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I am making an application which needs Java based AES Encryption and JavaScript based decryption. I am using the following code for encryption as a basic form.

public class AESencrp {

  private static final String ALGO = "AES";
  private static final byte[] keyValue = 
      new byte[] { 'A', 'b', 'c', 'd', 'e', 'f', 'g',
      'h', 'i', 'j', 'k','l', 'm', 'n', 'o', 'p'};

  public static String encrypt(String Data) throws Exception {
    Key key = generateKey();
    Cipher c = Cipher.getInstance(ALGO);
    c.init(Cipher.ENCRYPT_MODE, key);
    byte[] encVal = c.doFinal(Data.getBytes());
    String encryptedValue = new BASE64Encoder().encode(encVal);
    return encryptedValue;
  }


  private static Key generateKey() throws Exception {
    Key key = new SecretKeySpec(keyValue, ALGO);
    return key;
  }
}

The JavaScript that I am trying to use to decrypt is 

<script src="http://crypto-js.googlecode.com/svn/tags/3.1.2/build/rollups/aes.js">   </script>

var decrypted = CryptoJS.AES.decrypt(encrypted,"Abcdefghijklmnop").toString(CryptoJS.enc.Utf8);

But the JavaScript decryption is not working. I am new to this, could someone tell me a way to solve without changing the Java code block ?

I tried Base-64 decoding my text like this:

var words  = CryptoJS.enc.Base64.parse(encrKey);
var base64 = CryptoJS.enc.Base64.stringify(words);
var decrypted = CryptoJS.AES.decrypt(base64, "Abcdefghijklmnop");
alert("dec :" +decrypted);

but still no good.

I tried the solution suggested below to resolve possible padding issue but its not giving any solution.

var key = CryptoJS.enc.Base64.parse("QWJjZGVmZ2hpamtsbW5vcA==");
var decrypt = CryptoJS.AES.decrypt( encrKey, key, { mode: CryptoJS.mode.ECB,padding: CryptoJS.pad.Pkcs7 } );

alert("dec :" +decrypt);
share|improve this question
    
"But the JavaScript decryption is not working" > Can you please elaborate on this? –  Duncan Mar 24 at 11:58
    
I mean the page stops execution at the decryption line, I think there is some error in the way I am trying to decrypt it. –  rkj Mar 24 at 12:00
    
Is there an error printed in the JavaScript console? My first guess would be that you've not base64-decoded the ciphertext before you tried to decrypt it with CryptoJS. See code.google.com/p/crypto-js/#Encoders. –  Duncan Mar 24 at 12:02
    
Your attempt to base64 looks broken. Should it be: var words = CryptoJS.enc.Base64.parse(encrKey); var decrypted = CryptoJS.AES.decrypt(words, "Abcdefghijklmnop");? –  Duncan Mar 24 at 12:19
    
I tried doing as you said but still didnt work. I was wondering if the problem is that I am using secretkeyspec to generate key in java block and cryptojs in the js to decrypt, does it make any difference ? –  rkj Mar 24 at 12:25
show 2 more comments

1 Answer

up vote 2 down vote accepted

  1. Your Java code uses the 128-bit AES key while your JavaScript code uses the 256-bit AES key.

  2. Your Java code uses the "Abcdefghijklmnop".getBytes() as the actual key value, while your JavaScript code uses the "Abcdefghijklmnop" as the passphrase from which the actual key is derived.

  3. The default transformation for Java AES is AES/ECB/PKCS5Padding, while default transformation for CryptoJS is AES/CBC/PKCS7Padding.

One way to fix your example is to fix the JavaScript side:

// this is Base64 representation of the Java counterpart
// byte[] keyValue = new byte[] { 'A', 'b', 'c', 'd', 'e', 'f', 'g',
//                'h', 'i', 'j', 'k','l', 'm', 'n', 'o', 'p'};
// String keyForJS = new BASE64Encoder().encode(keyValue);
var base64Key = "QWJjZGVmZ2hpamtsbW5vcA==";
console.log( "base64Key = " + base64Key );

// this is the actual key as a sequence of bytes
var key = CryptoJS.enc.Base64.parse(base64Key);
console.log( "key = " + key );

// this is the plain text
var plaintText = "Hello, World!";
console.log( "plaintText = " + plaintText );

// this is Base64-encoded encrypted data
var encryptedData = CryptoJS.AES.encrypt(plaintText, key, {
    mode: CryptoJS.mode.ECB,
    padding: CryptoJS.pad.Pkcs7
});
console.log( "encryptedData = " + encryptedData );

// this is the decrypted data as a sequence of bytes
var decryptedData = CryptoJS.AES.decrypt( encryptedData, key, {
    mode: CryptoJS.mode.ECB,
    padding: CryptoJS.pad.Pkcs7
} );
console.log( "decryptedData = " + decryptedData );

// this is the decrypted data as a string
var decryptedText = decryptedData.toString( CryptoJS.enc.Utf8 );
console.log( "decryptedText = " + decryptedText );
share|improve this answer
    
Nope, still not working. Are you sure that your "var decrypt" is correct because I think the key should be in UTF-8 format. Anyway I tried it but didnt work. –  rkj Mar 25 at 4:54
    
Your question now contains CryptoJS.AES.decrypt( encrKey, key, ...) near the end, and it seems that you are trying to decrypt the key with key, which meaningless. The first parameter should be the encrypted data in base64. –  Oleg Estekhin Mar 25 at 5:52
    
Thats just the naming convention that I was following. The first parameter is indeed the encrypted data. –  rkj Mar 25 at 5:58
    
Try jsfiddle.net/pKNzV (the output is in the console) and try to encode the same data in Java and in that example. And do not forget to use the same key (use new BASE64Encoder().encode(keyValue) in Java to get the base64Key value for JS) –  Oleg Estekhin Mar 25 at 7:05
    
Its working !! Actually I was implementing the javascript using cordova and phonegap and there was an issue regarding the scripts not being downloaded. Once I downloaded the original script in the source code it statred working. –  rkj Mar 25 at 11:09
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