Tor, short for The Onion Router, is
free and open-source software
Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...
for enabling
anonymous communication. It directs
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...
traffic through a free, worldwide, volunteer
overlay network
An overlay network is a computer network that is layered on top of another network.
Structure
Nodes in the overlay network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through ...
, consisting of more than seven thousand relays,
to conceal a user's location and usage from anyone performing
network surveillance
Computer and network surveillance is the monitoring of computer activity and data stored locally on a computer or data being transferred over computer networks such as the Internet. This monitoring is often carried out covertly and may be comple ...
or
traffic analysis
Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication, it can be performed even when the messages are encrypted. In general, the greater the number of messages observe ...
. Using Tor makes it more difficult to trace a user's Internet activity. Tor's intended use is to protect the personal privacy of its users, as well as their freedom and ability to communicate confidentially through
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
anonymity using Tor exit nodes.
History
The core principle of Tor,
onion routing
Onion routing is a technique for anonymous communication over a computer network. In an onion network, messages are encapsulated in layers of encryption, analogous to layers of an onion. The encrypted data is transmitted through a series of net ...
, was developed in the mid-1990s by
United States Naval Research Laboratory
The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...
employees,
mathematician
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems.
Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change.
History
On ...
Paul Syverson
Paul may refer to:
*Paul (given name), a given name (includes a list of people with that name)
* Paul (surname), a list of people
People
Christianity
*Paul the Apostle (AD c.5–c.64/65), also known as Saul of Tarsus or Saint Paul, early Chri ...
, and
computer scientist
A computer scientist is a person who is trained in the academic study of computer science.
Computer scientists typically work on the theoretical side of computation, as opposed to the hardware side on which computer engineers mainly focus (a ...
s Michael G. Reed and David Goldschlag, to protect
American intelligence communications online.
Onion routing is implemented by means of
encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...
in the
application layer
An application layer is an abstraction layer that specifies the shared communications protocols and interface methods used by hosts in a communications network. An ''application layer'' abstraction is specified in both the Internet Protocol Su ...
of the
communication protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...
stack, nested like the layers of an
onion
An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the on ...
. The
alpha version
A software release life cycle is the sum of the stages of development and maturity for a piece of computer software ranging from its initial development to its eventual release, and including updated versions of the released version to help impro ...
of Tor, developed by Syverson and computer scientists
Roger Dingledine
Roger Dingledine is an American computer scientist known for having co-founded the Tor Project. A student of mathematics, computer science, and electrical engineering, Dingledine is also known by the pseudonym arma. As of December 2016, he contin ...
and
Nick Mathewson
Nick Mathewson is an American computer scientist and co-founder of The Tor Project. He, along with Roger Dingledine, began working on onion routing shortly after they graduated from Massachusetts Institute of Technology (MIT) in the early 2000s. ...
and then called The Onion Routing project (which was later given the acronym "Tor"), was launched on 20 September 2002.
The first public release occurred a year later.
In 2004, the Naval Research Laboratory released the code for Tor under a free license, and the
Electronic Frontier Foundation
The Electronic Frontier Foundation (EFF) is an international non-profit digital rights group based in San Francisco, California. The foundation was formed on 10 July 1990 by John Gilmore, John Perry Barlow and Mitch Kapor to promote Internet ...
(EFF) began funding Dingledine and Mathewson to continue its development.
In 2006, Dingledine, Mathewson, and five others founded
The Tor Project
The Tor Project, Inc. is a Seattle-based 501(c)(3) research-education nonprofit organization founded by computer scientists Roger Dingledine, Nick Mathewson and five others. The Tor Project is primarily responsible for maintaining software f ...
, a
Massachusetts
Massachusetts (Massachusett: ''Muhsachuweesut Massachusett_writing_systems.html" ;"title="nowiki/> məhswatʃəwiːsət.html" ;"title="Massachusett writing systems">məhswatʃəwiːsət">Massachusett writing systems">məhswatʃəwiːsət'' En ...
-based
501(c)(3)
A 501(c)(3) organization is a United States corporation, trust, unincorporated association or other type of organization exempt from federal income tax under section 501(c)(3) of Title 26 of the United States Code. It is one of the 29 types of ...
research-education
nonprofit organization
A nonprofit organization (NPO) or non-profit organisation, also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benefit, in co ...
responsible for maintaining Tor. The EFF acted as The Tor Project's
fiscal sponsor in its early years, and early financial supporters included the U.S.
Bureau of Democracy, Human Rights, and Labor
The Bureau of Democracy, Human Rights and Labor Affairs (DRL) is a bureau within the United States Department of State. The bureau is under the purview of the Under Secretary of State for Civilian Security, Democracy, and Human Rights.
