Tor (anonymity network)
|Developer(s)||The Tor Project, Inc|
|Initial release||20 September 2002|
|Stable release||0.2.4.24 (23 September 2014) [±]|
|Preview release||0.2.5.8-rc (23 September 2014 ) [±]|
|Type||Onion routing, Anonymity|
Tor (previously an acronym for The Onion Router) is free software for enabling online anonymity and resisting censorship. It is designed to make it possible for users to surf the Internet anonymously, so their activities and location cannot be discovered by government agencies, corporations, or anyone else.
Tor directs Internet traffic through a free, worldwide, volunteer network consisting of more than five thousand relays to conceal a user's location and usage from anyone conducting network surveillance or traffic analysis. Using Tor makes it more difficult for Internet activity to be traced back to the user: this includes "visits to Web sites, online posts, instant messages, and other communication forms". Tor's use is intended to protect the personal privacy of users, as well as their freedom and ability to conduct confidential communication by keeping their Internet activities from being monitored. An extract of a Top Secret appraisal by the National Security Agency (NSA) characterized Tor as "the King of high secure, low latency Internet anonymity" with "no contenders for the throne in waiting".
The term "onion routing" refers to application layers of encryption, nested like the layers of an onion, used to anonymize communication. Tor encrypts the original data, including the destination IP address, multiple times and sends it through a virtual circuit comprising successive, randomly selected Tor relays. Each relay decrypts a layer of encryption to reveal only the next relay in the circuit in order to pass the remaining encrypted data on to it. The final relay decrypts the innermost layer of encryption and sends the original data to its destination without revealing, or even knowing, the source IP address. Because the routing of the communication is partly concealed at every hop in the Tor circuit, this method eliminates any single point at which the communication can be de-anonymized through network surveillance that relies upon knowing its source and destination.
An adversary unable to defeat the strong anonymity that Tor provides may try to de-anonymize the communication by other means. One way this may be achieved is by exploiting vulnerable software on the user's computer. The NSA has a technique that targets outdated Firefox browsers codenamed EgotisticalGiraffe, and targets Tor users in general for close monitoring under its XKeyscore program. Attacks against Tor are an active area of academic research which is welcomed by Tor itself.
- 1 History
- 2 Reception and impact
- 3 Usage
- 4 Operation
- 5 Weaknesses
- 6 Implementations
- 7 See also
- 8 References
- 9 Footnotes
- 10 External links
The core principle behind Tor, "onion routing," was developed in the mid-1990s by U.S. Naval Research Laboratory employees mathematician Paul Syverson and computer scientists Michael Reed and David Goldschlag, with the purpose of protecting U.S. intelligence communications online. Onion routing was further developed by DARPA in 1997.
The alpha version of Tor, developed by Syverson and computer scientists Roger Dingledine and Nick Mathewson and then called The Onion Routing project or TOR project, launched on 20 September 2002. On 13 August 2004, Syverson, Dingledine and Mathewson presented "Tor: The Second-Generation Onion Router" at the 13th USENIX Security Symposium. In 2004, the Naval Research Laboratory released the code for Tor under a free licence, and the Electronic Frontier Foundation (EFF) began funding Dingledine and Mathewson to continue its development.
In December 2006, Dingledine, Mathewson and five others founded The Tor Project, a Massachusetts-based 501(c)(3) research-education nonprofit organization responsible for maintaining Tor. The EFF acted as The Tor Project's fiscal sponsor in its early years, and early financial supporters of The Tor Project included the U.S. International Broadcasting Bureau, Internews, Human Rights Watch, the University of Cambridge, Google, and Netherlands-based Stichting.net.
Reception and impact
Tor has been praised for providing privacy and anonymity to vulnerable Internet users such as political activists fearing surveillance and arrest, ordinary web users seeking to circumvent censorship, and women who have been threatened with violence or abuse by stalkers. The U.S. National Security Agency (NSA) has called Tor "the king of high-secure, low-latency internet anonymity," and BusinessWeek magazine has described it as "perhaps the most effective means of defeating the online surveillance efforts of intelligence agencies around the world." Other media have described Tor as "a sophisticated privacy tool," "easy to use" and "so secure that even the world's most sophisticated electronic spies haven't figured out how to crack it."
