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5) #include "head.wmi" TITLE="Tor FAQ" CHARSET="UTF-8"

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7) <div class="main-column">
8) 
9) <!-- PUT CONTENT AFTER THIS TAG -->
10) 

11) <h2>Tor FAQ</h2>
12) <hr />

13) 

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

15) <ul>

16) <li><a href="#WhatIsTor">What is Tor?</a></li>

17) <li><a href="#Torisdifferent">How is Tor different from other proxies?</a></li>

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

29) </ul>
30) 

31) <p>Compilation and Installation:</p>

32) <ul>
33) <li><a href="#HowUninstallTor">How do I uninstall Tor?</a></li>

34) <li><a href="#PGPSigs">What are these "sig" files on the download
35) page?</a></li>

36) <li><a href="#CompileTorWindows">How do I compile Tor under Windows?</a></li>

37) <li><a href="#VirusFalsePositives">Why does my Tor executable appear to
38) have a virus or spyware?</a></li>

39) <li><a href="#LiveCD">Is there a LiveCD or other bundle that includes Tor?</a></li>

40) </ul>

41) 
42) <p>Running Tor:</p>
43) 
44) <p>Running a Tor client:</p>

45) <ul>

46) <li><a href="#DoesntWork">I installed Tor and Polipo but it's not
47) working.</a></li>
48) <li><a href="#VidaliaPassword">Tor/Vidalia prompts for a password at
49) start.</a></li>
50) <li><a href="#ChooseEntryExit">Can I control which nodes (or country)
51) are used for entry/exit?</a></li>
52) <li><a href="#GoogleCaptcha">Google makes me solve a Captcha or tells
53) me I have spyware installed.</a></li>

54) <li><a href="#GmailWarning">Gmail warns me that my account may have
55) been compromised.</a></li>

56) </ul>

57) 
58) <p>Running a Tor relay:</p>

59) <ul>

60) <li><a href="#RelayFlexible">How stable does my relay need to be?</a></li>

61) <li><a href="#ExitPolicies">I'd run a relay, but I don't want to deal

62) with abuse issues.</a></li>

63) <li><a href="#RelayOrBridge">Should I be a normal relay or bridge
64) relay?</a></li>

65) <li><a href="#RelayMemory">Why is my Tor relay using so much memory?</a></li>

66) <li><a href="#WhyNotNamed">Why is my Tor relay not named?</a></li>

67) </ul>

68) 
69) <p>Running a Tor hidden service:</p>
70) 

71) <p>Anonymity and Security:</p>
72) <ul>

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

74) </ul>
75) 

76) <p>Alternate designs that we don't do (yet):</p>
77) <ul>
78) <li><a href="#EverybodyARelay">You should make every Tor user be a
79) relay.</a></li>
80) </ul>
81) 

82) <p>Abuse</p>
83) <ul>
84) <li><a href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></li>
85) <li><a href="#RespondISP">How do I respond to my ISP about my exit
86) relay?</a></li>
87) </ul>
88) 

89) <p>For other questions not yet on this version of the FAQ, see the <a

90) href="<wiki>TorFAQ">wiki

91) FAQ</a> for now.</p>
92) 

93) <hr />
94) 
95) <a id="General"></a>
96) 

97) <a id="WhatIsTor"></a>
98) <h3><a class="anchor" href="#WhatIsTor">What is Tor?</a></h3>
99) 
100) <p>
101) The name "Tor" can refer to several different components.
102) </p>
103) 
104) <p>
105) The Tor software is a program you can run on your computer that helps keep
106) you safe on the Internet. Tor protects you by bouncing your communications
107) around a distributed network of relays run by volunteers all around
108) the world: it prevents somebody watching your Internet connection from
109) learning what sites you visit, and it prevents the sites you visit
110) from learning your physical location. This set of volunteer relays is
111) called the Tor network. You can read more about how Tor works on the <a
112) href="<page overview>">overview page</a>.
113) </p>
114) 
115) <p>
116) The Tor Project is a non-profit (charity) organization that maintains

117) and develops the Tor software.

118) </p>
119) 

120) <hr />
121) 

122) <a id="Torisdifferent"></a>
123) <h3><a class="anchor" href="#Torisdifferent">How is Tor different from other proxies?</a></h3>
124) <p>
125) A typical proxy provider sets up a server somewhere on the Internet and allows you to use it to relay your traffic.  This creates a simple, easy to maintain architecture.  The users all enter and leave through the same server.  The provider may charge for use of the proxy, or fund their costs through advertisements on the server.  In the simplest configuration, you don't have to install anything.  You just have to point your browser at their proxy server.  Simple proxy providers are fine solutions if you do not want protections for your privacy and anonymity online and you trust the provider from doing bad things.  Some simple proxy providers use SSL to secure your connection to them.  This may protect you against local eavesdroppers, such as those at a cafe with free wifi Internet.
126) </p>
127) <p>
128) Simple proxy providers also create a single point of failure.  The provider knows who you are and where you browse on the Internet.  They can see your traffic as it passes through their server.  In some cases, they can see your encrypted traffic as they relay it to your banking site or to ecommerce stores.  You have to trust the provider isn't doing any number of things, such as watching your traffic, injecting their own advertisements into your traffic stream, and isn't recording your personal details.
129) </p>
130) <p>
131) Tor passes your traffic through at least 3 different servers before sending it on to the destination.  Tor does not modify, or even know, what you are sending into it.  It merely relays your traffic, completely encrypted through the Tor network and has it pop out somewhere else in the world, completely intact.  The Tor client is required because we assume you trust your local computer.  The Tor client manages the encryption and the path chosen through the network.  The relays located all over the world merely pass encrypted packets between themselves.</p>
132) <p>

133) <dl>

134) <dt>Doesn't the first server see who I am?</dt><dd>Possibly. A bad first of three servers can see encrypted Tor traffic coming from your computer.  It still doesn't know who you are and what you are doing over Tor.  It merely sees "This IP address is using Tor".  Tor is not illegal anywhere in the world, so using Tor by itself is fine.  You are still protected from this node figuring out who you are and where you are going on the Internet.</dd>

135) <dt>Can't the third server see my traffic?</dt><dd>Possibly.  A bad third of three servers can see the traffic you sent into Tor.  It won't know who sent this traffic.  If you're using encryption, such as visiting a bank or e-commerce website, or encrypted mail connections, etc, it will only know the destination.  It won't be able to see the data inside the traffic stream.  You are still protected from this node figuring out who you are and if using encryption, what data you're sending to the destination.</dd>

136) </dl>

137) </p>
138) 

139) <hr />
140) 

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

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

144) 
145) <p>
146) There are two pieces to "Torifying" a program: connection-level anonymity
147) and application-level anonymity. Connection-level anonymity focuses on

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

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

157) </p>
158) 
159) <p>

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

166) </p>
167) 
168) <p>

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

173) href="<wiki>TorifyHOWTO">Torifying

174) specific applications</a>. There's also a <a

175) href="<wiki>SupportPrograms">list

176) of applications that help you direct your traffic through Tor</a>.
177) Please add to these lists and help us keep them accurate!