DRL's res ...
and
International Broadcasting Bureau
The International Broadcasting Bureau (IBB) is the technical support outlet within the United States Agency for Global Media (USAGM) (former Broadcasting Board of Governors, BBG), which is a U.S. independent agency. The IBB supports the day-to- ...
,
Internews,
Human Rights Watch
Human Rights Watch (HRW) is an international non-governmental organization, headquartered in New York City, that conducts research and advocacy on human rights. The group pressures governments, policy makers, companies, and individual human ...
, the
University of Cambridge
, mottoeng = Literal: From here, light and sacred draughts.
Non literal: From this place, we gain enlightenment and precious knowledge.
, established =
, other_name = The Chancellor, Masters and Schola ...
,
Google
Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...
, and Netherlands-based
Stichting NLnet.
![Geographies of Tor](https://upload.wikimedia.org/wikipedia/commons/4/41/Geographies_of_Tor.png)
Over the course of its existence, various Tor
weaknesses have been discovered and occasionally exploited. Attacks against Tor are an active area of academic research that is welcomed by The Tor Project itself.
Usage
Tor enables its users to surf the Internet, chat and send instant messages anonymously, and is used by a wide variety of people for both licit and illicit purposes. Tor has, for example, been used by criminal enterprises,
hacktivism
In Internet activism, hacktivism, or hactivism (a portmanteau of ''hack'' and ''activism''), is the use of computer-based techniques such as hacking as a form of civil disobedience to promote a political agenda or social change. With roots in hac ...
groups, and law enforcement agencies at cross purposes, sometimes simultaneously;
likewise, agencies within the U.S. government variously fund Tor (the
U.S. State Department
The United States Department of State (DOS), or State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs of other n ...
, the National Science Foundation, and – through the Broadcasting Board of Governors, which itself partially funded Tor until October 2012 –
Radio Free Asia
Radio Free Asia (RFA) is a United States government-funded private non-profit news service that broadcasts radio programs and publishes online news, information, and commentary for its audiences in Asia. The service, which provides editoria ...
) and seek to subvert it.
Tor is not meant to completely solve the issue of anonymity on the web. Tor is not designed to completely erase tracking but instead to reduce the likelihood for sites to trace actions and data back to the user.
Tor is also used for illegal activities. These can include privacy protection or censorship circumvention,
as well as distribution of child abuse content, drug sales, or malware distribution.
Tor has been described by ''
The Economist
''The Economist'' is a British weekly newspaper printed in demitab format and published digitally. It focuses on current affairs, international business, politics, technology, and culture. Based in London, the newspaper is owned by The Eco ...
'', in relation to
Bitcoin
Bitcoin (abbreviation: BTC; sign: ₿) is a decentralized digital currency that can be transferred on the peer-to-peer bitcoin network. Bitcoin transactions are verified by network nodes through cryptography and recorded in a public distr ...
and
Silk Road
The Silk Road () was a network of Eurasian trade routes active from the second century BCE until the mid-15th century. Spanning over 6,400 kilometers (4,000 miles), it played a central role in facilitating economic, cultural, political, and rel ...
, as being "a dark corner of the web".
It has been targeted by the American
National Security Agency
The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collecti ...
and the British
GCHQ
Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Uni ...
signals intelligence
Signals intelligence (SIGINT) is intelligence-gathering by interception of '' signals'', whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication ...
agencies, albeit with marginal success,
and more successfully by the British
National Crime Agency
The National Crime Agency (NCA) is a national law enforcement agency in the United Kingdom. It is the UK's lead agency against organised crime; human, weapon and drug trafficking; cybercrime; and economic crime that goes across regional and in ...
in its Operation Notarise. At the same time, GCHQ has been using a tool named "Shadowcat" for "end-to-end encrypted access to VPS over SSH using the Tor network". Tor can be used for anonymous defamation, unauthorized
news leak
A news leak is the unsanctioned release of confidential information to news media. It can also be the premature publication of information by a news outlet, of information that it has agreed not to release before a specified time, in violation of ...
s of sensitive information,
copyright infringement
Copyright infringement (at times referred to as piracy) is the use of works protected by copyright without permission for a usage where such permission is required, thereby infringing certain exclusive rights granted to the copyright holder, ...
, distribution of illegal sexual content,
selling
controlled substance
A controlled substance is generally a drug or chemical whose manufacture, possession and use is regulated by a government, such as illicitly used drugs or prescription medications that are designated by law. Some treaties, notably the Single ...
s,
weapons, and stolen credit card numbers,
money laundering
Money laundering is the process of concealing the origin of money, obtained from illicit activities such as drug trafficking, corruption, embezzlement or gambling, by converting it into a legitimate source. It is a crime in many jurisdicti ...
