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4) #include "head.wmi" TITLE="Tor FAQ"
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10) # Translators: you probably don't want to translate this file yet,
11) # since I'm hoping it will keep changing for a while. Thanks! -RD
12) 

13) <h2>Tor FAQ</h2>
14) <hr />

15) 

16) <p>General questions:</p>

17) <ul>

18) <li><a href="#WhatIsTor">What is Tor?</a></li>
19) <li><a href="#CompatibleApplications">What programs can I use with
20) Tor?</a></li>
21) <li><a href="#WhyCalledTor">Why is it called Tor?</a></li>
22) <li><a href="#Backdoor">Is there a backdoor in Tor?</a></li>
23) <li><a href="#DistributingTor">Can I distribute Tor on my magazine's
24) CD?</a></li>
25) <li><a href="#SupportMail">How can I get an answer to my
26) Tor support mail?</a></li>
27) <li><a href="#WhySlow">Why is Tor so slow?</a></li>
28) <li><a href="#Funding">What would The Tor Project do with more
29) funding?</a></li>

30) </ul>
31) 

32) <p>Compilation and Installation:</p>
33) 
34) <p>Running Tor:</p>
35) 
36) <p>Running a Tor client:</p>
37) 
38) <p>Running a Tor relay:</p>
39) 
40) <p>Running a Tor hidden service:</p>
41) 

42) <p>Anonymity and Security:</p>
43) <ul>

44) <li><a href="#KeyManagement">Tell me about all the keys Tor uses.</a></li>

45) </ul>
46) 

47) <p>For other questions not yet on this version of the FAQ, see the <a
48) href="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ">wiki
49) FAQ</a> for now.</p>
50) 

51) <hr />
52) 
53) <a id="General"></a>
54) 

55) <a id="WhatIsTor"></a>
56) <h3><a class="anchor" href="#WhatIsTor">What is Tor?</a></h3>
57) 
58) <p>
59) The name "Tor" can refer to several different components.
60) </p>
61) 
62) <p>
63) The Tor software is a program you can run on your computer that helps keep
64) you safe on the Internet. Tor protects you by bouncing your communications
65) around a distributed network of relays run by volunteers all around
66) the world: it prevents somebody watching your Internet connection from
67) learning what sites you visit, and it prevents the sites you visit
68) from learning your physical location. This set of volunteer relays is
69) called the Tor network. You can read more about how Tor works on the <a
70) href="<page overview>">overview page</a>.
71) </p>
72) 
73) <p>
74) The Tor Project is a non-profit (charity) organization that maintains

75) and develops the Tor software.

76) </p>
77) 

78) <a id="CompatibleApplications"></a>

79) <h3><a class="anchor" href="#CompatibleApplications">What programs can
80) I use with Tor?</a></h3>

81) 
82) <p>
83) There are two pieces to "Torifying" a program: connection-level anonymity
84) and application-level anonymity. Connection-level anonymity focuses on

85) making sure the application's Internet connections get sent through Tor.
86) This step is normally done by configuring

87) the program to use your Tor client as a "socks" proxy, but there are
88) other ways to do it too. For application-level anonymity, you need to
89) make sure that the information the application sends out doesn't hurt
90) your privacy. (Even if the connections are being routed through Tor, you
91) still don't want to include sensitive information like your name.) This
92) second step needs to be done on a program-by-program basis, which is
93) why we don't yet recommend very many programs for safe use with Tor.

94) </p>
95) 
96) <p>

97) Most of our work so far has focused on the Firefox web browser. The
98) bundles on the <a href="<page download>">download page</a> automatically
99) install the <a href="<page torbutton/index>">Torbutton Firefox
100) extension</a> if you have Firefox installed. As of version 1.2.0,
101) Torbutton now takes care of a lot of the connection-level and
102) application-level worries.

103) </p>
104) 
105) <p>

106) There are plenty of other programs you can use with Tor,
107) but we haven't researched the application-level anonymity
108) issues on them well enough to be able to recommend a safe
109) configuration. Our wiki has a list of instructions for <a

110) href="https://wiki.torproject.org/noreply/TheOnionRouter/TorifyHOWTO">Torifying

111) specific applications</a>. There's also a <a
112) href="https://wiki.torproject.org/noreply/TheOnionRouter/SupportPrograms">list
113) of applications that help you direct your traffic through Tor</a>.
114) Please add to these lists and help us keep them accurate!

