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5) #include "head.wmi" TITLE="Tor Project: FAQ" CHARSET="UTF-8"
6) <div id="content" class="clearfix">
7)   <div id="breadcrumbs">

8)     <a href="<page index>">Home &raquo; </a>

9)     <a href="<page docs/documentation>">Documentation &raquo; </a>
10)     <a href="<page docs/faq>">FAQ</a>
11)   </div>
12)   <div id="maincol">
13)     <!-- PUT CONTENT AFTER THIS TAG -->
14)     <h1>Tor FAQ</h1>

15)     <hr>

16) 

17)     <p>General questions:</p>
18)     <ul>
19)     <li><a href="#WhatIsTor">What is Tor?</a></li>

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

22)     <li><a href="#CompatibleApplications">What programs can I use with
23)     Tor?</a></li>
24)     <li><a href="#WhyCalledTor">Why is it called Tor?</a></li>
25)     <li><a href="#Backdoor">Is there a backdoor in Tor?</a></li>

26)     <li><a href="#DistributingTor">Can I distribute Tor?</a></li>

27)     <li><a href="#SupportMail">How can I get support?</a></li>

28)     <li><a href="#Forum">Is there a Tor forum?</a></li>

29)     <li><a href="#WhySlow">Why is Tor so slow?</a></li>
30)     <li><a href="#Funding">What would The Tor Project do with more
31)     funding?</a></li>

32)     <li><a href="#Metrics">How many people use Tor? How many relays or
33)     exit nodes are there?</a></li>

34)     <li><a href="#SSLcertfingerprint">What are your SSL certificate

35)     fingerprints?</a></li>

36)     </ul>

37) 

38)     <p>Compilation and Installation:</p>
39)     <ul>
40)     <li><a href="#HowUninstallTor">How do I uninstall Tor?</a></li>
41)     <li><a href="#PGPSigs">What are these "sig" files on the download
42)     page?</a></li>

43)     <li><a href="#GetTor">Your website is blocked in my country. How
44)     do I download Tor?</a></li>

45)     <li><a href="#CompileTorWindows">How do I compile Tor under
46) Windows?</a></li>
47)     <li><a href="#VirusFalsePositives">Why does my Tor executable appear
48) to

49)     have a virus or spyware?</a></li>

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

52)     </ul>

53) 

54)     <p>Tor Browser Bundle:</p>
55)     <ul>

56) 

57)     <li><a href="#TBBFlash">Why can't I view videos on YouTube and other
58)     Flash-based sites?</a></li>

59)     <li><a href="#TBBSocksPort">I want to

60)     run another application through the Tor launched by Tor Browser

61)     Bundle.</a></li>

62)     <li><a href="#TBBPolipo">I need an HTTP proxy. Where did Polipo
63)     go?</a></li>

64)     <li><a href="#TBBOtherExtensions">Can I install other Firefox

65)     extensions? Which extensions should I avoid using?</a></li>

66)     <li><a href="#TBBJavaScriptEnabled">Why is NoScript configured to
67) allow JavaScript by default in the Tor Browser Bundle?  Isn't that
68) unsafe?</a></li>

69)     <li><a href="#TBBOtherBrowser">I want to use Chrome/IE/Opera/etc
70)     with Tor.</a></li>
71)     <li><a href="#TBBCloseBrowser">I want to leave Tor Browser Bundle
72)     running but close the browser.</a></li>
73) 

74)     <li><a href="#GoogleCAPTCHA">Google makes me solve a CAPTCHA or

75) tells

76)     me I have spyware installed.</a></li>
77)     <li><a href="#GmailWarning">Gmail warns me that my account may have
78)     been compromised.</a></li>
79)     </ul>
80) 
81)     <p>Advanced Tor usage:</p>

82)     <ul>
83)     <li><a href="#torrc">I'm supposed to "edit my torrc". What does
84)     that mean?</a></li>

85)     <li><a href="#Logs">How do I set up logging, or see Tor's

86)     logs?</a></li>

87)     <li><a href="#DoesntWork">Tor is running, but it's not working
88)     correctly.</a></li>

89)     <li><a href="#VidaliaPassword">Tor/Vidalia prompts for a password at
90)     start.</a></li>

91)     <li><a href="#ChooseEntryExit">Can I control which nodes (or
92) country)

93)     are used for entry/exit?</a></li>

94)     <li><a href="#FirewallPorts">My firewall only allows a few outgoing
95)     ports.</a></li>

96)     </ul>

97) 

98)     <p>Running a Tor relay:</p>
99)     <ul>

100)     <li><a href="#RelayFlexible">How stable does my relay need to
101) be?</a></li>
102)     <li><a href="#ExitPolicies">I'd run a relay, but I don't want to
103) deal

104)     with abuse issues.</a></li>
105)     <li><a href="#RelayOrBridge">Should I be a normal relay or bridge
106)     relay?</a></li>

107)     <li><a href="#MultipleRelays">I want to run more than one
108) relay.</a></li>
109)     <li><a href="#RelayMemory">Why is my Tor relay using so much
110) memory?</a></li>

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

112)     <li><a href="#RelayDonations">Can I donate for a relay rather than
113)     run my own?</a></li>

114)     </ul>

115) 

116)     <p>Running a Tor hidden service:</p>

117) 

118)     <p>Anonymity and Security:</p>
119)     <ul>

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

122)     <li><a href="#EntryGuards">What are Entry Guards?</a></li>

123)     </ul>

124) 

125)     <p>Alternate designs that we don't do (yet):</p>
126)     <ul>
127)     <li><a href="#EverybodyARelay">You should make every Tor user be a
128)     relay.</a></li>

129)     <li><a href="#TransportIPnotTCP">You should transport all IP
130) packets,

131)     not just TCP packets.</a></li>

132)     <li><a href="#HideExits">You should hide the list of Tor relays,
133)     so people can't block the exits.</a></li>

134)     </ul>

135) 

136)     <p>Abuse:</p>

137)     <ul>

138)     <li><a href="#Criminals">Doesn't Tor enable criminals to do bad
139) things?</a></li>

140)     <li><a href="#RespondISP">How do I respond to my ISP about my exit
141)     relay?</a></li>
142)     </ul>

143) 

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

146)     href="<wikifaq>">wiki FAQ</a> for now.</p>

147) 

148)     <hr>

149) 

150)     <a id="General"></a>

151) 

152)     <a id="WhatIsTor"></a>
153)     <h3><a class="anchor" href="#WhatIsTor">What is Tor?</a></h3>

154) 

155)     <p>
156)     The name "Tor" can refer to several different components.
157)     </p>

158) 

159)     <p>

160)     The Tor software is a program you can run on your computer that
161) helps keep
162)     you safe on the Internet. Tor protects you by bouncing your
163) communications

164)     around a distributed network of relays run by volunteers all around

165)     the world: it prevents somebody watching your Internet connection
166) from

167)     learning what sites you visit, and it prevents the sites you visit

168)     from learning your physical location. This set of volunteer relays
169) is
170)     called the Tor network. You can read more about how Tor works on the
171) <a