,
bank fraud,
credit card fraud
Credit card fraud is an inclusive term for fraud committed using a payment card, such as a credit card or debit card. The purpose may be to obtain goods or services or to make payment to another account, which is controlled by a criminal. The ...
,
identity theft
Identity theft occurs when someone uses another person's personal identifying information, like their name, identifying number, or credit card number, without their permission, to commit fraud or other crimes. The term ''identity theft'' was c ...
and the exchange of
counterfeit currency
Counterfeit money is currency produced without the legal sanction of a state or government, usually in a deliberate attempt to imitate that currency and so as to deceive its recipient. Producing or using counterfeit money is a form of fraud or fo ...
; the
black market
A black market, underground economy, or shadow economy is a clandestine market or series of transactions that has some aspect of illegality or is characterized by noncompliance with an institutional set of rules. If the rule defines the ...
utilizes the Tor infrastructure, at least in part, in conjunction with Bitcoin.
It has also been used to brick
IoT
The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other comm ...
devices.
In its complaint against
Ross William Ulbricht
Ross William Ulbricht (born March 27, 1984) is an American serving life imprisonment for creating and operating the darknet market website Silk Road from 2011 until his arrest in 2013. The site operated as a hidden service on the Tor network an ...
of
Silk Road
The Silk Road () was a network of Eurasian trade routes active from the second century BCE until the mid-15th century. Spanning over 6,400 kilometers (4,000 miles), it played a central role in facilitating economic, cultural, political, and rel ...
, the US
Federal Bureau of Investigation
The Federal Bureau of Investigation (FBI) is the domestic intelligence and security service of the United States and its principal federal law enforcement agency. Operating under the jurisdiction of the United States Department of Justice ...
acknowledged that Tor has "known legitimate uses".
According to
CNET
''CNET'' (short for "Computer Network") is an American media website that publishes reviews, news, articles, blogs, podcasts, and videos on technology and consumer electronics globally. ''CNET'' originally produced content for radio and televi ...
, Tor's anonymity function is "endorsed by the
Electronic Frontier Foundation
The Electronic Frontier Foundation (EFF) is an international non-profit digital rights group based in San Francisco, California. The foundation was formed on 10 July 1990 by John Gilmore, John Perry Barlow and Mitch Kapor to promote Internet ...
(EFF) and other civil liberties groups as a method for
whistleblower
A whistleblower (also written as whistle-blower or whistle blower) is a person, often an employee, who reveals information about activity within a private or public organization that is deemed illegal, immoral, illicit, unsafe or fraudulent. Whi ...
s and human rights workers to communicate with journalists".
EFF's Surveillance Self-Defense guide includes a description of where Tor fits in a larger strategy for protecting privacy and anonymity.
In 2014, the EFF's
Eva Galperin told ''
Businessweek
''Bloomberg Businessweek'', previously known as ''BusinessWeek'', is an American weekly business magazine published fifty times a year. Since 2009, the magazine is owned by New York City-based Bloomberg L.P. The magazine debuted in New York City ...
'' that "Tor's biggest problem is press. No one hears about that time someone wasn't
stalked by their abuser. They hear how somebody got away with downloading child porn."
The Tor Project states that Tor users include "normal people" who wish to keep their Internet activities private from websites and advertisers, people concerned about cyber-spying, and users who are evading censorship such as activists, journalists, and military professionals. In November 2013, Tor had about four million users. According to the ''Wall Street Journal'', in 2012 about 14% of Tor's traffic connected from the United States, with people in "Internet-censoring countries" as its second-largest user base. Tor is increasingly used by victims of
domestic violence
Domestic violence (also known as domestic abuse or family violence) is violence or other abuse that occurs in a domestic setting, such as in a marriage or cohabitation. ''Domestic violence'' is often used as a synonym for '' intimate partn ...
and the
social worker
Social work is an academic discipline and practice-based profession concerned with meeting the basic needs of individuals, families, groups, communities, and society as a whole to enhance their individual and collective well-being. Social wo ...
s and agencies that assist them, even though shelter workers may or may not have had professional training on cyber-security matters.
Properly deployed, however, it precludes digital stalking, which has increased due to the prevalence of digital media in contemporary
online
In computer technology and telecommunications, online indicates a state of connectivity and offline indicates a disconnected state. In modern terminology, this usually refers to an Internet connection, but (especially when expressed "on line" ...
life.
Along with
SecureDrop, Tor is used by news organizations such as ''
The Guardian
''The Guardian'' is a British daily newspaper. It was founded in 1821 as ''The Manchester Guardian'', and changed its name in 1959. Along with its sister papers '' The Observer'' and '' The Guardian Weekly'', ''The Guardian'' is part of the ...