In March 2011, The Tor Project was awarded the Free Software Foundation's 2010 Award for Projects of Social Benefit on the following grounds: "Using free software, Tor has enabled roughly 36 million people around the world to experience freedom of access and expression on the Internet while keeping them in control of their privacy and anonymity. Its network has proved pivotal in dissident movements in both Iran and more recently Egypt."
In 2013, Jacob Appelbaum described Tor as a "part of an ecosystem of software that helps people regain and reclaim their autonomy. It helps to enable people to have agency of all kinds; it helps others to help each other and it helps you to help yourself. It runs, it is open and it is supported by a large community spread across all walks of life."
Advocates for Tor say that it supports freedom of expression, including in countries where the Internet is heavily censored, by protecting the privacy and anonymity of internet users. However because the project was originally developed on behalf of the U.S. intelligence community and continues to receive U.S. government funding, it has been criticized as "more resembl[ing] a spook project than a tool designed by a culture that values accountability or transparency."
As of 2012, 80% of The Tor Project's $2M annual budget came from the United States government, with the U.S. State Department, the Broadcasting Board of Governors, and the National Science Foundation as major contributors, "to aid democracy advocates in authoritarian states". The Swedish government and other organizations provided the other 20%, including NGOs and thousands of individual sponsors. One of the founders of the project, Roger Dingledine, stated that the United States Department of Defense funds are more similar to a research grant than a procurement contract. Andrew Lewman, the executive director of Tor, stated that even though it accepts funds from the U.S. federal government, the Tor service did not necessarily collaborate with the NSA to reveal identities of users.
Critics say Tor is not as secure as it claims, pointing to U.S. law enforcement's investigations and shutdowns of Tor-using sites such as web-hosting company Freedom Hosting and online marketplace Silk Road. In October 2013, after analyzing documents leaked by Edward Snowden, the Guardian reported that the NSA had repeatedly tried to crack Tor and had failed to break its core security, although it had had some success attacking the computers of individual Tor users. The Guardian also published a 2012 NSA classified slide deck, entitled "Tor Stinks," which said "We will never be able to de-anonymize all Tor users all the time," but "with manual analysis we can de-anonymize a very small fraction of Tor users."
Tor enables 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. The Tor Project says Tor's users include "normal people" who want to keep their internet activities private from websites and advertisers, people concerned about cyber-spying, users who are evading censorship such as activists and journalists, and military professionals. As of late 2014 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 and the social workers and agencies which assist them inasmuch as digital stalking has also increased, given the prevalence of digital media in contemporary on-line life. Along with SecureDrop, Tor is used by news organizations such as the Guardian, the New Yorker, ProPublica and the Intercept to protect the privacy of whistleblowers.
Tor is used for matters that are, or may be, illegal in some countries, e.g., to gain access to censored information, to organize political activities, or to circumvent laws against criticism of heads of state. Tor has been described by The Economist, in relation to Bitcoin and the Silk Road, as being "a dark corner of the web." It has been targeted by both the American NSA and the British GCHQ signals intelligence agencies, albeit with marginal success, and more successfully by the British National Crime Agency 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 leaks of sensitive information and copyright infringement, distribution of illegal sexual content, selling controlled substances, money laundering, credit card fraud, and identity theft; the black market utilizes the Tor infrastructure at least in part, in conjunction with Bitcoin. Ironically, Tor has been used by criminal enterprises, hacktivism 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 National Science Foundation, and (via the Broadcasting Board of Governors, which itself partially funded Tor until October 2012), Radio Free Asia, and seek to subvert it. Tor's executive director, Andrew Lewman, said in August 2014 that agents of the NSA and the GCHQ have anonymously provided Tor with bug reports.
In its complaint against Ross William Ulbricht of the Silk Road the FBI acknowledged that Tor has "known legitimate uses". According to CNET, Tor's anonymity function is "endorsed by the Electronic Frontier Foundation and other civil liberties groups as a method for whistleblowers 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. The Tor Project's FAQ offers supporting reasons for EFF's endorsement:
Criminals can already do bad things. Since they're willing to break laws, they already have lots of options available that provide better privacy than Tor provides....
Tor aims to provide protection for ordinary people who want to follow the law. Only criminals have privacy right now, and we need to fix that....
So yes, criminals could in theory use Tor, but they already have better options, and it seems unlikely that taking Tor away from the world will stop them from doing their bad things. At the same time, Tor and other privacy measures can fight identity theft, physical crimes like stalking, and so on.