115) </p>
116) 
117) <a id="WhyCalledTor"></a>
118) <h3><a class="anchor" href="#WhyCalledTor">Why is it called Tor?</a></h3>
119) 
120) <p>

121) Because Tor is the onion routing network. When we were starting the
122) new next-generation design and implementation of onion routing in
123) 2001-2002, we would tell people we were working on onion routing,
124) and they would say "Neat. Which one?" Even if onion routing has
125) become a standard household term, Tor was born out of the actual <a
126) href="http://www.onion-router.net/">onion routing project</a> run by
127) the Naval Research Lab.

128) </p>
129) 
130) <p>

131) (It's also got a fine translation from German and Turkish.)

132) </p>
133) 
134) <p>

135) Note: even though it originally came from an acronym, Tor is not spelled

136) "TOR". Only the first letter is capitalized. In fact, we can usually
137) spot people who haven't read any of our website (and have instead learned
138) everything they know about Tor from news articles) by the fact that they
139) spell it wrong.

140) </p>
141) 
142) <a id="Backdoor"></a>
143) <h3><a class="anchor" href="#Backdoor">Is there a backdoor in Tor?</a></h3>
144) 
145) <p>

146) There is absolutely no backdoor in Tor. Nobody has asked us to put one

147) in, and we know some smart lawyers who say that it's unlikely that anybody

148) will try to make us add one in our jurisdiction (U.S.). If they do

149) ask us, we will fight them, and (the lawyers say) probably win.
150) </p>
151) 
152) <p>
153) We think that putting a backdoor in Tor would be tremendously
154) irresponsible to our users, and a bad precedent for security software

155) in general. If we ever put a deliberate backdoor in our security
156) software, it would ruin our professional reputations. Nobody would

157) trust our software ever again — for excellent reason!
158) </p>
159) 
160) <p>
161) But that said, there are still plenty of subtle attacks

162) people might try. Somebody might impersonate us, or break into our
163) computers, or something like that. Tor is open source, and you should

164) always check the source (or at least the diffs since the last release)

165) for suspicious things. If we (or the distributors) don't give you

166) source, that's a sure sign something funny might be going on. You

167) should also check the <a
168) href="https://wiki.torproject.org/noreply/TheOnionRouter/VerifyingSignatures">PGP
169) signatures</a> on the releases, to make sure nobody messed with the
170) distribution sites.

171) </p>
172) 
173) <p>
174) Also, there might be accidental bugs in Tor that could affect your

175) anonymity. We periodically find and fix anonymity-related bugs, so make
176) sure you keep your Tor versions up-to-date.

177) </p>
178) 
179) <a id="DistributingTor"></a>
180) <h3><a class="anchor" href="#DistributingTor">Can I distribute Tor on

181) my magazine's CD?</a></h3>

182) 
183) <p>
184) Yes.
185) </p>
186) 
187) <p>

188) The Tor software is <a href="https://www.fsf.org/">free software</a>. This

189) means we give you the rights to redistribute the Tor software, either
190) modified or unmodified, either for a fee or gratis. You don't have to
191) ask us for specific permission.
192) </p>
193) 
194) <p>
195) However, if you want to redistribute the Tor software you must follow our

196) <a href="<svnsandbox>license">LICENSE</a>.

197) Essentially this means that you need to include our LICENSE file along
198) with whatever part of the Tor software you're distributing.
199) </p>
200) 
201) <p>
202) Most people who ask us this question don't want to distribute just the
203) Tor software, though. They want to distribute the Tor bundles, which
204) typically include <a href="http://www.privoxy.org/">Privoxy</a>
205) and <a href="http://www.vidalia-project.net/">Vidalia</a>.
206) You will need to follow the licenses for those programs
207) as well. Both of them are distributed under the <a