178) </p>
179) 

180) <hr />
181) 

182) <a id="WhyCalledTor"></a>
183) <h3><a class="anchor" href="#WhyCalledTor">Why is it called Tor?</a></h3>
184) 
185) <p>

186) Because Tor is the onion routing network. When we were starting the
187) new next-generation design and implementation of onion routing in
188) 2001-2002, we would tell people we were working on onion routing,
189) and they would say "Neat. Which one?" Even if onion routing has
190) become a standard household term, Tor was born out of the actual <a
191) href="http://www.onion-router.net/">onion routing project</a> run by
192) the Naval Research Lab.

193) </p>
194) 
195) <p>

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

197) </p>
198) 
199) <p>

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

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

205) </p>
206) 

207) <hr />
208) 

209) <a id="Backdoor"></a>
210) <h3><a class="anchor" href="#Backdoor">Is there a backdoor in Tor?</a></h3>
211) 
212) <p>

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

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

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

216) ask us, we will fight them, and (the lawyers say) probably win.
217) </p>
218) 
219) <p>
220) We think that putting a backdoor in Tor would be tremendously
221) irresponsible to our users, and a bad precedent for security software

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

224) trust our software ever again — for excellent reason!
225) </p>
226) 
227) <p>
228) But that said, there are still plenty of subtle attacks

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

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

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

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

234) should also check the <a href="<page verifying-signatures>">PGP

235) signatures</a> on the releases, to make sure nobody messed with the
236) distribution sites.

237) </p>
238) 
239) <p>
240) Also, there might be accidental bugs in Tor that could affect your

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

243) </p>
244) 

245) <hr />
246) 

247) <a id="DistributingTor"></a>
248) <h3><a class="anchor" href="#DistributingTor">Can I distribute Tor on

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

250) 
251) <p>
252) Yes.
253) </p>
254) 
255) <p>

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

257) means we give you the rights to redistribute the Tor software, either
258) modified or unmodified, either for a fee or gratis. You don't have to
259) ask us for specific permission.
260) </p>
261) 
262) <p>
263) However, if you want to redistribute the Tor software you must follow our

264) <a href="<gitblob>LICENSE">LICENSE</a>.

265) Essentially this means that you need to include our LICENSE file along
266) with whatever part of the Tor software you're distributing.
267) </p>
268) 
269) <p>
270) Most people who ask us this question don't want to distribute just the
271) Tor software, though. They want to distribute the Tor bundles, which

272) typically include <a href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a>

273) and <a href="<page vidalia/index>">Vidalia</a>.

274) You will need to follow the licenses for those programs
275) as well. Both of them are distributed under the <a

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

277) Public License</a>. The simplest way to obey their licenses is to
278) include the source code for these programs everywhere you include
279) the bundles themselves. Look for "source" packages on the <a

280) href="<page vidalia/index>">Vidalia page</a> and the <a

281) href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo

282) download page</a>.
283) </p>
284) 
285) <p>

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

287) who makes it, and what properties it provides (and doesn't provide). See
288) our <a href="<page trademark-faq>">trademark FAQ</a> for details.
289) </p>
290) 
291) <p>
292) Lastly, you should realize that we release new versions of the
293) Tor software frequently, and sometimes we make backward incompatible
294) changes. So if you distribute a particular version of the Tor software, it
295) may not be supported &mdash; or even work &mdash; six months later. This
296) is a fact of life for all security software under heavy development.
297) </p>
298) 

299) <hr />
300) 

301) <a id="SupportMail"></a>
302) <h3><a class="anchor" href="#SupportMail">How can I get an answer to my
303) Tor support mail?</a></h3>
304) 
305) <p>
306) Many people send the Tor developers mail privately, or send mail to

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

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

309) they can't configure Polipo correctly, or so on. Sometimes our

310) volunteers can answer these mails, but typically they need to spend
311) most of their time on development tasks that will benefit more people.
312) This is especially true if your question is already covered in the <a

313) href="<page documentation>">documentation</a> or on this FAQ.

314) </p>
315) 
316) <p>
317) So if we don't answer your mail, first check the <a href="<page
318) documentation>">documentation</a> page, along with this FAQ,
319) to make sure your question isn't already answered.  Then read <a
320) href="http://www.catb.org/~esr/faqs/smart-questions.html">"How to ask
321) questions the smart way"</a>. If this doesn't help you, note that we
322) have <a href="<page documentation>#Support">an IRC channel</a> where you
323) can ask your questions (but if they are still open-ended, ill-formed,
324) or not about Tor, you likely won't get much help there either). Lastly,
325) people on the <a href="<page documentation>#MailingLists">or-talk
326) mailing list</a> may be able to provide some hints for you, if
327) others have experienced your problems too. Be sure to look over <a
328) href="http://archives.seul.org/or/talk/">the archives</a> first.
329) </p>
330) 
331) <p>
332) Another strategy is to <a href="<page docs/tor-doc-relay>">run a Tor
333) relay for a while</a>, and/or <a href="<page donate>">donate money</a>
334) <a href="<page volunteer>">or time</a> to the effort. We're more likely
335) to pay attention to people who have demonstrated interest and commitment
336) to giving back to the Tor community.
337) </p>
338) 
339) <p>

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

341) mailing list and answer questions from others.
342) </p>
343) 

344) <hr />
345) 

346) <a id="WhySlow"></a>
347) <h3><a class="anchor" href="#WhySlow">Why is Tor so slow?</a></h3>
348) 
349) <p>
350) There are many reasons why the Tor network is currently slow.
351) </p>
352) 
353) <p>
354) Before we answer, though, you should realize that Tor is never going to
355) be blazing fast. Your traffic is bouncing through volunteers' computers
356) in various parts of the world, and some bottlenecks and network latency
357) will always be present. You shouldn't expect to see university-style
358) bandwidth through Tor.
359) </p>
360) 
361) <p>
362) But that doesn't mean that it can't be improved. The current Tor network
363) is quite small compared to the number of people trying to use it, and
364) many of these users don't understand or care that Tor can't currently
365) handle file-sharing traffic load.
366) </p>
367) 

368) <p>
369) For the much more in-depth answer, see <a

370) href="<blog>why-tor-is-slow">Roger's blog

371) post on the topic</a>, which includes both a detailed PDF and a video
372) to go with it.
373) </p>
374) 