In 2014 the EFF's Eva Galperin told BusinessWeek magazine 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.”
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, which encrypts and then randomly bounces communications through a network of relays run by volunteers around the globe. These onion routers employ encryption in a multi-layered manner (hence the onion metaphor) to ensure perfect forward secrecy between relays, thereby providing users with anonymity in network location. That anonymity extends to the hosting of censorship-resistant content via Tor's anonymous hidden service feature. Furthermore, by keeping some of the entry relays (bridge relays) secret, users can evade Internet censorship that relies upon blocking public Tor relays.
Because the internet address of the sender and the recipient are not both in cleartext 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 (called the exit node), rather than the sender, is the originator of the communication.
A Tor user's SOCKS-aware applications can be configured to direct their network traffic through a Tor instance's SOCKS interface. Tor periodically creates virtual circuits through the Tor network through which it can multiplex 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 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's application independence sets it apart from most other anonymity networks: it works at the Transmission Control Protocol (TCP) stream level. Applications whose traffic is commonly anonymised using Tor include Internet Relay Chat (IRC), instant messaging, and World Wide Web browsing.
Tor can also provide anonymity to websites and other servers. Servers configured to receive inbound connections only through Tor are called hidden services. Rather than revealing a server's IP address (and thus its network location), a hidden service is accessed through its onion address. The Tor network understands these addresses and can route data to and from hidden services, even to those hosted behind firewalls or network address translators (NAT), while preserving the anonymity of both parties. Tor is necessary to access hidden services.
Hidden services have been deployed on the Tor network since 2004. Other than the database that stores the hidden-service descriptors, Tor is decentralized by design; there is no direct readable list of all hidden services, although a number of hidden services catalog publicly known onion addresses.
Because hidden services do not use exit nodes, connection to a hidden service is encrypted end-to-end and not subject to eavesdropping. There are, however, security issues involving Tor hidden services. For example, services that are reachable through Tor hidden 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.
Like all current low-latency anonymity networks, 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, it cannot prevent traffic confirmation (also called end-to-end correlation).
In spite of known weaknesses and attacks listed here, Tor and the alternative network system JonDonym (Java Anon Proxy, JAP) are considered more resilient than alternatives such as VPNs. Were a local observer on an ISP or WLAN to attempt to analyze the size and timing of the encrypted data stream going through the VPN, Tor, or JonDo system, the latter two would be harder to analyze, as demonstrated by a 2009 study.
Autonomous System (AS) eavesdropping
If an Autonomous System (AS) exists 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 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 path selection algorithm on client side. In this paper, they also improve latency by choosing shorter geographical paths between client and destination.
Exit node eavesdropping
In September 2007, Dan Egerstad, a Swedish security consultant, revealed that he had intercepted usernames and passwords for a large number of e-mail accounts by operating and monitoring Tor exit nodes. As Tor does not, and by design cannot, encrypt the traffic between an exit node and the target server, any exit node is in a position to capture any traffic passing through it that does not use end-to-end encryption such as SSL or TLS. While this may not inherently breach the anonymity of the source, traffic intercepted in this way by self-selected third parties 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 –
- "If you actually look in to where these Tor nodes are hosted and how big they are, some of these nodes cost thousands of dollars each month just to host because they're using lots of bandwidth, they're heavy-duty servers and so on. Who would pay for this and be anonymous?"
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 and algorithm seeds. 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-based attack. In order to redirect Tor traffic to the nodes they controlled, they used a denial-of-service attack. A response to this claim has been published on the official Tor Blog stating that these rumours of Tor's compromise are greatly exaggerated.
Steven J. Murdoch and George Danezis from University of Cambridge presented an article at the 2005 IEEE Symposium 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 to Tor users. For example, it is not generally possible to edit Wikipedia when using Tor, or when using an IP address that also is used by a Tor exit node, due to the use of the TorBlock MediaWiki extension, unless an exemption is obtained.
