Mcrypt js encryption value is different than that produced by PHP mcrypt / Mcrypt JS decrypt doesn't work for UTF-8 chars

Question

I have been trying to implement mcrypt encryption/ decryption technique on both server end, PHP and client end. I am trying to use mcrypt.js library at the moment as:

<?php 
$key = 'testtesttesttesttesttesttesttest';

function string_encrypt($string, $key) {
    $crypted_text = mcrypt_encrypt(
                        MCRYPT_RIJNDAEL_128, 
                        $key, 
                        $string, 
                        MCRYPT_MODE_ECB
                    );
    return base64_encode($crypted_text);
}

function string_decrypt($encrypted_string, $key) {
    $decrypted_text = mcrypt_decrypt(
                        MCRYPT_RIJNDAEL_128, 
                        $key, 
                        base64_decode($encrypted_string), 
                        MCRYPT_MODE_ECB
                    );
    return trim($decrypted_text);
}

echo 'Provided Text:    '.$test_str = 'This is test message.';
echo '<br />';
echo 'Encyrpted Value:  '.$enc_str = string_encrypt($test_str, $key);   
echo '<br />';
echo 'Decrypted Value:  '.string_decrypt($enc_str, $key);                               
echo '<br />';
?>

<script src='rijndael.js'></script>
<script src='mcrypt.js'></script>
<script src='base64v1_0.js'></script>

<script lang='javascript'>
    var enc_str = mcrypt.Encrypt('<?php echo $test_str ?>','');
    enc_str = B64.encode(enc_str);
    alert(enc_str); 
    // I don't get this same as encypted PHP text. i.e. $enc_str
    var dec_str = B64.decode('<?php echo $enc_str ?>');
    alert(mcrypt.Decrypt(dec_str,'')); 
    // I don't get this same as decypted PHP text. 
    // i.e. string_decrypt($enc_str)
</script>

I have used these following private vars at the mcrypt.js library.

 var cMode='ecb';
 var cCipher='rijndael-256';
 var cKey='testtesttesttesttesttesttesttest'; 
 //I am providing the same key

As I commented above, why is it enc_str not equal as $enc_str and why is it mcrypt.Decrypt('<?php echo $enc_str ?>', '') not equal as string_decrypt($enc_str, $key) ?

---

---

Updated question:

I tried both base64 encode/ decode and even hex2bin/ bin2hex to parse those strings but these two produced following results:

---

Using Hex2bin/ Bin2hex

PHP result:

Provided Text: This is test message.
Encyrpted Value: a51e970427ec8f666a5684cc1712ad03b29889cc10f4ccbf55733564d11c0386
Decrypted Value: This is test message.

JS result:

Provided Text:This is test message.
Mcrypted value:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Encyrpted Value:a51e970427ec8f666a5684cc1712ad03b29889cc10f4ccbf55733564d11c0386
After Hex to Bin Text:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Decrypted Value:This is test message.�����������
/*These diamond with question mark is produced while decypting the value.*/

---

Using Base64 encode/ decode:

PHP result:

Provided Text: This is test message.
Mcrypt encrypted value : ¥—'ìfjV„Ì­²˜‰ÌôÌ¿Us5dц
/*
 Here mcrypted value provided by JS and PHP is different
 That is causing to produce different value at two ends
*/
Encyrpted Value: pR6XBCfsj2ZqVoTMFxKtA7KYicwQ9My/VXM1ZNEcA4Y=
Decrypted Value: This is test message.

JS result:

Provided Text:This is test message.
Mcrypted value:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Encyrpted Value:wqUewpcEJ8Oswo9malbChMOMFxLCrQPCssKYwonDjBDDtMOMwr9VczVkw5EcA8KG
After Base64 Decode:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ���
Decrypted Value:This is test message.�����������bFaêF«+JéÓ!ÆÖ

And on both cases, UTf-8 content can not be decrypted on JS end.

---

*Links: *

Mcrypt JS library

Base64 JS library

Answer 1

The main issue appears to be that your string_encrypt and string_decrypt PHP functions don't have access to the $key variable, so for the encryption key mcrypt_encrypt is using \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0. See this question for an explanation. PHP should report a notice that key is undefined, have you turned off error reporting perhaps? Echo the key from inside the encrypt function to confirm this.

Another issue is a bug in the Mcrypt JS library. This library pads the encryption key with \0 if the key length is less than 32 bytes, the problem is that this is not how the PHP mcrypt_encrypt function pads the key. The mcrypt_encrypt function pads the key up to the nearest valid key length (16, 24, or 32 bytes). The issue in mcrypt.js is at lines 63 and 64, change this:

if(key.length<32)
    key+=Array(33-key.length).join(String.fromCharCode(0));

to this:

if(key.length<16)
    key+=Array(17-key.length).join(String.fromCharCode(0));
else if(key.length<24 && key.length>16)
    key+=Array(25-key.length).join(String.fromCharCode(0));
else if(key.length<32 && key.length>24)
    key+=Array(33-key.length).join(String.fromCharCode(0));

Now we can confirm the fix...