375) <p>
376) What can you do to help?
377) </p>
378) 
379) <ul>
380) 
381) <li>
382) <a href="<page docs/tor-doc-relay>">Configure your Tor to relay traffic
383) for others</a>. Help make the Tor network large enough that we can handle
384) all the users who want privacy and security on the Internet.
385) </li>
386) 
387) <li>
388) <a href="<page gui/index>">Help us make Tor more usable</a>. We
389) especially need people to help make it easier to configure your Tor
390) as a relay. Also, we need help with clear simple documentation to
391) walk people through setting it up.
392) </li>
393) 
394) <li>
395) There are some bottlenecks in the current Tor network. Help us design
396) experiments to track down and demonstrate where the problems are, and
397) then we can focus better on fixing them.
398) </li>
399) 
400) <li>
401) There are some steps that individuals
402) can take to improve their Tor performance. <a

403) href="<wiki>FireFoxTorPerf">You

404) can configure your Firefox to handle Tor better</a>, <a
405) href="http://www.pps.jussieu.fr/~jch/software/polipo/tor.html">you can use
406) Polipo with Tor</a>, or you can try <a href="<page download>">upgrading
407) to the latest version of Tor</a>.  If this works well, please help by
408) documenting what you did, and letting us know about it.
409) </li>
410) 
411) <li>
412) Tor needs some architectural changes too. One important change is to

413) start providing <a href="#EverybodyARelay">better service to people who
414) relay traffic</a>. We're working on this, and we'll finish faster if we
415) get to spend more time on it.

416) </li>
417) 
418) <li>
419) Help do other things so we can do the hard stuff. Please take a moment
420) to figure out what your skills and interests are, and then <a href="<page
421) volunteer>">look at our volunteer page</a>.
422) </li>
423) 
424) <li>
425) Help find sponsors for Tor. Do you work at a company or government agency
426) that uses Tor or has a use for Internet privacy, e.g. to browse the
427) competition's websites discreetly, or to connect back to the home servers
428) when on the road without revealing affiliations? If your organization has
429) an interest in keeping the Tor network working, please contact them about
430) supporting Tor. Without sponsors, Tor is going to become even slower.
431) </li>
432) 
433) <li>
434) If you can't help out with any of the above, you can still help out
435) individually by <a href="<page donate>">donating a bit of money to the
436) cause</a>. It adds up!
437) </li>
438) 
439) </ul>
440) 

441) <hr />
442) 

443) <a id="Funding"></a>

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

445) more funding?</a></h3>
446) 
447) <p>

448) We have about 1800 relays right now, pushing over 150 MB/s average

449) traffic. We have several hundred thousand active users. But the Tor
450) network is not yet self-sustaining.
451) </p>
452) 
453) <p>
454) There are six main development/maintenance pushes that need attention:
455) </p>
456) 
457) <ul>
458) 
459) <li>
460) Scalability: We need to keep scaling and decentralizing the Tor
461) architecture so it can handle thousands of relays and millions of
462) users. The upcoming stable release is a major improvement, but there's
463) lots more to be done next in terms of keeping Tor fast and stable.
464) </li>
465) 
466) <li>
467) User support: With this many users, a lot of people are asking questions
468) all the time, offering to help out with things, and so on. We need good
469) clean docs, and we need to spend some effort coordinating volunteers.
470) </li>
471) 
472) <li>
473) Relay support: the Tor network is run by volunteers, but they still need
474) attention with prompt bug fixes, explanations when things go wrong,
475) reminders to upgrade, and so on. The network itself is a commons, and
476) somebody needs to spend some energy making sure the relay operators stay
477) happy. We also need to work on <a href="#RelayOS">stability</a> on some
478) platforms &mdash; e.g., Tor relays have problems on Win XP currently.
479) </li>
480) 
481) <li>
482) Usability: Beyond documentation, we also need to work on usability of the
483) software itself. This includes installers, clean GUIs, easy configuration
484) to interface with other applications, and generally automating all of
485) the difficult and confusing steps inside Tor. We've got a start on this
486) with the <a href="<page gui/index>">GUI Contest</a>, but much more work
487) remains &mdash; usability for privacy software has never been easy.
488) </li>
489) 
490) <li>
491) Incentives: We need to work on ways to encourage people to configure
492) their Tors as relays and exit nodes rather than just clients.
493) <a href="#EverybodyARelay">We need to make it easy to become a relay,
494) and we need to give people incentives to do it.</a>
495) </li>
496) 
497) <li>
498) Research: The anonymous communications field is full
499) of surprises and gotchas. In our copious free time, we
500) also help run top anonymity and privacy conferences like <a
501) href="http://petsymposium.org/">PETS</a>. We've identified a set of
502) critical <a href="<page volunteer>#Research">Tor research questions</a>
503) that will help us figure out how to make Tor secure against the variety of
504) attacks out there. Of course, there are more research questions waiting
505) behind these.
506) </li>
507) 
508) </ul>
509) 
510) <p>
511) We're continuing to move forward on all of these, but at this rate
512) <a href="#WhySlow">the Tor network is growing faster than the developers
513) can keep up</a>.
514) Now would be an excellent time to add a few more developers to the effort
515) so we can continue to grow the network.
516) </p>
517) 
518) <p>
519) We are also excited about tackling related problems, such as
520) censorship-resistance.
521) </p>
522) 
523) <p>
524) We are proud to have <a href="<page sponsors>">sponsorship and support</a>
525) from the Omidyar Network, the International Broadcasting Bureau, Bell
526) Security Solutions, the Electronic Frontier Foundation, several government
527) agencies and research groups, and hundreds of private contributors.
528) </p>
529) 
530) <p>
531) However, this support is not enough to keep Tor abreast of changes in the
532) Internet privacy landscape. Please <a href="<page donate>">donate</a>
533) to the project, or <a href="<page contact>">contact</a> our executive
534) director for information on making grants or major donations.
535) </p>
536) 
537) <hr />
538) 

539) <a id="HowUninstallTor"></a>
540) <h3><a class="anchor" href="#HowUninstallTor">How do I uninstall Tor?</a></h3>
541) 
542) <p>
543) This depends entirely on how you installed it and which operating system you
544) have. If you installed a package, then hopefully your package has a way to

545) uninstall itself. The Windows packages include uninstallers. The proper way to

546) completely remove Tor, Vidalia, Torbutton for Firefox, and Polipo on any

547) version of Windows is as follows:
548) </p>
549) 
550) <ol>
551) <li>In your taskbar, right click on Vidalia (the green onion or the black head)
552) and choose exit.</li>
553) <li>Right click on the taskbar to bring up TaskManager. Look for tor.exe in the
554) Process List. If it's running, right click and choose End Process.</li>
555) <li>Click the Start button, go to Programs, go to Vidalia, choose Uninstall.

556) This will remove the Vidalia bundle, which includes Tor and Polipo.</li>

557) <li>Start Firefox. Go to the Tools menu, choose Add-ons. Select Torbutton.
558) Click the Uninstall button.</li>

559) </ol>

560) 
561) <p>

562) If you do not follow these steps (for example by trying to uninstall

563) Vidalia, Tor, and Polipo while they are still running), you will need to

564) reboot and manually remove the directory "Program Files\Vidalia Bundle".