Bad Apple attack
In March 2011, researchers with the Rocquencourt, France based National Institute for Research in Computer Science and Control (Institut national de recherche en informatique et en automatique, INRIA) documented an attack that is capable of revealing the IP addresses of BitTorrent users on the Tor network. The "bad apple attack" exploits Tor's design and takes advantage of insecure application use 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 distributed hash table tracking. According to the study:
This attack against Tor consists of two parts: (a) exploiting an insecure application to reveal the source IP address of, or trace, a Tor user and (b) exploiting Tor to associate the use of a secure application with the IP address of a user (revealed by the insecure application). As it is not a goal of Tor to protect against application-level attacks, Tor cannot be held responsible for the first part of this attack. However, because Tor's design makes it possible to associate streams originating from secure application with traced users, the second part of this attack is indeed an attack against Tor. We call the second part of this attack the bad apple attack. (The name of this attack refers to the saying 'one bad apple spoils the bunch.' We use this wording to illustrate that one insecure application on Tor may allow to trace other applications.)
The results presented in the bad apple attack research paper are based on an attack in the wild launched against the Tor network by the authors of the study. The attack targeted six exit nodes, lasted for 23 days, and revealed a total of 10,000 IP addresses of active Tor users. This study is particularly significant because it is the first documented attack designed to target P2P 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.
Some protocols leak IP addresses
Researchers from French Institute for Research in Computer Science and Control (INRIA) showed that Tor dissimulation technique in BitTorrent can be bypassed by attacker controlling Tor exit node. The study was conducted by monitoring 6 exit nodes for a period of 23 days. Researches used three attack vectors:
- Inspection of BitTorrent control messages
- Tracker announces and Extension Protocol handshakes may optionally contain client's IP address. Analysis of collected data revealed that 35% and 33% of respective messages contained real addresses of clients.:3
- Hijacking trackers' responses
- Due to lack of encryption or authentication in communication between tracker and peer typical man-in-the-middle attack allows attacker to determine peer's IP address and even verify the distribution of content. This attack works when Tor is used only for tracker communication.:4
- Exploiting distributed hash tables (DHT)
- This attack exploits the fact that DHT connections through Tor are impossible, so attacker is able to reveal target's IP address by looking it up in DHT even if target uses Tor to connect to other peers.:4–5
Using these techniques researchers were able to identify other streams initiated by users, whose IP addresses were revealed.
Jensen et al., describe DDoS attack targeted at the TOR node software, together with defences against that attack and 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.
The Heartbleed OpenSSL bug disrupted the Tor network for several days in April 2014 while private keys were renewed. The Tor Project recommended that Tor relay operators and hidden service operators revoke and generate fresh keys after patching OpenSSL, but noted that Tor relays use two sets of keys and that Tor's multi-hop design minimizes the impact of exploiting a single relay. 586 relays later found to be susceptible to the Heartbleed bug were taken off-line as a precautionary measure.
Tor Browser on Linux Mint showing its start page - about:tor
|Stable release||3.6.6 (25 September 2014 ) [±]|
|Preview release||4.0-alpha-3 (26 September 2014 ) [±]|
|Available in||15 languages|
|Type||Onion routing, Anonymity, Web browser, Feed reader|
Tor Browser (previously known as Tor Browser Bundle or TBB) is the Tor Project's flagship product. It consists of a modified Mozilla Firefox ESR web browser, the TorButton, TorLauncher, NoScript and HTTPS Everywhere Firefox extensions and the Tor proxy. It can be run from removable media and is available for Windows, Mac OS X, and Linux.
Tor Browser automatically starts Tor processes and routes traffic through the Tor network. Upon termination of a session the browser deletes privacy-sensitive data such as cookies and browsing history.
The FBI, in Operation Torpedo, has been targeting Tor hidden servers since 2012, such as in the case of Aaron McGrath, who was sentenced to 20 years for running three hidden Tor servers which contained child pornography.
The Guardian Project is actively developing a free and open-source suite of application programs and firmware for the Android operating system to help make mobile communications more secure. The applications include ChatSecure instant messaging client, Orbot Tor implementation, Orweb privacy-enhanced mobile browser, ProxyMob Firefox add-on and ObscuraCam.
Security-focused operating systems
Several security-focused operating systems like GNU/Linux distributions including Hardened Linux From Scratch, Incognito, Liberté Linux, Qubes OS, Tails, Tor-ramdisk and Whonix, make extensive use of Tor.
- Dingledine, Roger (20 September 2002). "pre-alpha: run an onion proxy now!". or-dev mailing list. http://archives.seul.org/or/dev/Sep-2002/msg00019.html. Retrieved 17 July 2008.
- "Tor Release Notes". Tor Project Source Repository. 23 September 2014. Retrieved 26 September 2014.
- "Tor Change Log". Tor Project Source Repository. 23 September 2014. Retrieved 26 September 2014.
