Php and cryptoJS IV

Question

I encrypt and decrypt data using PHP like this:

<?php 
function encrypt($data, $secret){
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    return base64_encode($iv.openssl_encrypt($data, 'aes-256-cbc', $secret, 0, $iv));
}

function decrypt($encryptedData, $secret){
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $data = base64_decode($encryptedData);
    $iv = substr($data, 0, $iv_size);
    return openssl_decrypt(substr($data, $iv_size), 'aes-256-cbc', $secret, 0, $iv);
}
?>

I am now wanting to be able to encrypt my data locally (identically to the PHP method) using Crypto-JS. I have done the same as above to get the key and iv:

var key = '<?php echo $secret;?>';
var iv = '<?php echo base64_encode(mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND));?>';

Now when using Crypto-JS I have tried to encrypt using:

var encrypted = CryptoJS.AES.encrypt(CryptoJS.enc.Utf8.parse(text), CryptoJS.enc.Hex.parse(key), { iv: CryptoJS.enc.Hex.parse(iv) });

But I also need to store the IV like I do with PHP So I have added:

var withIV = iv+encrypted;

but that is not encoded. So I have added:

CryptoJS.enc.Base64.stringify(CryptoJS.enc.Utf8.parse(withIV));

But this is not the same encoding as the PHP above for some reason?

Answer 1

Here's how I encrypt data with CryptoJS:

function encrypt(str, key, iv) {
    var key = CryptoJS.enc.Hex.parse(key);
    var iv = CryptoJS.enc.Hex.parse(iv);
    return CryptoJS.AES.encrypt(str, key, { iv: iv }).toString();
};

In PHP, I decrypt the encrypted string produced by that function using this line of code:

openssl_decrypt($encrypted_data_string, "AES-128-CBC", hex2bin($key_hex_string), 0, hex2bin($iv_hex_string));

I suppose you could encode/decode the encrypted data in base 64 instead of hexadecimal if you wanted to. Anyway, hope this helps!

Answer 2

It seems you have trouble concatenating IV and the ciphertext in CryptoJS. This is rather easy, because CryptoJS' native binary data format (WordArray) supports the concat function:

var ivWords = CryptoJS.enc.Hex.parse(iv); // WordArray instance
var plaintext = CryptoJS.enc.Utf8.parse(text); // WordArray instance
var keyWords = CryptoJS.enc.Hex.parse(key); // WordArray instance
var encrypted = CryptoJS.AES.encrypt(plaintext, keyWords, { iv: ivWords }); // CipherParams instance

var ct = ivWords.clone().concat(encrypted.ciphertext); // WordArray instance
var ct = ct.toString(CryptoJS.enc.Base64); // string instance
console.log(ct);

// example data
var iv = "0102030405060708090a0b0c0d0e0f";
var text = "text";
var key = "1112131415161718191a1b1c1d1e1f";

// actual code
var ivWords = CryptoJS.enc.Hex.parse(iv); // WordArray instance
var plaintext = CryptoJS.enc.Utf8.parse(text); // WordArray instance
var keyWords = CryptoJS.enc.Hex.parse(key); // WordArray instance
var encrypted = CryptoJS.AES.encrypt(plaintext, keyWords, { iv: ivWords }); // CipherParams instance

var ct = ivWords.clone().concat(encrypted.ciphertext); // WordArray instance
var ct = ct.toString(CryptoJS.enc.Base64); // string instance
output.innerHTML = ct;

<script src="https://cdn.rawgit.com/CryptoStore/crypto-js/3.1.2/build/components/enc-base64-min.js"></script>
<script src="https://cdn.rawgit.com/CryptoStore/crypto-js/3.1.2/build/rollups/aes.js"></script>
<div id="output"></div>

This would produce the same output as

base64_encode($iv.openssl_encrypt($data, 'aes-256-cbc', $secret, 0, $iv));

as long as iv is actually hex-encoded string with that contains the same bytes as the decoded version in $iv. The same must be true for text (except for the encoding), key and $data, $secret, respectively.