172)     href="<page about/overview>">overview page</a>.
173)     </p>

174) 

175)     <p>

176)     The Tor Project is a non-profit (charity) organization that
177) maintains

178)     and develops the Tor software.
179)     </p>

180) 

181)     <hr>

182) 

183)     <a id="Torisdifferent"></a>

184)     <h3><a class="anchor" href="#Torisdifferent">How is Tor different
185) from other proxies?</a></h3>
186)     <p>
187)     A typical proxy provider sets up a server somewhere on the Internet
188) and
189) allows you to use it to relay your traffic.  This creates a simple, easy
190) to
191) maintain architecture.  The users all enter and leave through the same
192) server.
193) The provider may charge for use of the proxy, or fund their costs
194) through
195) advertisements on the server.  In the simplest configuration, you don't
196) have to
197) install anything.  You just have to point your browser at their proxy
198) server.
199) Simple proxy providers are fine solutions if you do not want protections
200) for
201) your privacy and anonymity online and you trust the provider from doing
202) bad
203) things.  Some simple proxy providers use SSL to secure your connection
204) to them.
205) This may protect you against local eavesdroppers, such as those at a
206) cafe with

207) free wifi Internet.
208)     </p>
209)     <p>

210)     Simple proxy providers also create a single point of failure.  The
211) provider
212) knows who you are and where you browse on the Internet.  They can see
213) your
214) traffic as it passes through their server.  In some cases, they can even
215) see

216) inside your

217) encrypted traffic as they relay it to your banking site or to ecommerce
218) stores.

219) You have to trust the provider isn't doing any number of things, such as

220) watching your traffic, injecting their own advertisements into your
221) traffic

222) stream, and recording your personal details.

223)     </p>
224)     <p>

225)     Tor passes your traffic through at least 3 different servers before
226) sending
227) it on to the destination. Because there's a separate layer of encryption
228) for
229) each of the three relays, Tor does not modify, or even know, what you
230) are
231) sending into it.  It merely relays your traffic, completely encrypted
232) through
233) the Tor network and has it pop out somewhere else in the world,
234) completely
235) intact.  The Tor client is required because we assume you trust your
236) local
237) computer.  The Tor client manages the encryption and the path chosen
238) through
239) the network.  The relays located all over the world merely pass
240) encrypted

241) packets between themselves.</p>

242)     <p>
243)     <dl>

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

254) out who you are and where you are going on the Internet.</dd>

255)     <dt>Can't the third server see my traffic?</dt><dd>Possibly.  A bad
256) third
257) of three servers can see the traffic you sent into Tor.  It won't know
258) who sent

259) this traffic.  If you're using encryption, such as visiting a bank or

260) e-commerce website, or encrypted mail connections, etc, it will only
261) know the
262) destination.  It won't be able to see the data inside the traffic
263) stream.  You

264) are still protected from this node figuring out who you are and if using
265) encryption, what data you're sending to the destination.</dd>

266)     </dl>
267)     </p>

268) 

269)     <hr>

270) 

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

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

274) 

275)     <p>

276)     There are two pieces to "Torifying" a program: connection-level
277) anonymity
278)     and application-level anonymity. Connection-level anonymity focuses
279) on
280)     making sure the application's Internet connections get sent through
281) Tor.

282)     This step is normally done by configuring
283)     the program to use your Tor client as a "socks" proxy, but there are

284)     other ways to do it too. For application-level anonymity, you need
285) to
286)     make sure that the information the application sends out doesn't
287) hurt
288)     your privacy. (Even if the connections are being routed through Tor,
289) you
290)     still don't want to include sensitive information like your name.)
291) This

292)     second step needs to be done on a program-by-program basis, which is
293)     why we don't yet recommend very many programs for safe use with Tor.
294)     </p>

295) 

296)     <p>
297)     Most of our work so far has focused on the Firefox web browser. The

298)     bundles on the <a href="<page download/download>">download page</a>
299) automatically

300)     install the <a href="<page torbutton/index>">Torbutton Firefox

301)     extension</a> if you have Firefox installed. As of version 1.2.0,
302)     Torbutton now takes care of a lot of the connection-level and
303)     application-level worries.
304)     </p>

305) 

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

311)     href="<wiki>doc/TorifyHOWTO">Torifying

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

313)     href="<wiki>doc/SupportPrograms">list

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

317) 

318)     <hr>

319) 

320)     <a id="WhyCalledTor"></a>

321)     <h3><a class="anchor" href="#WhyCalledTor">Why is it called
322) Tor?</a></h3>

323) 

324)     <p>
325)     Because Tor is the onion routing network. When we were starting the
326)     new next-generation design and implementation of onion routing in
327)     2001-2002, we would tell people we were working on onion routing,
328)     and they would say "Neat. Which one?" Even if onion routing has
329)     become a standard household term, Tor was born out of the actual <a
330)     href="http://www.onion-router.net/">onion routing project</a> run by
331)     the Naval Research Lab.
332)     </p>

333) 

334)     <p>
335)     (It's also got a fine translation from German and Turkish.)
336)     </p>

337) 

338)     <p>

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

341)     "TOR". Only the first letter is capitalized. In fact, we can usually

342)     spot people who haven't read any of our website (and have instead
343) learned
344)     everything they know about Tor from news articles) by the fact that
345) they

346)     spell it wrong.
347)     </p>

348) 

349)     <hr>

350) 

351)     <a id="Backdoor"></a>

352)     <h3><a class="anchor" href="#Backdoor">Is there a backdoor in
353) Tor?</a></h3>

354) 

355)     <p>

356)     There is absolutely no backdoor in Tor. Nobody has asked us to put
357) one
358)     in, and we know some smart lawyers who say that it's unlikely that
359) anybody

360)     will try to make us add one in our jurisdiction (U.S.). If they do
361)     ask us, we will fight them, and (the lawyers say) probably win.
362)     </p>

363) 

364)     <p>
365)     We think that putting a backdoor in Tor would be tremendously

366)     irresponsible to our users, and a bad precedent for security
367) software

368)     in general. If we ever put a deliberate backdoor in our security
369)     software, it would ruin our professional reputations. Nobody would
370)     trust our software ever again — for excellent reason!
371)     </p>

372) 

373)     <p>
374)     But that said, there are still plenty of subtle attacks
375)     people might try. Somebody might impersonate us, or break into our

376)     computers, or something like that. Tor is open source, and you
377) should
378)     always check the source (or at least the diffs since the last
379) release)

380)     for suspicious things. If we (or the distributors) don't give you
381)     source, that's a sure sign something funny might be going on. You
382)     should also check the <a href="<page docs/verifying-signatures>">PGP
383)     signatures</a> on the releases, to make sure nobody messed with the
384)     distribution sites.
385)     </p>

386) 

387)     <p>
388)     Also, there might be accidental bugs in Tor that could affect your

389)     anonymity. We periodically find and fix anonymity-related bugs, so
390) make

391)     sure you keep your Tor versions up-to-date.
392)     </p>

393) 

394)     <hr>

395) 