- "Tor". Open HUB. Retrieved 20 September 2014.
- Li, Bingdong; Erdin, Esra; Güneş, Mehmet Hadi; Bebis, George; Shipley, Todd (14 June 2011). "An Analysis of Anonymity Usage". In Domingo-Pascual, Jordi; Shavitt, Yuval; Uhlig, Steve. Traffic Monitoring and Analysis: Third International Workshop, TMA 2011, Vienna, Austria, April 27, 2011, Proceedings. Berlin: Springer-Verlag. pp. 113–116. ISBN 978-3-642-20304-6. Retrieved 6 August 2012.
- "Tor Network Status". Retrieved 17 January 2014.
- "Tor: 'The king of high-secure, low-latency anonymity'". The Guardian. 4 October 2013. Retrieved 5 October 2013.
- Ball, James; Schneier, Bruce; Greenwald, Glenn (4 October 2013). "NSA and GCHQ target Tor network that protects anonymity of web users". The Guardian. Retrieved 5 October 2013.
- "'Peeling back the layers of Tor with EgotisticalGiraffe'". The Guardian. 4 October 2013. Retrieved 5 October 2013.
- J. Appelbaum, A. Gibson, J. Goetz, V. Kabisch, L. Kampf, L. Ryge (3 July 2014). "NSA targets the privacy-conscious". Panorama (Norddeutscher Rundfunk). Retrieved 4 July 2014.
- Fagoyinbo, Joseph Babatunde (2013-05-24). The Armed Forces: Instrument of Peace, Strength, Development and Prosperity. AuthorHouse. ISBN 9781477226476. Retrieved August 29, 2014.
- Leigh, David; Harding, Luke (2011-02-08). WikiLeaks: Inside Julian Assange's War on Secrecy. PublicAffairs. ISBN 1610390628. Retrieved August 29, 2014.
- Ligh, Michael; Adair, Steven; Hartstein, Blake; Richard, Matthew (2010-09-29). Malware Analyst's Cookbook and DVD: Tools and Techniques for Fighting Malicious Code. John Wiley & Sons. ISBN 9781118003367. Retrieved August 29, 2014.
- Levine, Yasha (16 July 2014). "Almost everyone involved in developing Tor was (or is) funded by the US government". Pando Daily. Retrieved 30 August 2014.
- "Tor FAQ: Why is it called Tor?". Tor Project. Retrieved 1 July 2011.
- Dingledine, Roger; Mathewson, Nick; Syverson, Paul (13 August 2004). "Tor: The Second-Generation Onion Router". Proc. 13th USENIX Security Symposium. San Diego, California. Retrieved 17 November 2008.
- "Tor Project: Core People". Tor Project. Retrieved 17 July 2008.
- "Tor Project Form 990 2008". Tor Project. Tor Project. 2009. Retrieved 30 August 2014.
- "Tor Project Form 990 2007". Tor Project. Tor Project. 2008. Retrieved 30 August 2014.
- "Tor Project Form 990 2009". Tor Project. Tor Project. 2010. Retrieved 30 August 2014.
- "Tor: Sponsors". Tor Project. Retrieved 11 December 2010.
- Krebs, Brian (8 August 2007). "Attacks Prompt Update for 'Tor' Anonymity Network". Washington Post. Retrieved 27 October 2007.
- Brandom, Russell (9 May 2014). "Domestic violence survivors turn to Tor to escape abusers". The Verge. Retrieved 30 August 2014.
- Lawrence, Dune (23 January 2014). "The Inside Story of Tor, the Best Internet Anonymity Tool the Government Ever Built". Businessweek magazine. Retrieved 30 August 2014.
- Zetter, Kim (1 June 2010). "WikiLeaks Was Launched With Documents Intercepted From Tor". Wired. Retrieved 30 August 2014.
- Lee, Timothy B. (10 June 2013). "Five ways to stop the NSA from spying on you". Washington Post. Retrieved 30 August 2014.
- "Not Even the NSA Can Crack the State Separtment's Favorite Anonymous Service". Foreign Policy. 24 October 2014. Retrieved 30 August 2014.
- "2010 Free Software Awards announced". Free Software Foundation. Retrieved 23 March 2011.
- Wittmeyer, Alicia P.Q. (26 November 2012). "The FP Top 100 Global Thinkers". Foreign Policy. Archived from the original on 28 November 2012. Retrieved 28 November 2012.
