BadPaddingException with DES

[Brian Boyle]

Hi!
I have an exception when I am decrypting a SealedObject:
javax.crypto.BadPaddingException: Given final block not properly padded
I encrypt my SealedObject using a DES key. This key is saved as a variable and passed to the decryption method and used to decrypt the SealedObject. This is the code for it

desKey = keyGen.generateKey();
public Vote decryptVote(SealedObject so, desKey)
{
Cipher decipher;
Vote vote = null;
try {   
  decipher = Cipher.getInstance("DES");
  decipher.init(Cipher.DECRYPT_MODE, [B]desKey[/B]);
  [B]vote = (Vote) so.getObject(decipher);[/B]
} catch (NoSuchPaddingException e) {  
  System.out.println("");
  e.printStackTrace();
  

I'd appreciate ann help,
Thanks,
B

[Bhiku Mhatre]

I am facing the same problem. Do you have any solution. If yes, can you please post it. Thanks in advance..

Regards,
Bhiku

[Abe Costello]

Resurrecting this topic again. Has anyone determined a cause or a solution to this?

Thanks,
Abe

[Ulf Dittmer]

It sounds like the last block of data does not have the necessary length. Encryption algorithms frequently can not encrypt data chunks of arbitrary size, but need a fixed size. So the last block of data needs to be padded in order to reach that size.

[William Frederico]

My 2 cents, just faced similar problem.

Make sure you store your generated keys and encrypted passwords as byte[] (byte array) and NOT in Strings.

http://archives.java.sun.com/cgi-bin/wa?A2=ind0111&L=java-security&F=&S=&P=7565

"One common mistakes that people made is to put the encrypted bytes inside a
string and upon decryption they use String.getBytes() to retrieve it.
Since String does its own character encoding, the byte[] that you used to
construct the String object and the byte[] that you get from its getBytes()
are not necessarily equal."

If you REALLY need a String to store, you can convert the byte array to hexadecimal then back to the byte array when you need to decrypt, just don't use a .getBytes() to get your byte array back from the hex, write a hex to byte array conversion function.

Hope this helps!

[Grant Gainey]

Treating ciphertext as a String is definitely a prime cause of "BadPaddingException". The other main contender is using the wrong key, or the right key that has itself been subjected to the

String s = new String(keyBytes); 
byte[] key = s.getBytes();

tango.

Note that different encodings will certainly cause you grief - but many standard encodings don't provide characters for every possible byte-combination. In that case, staying in the same encoding will still trash your ciphertext/key.

The moral? When you live in cipher-land, there are only bytes; all else is fiction. Strings are evil - eeeeviiiiiiilll, I tell you!

More generally, consider that a cipher is essentially an execution of an algorithm on a stream of bits (the cipher/plaintext) in the context of a second stream of bits (the key), resulting in a stream of bits. There's very little the Cipher "knows" about the result; the padding blocks are the only thing the Cipher really has control over. Using the wrong key, or trashing your key or ciphertext, or using the wrong mode or padding-scheme, all can/will end up throwing BPE, because that's one of the few errors a Cipher can really be cognizant of.

Good luck,
Grant

[Edited to fix the code-sample slightly, and to note "Holy Thread Necromancy, Batman!" Didn't see how old the original post was...]
[ January 09, 2006: Message edited by: Grant Gainey ]

[Ben Friedman]

I think I am experiencing this problem when encrypting with 256 bit AES encryption. I think I have corrected the problem and I'm ready to test. However, I don't have a string that reliably fails decryption so I can't be certain my fix truly works. I'm looking for a test case that will fail in my old algorithm. Anyone know how I can find or generate a string that will fail?

[Trey Howard]

Regarding the earlier comment 'create your own byte array conversion function', I thought I'd share a solution I found in the hopes of saving others some time and trouble.
You case use BASE64Encoder and BASE64Decoder (sun.misc package classes provided by JDK) to convert between String and byte[].

For example:

byte[] encryptedBytes = { ... };
String bytesAsString = new BASE64Encoder().encode(encryptedBytes);
byte[] encryptedBytes2 = new BASE64Decoder().decodeBuffer(bytesAsString);

where the byte[]s are equal.

HTH
-Trey

[Rahul Bhattacharjee]

How are you encrypting ? Please post the code for that too.

One more thing is you are providing only the algorithm , no mode , nor the padding.I think all the block ciphers need to have a padding associated , so that in case of incomplete block they can use the padding.