'', ''
The New Yorker
''The New Yorker'' is an American weekly magazine featuring journalism, commentary, criticism, essays, fiction, satire, cartoons, and poetry. Founded as a weekly in 1925, the magazine is published 47 times annually, with five of these issues ...
'',
ProPublica
ProPublica (), legally Pro Publica, Inc., is a nonprofit organization based in New York City. In 2010, it became the first online news source to win a Pulitzer Prize, for a piece written by one of its journalists''The Guardian'', April 13, 2010P ...
and ''
The Intercept
''The Intercept'' is an American left-wing news website founded by Glenn Greenwald, Jeremy Scahill, Laura Poitras and funded by billionaire eBay co-founder Pierre Omidyar. Its current editor is Betsy Reed. The publication initially report ...
'' to protect the privacy of whistleblowers.
In March 2015, the
Parliamentary Office of Science and Technology released a briefing which stated that "There is widespread agreement that banning online anonymity systems altogether is not seen as an acceptable policy option in the U.K." and that "Even if it were, there would be technical challenges." The report further noted that Tor "plays only a minor role in the online viewing and distribution of indecent images of children" (due in part to its inherent latency); its usage by the
Internet Watch Foundation
The Internet Watch Foundation (IWF) is a registered charity based in Cambridge, England. It states that its remit is "to minimise the availability of online sexual abuse content, specifically child sexual abuse images and videos hosted anywhe ...
, the utility of its onion services for
whistleblower
A whistleblower (also written as whistle-blower or whistle blower) is a person, often an employee, who reveals information about activity within a private or public organization that is deemed illegal, immoral, illicit, unsafe or fraudulent. Whi ...
s, and its circumvention of the
Great Firewall
The Great Firewall (''GFW''; ) is the combination of legislative actions and technologies enforced by the People's Republic of China to regulate the Internet domestically. Its role in internet censorship in China is to block access to selected for ...
of China were touted.
Tor's executive director, Andrew Lewman, also said in August 2014 that agents of the NSA and the GCHQ have anonymously provided Tor with bug reports.
The Tor Project's FAQ offers supporting reasons for the EFF's endorsement:
Operation
Tor aims to conceal its users' identities and their online activity from surveillance and traffic analysis by separating identification and routing. It is an implementation of
onion routing
Onion routing is a technique for anonymous communication over a computer network. In an onion network, messages are encapsulated in layers of encryption, analogous to layers of an onion. The encrypted data is transmitted through a series of net ...
, which encrypts and then randomly bounces communications through a network of relays run by volunteers around the globe. These onion routers employ
encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...
in a multi-layered manner (hence the onion metaphor) to ensure
perfect forward secrecy
In cryptography, forward secrecy (FS), also known as perfect forward secrecy (PFS), is a feature of specific key agreement protocols that gives assurances that session keys will not be compromised even if long-term secrets used in the session key ...
between relays, thereby providing users with anonymity in a network location. That anonymity extends to the hosting of censorship-resistant content by Tor's anonymous onion service feature.
Furthermore, by keeping some of the entry relays (bridge relays) secret, users can evade
Internet censorship
Internet censorship is the legal control or suppression of what can be accessed, published, or viewed on the Internet. Censorship is most often applied to specific internet domains (such as Wikipedia.org) but exceptionally may extend to all Int ...
that relies upon blocking public Tor relays.
Because the
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
of the sender and the recipient are not ''both'' in
cleartext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted.
Overview
With the advent of co ...
at any hop along the way, anyone eavesdropping at any point along the communication channel cannot directly identify both ends. Furthermore, to the recipient, it appears that the last Tor
node
In general, a node is a localized swelling (a " knot") or a point of intersection (a vertex).
Node may refer to:
In mathematics
* Vertex (graph theory), a vertex in a mathematical graph
* Vertex (geometry), a point where two or more curves, line ...
(called the exit node), rather than the sender, is the originator of the communication.
Originating traffic
![EtherApeTorScreenShot](https://upload.wikimedia.org/wikipedia/commons/7/72/EtherApeTorScreenShot.png)
A Tor user's
SOCKS
A sock is a piece of clothing worn on the feet and often covering the ankle or some part of the calf. Some types of shoes or boots are typically worn over socks. In ancient times, socks were made from leather or matted animal hair. In the late ...
-aware applications can be configured to direct their network traffic through a Tor instance's SOCKS interface, which is listening on TCP port 9050 (for standalone Tor) or 9150 (for Tor Browser bundle) at
localhost
In computer networking, localhost is a hostname that refers to the current device used to access it. It is used to access the network services that are running on the host via the loopback network interface. Using the loopback interface bypasses ...
