PHP function for generating cryptography secure strings of a given length

generate_key.php

<?php

/**
 * PHP function for generating cryptography secure strings of a given length
 *
 * @param  $length the length in bytes for the generated key
 * @return the cryptography secure string of {$length} length
 */
function generate_key($length) {
    $strong = FALSE;
    while($strong != TRUE){
        $key = base64_encode(openssl_random_pseudo_bytes($length, $strong));
    }
    return substr($key, 0, $length);
}