396)     <a id="DistributingTor"></a>

397)     <h3><a class="anchor" href="#DistributingTor">Can I distribute
398) Tor?</a></h3>

399) 

400)     <p>
401)     Yes.
402)     </p>

403) 

404)     <p>

405)     The Tor software is <a href="https://www.fsf.org/">free
406) software</a>. This
407)     means we give you the rights to redistribute the Tor software,
408) either
409)     modified or unmodified, either for a fee or gratis. You don't have
410) to

411)     ask us for specific permission.
412)     </p>

413) 

414)     <p>

415)     However, if you want to redistribute the Tor software you must
416) follow our

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

418)     Essentially this means that you need to include our LICENSE file
419) along

420)     with whatever part of the Tor software you're distributing.
421)     </p>

422) 

423)     <p>

424)     Most people who ask us this question don't want to distribute just
425) the

426)     Tor software, though. They want to distribute the <a

427)     href="<page projects/torbrowser>">Tor Browser</a>. This includes <a

428)     href="https://www.mozilla.org/en-US/firefox/all-aurora.html">Mozilla
429)     Aurora</a> and <a href="<page projects/vidalia>">Vidalia</a>.

430)     You will need to follow the licenses for those programs
431)     as well. Both of them are distributed under the <a
432)     href="https://www.fsf.org/licensing/licenses/gpl.html">GNU General

433)     Public License</a>. The simplest way to obey their licenses is
434)     to include the source code for these programs everywhere you
435)     include the bundles themselves. Look for "source" packages on
436)     the <a href="<page projects/vidalia>">Vidalia page</a> and <a
437)     href="https://www.mozilla.org/en-US/firefox/all-aurora.html">Mozilla
438)     Aurora</a> pages.

439)     </p>

440) 

441)     <p>

442)     Also, you should make sure not to confuse your readers about what
443) Tor is,
444)     who makes it, and what properties it provides (and doesn't provide).
445) See
446)     our <a href="<page docs/trademark-faq>">trademark FAQ</a> for
447) details.

448)     </p>

449) 

450)     <p>
451)     Lastly, you should realize that we release new versions of the
452)     Tor software frequently, and sometimes we make backward incompatible

453)     changes. So if you distribute a particular version of the Tor
454) software, it
455)     may not be supported — or even work — six months later.
456) This

457)     is a fact of life for all security software under heavy development.
458)     </p>

459) 

460)     <hr>

461) 

462)     <a id="SupportMail"></a>

463)     <h3><a class="anchor" href="#SupportMail">How can I get
464) support?</a></h3>

465) 

466)     <p>Your best bet is to first try the following:</p>

467)     <ol>
468)     <li>Read through this <a href="<page docs/faq>">FAQ</a>.</li>

469)     <li>Read through the <a href="<page
470) docs/documentation>">documentation</a>.</li>

471)     <li>Read through the <a

472) 
473) href="https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk">
474) tor-talk

475)     archives</a> and see if your question is already answered.</li>

476)     <li>Join our <a href="ircs://irc.torproject.org#tor">irc channel</a>
477) and

478)     state the issue and wait for help.</li>

479)     <li>Send an email to <a

480) 
481) href="mailto:help@rt.torproject.org">help@rt.torproject.org</a>.</li>
482)     <li>If all else fails, try <a href="<page about/contact>">contacting
483) us</a> directly.</li>

484)     </ol>

485) 

486)     <p>If you find your answer, please stick around on the IRC channel
487) or the

488)     mailing list to help others who were once in your position.</p>

489) 

490)     <hr>

491) 

492)     <a id="Forum"></a>
493)     <h3><a class="anchor" href="#Forum">Is there a Tor forum?</a></h3>
494) 
495)     <p>Not yet, but we're working on it. Most forum software is
496)     a disaster to maintain and keep secure, and at the same time
497)     too many of the Tor developers are spread too thin to be able

498)     to contribute enough to a forum.

499)     </p>
500) 
501)     <hr>
502) 

503)     <a id="WhySlow"></a>
504)     <h3><a class="anchor" href="#WhySlow">Why is Tor so slow?</a></h3>

505) 

506)     <p>
507)     There are many reasons why the Tor network is currently slow.
508)     </p>

509) 

510)     <p>

511)     Before we answer, though, you should realize that Tor is never going
512) to
513)     be blazing fast. Your traffic is bouncing through volunteers'
514) computers
515)     in various parts of the world, and some bottlenecks and network
516) latency

517)     will always be present. You shouldn't expect to see university-style
518)     bandwidth through Tor.
519)     </p>

520) 

521)     <p>

522)     But that doesn't mean that it can't be improved. The current Tor
523) network
524)     is quite small compared to the number of people trying to use it,
525) and
526)     many of these users don't understand or care that Tor can't
527) currently

528)     handle file-sharing traffic load.
529)     </p>

530) 

531)     <p>
532)     For the much more in-depth answer, see <a

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

534)     post on the topic</a>, which includes both a detailed PDF and a
535) video

536)     to go with it.
537)     </p>

538) 

539)     <p>
540)     What can you do to help?
541)     </p>

542) 

543)     <ul>

544) 

545)     <li>

546)     <a href="<page docs/tor-doc-relay>">Configure your Tor to relay
547) traffic
548)     for others</a>. Help make the Tor network large enough that we can
549) handle

550)     all the users who want privacy and security on the Internet.
551)     </li>

552) 

553)     <li>

554)     <a href="<page projects/vidalia>">Help us make Tor more usable</a>.
555) We

556)     especially need people to help make it easier to configure your Tor
557)     as a relay. Also, we need help with clear simple documentation to
558)     walk people through setting it up.
559)     </li>

560) 

561)     <li>

562)     There are some bottlenecks in the current Tor network. Help us
563) design
564)     experiments to track down and demonstrate where the problems are,
565) and

566)     then we can focus better on fixing them.
567)     </li>

568) 

569)     <li>
570)     Tor needs some architectural changes too. One important change is to

571)     start providing <a href="#EverybodyARelay">better service to people
572) who
573)     relay traffic</a>. We're working on this, and we'll finish faster if
574) we

575)     get to spend more time on it.
576)     </li>

577) 

578)     <li>

579)     Help do other things so we can do the hard stuff. Please take a
580) moment
581)     to figure out what your skills and interests are, and then <a
582) href="<page

583)     getinvolved/volunteer>">look at our volunteer page</a>.
584)     </li>

585) 

586)     <li>

587)     Help find sponsors for Tor. Do you work at a company or government
588) agency

589)     that uses Tor or has a use for Internet privacy, e.g. to browse the

590)     competition's websites discreetly, or to connect back to the home
591) servers
592)     when on the road without revealing affiliations? If your
593) organization has
594)     an interest in keeping the Tor network working, please contact them
595) about
596)     supporting Tor. Without sponsors, Tor is going to become even
597) slower.