208) href="https://www.fsf.org/licensing/licenses/gpl.html">GNU General

209) Public License</a>. The simplest way to obey their licenses is to
210) include the source code for these programs everywhere you include
211) the bundles themselves. Look for "source" packages on the <a
212) href="http://www.vidalia-project.net/download.php">Vidalia
213) download page</a> and the <a
214) href="http://sourceforge.net/project/showfiles.php?group_id=11118">Privoxy
215) download page</a>.
216) </p>
217) 
218) <p>

219) Also, you should make sure not to confuse your readers about what Tor is,

220) who makes it, and what properties it provides (and doesn't provide). See
221) our <a href="<page trademark-faq>">trademark FAQ</a> for details.
222) </p>
223) 
224) <p>
225) Lastly, you should realize that we release new versions of the
226) Tor software frequently, and sometimes we make backward incompatible
227) changes. So if you distribute a particular version of the Tor software, it
228) may not be supported &mdash; or even work &mdash; six months later. This
229) is a fact of life for all security software under heavy development.
230) </p>
231) 
232) <a id="SupportMail"></a>
233) <h3><a class="anchor" href="#SupportMail">How can I get an answer to my
234) Tor support mail?</a></h3>
235) 
236) <p>
237) Many people send the Tor developers mail privately, or send mail to

238) our internal <a href="<page contact>">lists</a>, with questions about their

239) specific setup — they can't get their firewall working right,

240) they can't configure Privoxy correctly, or so on. Sometimes our
241) volunteers can answer these mails, but typically they need to spend
242) most of their time on development tasks that will benefit more people.
243) This is especially true if your question is already covered in the <a
244) href="<page documentation>">documentation</a> or on this FAQ. We don't
245) hate you; we're just busy.
246) </p>
247) 
248) <p>
249) So if we don't answer your mail, first check the <a href="<page
250) documentation>">documentation</a> page, along with this FAQ,
251) to make sure your question isn't already answered.  Then read <a
252) href="http://www.catb.org/~esr/faqs/smart-questions.html">"How to ask
253) questions the smart way"</a>. If this doesn't help you, note that we
254) have <a href="<page documentation>#Support">an IRC channel</a> where you
255) can ask your questions (but if they are still open-ended, ill-formed,
256) or not about Tor, you likely won't get much help there either). Lastly,
257) people on the <a href="<page documentation>#MailingLists">or-talk
258) mailing list</a> may be able to provide some hints for you, if
259) others have experienced your problems too. Be sure to look over <a
260) href="http://archives.seul.org/or/talk/">the archives</a> first.
261) </p>
262) 
263) <p>
264) Another strategy is to <a href="<page docs/tor-doc-relay>">run a Tor
265) relay for a while</a>, and/or <a href="<page donate>">donate money</a>
266) <a href="<page volunteer>">or time</a> to the effort. We're more likely
267) to pay attention to people who have demonstrated interest and commitment
268) to giving back to the Tor community.
269) </p>
270) 
271) <p>

272) If you find your answer, please stick around on the IRC channel or the

273) mailing list and answer questions from others.
274) </p>
275) 
276) <a id="WhySlow"></a>
277) <h3><a class="anchor" href="#WhySlow">Why is Tor so slow?</a></h3>
278) 
279) <p>
280) There are many reasons why the Tor network is currently slow.
281) </p>
282) 
283) <p>
284) Before we answer, though, you should realize that Tor is never going to
285) be blazing fast. Your traffic is bouncing through volunteers' computers
286) in various parts of the world, and some bottlenecks and network latency
287) will always be present. You shouldn't expect to see university-style
288) bandwidth through Tor.
289) </p>
290) 
291) <p>
292) But that doesn't mean that it can't be improved. The current Tor network
293) is quite small compared to the number of people trying to use it, and
294) many of these users don't understand or care that Tor can't currently
295) handle file-sharing traffic load.
296) </p>
297) 
298) <p>
299) What can you do to help?
300) </p>
301) 
302) <ul>
303) 
304) <li>
305) <a href="<page docs/tor-doc-relay>">Configure your Tor to relay traffic
306) for others</a>. Help make the Tor network large enough that we can handle
307) all the users who want privacy and security on the Internet.
308) </li>
309) 
310) <li>
311) <a href="<page gui/index>">Help us make Tor more usable</a>. We
312) especially need people to help make it easier to configure your Tor
313) as a relay. Also, we need help with clear simple documentation to
314) walk people through setting it up.
315) </li>
316) 
317) <li>
318) There are some bottlenecks in the current Tor network. Help us design
319) experiments to track down and demonstrate where the problems are, and
320) then we can focus better on fixing them.
321) </li>
322) 
323) <li>
324) There are some steps that individuals
325) can take to improve their Tor performance. <a
326) href="https://wiki.torproject.org/noreply/TheOnionRouter/FireFoxTorPerf">You
327) can configure your Firefox to handle Tor better</a>, <a
328) href="http://www.pps.jussieu.fr/~jch/software/polipo/tor.html">you can use
329) Polipo with Tor</a>, or you can try <a href="<page download>">upgrading
330) to the latest version of Tor</a>.  If this works well, please help by
331) documenting what you did, and letting us know about it.
332) </li>
333) 
334) <li>
335) Tor needs some architectural changes too. One important change is to