565) </p>
566) 
567) <p>
568) For Mac OS X, follow the <a

569) href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.

570) </p>
571) 
572) <p>
573) If you installed by source, I'm afraid there is no easy uninstall method. But
574) on the bright side, by default it only installs into /usr/local/ and it should
575) be pretty easy to notice things there.
576) </p>
577) 
578) <hr />
579) 

580) <a id="PGPSigs"></a>
581) <h3><a class="anchor" href="#PGPSigs">What are these "sig" files on the
582) download page?</a></h3>

583) 
584) <p>
585) These are PGP signatures, so you can verify that the file you've downloaded is
586) exactly the one that we intended you to get.
587) </p>
588) 
589) <p>
590) Please read the <a

591) href="<page verifying-signatures>">verifying signatures</a> page for details.

592) </p>
593) 
594) <hr />
595) 
596) <a id="CompileTorWindows"></a>
597) <h3><a class="anchor" href="#CompileTorWindows">How do I compile Tor under
598) Windows?</a></h3>
599) 
600) <p>

601) Try following the steps at <a href="<gitblob>doc/tor-win32-mingw-creation.txt">
602) tor-win32-mingw-creation.txt</a>.

603) </p>
604) 

605) <p>
606) (Note that you don't need to compile Tor yourself in order to use
607) it. Most people just use the packages available on the <a href="<page
608) download>">download page</a>.)
609) </p>
610) 

611) <hr />
612) 

613) <a id="VirusFalsePositives"></a>
614) <h3><a class="anchor" href="#VirusFalsePositives">Why does my Tor
615) executable appear to have a virus or spyware?</a></h3>

616) 
617) <p>
618) Sometimes, overzealous Windows virus and spyware detectors trigger on some
619) parts of the Tor Windows binary. Our best guess is that these are false

620) positives — after all, the anti-virus and anti-spyware business is just a

621) guessing game anyway. You should contact your vendor and explain that you have
622) a program that seems to be triggering false positives. Or pick a better vendor.
623) </p>
624) 
625) <p>

626) In the meantime, we encourage you to not just take our word for
627) it. Our job is to provide the source; if you're concerned, please do <a
628) href="#CompileTorWindows">recompile it yourself</a>.

629) </p>
630) 
631) <hr />
632) 
633) <a id="LiveCD"></a>
634) <h3><a class="anchor" href="#LiveCD">Is there a LiveCD or other bundle that
635) includes Tor?</a></h3>
636) 
637) <p>
638) There isn't any official LiveCD at this point. We're still trying to find good
639) solutions and trying to understand the security and anonymity implications of
640) the various options. In the mean time, feel free to check out the list below
641) and use your best judgement:
642) </p>
643) 
644) <p>

645) LiveCDs:

646) </p>
647) 
648) <ol>

649) <li><a href="https://amnesia.boum.org/">The (Amnesic) Incognito Live
650) System</a> is a Live System aimed at preserving your privacy and
651) anonymity:

652) <ul>
653) <li> All outgoing connections to the Internet are forced to go through
654) the Tor network.</li>
655) <li> No trace is left on local storage devices unless explicitely asked.</li>
656) <li> It includes Firefox, Tor, Torbutton, Vidalia graphical Tor
657) controller, Pidgin Instant Messaging client, and lots of other
658) software.</li>
659) <li> It's based upon Debian gnu/linux and comes with the GNOME desktop
660) environment.</li>
661) </ul>

662) <li><a href="http://tork.sourceforge.net/wiki/index.php/LiveCD">TorK LiveCD</a>
663) is Knoppix-based with an emphasis on user-friendliness. You can work
664) anonymously or non-anonymously while TorK tries to keep you informed of the
665) consequences of your activity. The TorK LiveCD is experimental, so the aim is
666) to provide regular releases through 2007 and beyond.</li>

667) <li><a href="http://mandalka.name/privatix/">Privatix LiveCD/USB</a> is a
668) debian based live-system including tor, firefox and torbutton which can save
669) bookmarks and other settings or data on an encrypted usb-key</li>

670) </li>

671) </ol>
672) 
673) <p>
674) Windows bundles:
675) </p>
676) 
677) <ol>

678) <li><a href="<page torbrowser/index>">Tor Browser Bundle</a>

679) for Windows comes with a pre-configured web browser and is self contained
680) so you can run it from a USB stick.</li>
681) <li><a href="http://janusvm.com/">JanusVM</a> is a Linux kernel and software
682) running in VMWare that sits between your Windows computer and the Internet,
683) making sure that your Internet traffic is scrubbed and anonymized.</li>

684) </ol>
685) 
686) <p>
687) Not currently maintained as far as we know:
688) </p>
689) 
690) <ol>

691) <li>Polippix / Privatlivets Fred is a Danish Knoppix-based LiveCD with Tor
692) and utilities to encrypt IP-telephony. <a href="http://polippix.org/">Info and
693) download</a>.</li>

694) <li>ELE is a Linux LiveCD which is focused on privacy related
695) software. It includes Tor and you can download it at
696) <a
697) href="http://www.northernsecurity.net/download/ele/">http://www.northernsecurity.net/download/ele/</a>.</li>
698) <li>Anonym.OS is a LiveCD similar to the above but is based on OpenBSD rather
699) than Linux for maximum security. It was designed to be anonymous and secure
700) from the ground up, and thus has some features and limitations not found in
701) other LiveCDs (Tor related or otherwise). You can obtain more information and

702) download Anonym.OS from <a href="http://theory.kaos.to/projects.html">Kaos.Theory</a>.</li>

703) <li>Phantomix is a LiveCD for anonymous surfing and chatting based on the most

704) recent KNOPPIX release. It comes preconfigured with Privoxy, Tor and Polipo. You can

705) get it from the <a href="http://phantomix.ytternhagen.de/">Phantomix
706) Website</a>.</li>
707) </ol>
708) 

709) <p>
710) Please contact us if you know any others.
711) </p>
712) 

713) <hr />
714) 

715) <a id="DoesntWork"></a>
716) <h3><a class="anchor" href="#DoesntWork">I installed Tor and Polipo but
717) it's not working.</a></h3>
718) 
719) <p>

720) Once you've installed the Tor bundle, there are two questions to ask:

721) first, is your Tor able to establish a circuit? Second, is your

722) Firefox correctly configured to send its traffic through Tor?

723) </p>
724) 

725) <p>If Tor can establish a circuit, the onion icon in
726) Vidalia will turn green. You can also check in the Vidalia
727) Control Panel to make sure it says "Connected to the Tor
728) network!" under Status. For those not using Vidalia, check your <a
729) href="<wiki>TorFAQ#HowdoIsetuploggingorseeTorslogs">Tor logs</a> for
730) a line saying that Tor "has successfully opened a circuit. Looks like
731) client functionality is working."

