php encrypting and decrypting cookies - php

Question

I have the following class that I am trying to use to encrypt and decrypt my cookies. I need to store user id in cookies for the Keep Me Logged In feature so that the user stays logged in even if he closes the browser and returns later. The following function that I am using is working fine for the encryption. However, it's not working for decryption. I got this class from this question.
$key = 'alabooencryptionkey';
$iv = AES256Encryption::generateIv();
class AES256Encryption {
public const BLOCK_SIZE = 8;
public const IV_LENGTH = 16;
public const CIPHER = 'AES256';
public static function generateIv(bool $allowLessSecure = false): string {
$success = false;
$random = openssl_random_pseudo_bytes(openssl_cipher_iv_length(static::CIPHER));
if(!$success) {
if (function_exists('sodium_randombytes_random16')) {
$random = sodium_randombytes_random16();
}else{
try {
$random = random_bytes(static::IV_LENGTH);
}catch (Exception $e) {
if($allowLessSecure) {
$permitted_chars = implode('',
array_merge(
range('A', 'z'),
range(0, 9),
str_split('~!##$%&*()-=+{};:"<>,.?/\'')
)
);
$random = '';
for($i = 0; $i < static::IV_LENGTH; $i++) {
$random .= $permitted_chars[mt_rand(0, (static::IV_LENGTH) - 1)];
}
}else{
throw new RuntimeException('Unable to generate initialization vector (IV)');
}
}
}
}
return $random;
}
protected static function getPaddedText(string $plainText): string {
$stringLength = strlen($plainText);
if($stringLength % static::BLOCK_SIZE) {
$plainText = str_pad($plainText, $stringLength + static::BLOCK_SIZE - $stringLength % static::BLOCK_SIZE, "\0");
}
return $plainText;
}
public static function encrypt(string $plainText, string $key, string $iv): string {
$plainText = static::getPaddedText($plainText);
return base64_encode(openssl_encrypt($plainText, static::CIPHER, $key, OPENSSL_RAW_DATA, $iv));
}
public static function decrypt(string $encryptedText, string $key, string $iv): string {
return openssl_decrypt(base64_decode($encryptedText), static::CIPHER, $key, OPENSSL_RAW_DATA, $iv);
}
}
I am using it here for encrypting my cookie which works fine.
function setLoginCookieSession($user){
global $key, $iv;
$_SESSION['newchatapp'] = $user;
setcookie("newchatapp", AES256Encryption::encrypt($user, $key, $iv), time()+3600*24*365*10, '/');
}
And here for decrypting which is not working. It returns nothing.
function sessionUser(){
global $key, $iv;
// return (isset($_SESSION['newchatapp']))?$_SESSION['newchatapp']:AES256Encryption::decrypt($_COOKIE['newchatapp'], $key, $iv);
return AES256Encryption::decrypt($_COOKIE['newchatapp'], $key, $iv);
}
Even if I manually input try to decode the encrypted string it still returns nothing.
echo AES256Encryption::decrypt('ianXhsXhh6MWAHliZoshEA%3D%3D', $key, $iv);
This means that the decryption is not working at all. What can I do to make it work?