Rachita Nanda Rachita Nanda - 11 days ago 5
Android Question

Cipher bad decrypt java

I'm trying to decrypt the encrypted string from server. But when I decrypt it I get follwoing error. I need to decrypt the string successfully . We are using AES 256 cbc

> java.lang.Exception: [decrypt] error:1e06b065:Cipher
> functions:EVP_DecryptFinal_ex:BAD_DECRYPT
11-18 12:32:12.976 14325-14325/aes.example.com.aes_encyrption_demo W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: java.lang.Exception: [decrypt] error:1e06b065:Cipher functions:EVP_DecryptFinal_ex:BAD_DECRYPT
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at aes.example.com.aes_encyrption_demo.MCrypt.decrypt(MCrypt.java:73)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at aes.example.com.aes_encyrption_demo.MainActivity.onCreate(MainActivity.java:59)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.Activity.performCreate(Activity.java:6303)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2376)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.ActivityThread.access$900(ActivityThread.java:153)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.os.Handler.dispatchMessage(Handler.java:102)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.os.Looper.loop(Looper.java:148)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5442)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at java.lang.reflect.Method.invoke(Native Method)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
11-18 12:32:13.069 14325-14325/aes.example.com.aes_encyrption_demo W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)



When I use AES/CBC/NoPadding , I'm able to decrypt but the text is
appended with junk characters .


Decrypted a:2:{s:5:"email";s:24:"afroj.alam@broc.com";s:8:"password";s:7:"Test123";}��

Actual String
a:2:{s:5:"email";s:24:"afroj.alam@broc.com";s:8:"password";s:7:"Test123";}


Case 1: AES/CBC/PKCS5Padding : BAD_DECRYPT or BAD PADDING error

Case 2: AES/CBC/NoPadding : junk values at the end of decrypted text


public class MCrypt {

private String iv = "fedcba9876543210";//Dummy iv (CHANGE IT!)
private IvParameterSpec ivspec;
private SecretKeySpec keyspec;
private Cipher cipher;

private String SecretKey = "0123456789abcdef";//Dummy secretKey (CHANGE IT!)

public MCrypt()
{
ivspec = new IvParameterSpec(iv.getBytes());

keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");

try {
cipher = Cipher.getInstance("AES/CBC/NoPadding");
// cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
} catch (NoSuchAlgorithmException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchPaddingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

public byte[] encrypt(String text) throws Exception
{
if(text == null || text.length() == 0)
throw new Exception("Empty string");

byte[] encrypted = null;

try {
cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);

encrypted = cipher.doFinal(padString(text).getBytes());
} catch (Exception e)
{
throw new Exception("[encrypt] " + e.getMessage());
}

return encrypted;
}

public byte[] decrypt(String code) throws Exception
{
if(code == null || code.length() == 0)
throw new Exception("Empty string");

byte[] decrypted = null;

try {
cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);

decrypted = cipher.doFinal(hexToBytes(code));
} catch (Exception e)
{
throw new Exception("[decrypt] " + e.getMessage());
}
return decrypted;
}



public static String bytesToHex(byte[] data)
{
if (data==null)
{
return null;
}

int len = data.length;
String str = "";
for (int i=0; i<len; i++) {
if ((data[i]&0xFF)<16)
str = str + "0" + java.lang.Integer.toHexString(data[i]&0xFF);
else
str = str + java.lang.Integer.toHexString(data[i]&0xFF);
}
return str;
}


public static byte[] hexToBytes(String str) {
if (str==null) {
return null;
} else if (str.length() < 2) {
return null;
} else {
int len = str.length() / 2;
byte[] buffer = new byte[len];
for (int i=0; i<len; i++) {
buffer[i] = (byte) Integer.parseInt(str.substring(i*2,i*2+2),16);
}
return buffer;
}
}



private static String padString(String source)
{
char paddingChar = ' ';
int size = 16;
int x = source.length() % size;
int padLength = size - x;

for (int i = 0; i < padLength; i++)
{
source += paddingChar;
}

return source;
}


Activity.java

try{
decrypted = new String( mcrypt.decrypt( msg ) );
}catch (Exception e){
e.printStackTrace();
}
System.out.println("decrypted: " + decrypted);


PHP

<?php

class MCrypt
{
private $iv = 'fedcba9876543210'; #Same as in JAVA
private $key = '0123456789abcdef'; #Same as in JAVA


function __construct()
{
}

function encrypt($str) {

//$key = $this->hex2bin($key);
$iv = $this->iv;

$td = mcrypt_module_open('rijndael-128', '', 'cbc', $iv);

mcrypt_generic_init($td, $this->key, $iv);
$encrypted = mcrypt_generic($td, $str);

mcrypt_generic_deinit($td);
mcrypt_module_close($td);

return bin2hex($encrypted);
}

function decrypt($code) {
//$key = $this->hex2bin($key);
$code = $this->hex2bin($code);
$iv = $this->iv;

$td = mcrypt_module_open('rijndael-128', '', 'cbc', $iv);

mcrypt_generic_init($td, $this->key, $iv);
$decrypted = mdecrypt_generic($td, $code);

mcrypt_generic_deinit($td);
mcrypt_module_close($td);

return utf8_encode(trim($decrypted));
}

protected function hex2bin($hexdata) {
$bindata = '';

for ($i = 0; $i < strlen($hexdata); $i += 2) {
$bindata .= chr(hexdec(substr($hexdata, $i, 2)));
}

return $bindata;
}

}


I have already tried many links on stackoverflow.

Reference :
http://www.androidsnippets.com/encrypt-decrypt-between-android-and-php.html

EDIT

The decryption fails with error when I use AES/CBC/PKCS5Padding , is this because the padding is not correctly applied by the server php code , or is it something at my end? How can this be resolved.

EDIT 2

FOUND the problem
I tried with 16 byte key , but was getting a Bad padding exception, it was due to the fact the server side code did not implement PKCS7. After PKCS7 padding was implemented at server side , the issue was resolved. AES/CBC/PKCS5Padding mode will give bad padding exception if the padding is not added in encrypted string.

Answer

Found the problem when I tried with 16 byte key also. I was getting a Bad padding exception, it was due to the fact the server side code did not implement PKCS7.

When I was using AES/CBC/NoPadding mode , there was no error , but the decrypted string contained junk value at the end. This was because padding was not added in the encrypted string.

After PKCS7 padding was implemented at server side , the issue was resolved. AES/CBC/PKCS5Padding mode will give bad padding exception if the padding is not added in encrypted string.

Refer https://gist.github.com/Halama/5956871 for implementing padding in php while encryption.

Comments