. Tor periodically creates virtual circuits through the Tor network through which it can
multiplex
Multiplex may refer to:
* Multiplex (automobile), a former American car make
* Multiplex (comics), a DC comic book supervillain
* Multiplex (company), a global contracting and development company
* Multiplex (assay), a biological assay which measu ...
and onion-route that traffic to its destination. Once inside a Tor network, the traffic is sent from router to router along the circuit, ultimately reaching an exit node at which point the
cleartext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted.
Overview
With the advent of co ...
packet is available and is forwarded on to its original destination. Viewed from the destination, the traffic appears to originate at the Tor exit node.
![Tor-non-exit-relay-bandwidth-usage](https://upload.wikimedia.org/wikipedia/commons/e/ef/Tor-non-exit-relay-bandwidth-usage.jpg)
Tor's application independence sets it apart from most other anonymity networks: it works at the
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...
(TCP) stream level. Applications whose traffic is commonly anonymized using Tor include
Internet Relay Chat
Internet Relay Chat (IRC) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called '' channels'', but also allows one-on-one communication via private messages as well as chat an ...
(IRC),
instant messaging
Instant messaging (IM) technology is a type of online chat allowing real-time text transmission over the Internet or another computer network. Messages are typically transmitted between two or more parties, when each user inputs text and tri ...
, and
World Wide Web
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web se ...
browsing.
Onion services
Tor can also provide anonymity to websites and other servers. Servers configured to receive inbound connections only through Tor are called onion services (formerly, hidden services). Rather than revealing a server's IP address (and thus its network location), an onion service is accessed through its
onion address, usually via the
Tor Browser
Tor, short for The Onion Router, is free and open-source software for enabling anonymous communication. It directs Internet traffic through a free, worldwide, volunteer overlay network, consisting of more than seven thousand relays, to conc ...
. The Tor network understands these addresses by looking up their corresponding
public key
Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...
s and ''introduction points'' from a
distributed hash table
A distributed hash table (DHT) is a distributed system that provides a lookup service similar to a hash table: key–value pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key. The m ...
within the network. It can route data to and from onion services, even those hosted behind
firewalls or
network address translators (NAT), while preserving the anonymity of both parties. Tor is necessary to access these onion services.
Onion services were first specified in 2003 and have been deployed on the Tor network since 2004.
Other than the database that stores the onion service descriptors,
Tor is decentralized by design; there is no direct readable list of all onion services, although a number of onion services catalog publicly known onion addresses.
Because onion services route their traffic entirely through the Tor network, connection to an onion service is encrypted end-to-end and not subject to eavesdropping. There are, however, security issues involving Tor onion services. For example, services that are reachable through Tor onion services ''and'' the public Internet are susceptible to correlation attacks and thus not perfectly hidden. Other pitfalls include misconfigured services (e.g. identifying information included by default in web server error responses), uptime and downtime statistics, intersection attacks, and user error.
The
open source
Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...
OnionScan program, written by independent security researcher
Sarah Jamie Lewis
Sarah Jamie Lewis is an anonymity and privacy researcher with a special interest in the privacy protocols (or lack thereof) of sex toys. She has been cited in academic research regarding the security and ethics considerations associated with this t ...
, comprehensively examines onion services for numerous flaws and vulnerabilities.
(Lewis has also pioneered the field of "Onion Dildonics",
sex toy
A sex toy is an object or device that is primarily used to facilitate human sexual pleasure, such as a dildo, artificial vagina or vibrator. Many popular sex toys are designed to resemble human genitals, and may be vibrating or non-vibrating ...
s which make use of Tor through the
Ricochet
A ricochet ( ; ) is a rebound, bounce, or skip off a surface, particularly in the case of a projectile. Most ricochets are caused by accident and while the force of the deflection decelerates the projectile, it can still be energetic and almost ...
protocol)
Onion services can also be accessed from a standard web browser without
client-side
Client-side refers to operations that are performed by the client in a client–server relationship in a computer network.
General concepts
Typically, a client is a computer application, such as a web browser, that runs on a user's local compute ...
connection to the Tor network, using services like
Tor2web
Tor2web (pronounced "Tor to Web") is a software project to allow Tor hidden services to be accessed from a standard browser without being connected to the Tor network. It was created by Aaron Swartz and Virgil Griffith.
History
Tor is a networ ...
. Popular sources of
.onion
.onion is a special-use top level domain name designating an anonymous onion service, which was formerly known as a "hidden service", reachable via the Tor network. Such addresses are not actual DNS names, and the .onion TLD is not in the I ...
links include
Pastebin
A pastebin or text storage site is a type of online content-hosting service where users can store plain text (e.g. source code snippet (programming), snippets for code review via Internet Relay Chat (IRC)). The first pastebin was the eponymous ...
