Torrent, what it is and how to create a BitTorrent client

Torrent, what it is and how to create a BitTorrent client

When it comes to Torrent, the mind immediately turns to the unauthorized dissemination of copyrighted material. In reality, Torrent files and the BitTorrent protocol were created for absolutely legitimate uses that respect the intellectual property of others.

As we have seen in the cited article, BitTorrent it is a file sharing protocol peer-to-peer (P2P) which allows users to download and share files efficiently. The BitTorrent protocol is based on a decentralized network whose nodes, called peer, correspond to the devices of individual users. These share mutually parts of the files published on the internet.

What are Torrent files

To share a file using BitTorrent, a user must create a file meta-info called Torrent. It is a metadata file which contains information about the content to be shared, such as the list of included files, their sizes and the hashes of each item. Users interested in very specific files go in search of file Torrent through specialized engines or sites.

When a user decides to download a file, their BitTorrent client launches the download del file. The client begins to connect to peer who are already sharing the file or parts of it; During this initial phase, the client downloads pieces of the file from one or more peers.

After downloading a portion of the file, the BitTorrent client begins sharing that portion with other peers who are trying to download the same file. This process is known as “seeding” while the download phase of the various portions of a file is called “leeching“. A technique called “optimistic unchoking” causes BitTorrente to periodically select a random peer allowing it to download at a higher speed than other peers. This is a mechanism intended to maximize the mutual sharing and the diversification of content disseminated online.

What Torrent Files Contain

The Torrent file has small size, can be opened with a regular text editor and contains the necessary information for download content. The information includes the list of files included in the torrent, their names, sizes, hash of the pieces and a list of tracker. The torrent file usually has the extension .torrent. I tracker they are centralized servers that keep track of the sources sharing the Torrent: they help find other peers sharing the same content and coordinate the download process.

Il Torrent format it is widely used in the open source world for sharing files, Linux distributions, public material and more. The idea is to speed up downloads compared to the traditional approach (avoiding any bandwidth limitations with connections established towards a single remote server) and to promote the diffusion of knowledge. Once a file has been published on the BitTorrent network, it tends to spread like wildfire, making it virtually impossible to remove and therefore censorship.

In general, the term Torrent can still refer to both the metadata file itself and the process of it data sharing using the BitTorrent protocol. In the article presented at the beginning, we also talked about the future of Torrent and BitTorrent, highlighting projects such as IPFS (InterPlanetary File System), the latter focused on the construction of a distributed and decentralized storage solution, tend to support its use also for new application fields and innovative communication solutions.

Why create a BitTorrent-based application

The open architecture of the BitTorrent network allows anyone to develop applications capable of light the contents of a file Torrent and download a file from a peer. By developing a BitTorrent application yourself, you can have complete control over its features and customizations.

Creating an application capable of managing Torrent files can enable the functionality of file sharing within an existing service or platform. For example, a company that offers video streaming services could integrate sharing through the BitTorrent network to distribute its content more efficiently. If you plan to distribute content on a large scale or have high-capacity needs, a custom BitTorrent app can provide greater scalability.

The platform CodeCrafters hosts a thoughtful guide to creating a system file transfer based on BitTorrent. Page Build your own BitTorrent offers all the tools intended for developers to manage the various aspects of the BitTorrent protocol: from the technical details of Torrent files to communication with trackers, to communication protocols between peers.

What is bencode

Bencode is a binary serialization format used within the BitTorrent protocol to represent structured data. Developed by Bram Cohen, the creator of BitTorrent, Bencode is designed to be simple, compact and efficient in transmitting data over rarely peer-to-peer.

Wellcoded data is organized into several structures, including strings, integers, lists, and dictionaries. The stringhe bencoded they are sequences of ASCII characters: they are preceded by the length of the string followed by the “:” character. For example 4:ciao represents a 5-character string containing “hello”.

The wellcoded integers they are represented as sequences of ASCII digits, with a prefix “i” and a suffix “e”. For example, i42e represents the whole 42.

Wellcoded lists are enclosed in square brackets and contain a series of elements, which can be of different types (strings, integers, lists or dictionaries). Finally, wellcoded dictionaries are enclosed in curly brackets and contain key-value pairs, where the keys are strings.

Bencode is used for structure the information in Torrent files, including file details, hashes, and tracker and peer information. When a BitTorrent client downloads a Torrent file, it analyzes its contents using the codifica Bencode in order to obtain all the information necessary to start downloading the desired file.

What you need to know to develop a BitTorrent client

The programmer’s guide CodeCrafters begins with the presentation of the activities of decoding of the well-coded elements therefore addresses the topic of data extraction from the Torrent file, the management of the unique hash used in communications with trackers and peers, the identification of peers with the mediation of the tracker, i.e. the server that keeps track of the peers involved in sharing. To discover the peers from which to download a file, simply set and advance a simple GET request via HTTP.

The next steps have to do with the procedure handshake with peers, downloading individual pieces of files and the entire file. These last two operations involve a final check using the algorithm hashing SHA-1 in order to check that the downloaded file portions are intact.

Be careful about the files you share and download

The use of BitTorrent to share copyrighted material is not permitted. So long as “all bits are created equal” and the BitTorrent network is simply a means of communication, it is best to be wary of all those providers who, in defiance of the principle of net neutralitylimit the network speed with some specific protocols.

The theme of file security shared via Torrent, however, is absolutely crucial. Unlimited and unverified sharing of any kind of content forces users to raise their level of attention. Always choosing reliable sources with a good reputation for downloads, reading the comments, carrying out a thorough scan of the downloaded files are essential steps to avoid running into, for example, objects that integrate malware, spyware and ransomware.

I executable files they are obviously the ones that need to be paid the most attention but even unofficial ISO files downloaded via BitTorrent can contain harmful elements. Likewise, non-executable files taken from Torrent may still contain malicious code developed to exploit unresolved vulnerabilities (for example because the user did not install the patch corrections) from which the applications used to manage the same files suffer.

In any case, when using a BitTorrent client it is essential to ensure that you only download and share material that is not subject to the rights of others. Also because the sanctions for those who share material covered by the Copyright without having any title have recently been tightened, with a direct role of AGCOM (Communications Regulatory Authority) both for those who download and for those who, in turn,…

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