Encrypt in Javascript, decrypt in PHP, using public-key cryptography

I’ve used something similar for my login page; it encrypts login credentials using the given public key information (N, e) which can be decrypted in PHP.

It uses the following files that are part of JSBN:

• jsbn.js – to work with big integers
• rsa.js – for RSA encryption only (uses jsbn.js)
• rng.js – basic entropy collector
• prng4.js – ARC4 RNG backend

To encrypt data:

$pk = '-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----';
$kh = openssl_pkey_get_private($pk);
$details = openssl_pkey_get_details($kh);

function to_hex($data)
{
    return strtoupper(bin2hex($data));
}

?>
<script>
var rsa = new RSAKey();
rsa.setPublic('<?php echo to_hex($details['rsa']['n']) ?>', '<?php echo to_hex($details['rsa']['e']) ?>');

// encrypt using RSA
var data = rsa.encrypt('hello world');
</script>

This is how you would decode the sent data:

$kh = openssl_pkey_get_private($pk);
$details = openssl_pkey_get_details($kh);
// convert data from hexadecimal notation
$data = pack('H*', $data);
if (openssl_private_decrypt($data, $r, $kh)) {
   echo $r;
}