The Tor Application
Tor is an application that uses “onion routing.” Generically, onion routing was designed as an architecture to limit a network’s vulnerability to eavesdropping and traffic analysis. It uses multiple proxy servers or relays to provide anonymous connections. Each proxy server knows only the details from the previous proxy server or the next proxy server.
The proxy servers provide anonymity for users by requesting access to resources and making it appear as if the proxy server is requesting the access, not the original user.
FYI
Data leakage is a common problem with peer-to-peer (P2P) networks such as BitTorrent. Users share data they did not intend to share. As an example, the Top Secret plans for the U.S. president’s helicopter were leaked through a P2P network and found on servers in Iran. Some people think that organizations forbid these types of applications to prevent piracy of copyrighted material. However, the primary reason is due to the inherent security risks that most people simply do not understand. Of course, there is nothing wrong with helping prevent the theft of intellectual property.
Tor was derived from the Onion Routing Project managed by the U.S. Naval Research Lab. However, Tor is not an acronym for The Onion Routing project. Instead, it is simply a brand name—similar to Kleenex for facial tissues. The torproject.org website still uses an onion as a logo; however, Tor is not all uppercase.
The goal of Tor is to allow users to browse the Internet anonymously. Instead of going directly to an Internet site, Tor uses the computers of other Tor users as relays or proxies. Any single Tor connection will go through multiple other computers.
Interestingly, even though the U.S. Naval Research Lab originally designed Tor, it is forbidden on most government systems; the primary reason is related to data leakage. Although the Tor network does provide a level of anonymity, the user never knows what other computers the request will go through. Data sent and received can be captured by any of these computers.
For example, in 2007, Dan Egerstad, a security professional in Sweden, collected usernames and passwords for 100 email accounts of users at different embassies. He just installed Tor on his system and then captured all the data that went through it. His computer was used as a proxy in the Tor network for thousands of users, and a simple protocol analyzer captured the data. More than the credentials, he also captured a significant number of sensitive email messages from embassies and Fortune 500 companies. Tor was used by Edward Snowden to capture confidential information that he later shared publicly, which was illegal due to the confidentiality of the information. A 2018 Forbes article exposed Tor as the mechanism used to steal from several blockchain services.