732) </p>
733) 
734) <p>

735) If Tor can't establish a circuit, here are some hints:

736) </p>
737) 

738) <ol>
739) <li>Are you sure Tor is running? If you're using Vidalia, you may have
740) to click on the onion and select "Start" to launch Tor.</li>
741) <li>Check your system clock. If it's more than a few hours off, Tor will

742) refuse to build circuits. For XP users, synchronize your clock under
743) the clock -> Internet time tab. In addition, correct the day and date

744) under the 'Date &amp; Time' Tab.</li>
745) <li>Is your Internet connection <a

746) href="<wiki>TorFAQ#Myfirewallonlyallowsafewoutgoingports.">firewalled</a>,
747) or do you normally need to use a <a
748) href="<wiki>TorFAQ#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</a>?

749) </li>
750) <li>Are you running programs like Norton Internet Security or SELinux that
751) block certain connections, even though you don't realize they do? They
752) could be preventing Tor from making network connections.</li>
753) <li>Are you in China, or behind a restrictive corporate network firewall
754) that blocks the public Tor relays? If so, you should learn about <a
755) href="<page bridges>">Tor bridges</a>.</li>
756) <li>Check your <a href="<wiki>TorFAQ#HowdoIsetuploggingorseeTorslogs">Tor
757) logs</a>. Do they give you any hints about what's going wrong?</li>
758) </ol>

759) 
760) <p>

761) Step two is to confirm that Firefox is correctly configured to send its
762) traffic through Tor. Try the <a href="https://check.torproject.org/">Tor
763) Check</a> site and see whether it thinks you are using Tor. See <a
764) href="<wiki>TorFAQ#HowcanItellifTorisworkingandthatmyconnectionsreallyareanonymizedArethereexternalserversthatwilltestmyconnection">the
765) Tor check FAQ entry</a> for details.

766) <p>
767) 
768) <p>

769) If it thinks you're not using Tor, here are some hints:

770) </p>
771) 

772) <ol>
773) <li>Did you install the Torbutton extension for Firefox? The installation
774) bundles include it, but sometimes people forget to install it. Make sure
775) it says "Tor enabled" at the bottom right of your Firefox window. (For
776) expert users, make sure your http proxy is set to localhost port
777) 8118.)</li>

778) <li>Do you have incompatible Firefox extensions like FoxyProxy
779) installed? If so, uninstall them. (Note that using FoxyProxy is NOT

780) a sufficient substitute for Torbutton. There are many known attacks
781) against a browser setup that does not include Torbutton. Read more
782) in the <a href="<page torbutton/faq>">Torbutton FAQ</a> and the <a
783) href="https://www.torproject.org/torbutton/design/">Torbutton design</a>
784) specification.)</li>

785) <li>Check that Polipo (the http proxy that passes traffic between Firefox
786) and Tor) is running. On Windows, look in the task manager and check for

787) a polipo.exe. On OS X, open the utilities folder in your applications
788) folder, and open Terminal.app. Then run "ps aux|grep polipo".</li>

789) <li>If you're upgrading from OS X, some of the earlier OS X installers
790) were broken in really unfortunate ways. You may find that <a href="<page
791) docs/tor-doc-osx>#uninstall">uninstalling everything</a> and then
792) installing a fresh bundle helps. Alas, the current uninstall instructions
793) may not apply anymore to your old bundle. Sorry.</li>

794) <li>If you're on Linux, make sure Privoxy isn't running, since it will
795) conflict with the port that our Polipo configuration file picks.</li>
796) <li>If you installed Polipo yourself (not from a bundle), did you edit the
797) config file as described? Did you restart Polipo after this change?</li>
798) <li>For Red Hat Linux and related systems, do you have SELinux enabled? If
799) so, it might be preventing Polipo from talking to Tor. We also run across
800) BSD users periodically who have local firewall rules that prevent some
801) connections to localhost.</li>
802) </ol>
803) 

804) <hr />
805) 

806) <a id="VidaliaPassword"></a>
807) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for

808) a password at start.</a></h3>

809) 
810) <p>

811) Vidalia interacts with the Tor software via Tor's "control port". The
812) control port lets Vidalia receive status updates from Tor, request a new
813) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
814) Vidalia sets a random password for Tor's control port to prevent other
815) applications from also connecting to the control port and potentially
816) compromising your anonymity.
817) </p>
818) 
819) <p>
820) Usually this process of generating and setting a random control password

821) happens in the background. There are three common situations, though,

822) where Vidalia may prompt you for a password:

823) </p>
824) 

825) <ol>

826) <li>You're already running Vidalia and Tor. For example, this situation
827) can happen if you installed the Vidalia bundle and now you're trying to
828) run the Tor Browser Bundle. In that case, you'll need to close the old
829) Vidalia and Tor before you can run this one.
830) </li>

831) <li>Vidalia crashed, but left Tor running with the last known random
832) password. After you restart Vidalia, it generates a new random password,
833) but Vidalia can't talk to Tor, because the random passwords are different.
834) <br />
835) If the dialog that prompts you for a control password has a Reset button,
836) you can click the button and Vidalia will restart Tor with a new random
837) control password.
838) <br />
839) If you do not see a Reset button, or if Vidalia is unable to restart
840) Tor for you, you can still fix the problem manually. Simply go into your
841) process or task manager, and terminate the Tor process. Then use Vidalia
842) to restart Tor and all will work again.
843) </li>

844) <li>You had previously set Tor to run as a Windows NT service. When Tor
845) is set to

846) run as a service, it starts up when the system boots. If you configured
847) Tor to start as a service through Vidalia, a random password was set
848) and saved in Tor. When you reboot, Tor starts up and uses the random
849) password it saved. You login and start up Vidalia. Vidalia attempts to
850) talk to the already running Tor. Vidalia generates a random password,
851) but it is different than the saved password in the Tor service.
852) <br />
853) You need to reconfigure Tor to not be a service. See the FAQ entry on

854) <a href="<wiki>TorFAQ#HowdoIrunmyTorrelayasanNTservice">running Tor as a Windows NT service</a>

855) for more information on how to remove the Tor service.
856) </li>

857) </ol>

858) 
859) <hr />
860) 

861) <a id="ChooseEntryExit"></a>
862) <h3><a class="anchor" href="#ChooseEntryExit">Can I control which nodes (or country) are used for entry/exit?</a></h3>
863) 
864) <p>
865) Yes. You can set preferred entry and exit nodes as well as 
866) inform Tor which nodes you do not want to use. 
867) The following options can be added to your config file "torrc" 
868) or specified on the command line:
869) </p>
870) <dl>
871)   <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>
872)     <dd>A list of preferred nodes to use for the first hop in the circuit, if possible.
873)     </dd>
874)   <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>
875)     <dd>A list of preferred nodes to use for the last hop in the circuit, if possible. 
876)     </dd>
877)   <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>
878)     <dd>A list of nodes to never use when building a circuit. 
879)     </dd>
880)   <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>
881)     <dd>A list of nodes to never use when picking an exit. 
882)         Nodes listed in <tt>ExcludeNodes</tt> are automatically in this list. 
883)     </dd>
884) </dl>
885) <p>
886) <em>We recommend you do not use these</em> 

887) — they are intended for testing and may disappear in future versions. 

