How to encrypt JSON object with JS-NaCl and decrypt with php Libsodium

I managed to find a Libsodium js library (JS-NaCl) for front end encryption and has setup my PHP backend for Libsodium encrypt/decrypt also. When I encrypt a JSON object like below

const key = "827ccb0eea8a706c4c34a16891f84e7b";
const nonce = "0123456789abcdefghijvbnm";

var credentials = {
       "zip":"265",
       "account_number":"10028979739",
       "passcode":"1234",
       "account_type":"personal",
       "request":"login",
       "device":"iPhone 11"
   };


function encrypt(data){
 return sodium.crypto_secretbox(sodium.encode_utf8(data),nonce,key);
};

function decrypt(data){
 return sodium.decode_utf8(sodium.crypto_secretbox_open(data, nonce, key));
}

function login(data){
$.ajax({
       url:baseURL+"account/account.php",
       method:"POST",
       contentType:"application/x-www-form-urlencoded",
       dataType:"json",
       data:"datax="+JSON.stringify(encrypt(credentials)),
       beforeSend:()=>{
           console.log(credentials);
       },success:(response)=>{
          console.log(response);
       },error:(e)=>{
           swal("Connection Error","Failed to connect to the server!","error");
       }
   });

}

When I fire the login method with it encrypts the JSON object using the encrypt method hence I send something like this:

datax: {"0":191,"1":118,"2":248,"3":134,"4":45,"5":163,"6":3,"7":157,"8":78,"9":73,"10":157,"11":137,"12":178,"13":6,"14":68,"15":91,"16":217,"17":219,"18":50,"19":11,"20":127,"21":177,"22":130,"23":25,"24":209,"25":254,"26":210,"27":44,"28":119,"29":13,"30":144}

at the php backend code I am doing this:

<?php
function decrypt($data){
        $key = "e9897cea109576c2f8088c277125d553e4f83afbc0abbb92cfb1f7b776b4fee0";
        $nonce = "0123456789abcdefghijvbnm";
        return sodium_crypto_secretbox_open($data,$nonce,$key);
    }

    function encrypt($data){
        $data = utf8_encode($data);
        $key = "e9897cea109576c2f8088c277125d553e4f83afbc0abbb92cfb1f7b776b4fee0";
        $nonce = "0123456789abcdefghijvbnm";
        return sodium_crypto_secretbox($data,$nonce,$key);
    }


    $credentials = $_POST["datax"];
    echo decrypt($credentials);

    ?>

Same Key, Same nonce but it doesn’t echo back anything. How to I decrypt this??

Answer

The code needs some changes. On the JavaScript side (frontend):

• The JavaScript object must be converted into a string.

• Besides the data, nonce and key must also be encoded using Utf8. Although the key could also be hexadecimal encoded to a 16 bytes key, in this context it must be Utf8 encoded to a 32 bytes key, because sodium.crypto_secretbox expects a 32 bytes key. The expected nonce must be 24 bytes in size.

• Now the data can be encrypted.

• sodium.crypto_secretbox returns the data as Uint8Array, which must therefore be encoded for transfer into a suitable format, e.g. hexadecimal.

The corresponding code is:

nacl_factory.instantiate(function (sodium) {

    var credentials = {
        "zip":"265",
        "account_number":"10028979739",
        "passcode":"1234",
        "account_type":"personal",
        "request":"login",
        "device":"iPhone 11"
    };

    // Convert JavaScript object to string
    var data = JSON.stringify(credentials);

    // Utf8 encode key, nonce and data
    var keyUtf8 = sodium.encode_utf8("827ccb0eea8a706c4c34a16891f84e7b");
    var nonceUtf8 = sodium.encode_utf8("0123456789abcdefghijvbnm");
    var dataUtf8 = sodium.encode_utf8(data);
   
    // Encrypt
    var encrypted = sodium.crypto_secretbox(dataUtf8, nonceUtf8, keyUtf8);

    // Hex encode encrypted data for transfer 
    var encryptedHex = sodium.to_hex(encrypted);

    console.log("Ciphertext (hex):n" + encryptedHex.replace(/(.{64})/g, "$1n"));
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/js-nacl/1.3.2/nacl_factory.js"></script>

On the PHP side (backend):

• The hexadecimal string $encryptedHex must be decoded.

• The decoded data are to be decrypted. For this, key and nonce of the encryption must be used. In the posted code a different key is used, which is not possible in the context of crypto_secretbox (symmetric encryption), i.e. both sides use the same key. For asymmetric encryption there is crypto_box.

• The result can be decoded into a JavaScript object whose objects can be accessed as usual.

The corresponding code is:

// Hex decode
$encrypted = sodium_hex2bin($encryptedHex);

// Decrypt
$nonce = "0123456789abcdefghijvbnm";
$key = "827ccb0eea8a706c4c34a16891f84e7b";
$decrypted = sodium_crypto_secretbox_open($encrypted, $nonce, $key);

// Convert to JavaScript object
$decryptedJSON = json_decode($decrypted);
echo "Zip:            " . $decryptedJSON->zip . "n";
echo "Account number: " . $decryptedJSON->account_number . "n";
echo "Passcode:       " . $decryptedJSON->passcode . "n";
echo "Account type:   " . $decryptedJSON->account_type . "n";
echo "Request:        " . $decryptedJSON->request . "n";
echo "Device:         " . $decryptedJSON->device . "n";