598)     </li>

599) 

600)     <li>
601)     If you can't help out with any of the above, you can still help out

602)     individually by <a href="<page donate/donate>">donating a bit of
603) money to the

604)     cause</a>. It adds up!
605)     </li>

606) 

607)     </ul>

608) 

609)     <hr>

610) 

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

612)     <h3><a class="anchor" href="#Funding">What would The Tor Project do
613) with more funding?</a></h3>

614) 

615)     <p>

616)     The Tor network's <a

617) 
618) href="https://metrics.torproject.org/network.html#networksize">several

619)     thousand</a> relays push <a
620)     href="https://metrics.torproject.org/network.html#bandwidth">over
621)     1GB per second on average</a>. We have <a

622) 
623) href="https://metrics.torproject.org/users.html#direct-users">several

624)     hundred thousand daily users</a>. But the Tor network is not yet
625)     self-sustaining.

626)     </p>

627) 

628)     <p>

629)     There are six main development/maintenance pushes that need
630) attention:

631)     </p>

632) 

633)     <ul>

634) 

635)     <li>
636)     Scalability: We need to keep scaling and decentralizing the Tor
637)     architecture so it can handle thousands of relays and millions of

638)     users. The upcoming stable release is a major improvement, but
639) there's

640)     lots more to be done next in terms of keeping Tor fast and stable.
641)     </li>

642) 

643)     <li>

644)     User support: With this many users, a lot of people are asking
645) questions
646)     all the time, offering to help out with things, and so on. We need
647) good
648)     clean docs, and we need to spend some effort coordinating
649) volunteers.

650)     </li>

651) 

652)     <li>

653)     Relay support: the Tor network is run by volunteers, but they still
654) need

655)     attention with prompt bug fixes, explanations when things go wrong,

656)     reminders to upgrade, and so on. The network itself is a commons,
657) and
658)     somebody needs to spend some energy making sure the relay operators
659) stay
660)     happy. We also need to work on stability on some platforms —
661) e.g.,

662)     Tor relays have problems on Win XP currently.

663)     </li>

664) 

665)     <li>

666)     Usability: Beyond documentation, we also need to work on usability
667) of the
668)     software itself. This includes installers, clean GUIs, easy
669) configuration
670)     to interface with other applications, and generally automating all
671) of
672)     the difficult and confusing steps inside Tor. We've got a start on
673) this
674)     with the <a href="<page projects/vidalia>">Vidalia GUI</a>, but much
675) more work

676)     remains — usability for privacy software has never been easy.
677)     </li>

678) 

679)     <li>
680)     Incentives: We need to work on ways to encourage people to configure
681)     their Tors as relays and exit nodes rather than just clients.

682)     <a href="#EverybodyARelay">We need to make it easy to become a
683) relay,

684)     and we need to give people incentives to do it.</a>
685)     </li>

686) 

687)     <li>
688)     Research: The anonymous communications field is full
689)     of surprises and gotchas. In our copious free time, we
690)     also help run top anonymity and privacy conferences like <a
691)     href="http://petsymposium.org/">PETS</a>. We've identified a set of

692)     critical <a href="<page getinvolved/volunteer>#Research">Tor
693) research questions</a>
694)     that will help us figure out how to make Tor secure against the
695) variety of
696)     attacks out there. Of course, there are more research questions
697) waiting

698)     behind these.
699)     </li>

700) 

701)     </ul>

702) 

703)     <p>
704)     We're continuing to move forward on all of these, but at this rate

705)     <a href="#WhySlow">the Tor network is growing faster than the
706) developers

707)     can keep up</a>.

708)     Now would be an excellent time to add a few more developers to the
709) effort

710)     so we can continue to grow the network.
711)     </p>

712) 

713)     <p>
714)     We are also excited about tackling related problems, such as
715)     censorship-resistance.
716)     </p>

717) 

718)     <p>

719)     We are proud to have <a href="<page about/sponsors>">sponsorship and
720) support</a>
721)     from the Omidyar Network, the International Broadcasting Bureau,
722) Bell
723)     Security Solutions, the Electronic Frontier Foundation, several
724) government

725)     agencies and research groups, and hundreds of private contributors.
726)     </p>

727) 

728)     <p>

729)     However, this support is not enough to keep Tor abreast of changes
730) in the
731)     Internet privacy landscape. Please <a href="<page
732) donate/donate>">donate</a>
733)     to the project, or <a href="<page about/contact>">contact</a> our
734) executive

735)     director for information on making grants or major donations.
736)     </p>

737) 

738)     <hr>
739) 

740)     <a id="Metrics"></a>

741)     <h3><a class="anchor" href="#Metrics">How many people use Tor? How
742) many relays or exit nodes are there?</a></h3>

743) 

744)     <p>All this and more about measuring Tor can be found at the <a

745)     href="https://metrics.torproject.org/">Tor Metrics Portal</a>.</p>

746)     <hr>

747) 

748)     <a id="SSLcertfingerprint"></a>
749)     <h3><a class="anchor" href="#SSLcertfingerprint">What are the SSL

750) certificate fingerprints for Tor's various websites?</a></h3>
751)     <p>

752)     <pre>

753)     *.torproject.org SSL certificate from Digicert:

754)     The serial number is:

755) 06:DE:97:E5:1D:C3:9D:C2:64:8D:AC:72:DD:41:01:FC
756)     The SHA-1 fingerprint is: 1f9d306e8bfccfcb03981a71a27a9f5d1e0876ce

757)     The SHA-256 fingerprint is:

758) 3613d2b22a750094760c41ad19db52a4f05bdea80172e2578761ad967f7ed9aa

759) 

760)     blog.torproject.org SSL certificate from RapidSSL:

761)     The serial number is: 00:EF:A3
762)     The SHA-1 fingerprint is: 50af43db8438e67f305a3257d8ef198e8c42f13f

763)     </pre>

764)     </p>
765)     <hr>
766) 

767)     <a id="HowUninstallTor"></a>

768)     <h3><a class="anchor" href="#HowUninstallTor">How do I uninstall
769) Tor?</a></h3>
770) 
771)     <p>
772)     Tor Browser does not install itself in the classic sense of
773) applications. You just simply delete the folder or directory named "Tor
774) Browser" and it is removed from your system.
775)     </p>

776) 

777)     <p>

778)     If this is not related to Tor Browser, uninstallation depends
779) entirely on how you installed it and which operating system you
780)     have. If you installed a package, then hopefully your package has a
781) way to
782)     uninstall itself. The Windows packages include uninstallers. The
783) proper way to
784)     completely remove Tor, Vidalia, and Torbutton for Firefox on any
785) version of Windows is as follows:

786)     </p>

787) 

788)     <ol>

789)     <li>In your taskbar, right click on Vidalia (the green onion or the
790) black head)

791)     and choose exit.</li>

792)     <li>Right click on the taskbar to bring up TaskManager. Look for
793) tor.exe in the
794)     Process List. If it's running, right click and choose End
795) Process.</li>
796)     <li>Click the Start button, go to Programs, go to Vidalia, choose
797) Uninstall.
798)     This will remove the Vidalia bundle, which includes Tor.</li>
799)     <li>Start Firefox. Go to the Tools menu, choose Add-ons. Select
800) Torbutton.