- Sirius, R. U. (11 March 2013). "Interview uncut: Jacob Appelbaum". theverge.com.
- Gaertner, Joachim (1 July 2013). "Darknet – Netz ohne Kontrolle". Das Erste (in German). Retrieved 28 August 2013.
- Gallagher, Sean (25 July 2014). "Russia publicly joins war on Tor privacy with $111,000 bounty". Ars Technica. Retrieved 26 July 2014.
- Lucian, Constantin (25 July 2014). "Russian government offers huge reward for help unmasking anonymous Tor users". PC World. Retrieved 26 July 2014.
- McKim, Jenifer B. (8 March 2012). "Privacy software, criminal use". The Boston Globe. Archived from the original on 12 March 2012.
- Fowler, Geoffrey A. (17 December 2012). "Tor: an anonymous, and controversial, way to web-surf". Wall Street Journal. Retrieved 19 May 2013.
- Fung, Brian (6 September 2013). "The feds pay for 60 percent of Tor’s development. Can users trust it?". The Switch (Washington Post). Retrieved 6 February 2014.
- "Tor is Not as Safe as You May Think". Infosecurity magazine. 2 September 2013. Retrieved 30 August 2014.
- "'Tor Stinks' presentation – read the full document". The Guardian. 4 October 2014. Retrieved 30 August 2014.
- Zetter, Kim (17 May 2005). "Tor Torches Online Tracking". Wired. Retrieved 30 August 2014.
- Dredge, Stuart (5 November 2013). "What is Tor? A beginner's guide to the privacy tool". Guardian. Retrieved 30 August 2014.
- Fowler, Geoffrey A. (17 December 2012). "Tor: An Anonymous, And Controversial, Way to Web-Surf". Wall Street Journal. Retrieved 30 August 2014.
- LeVines, George (7 May 2014). "As domestic abuse goes digital, shelters turn to counter-surveillance with Tor". Boston Globe. Retrieved 8 May 2014.
- "The Guardian introduces SecureDrop for document leaks". Nieman Journalism Lab. 5 June 2014. Retrieved 30 August 2014.
- Cochrane, Nate (2 February 2011). "Egyptians turn to Tor to organise dissent online". SC Magazine. Retrieved 10 December 2011.
- "Bitcoin: Monetarists Anonymous". The Economist. 29 September 2012. Retrieved 19 May 2013.
- Boiten, Eerke; Hernandez-Castro, Julio (July 28, 2014). "Can you really be identified on Tor or is that just what the cops want you to believe?". Phys.org.
- "JTRIG Tools and Techniques". The Intercept. 14 Jul 2014.
- "document from an internal GCHQ wiki lists tools and techniques developed by the Joint Threat Research Intelligence Group". documentcoud.org. 5 July 2012. Retrieved 30 July 2014.
- Bode, Karl (12 March 2007). "Cleaning up Tor". Broadband.com. Retrieved 28 April 2014.
- Jones, Robert (2005). Internet forensics. O'Reilly. p. 133. ISBN 0-596-10006-X.
- Chen, Adrian (11 June 2012). "'Dark Net' Kiddie Porn Website Stymies FBI Investigation". Gawker. Retrieved 6 August 2012.
- Chen, Adrian (1 June 2011). "The Underground Website Where You Can Buy Any Drug Imaginable". Gawker. Retrieved 20 April 2012.
- Goodin, Dan (16 April 2012). "Feds shutter online narcotics store that used TOR to hide its tracks". Ars Technica. Retrieved 20 April 2012.
- Gregg, Brandon (30 April 2012). "How online black markets work". CSO Online. Retrieved 6 August 2012.
- Morisy, Michael (8 June 2012). "Hunting for child porn, FBI stymied by Tor undernet". Muckrock. Retrieved 6 August 2012.
- Lawrence, Dune (23 January 2014). "The Inside Story of Tor, the Best Internet Anonymity Tool the Government Ever Built". Bloomberg Businessweek. Retrieved 28 April 2014.
- http://www.bbc.com/news/technology-28886462 NSA & GCHQ "leak Tor bugs" alleges developer.
- Turner, Serrin (27 September 2013). "Sealed compaint". United States of America v. Ross William Ulbricht. Archived from the original on 2 October 2013.
