If you want to download a file with paid permissions, what will you do? The easiest way is of course to find a buddy with resources and ask him to share this file with you. This was how everyone shared files in the early days of the Internet, but there were many problems with this. For example, as more people downloaded, the download bandwidth shared by each person became smaller, and the download speed became very slow. What's even more dangerous is that this file is a copyrighted resource, and your buddy should not have shared it with you in the first place. If this buddy of yours is caught, everyone should stop downloading it.
In response to the problems mentioned above by Goshawk, American software engineer Bram Cohen designed the Bittorrent file sharing protocol in April 2001. The principle of the BitTorrent file sharing protocol is that resources are no longer provided by one person or a central server, but are provided to everyone by everyone. In this way, the more people who download, the faster the download speed. This model is also called pear to pear, which is what we often call P2P downloading now. The core idea of
BitTorrent is to divide the file into many small pieces so that downloaders can connect to each other. Goshawk takes a 117.3MB file as an example. After it is divided into 895 128KB file blocks, user A who downloaded the 20th block can exchange the downloaded parts with user B who downloaded the 11th block. The more people involved, the denser the file blocks will be exchanged with each other, and the faster the download speed will be. In order to do this, the BitTorrent protocol requires the resource sharer to generate a torrent file containing download information, which is now commonly known as BT seed , and the file format is torrent. The seed file
contains the file name, size, the size of each file after chunking, hash value and the address of the tracker server. The tracker server is very important here. Only through the tracker server can we find other online downloaders. When you open this torrent file with download software, it will start to contact the tracker server built into the torrent file. The server will record your network IP and return to you the network IPs of other people who are downloading or have finished downloading, so that everyone can happily team up to download files. But if no one is found who is downloading or the resource publisher is not online, then you can only wait at a download speed of 0KB/s. It is not difficult to find that the tracker server is a weakness of the BitTorrent protocol. If the tracker server is closed or blocked, the file cannot be downloaded.
In order to get rid of the dependence on the tracker server, software engineers have improved the seed file, which is the most popular download method today, magnetic link or magnetic seed. It is usually a string of mysterious codes. The front code is in a standard format, and the most important thing is the 40 hexadecimal numbers that follow. Any file thrown into the hash algorithm can get a string of 40 hexadecimal characters, which you can think of as a file ID. It can help us find what we want to download. The essence of a magnet link is to turn all downloaders into a tracker server, and everyone holds a dynamically updated address and file information.
The design of these geniuses allows us to have a decentralized network that cannot be censored and tracked. This has given rise to a huge pirated software industry, giving a lot of content the opportunity to evade censorship, because websites can be isolated, unplugged, and banned from access, but torrent files cannot. As long as the torrent files do not die, those non-existent music, pictures and videos are still alive on the Internet, and no one can destroy them.
