AES Encryption in PHP and Decryption in Javascript

Question

I have an application in which I am encrypting a json encoded array using AES CBC 128 algorithm and then Decrypting it in javascript(React/Next Js Project). My Encryption in php is as shown in the below code

ENCRYPTION PHP

$plaintext = "message to be encrypted";
$ivlen = openssl_cipher_iv_length($cipher="AES-128-CBC");
$iv = openssl_random_pseudo_bytes($ivlen);
$ciphertext_raw = openssl_encrypt($plaintext, $cipher, $key, $options=OPENSSL_RAW_DATA, $iv);
$hmac = hash_hmac('sha256', $ciphertext_raw, $key, $as_binary=true);
$ciphertext = base64_encode( $iv.$hmac.$ciphertext_raw );

I am facing problems in decryption of this in Javascript

my code so far is as shown below

 const baseenc = CryptoJS.enc.Base64.parse(cipher).toString();
  var encrypted = CryptoJS.AES.decrypt(cipher, key, { iv: iv }).toString();
  var plaintext = CryptoJS.enc.Latin1.stringify(encrypted);

Can any body please show what is the error or help me in getting the correct output

Answer 1

The following steps must be implemented in the CryptoJS code:

• Separate IV, HMAC and ciphertext (after Base64 decoding)
• Calculate the HMAC for the ciphertext
• Check the authenticity of the ciphertext. The ciphertext is authentic if the received and calculated HMAC are identical.
• Perform decryption, only if the ciphertext is authentic

The following code is a possible implementation. As key 0123456789012345 was applied and with the PHP code the used ciphertext was generated:

var ciphertext = 'WqfMfCxKg7U7h5S1mbx7mSHOkkkIrUUpg++mX4ZdWt0I26VfKn7bsi60Oo/SIsWQGyC4dF5z081NvjTXwZGjIpguA0k/QqIM/GDEpCojaro=';
var key = '0123456789012345';

// Convert key and ciphertext into WordArrays
var ciphertextWA = CryptoJS.enc.Base64.parse(ciphertext);
var keyWA = CryptoJS.enc.Utf8.parse(key);

// Separate IV, HMAC and ciphertext
var ivWA = CryptoJS.lib.WordArray.create(ciphertextWA.words.slice(0, 4)); 
var hmacWA = CryptoJS.lib.WordArray.create(ciphertextWA.words.slice(4, 4 + 8)); 
var actualCiphertextWA = CryptoJS.lib.WordArray.create(ciphertextWA.words.slice(4 + 8)); 

// Authenticate
var hmacCalculatedWA = CryptoJS.HmacSHA256(actualCiphertextWA, keyWA); 
if(CryptoJS.enc.Base64.stringify(hmacCalculatedWA) === CryptoJS.enc.Base64.stringify(hmacWA)) {
  
  // Decrypt if authentication is successfull
  var decryptedMessageWA = CryptoJS.AES.decrypt({ciphertext: actualCiphertextWA}, keyWA, {iv: ivWA});
  var decryptedMessage = CryptoJS.enc.Utf8.stringify(decryptedMessageWA);
  console.log(decryptedMessage);
} else {
  console.log('Authentication failed!');
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/crypto-js/4.0.0/crypto-js.min.js"></script>

Please note that it is better to use different keys for encryption and authentication, see here.