888) You get the best security that Tor can provide when you leave the route selection to Tor; 
889) overriding the entry / exit nodes can mess up your anonymity in ways we don't understand.
890) </p>
891) <p>
892) The <tt>EntryNodes</tt> and <tt>ExitNodes</tt> config options are treated as a request, 
893) meaning if the nodes are down or seem slow, Tor will still avoid them. 
894) You can make the option mandatory by setting 
895) <tt>StrictExitNodes 1</tt> or <tt>StrictEntryNodes 1</tt> 

896) — but if you do, your Tor connections will stop working 

897) if all of the nodes you have specified become unreachable. 

898) See the <a href="<page documentation>#NeatLinks">Tor status pages</a>

899) for some nodes you might pick.
900) </p>
901) <p>
902) Instead of <tt>$fingerprint</tt> you can also specify 
903) a 2 letter ISO3166 country code in curly braces 
904) (for example {de}), 
905) or an ip address pattern (for example 255.254.0.0/8), 
906) or a node nickname. 
907) Make sure there are no spaces between the commas and the list items. 
908) </p>
909) <p>
910) If you want to access a service directly through Tor's SOCKS interface 
911) (eg. using ssh via connect.c), another option is to 
912) set up an internal mapping in your configuration file using <tt>MapAddress</tt>. 
913) See the manual page for details.
914) </p>
915) 
916) <hr />
917) 

918) <a id="GoogleCaptcha"></a>
919) <h3><a class="anchor" href="#GoogleCaptcha">Google makes me solve a
920) Captcha or tells me I have spyware installed.</a></h3>
921) 
922) <p>
923) This is a known and intermittent problem; it does not mean that Google

924) considers Tor to be spyware.

925) </p>
926) 
927) <p>

928) When you use Tor, you are sending queries through exit relays that are also
929) shared by thousands of other users. Tor users typically see this message
930) when many Tor users are querying Google in a short period of time. Google
931) interprets the high volume of traffic from a single IP address (the exit
932) relay you happened to pick) as somebody trying to "crawl" their website,
933) so it slows down traffic from that IP address for a short time.

934) </p>
935) 
936) <p>

937) An alternate explanation is that Google tries to detect certain
938) kinds of spyware or viruses that send distinctive queries to Google
939) Search. It notes the IP addresses from which those queries are received
940) (not realizing that they are Tor exit relays), and tries to warn any
941) connections coming from those IP addresses that recent queries indicate
942) an infection.

943) </p>
944) 
945) <p>
946) To our knowledge, Google is not doing anything intentionally specifically
947) to deter or block Tor use. The error message about an infected machine
948) should clear up again after a short time.
949) </p>
950) 
951) <p>

952) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
953) automatically redirect you to a more Tor-friendly search engine such as
954) Ixquick or Bing.

955) </p>
956) 
957) <hr />
958) 

959) <a id="GmailWarning"></a>
960) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my account
961) may have been compromised.</a></h3>
962) 
963) <p>
964) Sometimes, after you've used Gmail over Tor recently, you'll get a pop-up
965) notice from Google that says your account may have been compromised. The
966) window lists a series of IP addresses and locations throughout the world.
967) </p>
968) 
969) <p>
970) In general this is a false alarm: Google saw a bunch of logins from
971) different places, thought that was unusual for you, and wanted to let
972) you know. If you use Tor to access a Google service, then it will appear
973) like you're coming from lots of different places. Nothing to worry about
974) in particular.
975) </p>
976) 
977) <p>
978) But that doesn't mean you can entirely ignore the warning. It's
979) <i>probably</i> a false positive, but it might not be. It is possible
980) that somebody could at some point steal your Google cookie, which would
981) allow them to log in to the Google service as you. They might steal it
982) by breaking into your computer, or by watching your network traffic at
983) Starbucks or sniffing your wireless at home (when you're not using Tor),
984) or by watching traffic going over the Tor network. In theory none of
985) this should be possible because Gmail and similar services should only
986) send the cookie over an SSL link. In practice, alas, it's <a
987) href="http://fscked.org/blog/fully-automated-active-https-cookie-hijacking">way
988) more complex than that</a>.
989) </p>
990) 
991) <p>
992) And if somebody <i>did</i> steal your google cookie, they might end
993) up logging in from unusual places (though of course they also might
994) not). So the summary is that since you're using Tor, this security
995) measure that Google uses isn't so useful for you, because it's full of
996) false positives. You'll have to use other approaches, like seeing if
997) anything looks weird on the account, or looking at the timestamps for
998) recent logins and wondering if you actually logged in at those times.
999) </p>
1000) 
1001) <hr />
1002) 

1003) <a id="RelayFlexible"></a>
1004) <h3><a class="anchor" href="#RelayFlexible">How stable does my relay
1005) need to be?</a></h3>
1006) 
1007) <p>
1008) We aim to make setting up a Tor relay easy and convenient:
1009) </p>
1010) 
1011) <ul>
1012) <li>Tor has built-in support for <a

1013) href="<wiki>TorFAQ#LimitBandwidth">

1014) rate limiting</a>. Further, if you have a fast
1015) link but want to limit the number of bytes per
1016) day (or week or month) that you donate, check out the <a

1017) href="<wiki>TorFAQ#Hibernation">hibernation

1018) feature</a>.
1019) </li>

1020) <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a> that
1021) specifies what sort of outbound connections are allowed or refused from
1022) that relay. If you are uncomfortable allowing people to exit from your
1023) relay, you can set it up to only allow connections to other Tor relays.

1024) </li>
1025) <li>It's fine if the relay goes offline sometimes. The directories
1026) notice this quickly and stop advertising the relay. Just try to make
1027) sure it's not too often, since connections using the relay when it
1028) disconnects will break.
1029) </li>
1030) <li>We can handle relays with dynamic IPs just fine &mdash; simply
1031) leave the Address config option blank, and Tor will try to guess.
1032) </li>
1033) <li>If your relay is behind a NAT and it doesn't know its public
1034) IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1035) forwarding. Forwarding TCP connections is system dependent but 

1036) <a href="<wiki>TorFAQ#ServerForFirewalledClients">this FAQ entry</a>

1037) offers some examples on how to do this.

