In this blog post, we’ll examine the basic operating principles of BitTorrent, how it differs from traditional client-server and P2P models, the roles of torrent files, peers, and seeders, and the precautions you should take when using copyrighted material.
When we want information, we search the internet, and when we need files, we download them for use. There are many ways to obtain files online, and one of them is BitTorrent. BitTorrent is a P2P-based file transfer protocol developed by American software developer Bram Cohen, and it is still used today as a technology for efficiently distributing large files. So, how does BitTorrent exchange files, and how does it differ from conventional file download methods?
There are several ways to store or provide files, and the most basic method involves users downloading files directly from a central server. This is generally referred to as the client-server model. In the client-server model, as long as the server is operating normally and connected to the network, users can connect to the server and download the files they need. A prime example is downloading programs, documents, videos, and other files from a website. However, when many users download large files simultaneously, it can place a significant load on the server and network. Since the provider must secure not only storage space but also sufficient server performance and network bandwidth, operating costs can increase as the scale of usage grows.
An alternative approach is P2P (peer-to-peer). P2P is a communication method designed to allow users participating in the network to exchange data directly with one another, rather than relying entirely on a central server for file transfer. Unlike the traditional client-server model, where the roles of the server providing the file and the client downloading it are clearly divided, in a P2P environment, each participant can receive data while simultaneously providing data to other participants. In other words, depending on the situation, a participant can be both a provider and a consumer. In the past, file-sharing services such as Pruna and eDonkey, which utilized this P2P technology, emerged and gained immense popularity.
BitTorrent also uses P2P technology but is distinguished by its ability to efficiently distribute files. In BitTorrent, a single file is divided into multiple pieces, and users receive different pieces from various peers to ultimately assemble the complete file. At the same time, users can transmit the pieces they have already received to other peers. Therefore, unlike a structure where the entire file is downloaded sequentially from a single provider, this system leverages the upload bandwidth of multiple participants collectively, which can enhance the efficiency of large-scale file distribution under certain conditions. Computers participating in BitTorrent exchange the necessary file pieces with one another, forming a distributed file-transfer network.
In BitTorrent, users typically use a torrent file (.torrent) or a magnet link to identify the content to be shared and locate other peers. Although the term “seed file” was commonly used in the past, the more accurate term is “torrent file.” A torrent file may contain metadata about the file or set of files to be shared, as well as hash information needed to verify the integrity of the fragments; in traditional setups, it may also include information about a tracker that connects peers. However, modern BitTorrent does not necessarily rely solely on torrent files and central trackers. It can also discover and connect to other peers through technologies such as magnet links, DHT (Distributed Hash Table), and PEX (Peer Exchange). Therefore, it is accurate to understand that the torrent file itself does not actually store the file being shared, but rather serves as metadata that identifies the file and peers and provides the information necessary to verify the integrity of file pieces.
In BitTorrent, a user who possesses the complete file and provides data to other participants is generally called a seeder, while participants who exchange data on the network are called peers. Peers who are in the process of downloading a file can also transmit the pieces they have already acquired to other peers. Therefore, if there are sufficient seeders and peers for a single file and their network conditions are favorable, file pieces can be obtained simultaneously from multiple sources, which can improve transfer efficiency. Conversely, if there are no seeders with the complete file and the entire file cannot be reconstructed using only the pieces held by the participants, the download may never complete.
This structure is one of BitTorrent’s key advantages. In typical one-to-one file transfers, a download may be interrupted if the connection to the server or user providing the file is lost; however, with BitTorrent, data can be received from multiple peers who possess fragments of the same file. Additionally, since users who have downloaded the file can in turn provide file fragments to other users, this reduces the burden of transmission from being concentrated on a single server. While a large number of participants does not always guarantee faster speeds, efficient file distribution is possible if there are a sufficient number of seeders and peers, and if their upload speeds and connection statuses are good. As explained in the original text, the core operating principle of BitTorrent is that multiple computers download a file simultaneously while also providing the pieces they possess to other computers.
BitTorrent technology itself is not illegal. It is a file-transfer technology capable of efficiently distributing large amounts of data to multiple users, and it can be used to distribute legal materials such as content authorized by copyright holders, freely distributable content, and open-source software. The problem arises when copyrighted works—such as movies, TV shows, music, software, and e-books—are shared without the copyright holder’s permission. Under the Republic of Korea’s Copyright Act, authors hold rights such as the right to reproduce and the right to public transmission; therefore, reproducing a protected work or transmitting it to others for their use without the rights holder’s permission may constitute copyright infringement.
In particular, when using BitTorrent, one should not assume that they are merely “downloading.” This is because BitTorrent clients can typically upload fragments they have already acquired to other peers simultaneously while downloading file fragments. The Korea Copyright Commission also explains that the fact that downloading and uploading can occur simultaneously in P2P networks is a characteristic that requires attention from a copyright perspective. In fact, there have been cases in South Korean courts where the act of downloading audiovisual works via torrent while simultaneously uploading them so that other users could download them was recognized as an infringement of economic copyright. Therefore, it is important to understand that if material is being shared without the copyright holder’s permission, an action you might have considered a simple download could result in the transmission of that work to other users.
That said, not all content shared via BitTorrent can be considered illegal. Content that the copyright holder has directly authorized for distribution, content whose copyright protection period has expired, and content that can be freely used and distributed under a valid license can all be legally shared via BitTorrent. Ultimately, the crux of the issue lies not in the BitTorrent technology itself, but in what content is being shared and under what permissions and conditions. One should not assume that permission from the copyright holder has been granted simply because a file is offered for free; it is particularly important to verify whether the distribution is legal when downloading commercially distributed movies, TV shows, music, games, software, books, and other materials via torrent.
BitTorrent is a technology designed to distribute large amounts of data efficiently by dividing files into multiple pieces that are exchanged among numerous participants, thereby reducing the load on central servers. While these technical characteristics offer considerable convenience for the distribution of information over the Internet, they also create the potential for the technology to be used as a channel for the rapid spread of content without the copyright holder’s permission. In particular, because users can provide some data to others while simultaneously downloading a file, it is crucial to be fully aware of exactly what material you are sharing. Advances in science and technology provide people with new conveniences and possibilities, but depending on how the technology is used, it can also infringe on the rights of others. When using BitTorrent, it is essential to develop the habit of verifying the source of the file you intend to share, its terms of use, and whether the copyright holder has granted permission for distribution, to ensure that the material can be used legally. To properly leverage the benefits of technology, one must not only understand how it works but also recognize the responsibilities that come with its use.
