.generateSecret( keySpec );
			cipher.init( Cipher.DECRYPT_MODE, key );
			BASE64Decoder base64decoder = new BASE64Decoder();
			byte[] cleartext = base64decoder.decodeBuffer( encryptedString );
			byte[] ciphertext = cipher.doFinal( cleartext );

			return bytes2String( ciphertext );
		}
		catch (Exception e)
		{
			throw new EncryptionException( e );
		}
	}


  

Thanks In Advance
Jason

[Jason Wylde]

After some testing I determined that if I go beyond 56 characters that I am encrypting then decrypting , that is where it fails ( on the decrypt ) . Does this have something to do with DES being 56bit ?

[Jason Wylde]

I think I may have figured it out. When writing the encrypted value to a file if it's too long it is putting a line break/carriage return into the string and then when it tries to decrypt the line ( which is now stored as 2 lines ) it doesn't match and thus won't work.

Can I prevent the carriage return / line feeds ?

[greg stark]

The code you showed doesn't write or read anything, so there's no way of knowing! It sounds like it is an issue with your base64 encoder/decoder.

[Jason Wylde]

Here is the code that is doing the writing to the file. Hopefully someone can notice something I have missed which would cause line breaks within the encrypted text.

 

File f2 = new File(getSelectedFile()); 
private static StringEncrypter se;

try{
  BufferedWriter out = new BufferedWriter(new FileWriter(f2));
  BufferedReader input = new BufferedReader(new StringReader(jTextArea.getText()));
  String line;
  int i = 0;
  while((line = input.readLine()) != null)
  {
    out.write(line.substring(0,line.indexOf("ftp") + 3));
    out.write(se.encrypt(line.substring(line.indexOf("ftp") + 3)));							
    out.newLine();
  } // end of for loop
  out.close();
}
catch(Exception ex){
// Do something here
}

[Pat Farrell]

Jason Wylde wrote:Can I prevent the carriage return / line feeds ?

Don't use a Base64 decoder. The standard specs for it say that it wraps lines. Or, make sure you filter out the whitespace properly both in and out.

Also, the algorithms are defined on arrays of unsigned octets. This is not at all the same as a Java String.