Hello! I'm new to Stack Overflow. I'm building a YouTube Downloader in PHP. But YouTube have some IP-checks. Because the PHP file is on a remote server, the ip of the server != the ip of the user and the video-download fails. So, maybe I've found a solution. YouTube sends a cookie with an encrypted string, which is the user IP. I need to know the encrypted-string algorithm and know how to crypt a string with this. Here there is the string: nQ0CrJmASJk . It could be base64, but when I try to decode it with base64_decode, it gives me strange characters. You could check the cookie by requesting the main page of youtube, and check the headers "Set-Cookie". You will found a cookie with the name "VISITOR_INFO1_LIVE". Here there is the encrypyed string. Anyone knows what is the algorithm? Thanks. PS: sorry for my bad english. Cheers, Roberto.