Random Is Not Random

Énoncé

function encrypt($plaintext) {
    srand(time()); 
    $cipher = '';
    for ($i = 0; $i < strlen($plaintext); $i++) {
        $key = rand(0, 255);
        $cipher .= chr(ord($plaintext[$i]) ^ $key);
    }
    return bin2hex($cipher);
}
$flag = "CTF{****************}";
echo $cipher_hex = encrypt($flag);