- Higgins, Parker (2013-10-03). "In the Silk Road Case, Don't Blame the Technology". Electronic Frontier Foundation. Retrieved 2013-12-22.
- Soghoian, Chris (16 September 2007). "Tor anonymity server admin arrested". CNET News. Retrieved 17 January 2011.
- "Surveillance Self-Defense: Tor". Electronic Frontier Foundation. Retrieved 28 April 2014.
- "Doesn't Tor enable criminals to do bad things?". Tor Project. Retrieved 28 August 2013.
- "Tor: Bridges". Tor Project. Retrieved 9 January 2011.
- Øverlier, Lasse; Syverson, Paul (21 June 2006). "Locating Hidden Servers" (PDF). Proceedings of the 2006 IEEE Symposium on Security and Privacy. IEEE Symposium on Security and Privacy. Oakland, CA: IEEE CS Press. p. 1. doi:10.1109/SP.2006.24. ISBN 0-7695-2574-1. Retrieved 9 November 2013.
- Goodin, Dan (10 September 2007). "Tor at heart of embassy passwords leak". TheRegister. Retrieved 20 September 2007.
- Dingledine, Roger (18 February 2009). "One cell is enough to break Tor's anonymity". Tor Project. Retrieved 9 January 2011.
- "TheOnionRouter/TorFAQ". Retrieved 18 September 2007. "Tor (like all current practical low-latency anonymity designs) fails when the attacker can see both ends of the communications channel"
- Herrmann, Dominik; Wendolsky, Rolf; Federrath, Hannes (13 November 2009). "Website Fingerprinting: Attacking Popular Privacy Enhancing Technologies with the Multinomial Naïve-Bayes Classifier". Proceedings of the 2009 ACM Cloud Computing Security Workshop (CCSW). Cloud Computing Security Workshop. New York, USA: Association for Computing Machinery. Retrieved 2 September 2010.
- Judge, Peter (20 August 2013). "Zmap’s Fast Internet Scan Tool Could Spread Zero Days In Minutes". TechWeek Europe. Retrieved 28 April 2014.
- Akhoondi, Masoud; Yu, Curtis; Madhyastha, Harsha V. (May 2012). "LASTor: A Low-Latency AS-Aware Tor Client". IEEE Symposium on Security and Privacy. Oakland, USA. Retrieved 28 April 2014.
- Zetter, Kim (10 September 2007). "Rogue Nodes Turn Tor Anonymizer Into Eavesdropper's Paradise". Wired. Retrieved 16 September 2007.
- Lemos, Robert (8 March 2007). "Tor hack proposed to catch criminals". SecurityFocus.
- Gray, Patrick (13 November 2007). "The hack of the year". Sydney Morning Herald. Retrieved 28 April 2014.
- "Tor anonymizing network Compromised by French researchers". The Hacker News. Thehackernews.com. 24 October 2011. Retrieved 10 December 2011.
- "Announcement on 01net.com". Retrieved 17 October 2011.(French)
- phobos (24 October 2011). "Rumors of Tor's compromise are greatly exaggerated". Tor Project. Retrieved 20 April 2012.
- Murdoch, Steven J.; Danezis, George (19 January 2006). "Low-Cost Traffic Analysis of Tor". Proceedings of the 2005 IEEE Symposium on Security and Privacy. IEEE CS. IEEE Symposium on Security and Privacy. Retrieved 21 May 2007.
- Le Blond, Stevens; Manils, Pere; Chaabane, Abdelberi; Ali Kaafar, Mohamed; Castelluccia, Claude; Legout, Arnaud; Dabbous, Walid (March 2011). "One Bad Apple Spoils the Bunch: Exploiting P2P Applications to Trace and Profile Tor Users". 4th USENIX Workshop on Large-Scale Exploits and Emergent Threats (LEET '11). National Institute for Research in Computer Science and Control. Retrieved 13 April 2011.
- McCoy, Damon; Bauer, Kevin; Grunwald, Dirk; Kohno, Tadayoshi; Sicker, Douglas (2008). "Shining Light in Dark Places: Understanding the Tor Network". Proceedings of the 8th International Symposium on Privacy Enhancing Technologies. 8th International Symposium on Privacy Enhancing Technologies. Berlin, Germany: Springer-Verlag. pp. 63–76. doi:10.1007/978-3-540-70630-4_5. ISBN 978-3-540-70629-8.