801)     Click the Uninstall button.</li>
802)     </ol>

803) 

804)     <p>
805)     If you do not follow these steps (for example by trying to uninstall

806)     Vidalia and Tor while they are still running), you will need to
807)     reboot and manually remove the directory "Program Files\Vidalia
808) Bundle".

809)     </p>

810) 

811)     <p>
812)     For Mac OS X, follow the <a
813)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
814)     </p>

815) 

816)     <p>

817)     If you installed by source, I'm afraid there is no easy uninstall
818) method. But
819)     on the bright side, by default it only installs into /usr/local/ and
820) it should

821)     be pretty easy to notice things there.
822)     </p>

823) 

824)     <hr>

825) 

826)     <a id="PGPSigs"></a>

827)     <h3><a class="anchor" href="#PGPSigs">What are these "sig" files on
828) the download page?</a></h3>

829) 

830)     <p>

831)     These are PGP signatures, so you can verify that the file you've
832) downloaded is

833)     exactly the one that we intended you to get.
834)     </p>

835) 

836)     <p>
837)     Please read the <a

838)     href="<page docs/verifying-signatures>">verifying signatures</a>
839) page for details.

840)     </p>

841) 

842) <hr>
843) 
844) <a id="GetTor"></a>
845) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
846) country. How do I download Tor?</a></h3>
847) 
848) <p>
849) Some government or corporate firewalls censor connections to Tor's
850) website. In those cases, you have three options. First, get it from

851) a friend &mdash; the <a href="<page projects/torbrowser>">Tor Browser

852) Bundle</a> fits nicely on a USB key. Second, find the <a

853) href="https://encrypted.google.com/search?q=tor+mirrors">google
854) cache</a>

855) for the <a href="<page getinvolved/mirrors>">Tor mirrors</a> page
856) and see if any of those copies of our website work for you. Third,
857) you can download Tor via email: log in to your Gmail account and mail

858) '<tt>gettor@gettor.torproject.org</tt>'. If you include the word 'help'

859) in the body of the email, it will reply with instructions. Note that
860) only a few webmail providers are supported, since they need to be able
861) to receive very large attachments.
862) </p>
863) 
864) <p>

865) Be sure to <a href="<page docs/verifying-signatures>">verify the
866) signature</a>

867) of any package you download, especially when you get it from somewhere
868) other than our official HTTPS website.

869) </p>
870) 
871) <hr>

872) 

873)     <a id="CompileTorWindows"></a>

874)     <h3><a class="anchor" href="#CompileTorWindows">How do I compile Tor
875) under Windows?</a></h3>

876) 

877)     <p>

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

880)     tor-win32-mingw-creation.txt</a>.
881)     </p>

882) 

883)     <p>
884)     (Note that you don't need to compile Tor yourself in order to use

885)     it. Most people just use the packages available on the <a
886) href="<page

887)     download/download>">download page</a>.)
888)     </p>

889) 

890)     <hr>

891) 

892)     <a id="VirusFalsePositives"></a>

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

895) 

896)     <p>

897)     Sometimes, overzealous Windows virus and spyware detectors trigger
898) on some
899)     parts of the Tor Windows binary. Our best guess is that these are
900) false
901)     positives — after all, the anti-virus and anti-spyware
902) business is just a
903)     guessing game anyway. You should contact your vendor and explain
904) that you have
905)     a program that seems to be triggering false positives. Or pick a
906) better vendor.

907)     </p>

908) 

909)     <p>
910)     In the meantime, we encourage you to not just take our word for

911)     it. Our job is to provide the source; if you're concerned, please do
912) <a

913)     href="#CompileTorWindows">recompile it yourself</a>.
914)     </p>

915) 

916)     <hr>

917) 

918)     <a id="LiveCD"></a>

919)     <h3><a class="anchor" href="#LiveCD">Is there a LiveCD or other
920) bundle that includes Tor?</a></h3>

921) 

922)     <p>

923)     Yes.  Use <a href="https://tails.boum.org/">The Amnesic Incognito

924)     Live System</a> or <a href="<page projects/torbrowser>">the Tor
925) Browser

926)     Bundle</a>.

927)     </p>

928) 
929) <hr>
930) 

931) <a id="TBBFlash"></a>

932) <h3><a class="anchor" href="#TBBFlash">Why can't I view videos on
933) YouTube

934) and other Flash-based sites?</a></h3>

935) 
936) <p>

937) YouTube and similar sites require third party browser plugins such as Flash.
938) Plugins operate independently from Firefox and can perform
939) activity on your computer that ruins your anonymity. This includes
940) but is not limited to: <a href="http://decloak.net">completely disregarding
941) proxy settings</a>, querying your <a
942) href="http://forums.sun.com/thread.jspa?threadID=5162138&amp;messageID=9618376">local
943) IP address</a>, and <a
944) href="http://epic.org/privacy/cookies/flash.html">storing their own
945) cookies</a>. It is possible to use a LiveCD solution such as
946) or <a href="https://tails.boum.org/">The Amnesic Incognito Live System</a> that creates a
947) secure, transparent proxy to protect you from proxy bypass, however issues
948) with local IP address discovery and Flash cookies still remain.  </p>
949) 
950) <p>

951) <a href="https://www.youtube.com/html5">YouTube offers experimental HTML5 video
952) support</a> for many of their videos. You can use their Advanced Search to

953) find HTML5 videos.
954) </p>
955) 

956) <hr>
957) 

958) <a id="TBBSocksPort"></a>

959) <h3><a class="anchor" href="#TBBSocksPort">

960) I want to run another application through the Tor launched by Tor

961) Browser Bundle.</a></h3>

962) 
963) <p>

964) Typically Tor listens for Socks connections on port 9050. TBB listens

965) on port 9150.

966) The goal is to avoid conflicting with a "system" Tor install,

967) so you can run a system Tor and TBB at the same time. We're <a
968) href="https://trac.torproject.org/projects/tor/ticket/3948">working on
969) a feature</a> where Tor will try the usual ports first and then back

970) off to a random choice if they're already in use.

971) </p>
972) 
973) <hr>
974) 
975) <a id="TBBPolipo"></a>
976) <h3><a class="anchor" href="#TBBPolipo">I need an HTTP proxy. Where did
977) Polipo go?</a></h3>
978) 
979) <p>
980) In the past, Tor bundles included an HTTP proxy like Privoxy or Polipo,
981) solely to work around a bug in Firefox that was finally fixed in Firefox
982) 6. Now you don't need a separate HTTP proxy to use Tor, and in fact
983) leaving it out makes you safer because Torbutton has better control over
984) Firefox's interaction with websites.
985) </p>
986) 
987) <p>
988) If you are trying to use some external application with Tor, step zero

989) should be to <a href="<page download/download>#warning">reread the set

990) of warnings</a> for ways you can screw up. Step one should be to try

991) to use a Socks proxy rather than an http proxy — Tor runs a Socks

992) proxy on port 9050 on Windows, or <a href="#TBBSocksPort">see above</a>
993) for OSX and Linux.
994) </p>
995) 
996) <p>

997) If that fails, feel free to install <a

998) href="http://www.privoxy.org/">privoxy</a>.
999) However, please realize that this approach is not recommended for novice
1000) users. Privoxy has an <a
1001) href="http://www.privoxy.org/faq/misc.html#TOR">example
1002) configuration</a> of Tor and Privoxy.