[Test User]

Hi,
I too am facing the same exception BadPaddingException: Given final block not properly padded

I have tried converting the ChiperText String to bytes using the Base64Decoder as well as String.getBytes(). even after doing this I see the same Exception.
In my case The encryption is being done in Dot Net code. and the decryption happens in Java Code.
I suspect the Issue here in the Below Code:
The Encryption Algorithm is TripleDES ( DESede).
and to encrypt the mode and padding is given as below:
Mode: CBC
Padding = Padding.Zeros

But I am not sure which Padding mode to be used. I am using CBC/PKCS5Padding mode/padding.

Can any one specify which is the equivalent Padding mode to the DotNet Zeros Padding.

You Suggestions are most awaited..
Thanks

[Ulf Dittmer]

I have tried converting the ChiperText String to bytes using the Base64Decoder

This sounds fishy. Are you certain that the string has been base-64 encoded before? If you're at least superficially familiar with that encoding, you can tell by looking at the string.

[Test User]

HI while encrypting Code is not using Bas64Endoder to encode . They have written there own custom Method to Encode the bytes to String
and have a custom Method to Decode the string before decrypting.
The whole process of encrypting and decrypting works fine if its totally done in Dot Net.
But If I try to Encrypt in Dotnet and try tp decrpyt in Java. I am getting the Badpadding Exception.
The Padding Mode used in Dotnet code in Padding.Zeros. But I do not find the equivalent padding mode in Java ( JCE). Could any one suggest how it can be done.

I found that if the Dotnet COde uses padding Mode as PKCS7 then it could be decrpted in my Java code using PKCS5PAdding... But our requirement is it needs to be done PAddingZeros in Dot net and have to get a solution in Java?
You Suggestions are welcome

[Bear Bibeault]

"Test User",

There aren't many rules that you need to worry about here on the Ranch, but one that we take very seriously regards the use of proper names. Please take a look at the JavaRanch Naming Policy and adjust your display name to match it.

In particular, your display name must be a first and a last name separated by a space character, and must not be obviously fictitious.

Thanks!
bear
JavaRanch Sheriff

[Serch Hdez]

Hello I'm facing the same problem and so far I could have not found any solution to come around it, I tried getting the char array from the string and then converting to byte each char from it but I get the same result, I also try the BASEDecoder algorithm but it's the same, I'm saving the bytes I'm getting into a file using the FileOutputStream and then the FileInputStream, but everytime I read the password from the file I get the error, has anyone found a way to do this?.. the code works as long as you encrypt and decrypt using the very same string, but once I store the bytes and try to retrieve those I get the error.. please help.. thanks.

Regards.

[greg stark]

Serch Hdez wrote:Hello I'm facing the same problem and so far I could have not found any solution to come around it, I tried getting the char array from the string and then converting to byte each char from it but I get the same result, I also try the BASEDecoder algorithm but it's the same, I'm saving the bytes I'm getting into a file using the FileOutputStream and then the FileInputStream, but everytime I read the password from the file I get the error, has anyone found a way to do this?.. the code works as long as you encrypt and decrypt using the very same string, but once I store the bytes and try to retrieve those I get the error.. please help.. thanks.

Regards.

Perhaps you can show us the code that works and the code that doesn't work.

[Serch Hdez]

Sure here is the code that works:

public static void main(String[] args) {
        Security.addProvider(new com.sun.crypto.provider.SunJCE());
        try {
            KeyGenerator kg = KeyGenerator.getInstance("DES");
            Key key = kg.generateKey();
            Cipher cipher = Cipher.getInstance("DES");
            byte[] data = "Hello World!".getBytes();
            System.out.println("Original data : " + new String(data));
            cipher.init(Cipher.ENCRYPT_MODE, key);
            byte[] result = cipher.doFinal(data);
            System.out.println("Encrypted data: " + new String(result));
            cipher.init(Cipher.DECRYPT_MODE, key);
            byte[] original = cipher.doFinal(result);
            System.out.println("Decrypted data: " + new String(original));
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchPaddingException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        } catch (IllegalStateException e) {
            e.printStackTrace();
        } catch (IllegalBlockSizeException e) {
            e.printStackTrace();
        } catch (BadPaddingException e) {
            e.printStackTrace();
        }
    }
    

But when I put some methods to save the encrypted text and then to read it from the file I got the error:

public static byte[] stringToBytes(String strParam){

     char[] chars = strParam.toCharArray();

     byte[] result = new byte[chars.length];

     for(int i=0;i<chars.length;i++){

          result[i] = (byte)chars[i];
     }
      
     return result;

