DeMISTIfying Infosec: BitTorrent

By Katherine Teitler


BitTorrent was created in 2001 by Bram Cohen with the stated purpose: “to build a better internet.”

BitTorrent is a content distribution and peer-to-peer software/file sharing system that speeds up the sharing process by breaking large files into small data pieces which are distributed across a network of users (sometimes called “swarms”).

The system starts when a user downloads a file (torrent); that file is then scattered across the network to accepting peers and placed on upload. When future users want to download that file, they receive it in pieces from multiple users in the network instead of one centralized source. This method decreases download time and bandwidth requirements. As users retrieve files, either in pieces or in the final form of the whole, the files continue to be scattered to other users still. Users are thus incentivized to share, because the more places to which files are distributed, the easier and quicker it is to obtain files.

To exchange pieces, peers in the network connect to the IP address and port of another peer and exchange a “handshake,” which is a message that includes information about the user and the data file to be shared. Members decide what pieces of data they want to share. “Trackers”—servers that maintain an active list of valid users and data files—provide the information about peers, IP addresses, and listening ports. Theoretically trackers also help identify and eliminate illegal files or illegitimate users. Commonly exchanged file types include movies, videos, and music distributed by the owners, but because of the nature of the system, piracy occurs, as does the illicit sharing of less legitimate items, like child pornography.

Hosting sites on the BitTorrent network can’t differentiate between legal and illegal files; trackers are supposed to identify illegal usage and block illegal files. Still, malicious users can embed malware in legitimate files and distribute them throughout the network quickly and efficiently.

Source: BitTorrent Official Website

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