1038) </li>
1039) <li>Your relay will passively estimate and advertise its recent
1040) bandwidth capacity, so high-bandwidth relays will attract more users than
1041) low-bandwidth ones. Therefore having low-bandwidth relays is useful too.
1042) </li>
1043) </ul>
1044) 
1045) <hr />
1046) 

1047) <a id="RunARelayBut"></a>

1048) <a id="ExitPolicies"></a>
1049) <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I don't

1050) want to deal with abuse issues.</a></h3>
1051) 
1052) <p>
1053) Great. That's exactly why we implemented exit policies.
1054) </p>
1055) 
1056) <p>

1057) Each Tor relay has an exit policy that specifies what sort of
1058) outbound connections are allowed or refused from that relay. The exit

1059) policies are propagated to Tor clients via the directory, so clients

1060) will automatically avoid picking exit relays that would refuse to
1061) exit to their intended destination. This way each relay can decide
1062) the services, hosts, and networks he wants to allow connections to,

1063) based on abuse potential and his own situation. Read the FAQ entry on 
1064) <a href="<page faq-abuse>#TypicalAbuses">issues you might encounter</a> 
1065) if you use the default exit policy, and then read Mike Perry's 

1066) <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1067) for running an exit node with minimal harassment</a>.
1068) </p>
1069) 
1070) <p>

1071) The default exit policy allows access to many popular services (e.g. web browsing), but 

1072) <a href="<wiki>TorFAQ#DefaultPorts">restricts</a>

1073) some due to abuse potential (e.g. mail) and some since
1074) the Tor network can't handle the load (e.g. default
1075) file-sharing ports). You can change your exit policy

1076) using Vidalia's "Sharing" tab, or by manually editing your 

1077) <a href="<wiki>TorFAQ#torrc">torrc</a>

1078) file. If you want to avoid most if not all abuse potential, set it to

1079) "reject *:*" (or un-check all the boxes in Vidalia). This setting means
1080) that your relay will be used for relaying traffic inside the Tor network,
1081) but not for connections to external websites or other services.

1082) </p>
1083) 
1084) <p>

1085) If you do allow any exit connections, make sure name resolution works
1086) (that is, your computer can resolve Internet addresses correctly).

1087) If there are any resources that your computer can't reach (for example,
1088) you are behind a restrictive firewall or content filter), please
1089) explicitly reject them in your exit policy — otherwise Tor users
1090) will be impacted too.

1091) </p>
1092) 
1093) <hr />
1094) 

1095) <a id="RelayOrBridge"></a>
1096) <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal relay
1097) or bridge relay?</a></h3>
1098) 
1099) <p><a href="<page bridges>">Bridge relays</a> (or "bridges" for short)

1100) are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't listed
1101) in the main Tor directory. That means

1102) that even an ISP or government trying to filter connections to the Tor
1103) network probably won't be able to block all the bridges.
1104) </p>
1105) 
1106) <p>Being a normal relay vs being a bridge relay is almost the same
1107) configuration: it's just a matter of whether your relay is listed
1108) publically or not.
1109) </p>
1110) 

1111) <p>Right now, there are a small number of places in the world that filter

1112) connections to the Tor network. So getting a lot of bridges running
1113) right now is mostly a backup measure, a) in case the Tor network does
1114) get blocked somewhere, and b) for people who want an extra layer of
1115) security because they're worried somebody will recognize that it's a

1116) public Tor relay IP address they're contacting.

1117) </p>
1118) 
1119) <p>So should you run a normal relay or bridge relay? If you have
1120) lots of bandwidth, you should definitely run a normal relay &mdash;

1121) bridge relays see very little use these days. If you're willing to 
1122) <a href="#ExitPolicies">be an exit</a>, you should definitely run a normal

1123) relay, since we need more exits. If you can't be an exit and only have
1124) a little bit of bandwidth, then flip a coin. Thanks for volunteering!
1125) </p>
1126) 
1127) <hr />
1128) 

1129) <a id="RelayMemory"></a>
1130) <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using so
1131) much memory?</a></h3>
1132) 

1133) <p>If your Tor relay is using more memory than you'd like, here are some
1134) tips for reducing its footprint:
1135) </p>
1136) 
1137) <ol>
1138) <li>If you're on Linux, you may be encountering memory fragmentation
1139) bugs in glibc's malloc implementation. That is, when Tor releases memory
1140) back to the system, the pieces of memory are fragmented so they're hard
1141) to reuse. The Tor tarball ships with OpenBSD's malloc implementation,
1142) which doesn't have as many fragmentation bugs (but the tradeoff is higher
1143) CPU load). You can tell Tor to use this malloc implementation instead:
1144) <tt>./configure --enable-openbsd-malloc</tt></li>
1145) 
1146) <li>If you're running a fast relay, meaning you have many TLS connections
1147) open, you are probably losing a lot of memory to OpenSSL's internal

1148) buffers (38KB+ per socket). We've patched OpenSSL to <a
1149) href="http://archives.seul.org/or/dev/Jun-2008/msg00001.html">release
1150) unused buffer memory more aggressively</a>. If you update to OpenSSL
1151) 1.0.0-beta5, Tor's build process will automatically recognize and use
1152) this feature.</li>

1153) 
1154) <li>If you're running on Solaris, OpenBSD, NetBSD, or
1155) old FreeBSD, Tor is probably forking separate processes
1156) rather than using threads. Consider switching to a <a

1157) href="<wiki>TorFAQ#RelayOS">better

1158) operating system</a>.</li>
1159) 
1160) <li>If you still can't handle the memory load, consider reducing the
1161) amount of bandwidth your relay advertises. Advertising less bandwidth
1162) means you will attract fewer users, so your relay shouldn't grow
1163) as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1164) page.</li>
1165) 
1166) </ol>
1167) 
1168) <p>
1169) All of this said, fast Tor relays do use a lot of ram. It is not unusual
1170) for a fast exit relay to use 500-1000 MB of memory.

1171) </p>
1172) 
1173) <hr />
1174) 

1175) <a id="WhyNotNamed"></a>
1176) <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not named?</a></h3>
1177) 
1178) <p>
1179) We currently use these metrics to determine if your relay should be named:<br />
1180) </p>
1181) <ul>
1182) <li>The name is not currently mapped to a different key. Existing mappings
1183) are removed after 6 months of inactivity from a relay.</li>
1184) <li>The relay must have been around for at least two weeks.</li>
1185) <li>No other router may have wanted the same name in the past month.</li>
1186) </ul>
1187) 
1188) <hr />
1189) 

1190) <a id="KeyManagement"></a>

1191) <h3><a class="anchor" href="#KeyManagement">Tell me about all the keys
1192) Tor uses.</a></h3>

1193) 
1194) <p>

1195) Tor uses a variety of different keys, with three goals in mind: 1)

1196) encryption to ensure privacy of data within the Tor network, 2)
1197) authentication so clients know they're
1198) talking to the relays they meant to talk to, and 3) signatures to make
1199) sure all clients know the same set of relays.

