Encrypt a string in PHP where the output is URL safe

Oh hey, I've actually done this in one of my applications. My code looks a lot different (because of my custom tools, it's a one-liner), but works basically like this (uses defuse/php-encryption):

use \Defuse\Crypto\Crypto;

$url = "/my/endpoint?".http_build_query([
    'something' => base64_encode(
        Crypto::encrypt('my_secret_info', CRYPTO_SECRET_KEY)
    )
]);
// Then you can either use $url in header('Location: '.$url) or in an HTML link safely.

Further reading:

• base64_encode()
• http_build_query()
• urlencode() (if you don't want to use http_build_query())
• Why you want authenticated encryption (which defuse/php-encryption provides) rather than just encryption (which OpenSSL's AES-CBC provides)

Footnote: If you (or anyone else) want a short encrypted URL parameter, read this answer instead. (I know what's not what you were asking for, but just in case someone finds this question years down the line...)

The code below allow you to encrypt (alpha/num) and decrypt a string. But you need Mcrypt php module installed to make it run.

static public function encrypt($text){
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);                                                                           
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $key = "useasuperkey";

    return (bin2hex(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_ECB, $iv)));
}

static public function decrypt($text){
    $len = strlen($text);  
    $text = pack("H" . $len, $text);
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);                                                                           
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $key = "useasuperkey";

    return trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_ECB, $iv));
}

I had to do exactly same thing.

My solution was encrypting string with openssl_encrypt($str, "AES-128-CBC", $key).

Then sending the URL using url_encode($str).

Destination page decodes data with openssl_decrypt($str, "AES-128-CBC", $key)