1003) </p>
1004) 
1005) <hr>
1006) 

1007) <a id="TBBOtherExtensions"></a>
1008) <h3><a class="anchor" href="#TBBOtherExtensions">Can I install other
1009) Firefox extensions?</a></h3>
1010) 
1011) <p>
1012) Yes. Just install them like normal. But be sure to avoid extensions like

1013) Foxyproxy that screw up your proxy settings. Also, avoid
1014) privacy-invasive

1015) extensions (for example, pretty much anything with the word Toolbar in
1016) its name).
1017) </p>
1018) 

1019) <p>

1020) Generally, extensions that require registration, and/or provide
1021) additional information about websites you are visiting, should be

1022) suspect.
1023) </p>
1024) 
1025) <p>
1026) Extensions you might like include
1027)  <a href="https://addons.mozilla.org/firefox/addon/953">RefControl</a> (referer spoofing),
1028)  <a href="https://addons.mozilla.org/firefox/addon/1474">SafeCache</a>,
1029)  <a href="https://addons.mozilla.org/en-US/firefox/addon/6623">Better Privacy</a>,
1030)  <a href="https://addons.mozilla.org/firefox/addon/1865">AdBlock Plus</a> (EasyPrivacy+EasyList),
1031)  <a href="https://addons.mozilla.org/firefox/addon/82">Cookie Culler</a>,
1032)  <a href="https://addons.mozilla.org/en-US/firefox/addon/9727/">Request Policy</a> and
1033)  <a href="https://addons.mozilla.org/en-US/firefox/addon/certificate-patrol/">Certificate Patrol</a>.

1034) </p>

1035) 

1036) <hr>
1037) 

1038) <a id="TBBJavaScriptEnabled"></a>

1039) <a id="TBBCanIBlockJS"></a>

1040) <h3><a class="anchor" href="#TBBJavaScriptEnabled">Why is NoScript
1041) configured to allow JavaScript by default in the Tor Browser Bundle?
1042) Isn't that unsafe?</a></h3>

1043) 
1044) <p>
1045) We configure NoScript to allow JavaScript by default in the Tor
1046) Browser Bundle because many websites will not work with JavaScript
1047) disabled.  Most users would give up on Tor entirely if a website
1048) they want to use requires JavaScript, because they would not know
1049) how to allow a website to use JavaScript (or that enabling
1050) JavaScript might make a website work).
1051) </p>
1052) 

1053) <p>
1054) There's a tradeoff here. On the one hand, we should leave
1055) JavaScript enabled by default so websites work the way
1056) users expect. On the other hand, we should disable JavaScript
1057) by default to better protect against browser vulnerabilities (<a
1058) href="https://blog.torproject.org/blog/tor-security-advisory-old-tor-browser-bundles-vulnerable">not
1059) just a theoretical concern!</a>). But there's a third issue: websites
1060) can easily determine whether you have allowed JavaScript for them,
1061) and if you disable JavaScript by default but then allow a few websites
1062) to run scripts (the way most people use NoScript), then your choice of
1063) whitelisted websites acts as a sort of cookie that makes you recognizable
1064) (and distinguishable), thus harming your anonymity.
1065) </p>

1066) 
1067) <p>

1068) Ultimately, we want the default Tor bundles to use
1069) a combination of firewalls (like the iptables rules
1070) in <a href="https://tails.boum.org/">Tails</a>) and <a
1071) href="https://trac.torproject.org/projects/tor/ticket/7680">sandboxes</a>
1072) to make JavaScript not so scary. In
1073) the shorter term, TBB 3.0 will hopefully <a
1074) href="https://trac.torproject.org/projects/tor/ticket/9387">allow users
1075) to choose their JavaScript settings more easily</a> &mdash; but the
1076) partitioning concern will remain.

1077) </p>
1078) 
1079) <p>

1080) Until we get there, feel free to leave JavaScript on or off depending
1081) on your security, anonymity, and usability priorities.

1082) </p>
1083) 
1084) <hr>
1085) 

1086) <a id="TBBOtherBrowser"></a>
1087) <h3><a class="anchor" href="#TBBOtherBrowser">I want to use
1088) Chrome/IE/Opera/etc with Tor.</a></h3>
1089) 
1090) <p>
1091) Unfortunately, Torbutton only works with Firefox right now, and without
1092) <a href="https://www.torproject.org/torbutton/en/design/">Torbutton's
1093) extensive privacy fixes</a> there are many ways for websites or other

1094) attackers to recognize you, track you back to your IP address, and so
1095) on.

1096) In short, using any browser besides Tor Browser Bundle with Tor is a
1097) really bad idea.
1098) </p>
1099) 
1100) <p>
1101) We're working with the Chrome team to <a

1102) href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-
1103) and-fingerprinting">fix
1104) some bugs and missing APIs in Chrome</a> so it will be possible to write
1105) a
1106) Torbutton for Chrome. No support for any other browser is on the
1107) horizon.

1108) </p>
1109) 
1110) <hr>
1111) 
1112) <a id="TBBCloseBrowser"></a>

1113) <h3><a class="anchor" href="#TBBCloseBrowser">I want to leave Tor
1114) Browser

1115) Bundle running but close the browser.</a></h3>
1116) 
1117) <p>
1118) We're working on a way to make this possible on all platforms. Please
1119) be patient.
1120) </p>
1121) 
1122) <hr>
1123) 

1124) <a id="GoogleCAPTCHA"></a>
1125) <h3><a class="anchor" href="#GoogleCAPTCHA">Google makes me solve a
1126) CAPTCHA or tells me I have spyware installed.</a></h3>

1127) 
1128) <p>
1129) This is a known and intermittent problem; it does not mean that Google
1130) considers Tor to be spyware.
1131) </p>
1132) 
1133) <p>

1134) When you use Tor, you are sending queries through exit relays that are
1135) also

1136) shared by thousands of other users. Tor users typically see this message

1137) when many Tor users are querying Google in a short period of time.
1138) Google

1139) interprets the high volume of traffic from a single IP address (the exit
1140) relay you happened to pick) as somebody trying to "crawl" their website,
1141) so it slows down traffic from that IP address for a short time.
1142) </p>
1143) <p>
1144) An alternate explanation is that Google tries to detect certain
1145) kinds of spyware or viruses that send distinctive queries to Google
1146) Search. It notes the IP addresses from which those queries are received
1147) (not realizing that they are Tor exit relays), and tries to warn any
1148) connections coming from those IP addresses that recent queries indicate
1149) an infection.
1150) </p>
1151) 
1152) <p>

1153) To our knowledge, Google is not doing anything intentionally
1154) specifically

1155) to deter or block Tor use. The error message about an infected machine
1156) should clear up again after a short time.
1157) </p>
1158) 
1159) <p>
1160) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
1161) automatically redirect you to a more Tor-friendly search engine such as

1162) DuckDuckGo, ixquick, or Bing.

