Encrypt and decrypt with secret key PHP algorithm

<?php
    /*
     * https://bhoover.com/using-php-openssl_encrypt-openssl_decrypt-encrypt-decrypt-data/
     * @param $data
     * @param $key
     * @return string
     */

    function encrypt($data, $key)
    {
        //Remove the base64 encoding from our key
        $encryption_key = base64_decode($key);
        // Generate an initialization vector
        $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
        // Encrypt the data using AES 256 encryption in CBC mode using our encryption key and initialization vector.
        $encrypted = openssl_encrypt($data, 'aes-256-cbc', $encryption_key, 0, $iv);
        // The $iv is just as important as the key for decrypting, so save it with our encrypted data using a unique separator (::)
        return base64_encode($encrypted . '::' . $iv);
    }
    echo encrypt('string', 1234);
    echo '<br />';

    function decrypt($data, $key)
    {
        //Remove the base64 encoding from our key
        $encryption_key = base64_decode($key);
        // To decrypt, split the encrypted data from our IV - our unique separator used was "::"
        list($encrypted_data, $iv) = explode('::', base64_decode($data), 2);
        return openssl_decrypt($encrypted_data, 'aes-256-cbc', $encryption_key, 0, $iv);

    }
    echo decrypt('NlZDN2trR1R1K3diaERNa2ROMjZ2dz09OjoRssvy+nlh9tszAHCXW3E8', 1234);



?>