PHP:

function string_encrypt($string) {
    $crypted_text = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, "", $string, MCRYPT_MODE_ECB);
    return $crypted_text;
}

$test_str = "This is test message to be encrypted.";
$enc_str = string_encrypt($test_str);
echo bin2hex($enc_str);

Output:
f98fca4ddc4c10d6cd47df56b081b78566ee4facbcf2254b46f7809d9b255529d2078f28b150e802d72818be1888536fac6219f6ce7b9d9332a24afa09288f0e

Javascript:

function toHex(str) {
    var hex = '';
    for(var i=0;i<str.length;i++) {
        var val = ''+str.charCodeAt(i).toString(16);
        if(val.length == 1)
            hex += '0'+val;
        else
            hex += val;
    }
    return hex;
}

var enc_str = mcrypt.Encrypt("This is test message to be encrypted.", "", "", "rijndael-256", "ecb");
alert(toHex(enc_str));

Output:
f98fca4ddc4c10d6cd47df56b081b78566ee4facbcf2254b46f7809d9b255529d2078f28b150e802d72818be1888536fac6219f6ce7b9d9332a24afa09288f0e

Finally, all of these encryption functions produce binary as their output. Binary cannot be written as plain text in most cases without damaging the data. To solve this, either encode the binary to Hex or Base64 and then decode it before trying to decrypt.

So to get everything working...

<?php 
$key = 'testtesttesttesttesttesttesttest';

function string_encrypt($string, $key) {
    $crypted_text = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $string, MCRYPT_MODE_ECB);
    return $crypted_text;
}

function string_decrypt($encrypted_string, $key) {
    $decrypted_text = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted_string, MCRYPT_MODE_ECB);
    return trim($decrypted_text);
}

echo $test_str = 'This is test message to be encrypted.';   echo '<br />';
$enc_str = string_encrypt($test_str, $key);
echo bin2hex($enc_str);                                     echo '<br />';
echo string_decrypt($enc_str, $key);                        echo '<br />';

?>

<script src='rijndael.js'></script>
<script src='mcrypt.js'></script>

<script lang='javascript'>
    function toHex(str) {
        var hex = '';
        for(var i=0;i<str.length;i++) {
            var val = ''+str.charCodeAt(i).toString(16);
            if(val.length == 1)
                hex += '0'+val;
            else
                hex += val;
        }
        return hex;
    }
    function hexToString (hex) {
        var str = '';
        for (var i=0; i<hex.length; i+=2) {
            str += ''+String.fromCharCode(parseInt(hex.charAt(i)+hex.charAt(i+1), 16));
        }
        return str;
    }
    var enc_str = mcrypt.Encrypt('<?php echo $test_str ?>', '', 'testtesttesttesttesttesttesttest', 'rijndael-256', 'ecb');
    alert(toHex(enc_str));
    alert(mcrypt.Decrypt(hexToString('<?php echo bin2Hex($enc_str) ?>'), '', 'testtesttesttesttesttesttesttest', 'rijndael-256', 'ecb').replace(/\x00+$/g, '')); 
</script>

A few more notes...

1. You cannot trim the output of the string_encrypt function. This will cause leading or trailing zeros to be removed, which will make it so that you cannot decrypt the output.
2. ECB mode is insecure and you really shouldn't use it. CBC is the way to go. CBC does require an IV, and the IV must be the same for both encryption and decryption.
3. Javascript encryption is not secure for various reasons, given your usage of it anyone could simply view the pages source or debug the running javascript to get the encryption key. Read the link posted by ntoskrnl in your question comments.

Update:

Your Base64 encoding issue occurs because the library you're using doesn't work with binary data. This is a fairly common issue for Base64 javascript libraries. I'd recommend using this library instead.

As for the trailing � characters when decrypting with javascript, you need to trim the decrypted output. You're doing this in your PHP string_decrypt method, but not in your javascript. You can trim the decrypted output by doing a regex replace on all \0 characters at the end of the string.

Example:

mcrypt.Decrypt(dec_str,'').replace(/\x00+$/g, '')

I should have included this in my original post, but I didn't notice the \0 characters in the output because FF's alert box doesn't display them. Sorry about that.

Finally, I noticed another bug in the Mcrypt JS library. Lines 41 to 47:

var ciphers={       //  block size, key size
    "rijndael-128"  :[  16,         32],
    "rijndael-192"  :[  24,         32],
    "rijndael-256"  :[  32,         32],
    "serpent"       :[  16,         32],
    "twofish"       :[  16,         32],
}

Notice the comma at the end of the "twofish" line. Firefox and Chrome don't seem to mind this, but IE8 will report an error and fail to load the mcrypt library because of it. To fix the issue change:

"twofish"       :[  16,         32],

to:

"twofish"       :[  16,         32]