1163) </p>
1164) 
1165) <hr />
1166) 
1167) <a id="GmailWarning"></a>

1168) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my
1169) account

1170) may have been compromised.</a></h3>

1171) 
1172) <p>
1173) Sometimes, after you've used Gmail over Tor, Google presents a
1174) pop-up notification that your account may have been compromised.
1175) The notification window lists a series of IP addresses and locations
1176) throughout the world recently used to access your account.
1177) </p>
1178) 
1179) <p>
1180) In general this is a false alarm: Google saw a bunch of logins from

1181) different places, as a result of running the service via Tor, and
1182) decided

1183) it was a good idea to confirm the account was being accessed by it's
1184) rightful owner.
1185) </p>
1186) 
1187) <p>
1188) Even though this may be a biproduct of using the service via tor,
1189) that doesn't mean you can entirely ignore the warning. It is
1190) <i>probably</i> a false positive, but it might not be since it is
1191) possible for someone to hijack your Google cookie.
1192) </p>
1193) 
1194) <p>
1195) Cookie hijacking is possible by either physical access to your computer
1196) or by watching your network traffic.  In theory only physical access
1197) should compromise your system because Gmail and similar services
1198) should only send the cookie over an SSL link. In practice, alas, it's <a

1199) href="http://fscked.org/blog/fully-automated-active-https-cookie-
1200) hijacking">

1201) way more complex than that</a>.
1202) </p>
1203) 
1204) <p>
1205) And if somebody <i>did</i> steal your google cookie, they might end
1206) up logging in from unusual places (though of course they also might
1207) not). So the summary is that since you're using Tor, this security
1208) measure that Google uses isn't so useful for you, because it's full of
1209) false positives. You'll have to use other approaches, like seeing if
1210) anything looks weird on the account, or looking at the timestamps for
1211) recent logins and wondering if you actually logged in at those times.
1212) </p>
1213) 
1214) <hr>
1215) 

1216) <a id="torrc"></a>

1217) <h3><a class="anchor" href="#torrc">I'm supposed to "edit my torrc".
1218) What does that mean?</a></h3>

1219) 
1220) <p>
1221) Tor installs a text file called torrc that contains configuration
1222) instructions for how your Tor program should behave. The default
1223) configuration should work fine for most Tor users. Users of Vidalia can
1224) make common changes through the Vidalia interface &mdash; only advanced
1225) users should need to modify their torrc file directly.
1226) </p>

1227) <p>

1228) Tor Browser Bundle users should edit your torrc through Vidalia. Open
1229) the
1230) Vidalia Control Panel. Choose Settings. Choose Advanced. Click the
1231) button

1232) labelled "Edit current torrc". Remember to make sure the checkbox for
1233) "Save Settings." is checked. Hit the Ok button and you are done.
1234) </p>

1235) <p>

1236) Otherwise, you will need to edit the file manually.

1237) The location of your torrc file depends on the way you installed Tor:
1238) </p>
1239) <ul>

1240) <li>If you installed Tor Browser Bundle, look for
1241) <code>Data/Tor/torrc</code> inside your Tor Browser Bundle directory.
1242) </li>

1243) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
1244) find your torrc file in the Start menu under Programs -&gt; Vidalia
1245) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
1246) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
1247) installed Tor without Vidalia, you can find your torrc in the Start
1248) menu under Programs -&gt; Tor, or manually in either <code>\Documents
1249) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
1250) Settings\<i>username</i>\Application Data\tor\torrc</code>.
1251) </li>
1252) <li>On OS X, if you use Vidalia, edit
1253) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
1254) and load <code>/Library/Tor/torrc</code>.
1255) </li>
1256) <li>On Unix, if you installed a pre-built package, look for
1257) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
1258) package's documentation.
1259) </li>
1260) <li>Finally, if you installed from source, you may not have a torrc
1261) installed yet: look in <code>/usr/local/etc/</code> and note that you

1262) may need to manually copy <code>torrc.sample</code> to
1263) <code>torrc</code>.

1264) </li>
1265) </ul>
1266) 
1267) <p>
1268) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit

1269) your torrc file manually. Otherwise Vidalia might overwrite your
1270) changes.

1271) </p>
1272) 
1273) <p>
1274) Once you've changed your torrc, you will need to restart Tor for the
1275) changes to take effect. (For advanced users on OS X and Unix, note that

1276) you actually only need to send Tor a HUP signal, not actually restart
1277) it.)

1278) </p>
1279) 
1280) <p>
1281) For other configuration options you can use, look at the <a href="<page
1282) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
1283) with # in torrc are treated as comments and have no effect on Tor's
1284) configuration.
1285) </p>
1286) 
1287) <hr>
1288) 

1289) <a id="Logs"></a>

1290) <h3><a class="anchor" href="#Logs">How do I set up logging, or see Tor's
1291) logs?</a></h3>

1292) 
1293) <p>

1294) If you installed a Tor bundle that includes Vidalia, then Vidalia has a

1295) window called "Message Log" that will show you Tor's log messages. Click
1296) on "Advanced" to see more details. You can click on "Settings" to change
1297) your log verbosity or save the messages to a file. You're all set.

1298) </p>
1299) 
1300) <p>
1301) If you're not using Vidalia, you'll have to go find the log files by

1302) hand. Here are some likely places for your logs to be:

1303) </p>
1304) 
1305) <ul>
1306) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
1307) </li>

1308) <li>On Windows, there are no default log files currently. If you enable
1309) logs in your torrc file, they default to <code>\username\Application
1310) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
1311) </li>
1312) <li>If you compiled Tor from source, by default your Tor logs to <a
1313) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
1314) at log-level notice. If you enable logs in your torrc file, they
1315) default to <code>/usr/local/var/log/tor/</code>.

1316) </li>
1317) </ul>
1318) 
1319) <p>

1320) To change your logging setup by hand, <a href="#torrc">edit your
1321) torrc</a>

1322) and find the section (near the top of the file) which contains the
1323) following line:

1324) </p>
1325) 
1326) <pre>

1327) \## Logs go to stdout at level "notice" unless redirected by something
1328) \## else, like one of the below lines.

1329) </pre>

1330) 
1331) <p>

1332) For example, if you want Tor to send complete debug, info, notice, warn,

1333) and err level messages to a file, append the following line to the end
1334) of the section:
1335) </p>
1336) 
1337) <pre>
1338) Log debug file c:/program files/tor/debug.log
1339) </pre>
1340) 
1341) <p>

1342) Replace <code>c:/program files/tor/debug.log</code> with a directory
1343) and filename for your Tor log.

1344) </p>
1345) 
1346) <hr>
1347) 

1348) <a id="DoesntWork"></a>

1349) <h3><a class="anchor" href="#DoesntWork">I installed Tor but it's not
1350) working.</a></h3>

1351) 
1352) <p>

1353) Once you've got the Tor bundle up and running, the first question to
1354) ask is whether your Tor client is able to establish a circuit.