336) start providing <a
337) href="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#EverybodyARelay">better
338) service to people who relay traffic</a>. We're working on this, and
339) we'll finish faster if we get to spend more time on it.

340) </li>
341) 
342) <li>
343) Help do other things so we can do the hard stuff. Please take a moment
344) to figure out what your skills and interests are, and then <a href="<page
345) volunteer>">look at our volunteer page</a>.
346) </li>
347) 
348) <li>
349) Help find sponsors for Tor. Do you work at a company or government agency
350) that uses Tor or has a use for Internet privacy, e.g. to browse the
351) competition's websites discreetly, or to connect back to the home servers
352) when on the road without revealing affiliations? If your organization has
353) an interest in keeping the Tor network working, please contact them about
354) supporting Tor. Without sponsors, Tor is going to become even slower.
355) </li>
356) 
357) <li>
358) If you can't help out with any of the above, you can still help out
359) individually by <a href="<page donate>">donating a bit of money to the
360) cause</a>. It adds up!
361) </li>
362) 
363) </ul>
364) 
365) <a id="Funding"></a>

366) <h3><a class="anchor" href="#Funding">What would The Tor Project do with

367) more funding?</a></h3>
368) 
369) <p>
370) We have about 1500 relays right now, pushing over 150 MB/s average
371) traffic. We have several hundred thousand active users. But the Tor
372) network is not yet self-sustaining.
373) </p>
374) 
375) <p>
376) There are six main development/maintenance pushes that need attention:
377) </p>
378) 
379) <ul>
380) 
381) <li>
382) Scalability: We need to keep scaling and decentralizing the Tor
383) architecture so it can handle thousands of relays and millions of
384) users. The upcoming stable release is a major improvement, but there's
385) lots more to be done next in terms of keeping Tor fast and stable.
386) </li>
387) 
388) <li>
389) User support: With this many users, a lot of people are asking questions
390) all the time, offering to help out with things, and so on. We need good
391) clean docs, and we need to spend some effort coordinating volunteers.
392) </li>
393) 
394) <li>
395) Relay support: the Tor network is run by volunteers, but they still need
396) attention with prompt bug fixes, explanations when things go wrong,
397) reminders to upgrade, and so on. The network itself is a commons, and
398) somebody needs to spend some energy making sure the relay operators stay
399) happy. We also need to work on <a href="#RelayOS">stability</a> on some
400) platforms &mdash; e.g., Tor relays have problems on Win XP currently.
401) </li>
402) 
403) <li>
404) Usability: Beyond documentation, we also need to work on usability of the
405) software itself. This includes installers, clean GUIs, easy configuration
406) to interface with other applications, and generally automating all of
407) the difficult and confusing steps inside Tor. We've got a start on this
408) with the <a href="<page gui/index>">GUI Contest</a>, but much more work
409) remains &mdash; usability for privacy software has never been easy.
410) </li>
411) 
412) <li>
413) Incentives: We need to work on ways to encourage people to configure
414) their Tors as relays and exit nodes rather than just clients.
415) <a href="#EverybodyARelay">We need to make it easy to become a relay,
416) and we need to give people incentives to do it.</a>
417) </li>
418) 
419) <li>
420) Research: The anonymous communications field is full
421) of surprises and gotchas. In our copious free time, we
422) also help run top anonymity and privacy conferences like <a
423) href="http://petsymposium.org/">PETS</a>. We've identified a set of
424) critical <a href="<page volunteer>#Research">Tor research questions</a>
425) that will help us figure out how to make Tor secure against the variety of
426) attacks out there. Of course, there are more research questions waiting
427) behind these.
428) </li>
429) 
430) </ul>
431) 
432) <p>
433) We're continuing to move forward on all of these, but at this rate
434) <a href="#WhySlow">the Tor network is growing faster than the developers
435) can keep up</a>.
436) Now would be an excellent time to add a few more developers to the effort
437) so we can continue to grow the network.
438) </p>
439) 
440) <p>
441) We are also excited about tackling related problems, such as
442) censorship-resistance.
443) </p>
444) 
445) <p>
446) We are proud to have <a href="<page sponsors>">sponsorship and support</a>
447) from the Omidyar Network, the International Broadcasting Bureau, Bell
448) Security Solutions, the Electronic Frontier Foundation, several government
449) agencies and research groups, and hundreds of private contributors.
450) </p>
451) 
452) <p>
453) However, this support is not enough to keep Tor abreast of changes in the
454) Internet privacy landscape. Please <a href="<page donate>">donate</a>
455) to the project, or <a href="<page contact>">contact</a> our executive
456) director for information on making grants or major donations.
457) </p>
458) 
459) <hr />
460) 