1200) </p>
1201) 
1202) <p>
1203) <b>Encryption</b>: first, all connections in Tor use TLS link encryption,
1204) so observers can't look inside to see which circuit a given cell is
1205) intended for. Further, the Tor client establishes an ephemeral encryption
1206) key with each relay in the circuit, so only the exit relay can read
1207) the cells. Both sides discard the circuit key when the circuit ends,
1208) so logging traffic and then breaking into the relay to discover the key
1209) won't work.
1210) </p>
1211) 
1212) <p>
1213) <b>Authentication</b>:
1214) Every Tor relay has a public decryption key called the "onion key".
1215) When the Tor client establishes circuits, at each step it <a

1216) href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands

1217) that the Tor relay prove knowledge of its onion key</a>. That way

1218) the first node in the path can't just spoof the rest of the path.

1219) Each relay rotates its onion key once a week.

1220) </p>
1221) 
1222) <p>

1223) <b>Coordination</b>:

1224) How do clients know what the relays are, and how do they know that they

1225) have the right keys for them? Each relay has a long-term public signing
1226) key called the "identity key". Each directory authority additionally has a

1227) "directory signing key". The directory authorities <a

1228) href="<gitblob>doc/spec/dir-spec.txt">provide a signed list</a>

1229) of all the known relays, and in that list are a set of certificates from
1230) each relay (self-signed by their identity key) specifying their keys,
1231) locations, exit policies, and so on. So unless the adversary can control
1232) a threshold of the directory authorities, he can't trick the Tor client
1233) into using other Tor relays.

1234) </p>
1235) 
1236) <p>

1237) How do clients know what the directory authorities are? The Tor software
1238) comes with a built-in list of location and public key for each directory
1239) authority. So the only way to trick users into using a fake Tor network

1240) is to give them a specially modified version of the software.
1241) </p>

1242) 

1243) <p>
1244) How do users know they've got the right software? When we distribute
1245) the source code or a package, we digitally sign it with <a

1246) href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a

1247) href="<page verifying-signatures>">instructions

1248) on how to check Tor's signatures</a>.
1249) </p>

1250) 

1251) <p>

1252) In order to be certain that it's really signed by us, you need to have
1253) met us in person and gotten a copy of our GPG key fingerprint, or you
1254) need to know somebody who has. If you're concerned about an attack on
1255) this level, we recommend you get involved with the security community
1256) and start meeting people.

1257) </p>

1258) 

1259) <hr />
1260) 

1261) <a id="EverybodyARelay"></a>
1262) <h3><a class="anchor" href="#EverybodyARelay">You should make every Tor
1263) user be a relay.</a></h3>
1264) 
1265) <p>
1266) Requiring every Tor user to be a relay would help with scaling the

1267) network to handle all our users, and <a href="<wiki>TorFAQ#RelayAnonymity">running a Tor

1268) relay may help your anonymity</a>. However, many Tor users cannot be good
1269) relays &mdash; for example, some Tor clients operate from behind restrictive
1270) firewalls, connect via modem, or otherwise aren't in a position where they
1271) can relay traffic. Providing service to these clients is a critical

1272) part of providing effective anonymity for everyone, since many Tor users
1273) are subject to these or similar constraints and including these clients
1274) increases the size of the anonymity set.
1275) </p>
1276) 
1277) <p>
1278) That said, we do want to encourage Tor users to run relays, so what we
1279) really want to do is simplify the process of setting up and maintaining

1280) a relay. We've made a lot of progress with easy configuration in the past
1281) few years: Vidalia has an easy relay configuration interface, and supports
1282) uPnP too. Tor is good at automatically detecting whether it's reachable and
1283) how much bandwidth it can offer.

1284) </p>
1285) 
1286) <p>
1287) There are five steps we need to address before we can do this though:
1288) </p>
1289) 
1290) <p>

1291) First, we need to make Tor stable as a relay on all common
1292) operating systems. The main remaining platform is Windows,
1293) and we plan to finally address that in 2009. See Section 4.1 of <a
1294) href="https://www.torproject.org/press/2008-12-19-roadmap-press-release">our
1295) development roadmap</a>.

1296) </p>
1297) 
1298) <p>

1299) Second, we still need to get better at automatically estimating
1300) the right amount of bandwidth to allow. See item #7 on the
1301) <a href="<page volunteer>#Research">research section of the
1302) volunteer page</a>: "Tor doesn't work very well when relays
1303) have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

1304) href="<wiki>TorFAQ#TransportIPnotTCP">switching

1305) to UDP transport</a> is the simplest answer here &mdash; which alas is
1306) not a very simple answer at all.

1307) </p>
1308) 
1309) <p>

1310) Third, we need to work on scalability, both of the network (how to
1311) stop requiring that all Tor relays be able to connect to all Tor
1312) relays) and of the directory (how to stop requiring that all Tor
1313) users know about all Tor relays). Changes like this can have large
1314) impact on potential and actual anonymity. See Section 5 of the <a

1315) href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper

1316) for details. Again, UDP transport would help here.

1317) </p>
1318) 
1319) <p>

1320) Fourth, we need to better understand the risks from
1321) letting the attacker send traffic through your relay while
1322) you're also initiating your own anonymized traffic. <a
1323) href="http://freehaven.net/anonbib/#back01">Three</a> <a
1324) href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
1325) <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
1326) describe ways to identify the relays in a circuit by running traffic
1327) through candidate relays and looking for dips in the traffic while the
1328) circuit is active. These clogging attacks are not that scary in the Tor
1329) context so long as relays are never clients too. But if we're trying to
1330) encourage more clients to turn on relay functionality too (whether as
1331) <a href="<page bridges>">bridge relays</a> or as normal relays), then
1332) we need to understand this threat better and learn how to mitigate it.

1333) </p>
1334) 
1335) <p>
1336) Fifth, we might need some sort of incentive scheme to encourage people
1337) to relay traffic for others, and/or to become exit nodes. Here are our

1338) <a href="<blog>two-incentive-designs-tor">current

1339) thoughts on Tor incentives</a>.

1340) </p>
1341) 
1342) <p>
1343) Please help on all of these!
1344) </p>
1345) 
1346) <hr />
1347) 

1348) <a id="Criminals"></a>
1349) <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals to do bad
1350) things?</a></h3>
1351) 
1352) <p>

1353) For the answer to this question and others, please see our <a

1354) href="<page faq-abuse>">Tor Abuse FAQ</a>.

1355) </p>
1356) 
1357) <hr />
1358) 
1359) <a id="RespondISP"></a>
1360) <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP about my
1361) exit relay?</a></h3>
1362) 
1363) <p>
1364) A collection of templates for successfully responding to ISPs is <a

1365) href="<wiki>TorAbuseTemplates">collected

1366) here</a>.
1367) </p>
1368) 

1369) <hr />

1370) 

1371)   </div><!-- #main -->

1372) 
1373) #include <foot.wmi>