}

public static String encrypt(String plaintext) throws Exception
  {
        String strEncryptedText = "";
    
        try {
            KeyGenerator kg = KeyGenerator.getInstance("DES");
            Key key = kg.generateKey();
            Cipher cipher = Cipher.getInstance("DES");
            byte[] data = stringToBytes(plaintext);
            System.out.println("Original data : " + new String(data));
            cipher.init(Cipher.ENCRYPT_MODE, key);
            byte[] result = cipher.doFinal(data);           
            strEncryptedText = new String(result);
            writeInFile(result);
            
        } catch (Exception e) {
            e.printStackTrace();
        }
        return strEncryptedText;
  }
public static byte[] readFromFile() throws IOException{

                 File file = new File("File1");
               
                 FileInputStream is = new FileInputStream(file);
    
        // Get the size of the file
        long length = file.length();
    
        if (length > Integer.MAX_VALUE) {
            // File is too large
        }
    
        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];
    
        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while (offset < bytes.length
               && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
            offset += numRead;
        }
    
        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "+file.getName());
        }
    
        // Close the input stream and return bytes
        is.close();
        return bytes;

  }

  public static String decrypt(String strParam){

        Security.addProvider(new com.sun.crypto.provider.SunJCE());
         byte[] byteArrEncText = null;
        String strDecryptedText = "";
        try {
            KeyGenerator kg = KeyGenerator.getInstance("DES");
            Key key = kg.generateKey();
            Cipher cipher = Cipher.getInstance("DES");
            cipher.init(Cipher.DECRYPT_MODE, key);
            byteArrEncText = readFromFile();            
            System.out.println("Decrypted data from file: " + new String(byteArrEncText));
            byte[] original = cipher.doFinal(byteArrEncText);            
            strDecryptedText = new String(original);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return strDecryptedText;

  }

public static void writeInFile(byte[] byteArr) throws IOException{               

                FileOutputStream fos = new FileOutputStream("File1");		
		
		fos.write(byteArr);

                fos.flush();

               	fos.close();	

  }

public static void main(String args[]) throws Exception
     
  {
    Security.addProvider(new com.sun.crypto.provider.SunJCE());
     if (args.length == 0)

        System.out.println( "This cannot be empty");

     else        
      
           System.out.println("Encrypting this text:" + args[0]  + ", Encrypted:" + encrypt(args[0]));
    
           System.out.println("Encrypting this text:" + args[0]  + ", Decrypted:" + decrypt(args[0]));

  }
}

So the first code works but this second one with file functionality won't work... any ideas?.. thank you.

[Ulf Dittmer]

strEncryptedText = new String(result);

This is wrong. You simply can't convert a byte[] that holds binary data into a String. If you need to treat a byte[] as String (why?), run it through base-64 or something similar.

[Serch Hdez]

Ulf Dittmer wrote:

strEncryptedText = new String(result);

This is wrong. You simply can't convert a byte[] that holds binary data into a String. If you need to treat a byte[] as String (why?), run it through base-64 or something similar.

Yeah but well, the error does not happen there.. it happens when I do the cipher

byte[] original = cipher.doFinal(byteArrEncText);    

so, do you know why? I'm reading bytes... but still getting the padding exception...

[Ulf Dittmer]

You're using different keys for encryption and decryption. "generateKey" create a random key, which will be different each time.

Also, don't use "DES" as the cipher, use "DESede". DES is obsolete these days, but Triple-DES (a.k.a. DESede) is still OK to use.

[Serch Hdez]

Ulf Dittmer wrote:You're using different keys for encryption and decryption. "generateKey" create a random key, which will be different each time.

Also, don't use "DES" as the cipher, use "DESede". DES is obsolete these days, but Triple-DES (a.k.a. DESede) is still OK to use.

Ok thanks for your reply, do you know how I could create a key so I can use it in both encryption and decryption?.. thanks.

[Ulf Dittmer]

You'll have to store the key that is used for encryption somewhere, so that you can retrieve it for decryption.

[Nayan Wiz]

Trey Howard wrote:Regarding the earlier comment 'create your own byte array conversion function', I thought I'd share a solution I found in the hopes of saving others some time and trouble.
You case use BASE64Encoder and BASE64Decoder (sun.misc package classes provided by JDK) to convert between String and byte[].

For example:

byte[] encryptedBytes = { ... };
String bytesAsString = new BASE64Encoder().encode(encryptedBytes);
byte[] encryptedBytes2 = new BASE64Decoder().decodeBuffer(bytesAsString);

where the byte[]s are equal.

HTH
-Trey

Thanks. Solution helped a lot.