,
Twitter
Twitter is an online social media and social networking service owned and operated by American company Twitter, Inc., on which users post and interact with 280-character-long messages known as "tweets". Registered users can post, like, and ...
,
Reddit
Reddit (; stylized in all lowercase as reddit) is an American social news aggregation, content rating, and discussion website. Registered users (commonly referred to as "Redditors") submit content to the site such as links, text posts, images ...
, and other
Internet forum
An Internet forum, or message board, is an online discussion site where people can hold conversations in the form of posted messages. They differ from chat rooms in that messages are often longer than one line of text, and are at least temporar ...
s.
Nyx status monitor
Nyx (formerly ARM) is a
command-line
A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
status monitor written in
Python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
for Tor. This functions much like
top
A spinning top, or simply a top, is a toy with a squat body and a sharp point at the bottom, designed to be spun on its vertical axis, balancing on the tip due to the gyroscopic effect.
Once set in motion, a top will usually wobble for a few ...
does for system usage, providing real time statistics for:
* Resource usage (Bandwidth, CPU, and memory usage)
* General relaying information (Nickname, fingerprint, flags, or/dir/controlports)
* Event log with optional
regex
A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or ...
filtering and
deduplication
The term deduplication refers generally to eliminating duplicate or redundant information.
*Data deduplication, in computer storage, refers to the elimination of redundant data
*Record linkage
Record linkage (also known as data matching, data l ...
* Connections correlated against Tor's consensus data (IP address, connection types, relay details, etc.)
* Torrc configuration file with
syntax highlighting
Syntax highlighting is a feature of text editors that are used for programming, scripting, or markup languages, such as HTML. The feature displays text, especially source code, in different colours and fonts according to the category of terms ...
and validation
Most of Nyx's attributes are configurable through an optional
configuration file
In computing, configuration files (commonly known simply as config files) are computer file, files used to configure the Parameter (computer programming), parameters and Initialization (programming), initial settings for some computer programs. T ...
. It runs on any platform supported by
curses
A curse (also called an imprecation, malediction, execration, malison, anathema, or commination) is any expressed wish that some form of adversity or misfortune will befall or attach to one or more persons, a place, or an object. In particular, ...
including
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
,
macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
, and other
Unix-like
A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
variants.
The project began in the summer of 2009,
and since 18 July 2010 it has been an official part of the Tor Project. It is
free software
Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
, available under the
GNU General Public License
The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was th ...
.
[
]
Weaknesses
Like all current low-latency
Latency, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and ...
anonymity network
In computer networking, a proxy server is a server application that acts as an intermediary between a client requesting a resource and the server providing that resource.
Instead of connecting directly to a server that can fulfill a request ...
s, Tor cannot and does not attempt to protect against monitoring of traffic at the boundaries of the Tor network (i.e., the traffic entering and exiting the network). While Tor does provide protection against traffic analysis
Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication, it can be performed even when the messages are encrypted. In general, the greater the number of messages observed ...
, it cannot prevent traffic confirmation (also called ''end-to-end correlation'').
A 2009 study revealed that Tor and the alternative network system JonDonym (Java Anon Proxy, JAP) are considered more resilient to website fingerprinting techniques than other tunneling protocol
In computer networks, a tunneling protocol is a communication protocol which allows for the movement of data from one network to another. It involves allowing private network communications to be sent across a public network (such as the Internet ...
s.
The reason for this is that conventional single-hop VPN
A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. The be ...
protocols do not need to reconstruct packet data nearly as much as a multi-hop service like Tor or JonDonym. Website fingerprinting yielded greater than 90% accuracy for identifying HTTP
The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, ...
packets on conventional VPN protocols versus Tor which yielded only 2.96% accuracy. However, some protocols like OpenSSH
OpenSSH (also known as OpenBSD Secure Shell) is a suite of secure networking utilities based on the Secure Shell (SSH) protocol, which provides a secure channel over an unsecured network in a client–server architecture.
Network Working Gr ...
and OpenVPN
OpenVPN is a virtual private network (VPN) system that implements techniques to create secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It implements both client and server appl ...
required a large amount of data before HTTP packets were identified.
Researchers from the University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
developed a network scanner allowing identification of 86% of live Tor "bridges" with a single scan.
Consensus blocking
Like many decentralized systems, Tor relies on a consensus mechanism to periodically update its current operating parameters, which for Tor are network parameters like which nodes are good/bad relays, exits, guards, and how much traffic each can handle. Tor's architecture for deciding the consensus relies on a small number of directory authority nodes voting on current network parameters. Currently, there are eight directory authority nodes, and their health is publicly monitored. The IP addresses of the authority nodes are hard coded into each Tor client. The authority nodes vote every hour to update the consensus, and clients download the most recent consensus on startup. A network congestion attack, such as a DDoS
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host
A ...