- Manils, Pere; Abdelberri, Chaabane; Le Blond, Stevens; Kaafar, Mohamed Ali; Castelluccia, Claude; Legout, Arnaud; Dabbous, Walid (April 2010). "Compromising Tor Anonymity Exploiting P2P Information Leakage". 7th USENIX Symposium on Network Design and Implementation. arXiv:1004.1461. Bibcode:2010arXiv1004.1461M.
- Jansen, Rob; Tschorsch, Florian; Johnson, Aaron; Scheuermann, Björn (2014). "The Sniper Attack: Anonymously Deanonymizing and Disabling the Tor Network". 21st Annual Network & Distributed System Security Symposium. Retrieved 28 April 2014.
- Dingledine, Roger (7 April 2014). "OpenSSL bug CVE-2014-0160". Tor Project. Retrieved 28 April 2014.
- Dingledine, Roger (16 April 2014). "Rejecting 380 vulnerable guard/exit keys". tor-relays mailing list. https://lists.torproject.org/pipermail/tor-relays/2014-April/004336.html. Retrieved 28 April 2014.
- Lunar (16 April 2014). "Tor Weekly News — April 16th, 2014". Tor Project. Retrieved 28 April 2014.
- Gallagher, Sean (18 April 2014). "Tor network’s ranks of relay servers cut because of Heartbleed bug". Ars Technica. Retrieved 28 April 2014.
- Mimoso, Michael (17 April 2014). "Tor begins blacklisting exit nodes vulnerable to Heartbleed". Threat Post. Retrieved 28 April 2014.
- Perry, Mike (25 September 2014). "Tor Browser 3.6.6 is released". Tor Project Blog. Retrieved 26 September 2014.
- Perry, Mike (26 September 2014). "Tor Browser 4.0-alpha-3 is released". Tor Project Blog. Retrieved 26 September 2014.
- "The Design and Implementation of the Tor Browser [DRAFT]". Tor Project. 15 March 2013. Retrieved 28 April 2014.
- Alin, Andrei (2 December 2013). "Tor Browser Bundle Ubuntu PPA". Web Upd8. Retrieved 28 April 2014.
- Knight, John (1 September 2011). "Tor Browser Bundle-Tor Goes Portable". Linux Journal. Retrieved 28 April 2014.
- Dredge, Stuart (5 November 2013). "What is Tor? A beginner's guide to the privacy tool". The Guardian. Retrieved 28 April 2014.
- Samson, Ted (5 August 2013). "Tor Browser Bundle for Windows users susceptible to info-stealing attack". InfoWorld. Retrieved 28 April 2014.
- Poulsen, Kevin (8 May 2013). "Feds Are Suspects in New Malware That Attacks Tor Anonymity". Wired. Retrieved 29 April 2014.
- Owen, Gareth. "FBI Malware Analysis". Retrieved 6 May 2014.[self-published source?]
- Best, Jessica (21 January 2014). "Man branded 'largest facilitator of child porn on the planet' remanded in custody again". Daily Mirror. Retrieved 29 April 2014.
- Dingledine, Roger (5 August 2013). "Tor security advisory: Old Tor Browser Bundles vulnerable". Tor Project. Retrieved 28 April 2014.
- Poulsen, Kevin (13 September 2013). "FBI Admits It Controlled Tor Servers Behind Mass Malware Attack". Wired. Retrieved 22 December 2013.
- Schneier, Bruce (4 October 2013). "Attacking Tor: how the NSA targets users' online anonymity". The Guardian. Retrieved 22 December 2013.
- "Tor". Vuze. Retrieved 3 March 2010.
- "Bitmessage FAQ". Bitmessage. Retrieved 17 July 2013.
- "About". The Guardian Project. Retrieved 10 May 2011.
- "ChatSecure: Private Messaging". The Guardian Project. Retrieved 20 September 2014.
- "Orbot: Mobile Anonymity + Circumvention". The Guardian Project. Retrieved 10 May 2011.
- "Orweb: Privacy Browser". The Guardian Project. Retrieved 10 May 2011.
- "ProxyMob: Firefox Mobile Add-on". The Guardian Project. Retrieved 10 May 2011.
- "Obscura: Secure Smart Camera". The Guardian Project. Retrieved 19 September 2014.
- Жуков, Антон (15 December 2009). "Включаем Tor на всю катушку" [Make Tor go the whole hog]. Xakep. Retrieved 28 April 2014.[dead link]
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