461) <a id="KeyManagement"></a>

462) <h3><a class="anchor" href="#KeyManagement">Tell me about all the keys
463) Tor uses.</a></h3>

464) 
465) <p>

466) Tor uses a variety of different keys, with three goals in mind: 1)

467) encryption to ensure privacy of data within the Tor network, 2)
468) authentication so clients know they're
469) talking to the relays they meant to talk to, and 3) signatures to make
470) sure all clients know the same set of relays.

471) </p>
472) 
473) <p>
474) <b>Encryption</b>: first, all connections in Tor use TLS link encryption,
475) so observers can't look inside to see which circuit a given cell is
476) intended for. Further, the Tor client establishes an ephemeral encryption
477) key with each relay in the circuit, so only the exit relay can read
478) the cells. Both sides discard the circuit key when the circuit ends,
479) so logging traffic and then breaking into the relay to discover the key
480) won't work.
481) </p>
482) 
483) <p>
484) <b>Authentication</b>:
485) Every Tor relay has a public decryption key called the "onion key".
486) When the Tor client establishes circuits, at each step it <a
487) href="<svnsandbox>doc/design-paper/tor-design.html#subsec:circuits">demands
488) that the Tor relay prove knowledge of its onion key</a>. That way

489) the first node in the path can't just spoof the rest of the path.

490) Each relay rotates its onion key once a week.

491) </p>
492) 
493) <p>

494) <b>Coordination</b>:

495) How do clients know what the relays are, and how do they know that they

496) have the right keys for them? Each relay has a long-term public signing
497) key called the "identity key". Each directory authority additionally has a
498) "directory signing key". The directory authorities provide a signed list
499) of all the known relays, and in that list are a set of certificates from
500) each relay (self-signed by their identity key) specifying their keys,
501) locations, exit policies, and so on. So unless the adversary can control
502) a threshold of the directory authorities, he can't trick the Tor client
503) into using other Tor relays.

504) </p>
505) 
506) <p>

507) How do clients know what the directory authorities are? The Tor software
508) comes with a built-in list of location and public key for each directory
509) authority. So the only way to trick users into using a fake Tor network

510) is to give them a specially modified version of the software.
511) </p>

512) 

513) <p>
514) How do users know they've got the right software? When we distribute
515) the source code or a package, we digitally sign it with <a

516) href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a

517) href="https://wiki.torproject.org/noreply/TheOnionRouter/VerifyingSignatures">instructions
518) on how to check Tor's signatures</a>.
519) </p>

520) 

521) <p>

522) In order to be certain that it's really signed by us, you need to have
523) met us in person and gotten a copy of our GPG key fingerprint, or you
524) need to know somebody who has. If you're concerned about an attack on
525) this level, we recommend you get involved with the security community
526) and start meeting people.

527) </p>

528) 

529) <hr />

530) 

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