, can prevent the consensus nodes from communicating and thus prevent voting to update the consensus.
Eavesdropping
Autonomous system (AS) eavesdropping
If the same autonomous system (AS), responsible for routing packets at least partly, is present on both path segments from a client to entry relay and from exit relay to destination, such an AS can statistically correlate traffic on the entry and exit segments of the path (i.e. traffic confirmation) and potentially infer the destination with which the client communicated. In 2012, LASTor proposed a method to predict a set of potential ASes on these two segments and then avoid choosing this path during the path selection algorithm on the client side. In this paper, they also improve latency by choosing shorter geographical paths between a client and destination.
Exit node eavesdropping
In September 2007, Dan Egerstad, a Swedish security consultant, revealed he had intercepted usernames and passwords for email accounts by operating and monitoring Tor exit nodes. As Tor cannot encrypt the traffic between an exit node and the target server, any exit node is in a position to capture traffic passing through it that does not use end-to-end encryption
End-to-end encryption (E2EE) is a system of communication where only the communicating users can read the messages. In principle, it prevents potential eavesdroppers – including telecom providers, Internet providers, malicious actors, and even ...
such as Secure Sockets Layer
Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securi ...
(SSL) or Transport Layer Security
Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securi ...
(TLS). While this may not inherently breach the anonymity of the source, traffic intercepted in this way by malicious Tor exit nodes operators can expose information about the source in either or both of payload and protocol data. Furthermore, Egerstad is circumspect about the possible subversion of Tor by intelligence agencies:
In October 2019, a Tor researcher revealed that since at least 2017, there were hundreds of highly suspicious entry, relay, and exit nodes, run by an unknown group, in an unprecedented scale. It was alleged that this number of servers could pose the risk of a sybil attack
Sibyls were oracular women believed to possess prophetic powers in ancient Greece.
Sybil or Sibyl may also refer to:
Films
* ''Sybil'' (1921 film)
* ''Sybil'' (1976 film), a film starring Sally Field
* ''Sybil'' (2007 film), a remake of the 19 ...
as it could map Tor users' routes inside the network, increasing risk of deanonymization. At some point there were about 900 nodes running and by November 2021 about 600 of them were purged.
Although described as being a deanonymization attempt, the motives and the achievements of this possibly on-going event are still unknown.
Internal communication attack
In October 2011, a research team from ESIEA claimed to have discovered a way to compromise the Tor network by decrypting communication passing over it. The technique they describe requires creating a map of Tor network nodes, controlling one-third of them, and then acquiring their encryption keys
Key or The Key may refer to:
Common meanings
* Key (cryptography), a piece of information that controls the operation of a cryptography algorithm
* Key (lock), device used to control access to places or facilities restricted by a lock
* Key (map ...
and algorithm seeds
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm pl ...
. Then, using these known keys and seeds, they claim the ability to decrypt two encryption layers out of three. They claim to break the third key by a statistical attack. In order to redirect Tor traffic to the nodes they controlled, they used a denial-of-service
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...
attack. A response to this claim has been published on the official Tor Blog stating these rumors of Tor's compromise are greatly exaggerated.
Traffic-analysis attack
There are two methods of traffic-analysis attack, passive and active. In the passive traffic-analysis method, the attacker extracts features from the traffic of a specific flow on one side of the network and looks for those features on the other side of the network. In the active traffic-analysis method, the attacker alters the timings of the packets of a flow according to a specific pattern and looks for that pattern on the other side of the network; therefore, the attacker can link the flows in one side to the other side of the network and break the anonymity of it. It is shown that, although timing noise is added to the packets, there are active traffic analysis methods that are robust against such a noise.
Steven Murdoch
Steven James Murdoch is Professor of Security Engineering in the Computer Science Department, University College London. His research covers privacy-enhancing technology, Internet censorship, and anonymous communication, in particular Tor. He i ...
and George Danezis from University of Cambridge
, mottoeng = Literal: From here, light and sacred draughts.
Non literal: From this place, we gain enlightenment and precious knowledge.
, established =
, other_name = The Chancellor, Masters and Schola ...
presented an article at the 2005 IEEE
The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
Symposium
In ancient Greece, the symposium ( grc-gre, συμπόσιον ''symposion'' or ''symposio'', from συμπίνειν ''sympinein'', "to drink together") was a part of a banquet that took place after the meal, when drinking for pleasure was acc ...
on security and privacy on traffic-analysis techniques that allow adversaries with only a partial view of the network to infer which nodes are being used to relay the anonymous streams. These techniques greatly reduce the anonymity provided by Tor. Murdoch and Danezis have also shown that otherwise unrelated streams can be linked back to the same initiator. This attack, however, fails to reveal the identity of the original user. Murdoch has been working with and has been funded by Tor since 2006.
