AES128 Decryption :javax.crypto.badpaddingexception pad block corrupted

Question

I try to decrypt an encrypted data that I receive from a web service.

The encryption is done using AES 128.

I use the following code to decrypt the data:

public static String decrypt(String strToDecrypt)
{       
    try
    {
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding"); //AES/CBC/PKCS7Padding
        SecretKeySpec secretKey = new SecretKeySpec(AppConstants.AESEncryptionKey.getBytes("UTF8"), "AES");
        int blockSize = cipher.getBlockSize();
        cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(new byte[blockSize])); //new IvParameterSpec(new byte[16])
        byte decBytes[] = cipher.doFinal(Base64.decode(strToDecrypt, 0));
        // byte decBytes[] = cipher.doFinal(Base64.decodeBase64(strToDecrypt));
        String decStr = new String(decBytes);
        System.out.println("After decryption :" + decStr);
        return decStr;
    }
    catch (Exception e)
    {
        System.out.println("Exception in decryption : " + e.getMessage());
    }
    return null;
}

At

cipher.doFinal()

I got the following Exception:

javax.crypto.badpaddingexception pad block corrupted

I went through my post but ended up with no solution. I am badly stuck over here.

Either the encrypting side uses some other padding (or mode, or cipher) or the `strToDecrypt` contains truncated or otherwise corrupted data (the string itself can be proper Base64, but the data it represents is corrupted). — Oleg Estekhin, May 06 '14 at 10:32
strToDecrypt has the perfect encrypted data encoded using Base64 and even the padding,mode and Algorithm is same — iAviatorJose, May 06 '14 at 12:40
In that case the last option is that the keys used for encoding and decoding are different: decrypting with the wrong key will result in the last block which does not contain the properly padded data and this condition is detectable and causes BadPaddingException. — Oleg Estekhin, May 06 '14 at 13:35

score 11 · Answer 1 · edited Oct 21 '16 at 08:55

11

SecureRandom sr = SecureRandom.getInstance("SHA1PRNG","Crypto");

works perfectly

Note: This code works only on devices up to Android 6. Starting with Android 7.0 the "Crypto" provider has been removed, therefore this code will fail.

edited Oct 21 '16 at 08:55

Robert

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answered Jan 27 '15 at 11:10

Pavan Pyati

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Thank you for your reply !! anyways i have solved this problem – iAviatorJose Jan 27 '15 at 11:50
I was rereading my answer here when I read this answer. Could you indicate how this answer solves the question? Where do you use the generated random? Why do you need to specify a provider? Why SHA1PRNG? – Maarten Bodewes May 16 '16 at 15:23
This exactly solved the problem. I prefer it should be the accepted answer :) – King of Masses Aug 09 '16 at 14:19
1

Thanks @KingofMasses :) – Pavan Pyati Aug 09 '16 at 18:15

Maarten Bodewes · Accepted Answer · 2016-05-16T15:29:23.500

4

AES keys should consist of random data. If you store them as a String then you are likely to loose information, especially if you use encodings such as UTF-8. Your line:

AppConstants.AESEncryptionKey.getBytes("UTF8")

Makes it likely that you've lost data during conversion to/from a string. Use hexadecimals instead if you require a string, or simply store the key as a byte array.

Note that this answer doesn't indicate any security related hints. In general you only want to derive keys or store them in containers. You don't want to use CBC over an insecure channel either.

edited May 16 '16 at 15:29

answered May 06 '14 at 18:41

Maarten Bodewes

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Then How should i prevent this losss – iAviatorJose May 07 '14 at 04:44
use `.getBytes("UTF-8")` instead. – petey Dec 28 '16 at 15:32
@petey No, the idea was to use hexadecimals instead of character-encoding such as UTF-8. Obviously how to do this has been answered [*long ago*](http://stackoverflow.com/q/9655181/589259). – Maarten Bodewes Dec 28 '16 at 17:29

score 2 · Answer 3 · answered May 16 '16 at 11:36

2

In my case issue is came because encrypted key and decrypted key both are different, when I check both key with same value then issue is not came

answered May 16 '16 at 11:36

Yogesh Rathi

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AES128 Decryption :javax.crypto.badpaddingexception pad block corrupted

3 Answers3