Tor exit node block
Operators of Internet sites have the ability to prevent traffic from Tor exit nodes or to offer reduced functionality for Tor users. For example, it is not generally possible to edit Wikipedia
Wikipedia is a multilingual free online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and using a wiki-based editing system. Wikipedia is the largest and most-read refer ...
when using Tor or when using an IP address also used by a Tor exit node. The BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
...
service, although non-exit relays and bridges are not blocked.
(''Institut national de recherche en informatique et en automatique'', INRIA), documented an attack that is capable of revealing the IP addresses of
users on the Tor network. The "bad apple attack" exploits Tor's design and takes advantage of insecure application used to associate the simultaneous use of a secure application with the IP address of the Tor user in question. One method of attack depends on control of an exit node or hijacking tracker responses, while a secondary attack method is based in part on the statistical exploitation of
tracking.
The results presented in the bad apple attack research paper are based on an attack launched against the Tor network by the authors of the study. The attack targeted six exit nodes, lasted for twenty-three days, and revealed a total of 10,000 IP addresses of active Tor users. This study is significant because it is the first documented attack designed to target
file-sharing applications on Tor.
BitTorrent may generate as much as 40% of all traffic on Tor.
Furthermore, the bad apple attack is effective against insecure use of any application over Tor, not just BitTorrent.
can be bypassed by attackers controlling a Tor exit node. The study was conducted by monitoring six exit nodes for a period of twenty-three days. Researches used three
;Inspection of BitTorrent control messages: Tracker announces and extension protocol handshakes may optionally contain a client
. Analysis of collected data revealed that 35% and 33% of messages, respectively, contained addresses of clients.
;Hijacking trackers' responses: Due to lack of encryption or authentication in communication between the tracker and peer, typical
s allow attackers to determine peer IP addresses and even verify the distribution of content. Such attacks work when Tor is used only for tracker communication.
(DHT) connections through Tor are impossible, so an attacker is able to reveal a target's IP address by looking it up in the DHT even if the target uses Tor to connect to other peers.
With these techniques, researchers were able to identify other streams initiated by users, whose IP addresses were revealed.
attack targeted at the Tor node software, as well as defenses against that attack and its variants. The attack works using a colluding client and server, and filling the queues of the exit node until the node runs out of memory, and hence can serve no other (genuine) clients. By attacking a significant proportion of the exit nodes this way, an attacker can degrade the network and increase the chance of targets using nodes controlled by the attacker.
s were renewed. The Tor Project recommended Tor relay operators and onion service operators revoke and generate fresh keys after patching OpenSSL, but noted Tor relays use two sets of keys and Tor's multi-hop design minimizes the impact of exploiting a single relay.
Five hundred eighty-six relays later found to be susceptible to the Heartbleed bug were taken offline as a precautionary measure.
On 30 July 2014, the Tor Project issued the security advisory "relay early traffic confirmation attack" in which the project discovered a group of relays that tried to de-anonymize onion service users and operators. In summary, the attacking onion service directory node changed the headers of cells being relayed tagging them as "relay" or "relay early" cells differently to encode additional information and sent them back to the requesting user/operator. If the user's/operator's guard/entry node was also part of the attacking relays, the attacking relays might be able to capture the IP address of the user/operator along with the onion service information that the user/operator was requesting. The attacking relays were stable enough to be designated as "suitable as hidden service directory" and "suitable as entry guard"; therefore, both the onion service users and the onion services might have used those relays as guards and hidden service directory nodes.
The attacking nodes joined the network early in the year on 30 January and the project removed them on 4 July.
Although the attack's beginning is unclear, the project implied that between February and July, IP addresses of onion service users and operators might have been exposed.
The project mentioned the following mitigations besides removing the attacking relays from the network:
* patched relay software to prevent relays from relaying cells with "relay early" headers that were not intended.
* planned update for users' proxy software so that they could inspect if they received "relay early" cells from the relays (as they are not supposed to), along with the settings to connect to just one guard node instead of selecting randomly from 3 to reduce the probability of connecting to an attacking relay
* recommended that onion services should consider changing their locations
* reminded users and onion service operators that Tor could not prevent de-anonymization if the attacker controlled or could listen to both ends of the Tor circuit, like in this attack.
In November 2014 there was speculation in the aftermath of
, resulting in 17 arrests internationally, that a Tor weakness had been exploited. A representative of
was secretive about the method used, saying: "''This is something we want to keep for ourselves. The way we do this, we can't share with the whole world, because we want to do it again and again and again.''"
...