1355) </p>
1356) 
1357) <p>If Tor can establish a circuit, the onion icon in

1358) Vidalia will turn green (and if you're running Tor Browser Bundle, it
1359) will
1360) automatically launch a browser for you). You can also check in the
1361) Vidalia

1362) Control Panel to make sure it says "Connected to the Tor
1363) network!" under Status. For those not using Vidalia, check your <a

1364) href="#Logs">Tor logs</a> for

1365) a line saying that Tor "has successfully opened a circuit. Looks like
1366) client functionality is working."
1367) </p>
1368) 
1369) <p>
1370) If Tor can't establish a circuit, here are some hints:
1371) </p>
1372) 
1373) <ol>
1374) <li>Are you sure Tor is running? If you're using Vidalia, you may have
1375) to click on the onion and select "Start" to launch Tor.</li>
1376) <li>Check your system clock. If it's more than a few hours off, Tor will

1377) refuse to build circuits. For Microsoft Windows users, synchronize your
1378) clock under the clock -> Internet time tab. In addition, correct the

1379) day and date under the 'Date & Time' Tab. Also make sure your time
1380) zone is correct.</li>

1381) <li>Is your Internet connection <a href="#FirewallPorts">firewalled
1382) by port</a>, or do you normally need to use a <a

1383) href="<wikifaq>#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</
1384) a>?

1385) </li>

1386) <li>Are you running programs like Norton Internet Security or SELinux
1387) that

1388) block certain connections, even though you don't realize they do? They
1389) could be preventing Tor from making network connections.</li>
1390) <li>Are you in China, or behind a restrictive corporate network firewall
1391) that blocks the public Tor relays? If so, you should learn about <a

1392) href="<page docs/bridges>">Tor bridges</a>.</li>

1393) <li>Check your <a href="#Logs">Tor logs</a>. Do they give you any hints
1394) about what's going wrong?</li>

1395) </ol>
1396) 
1397) <hr />
1398) 
1399) <a id="VidaliaPassword"></a>

1400) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for a
1401) password at start.</a></h3>

1402) 
1403) <p>
1404) Vidalia interacts with the Tor software via Tor's "control port". The
1405) control port lets Vidalia receive status updates from Tor, request a new
1406) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
1407) Vidalia sets a random password for Tor's control port to prevent other
1408) applications from also connecting to the control port and potentially
1409) compromising your anonymity.
1410) </p>
1411) 
1412) <p>
1413) Usually this process of generating and setting a random control password
1414) happens in the background. There are three common situations, though,
1415) where Vidalia may prompt you for a password:
1416) </p>
1417) 
1418) <ol>
1419) <li>You're already running Vidalia and Tor. For example, this situation
1420) can happen if you installed the Vidalia bundle and now you're trying to
1421) run the Tor Browser Bundle. In that case, you'll need to close the old
1422) Vidalia and Tor before you can run this one.
1423) </li>
1424) <li>Vidalia crashed, but left Tor running with the last known random
1425) password. After you restart Vidalia, it generates a new random password,

1426) but Vidalia can't talk to Tor, because the random passwords are
1427) different.

1428) <br />

1429) If the dialog that prompts you for a control password has a Reset
1430) button,

1431) you can click the button and Vidalia will restart Tor with a new random
1432) control password.
1433) <br />
1434) If you do not see a Reset button, or if Vidalia is unable to restart
1435) Tor for you, you can still fix the problem manually. Simply go into your
1436) process or task manager, and terminate the Tor process. Then use Vidalia
1437) to restart Tor and all will work again.
1438) </li>
1439) <li>You had previously set Tor to run as a Windows NT service. When Tor
1440) is set to
1441) run as a service, it starts up when the system boots. If you configured
1442) Tor to start as a service through Vidalia, a random password was set
1443) and saved in Tor. When you reboot, Tor starts up and uses the random
1444) password it saved. You login and start up Vidalia. Vidalia attempts to
1445) talk to the already running Tor. Vidalia generates a random password,
1446) but it is different than the saved password in the Tor service.
1447) <br />
1448) You need to reconfigure Tor to not be a service. See the FAQ entry on

1449) <a href="<wikifaq>#HowdoIrunmyTorrelayasanNTservice">running Tor as a
1450) Windows NT service</a>

1451) for more information on how to remove the Tor service.
1452) </li>
1453) </ol>
1454) 

1455)     <hr>

1456) 

1457)     <a id="ChooseEntryExit"></a>

1458)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which
1459) nodes (or country) are used for entry/exit?</a></h3>

1460) 

1461)     <p>

1462)     Yes. You can set preferred entry and exit nodes as well as
1463)     inform Tor which nodes you do not want to use.

1464)     The following options can be added to your config file <a
1465)     href="#torrc">"torrc"</a> or specified on the command line:

1466)     </p>
1467)     <dl>
1468)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>

1469)         <dd>A list of preferred nodes to use for the first hop in the
1470) circuit, if possible.

1471)         </dd>
1472)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1473)         <dd>A list of preferred nodes to use for the last hop in the
1474) circuit, if possible.

1475)         </dd>
1476)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1477)         <dd>A list of nodes to never use when building a circuit.

1478)         </dd>
1479)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1480)         <dd>A list of nodes to never use when picking an exit.

1481)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in
1482) this list.

1483)         </dd>
1484)     </dl>
1485)     <p>

1486)     <em>We recommend you do not use these</em>

1487)     — they are intended for testing and may disappear in future
1488) versions.

1489)     You get the best security that Tor can provide when you leave the
1490)     route selection to Tor; overriding the entry / exit nodes can mess
1491)     up your anonymity in ways we don't understand.

1492)     </p>
1493)     <p>

1494)     Note also that not every circuit is used to deliver traffic outside of the Tor network. It is normal to see non-exit circuits (such as those used to connect to hidden services, those that do directory fetches, those used for relay reachability self-tests, and so on) that end at a non-exit node. To keep a node from being used entirely, see <tt>ExcludeNodes</tt> and <tt>StrictNodes</tt> in the <a href="<page docs/tor-manual>">manual</a>.

1495)     </p>
1496)     <p>

1497)     Instead of <tt>$fingerprint</tt> you can also specify a <a

1498) 
1499) href="https://secure.wikimedia.org/wikipedia/en/wiki/ISO_3166-1_alpha-2"
1500) >2

1501)     letter ISO3166 country code</a> in curly braces (for example <tt>{de}</tt>),

1502)     or an ip address pattern (for example 255.254.0.0/8), or a node
1503)     nickname. Make sure there are no spaces between the commas and the
1504)     list items.

1505)     </p>
1506)     <p>

1507)     If you want to access a service directly through Tor's Socks
1508) interface

1509)     (eg. using ssh via connect.c), another option is to set up an

1510)     internal mapping in your configuration file using
1511) <tt>MapAddress</tt>.

1512)     See the manual page for details.
1513)     </p>

1514) 

1515)     <hr>

1516) 

1517) <a id="FirewallPorts"></a>

1518) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a
1519) few outgoing ports.</a></h3>

1520) 
1521) <p>
1522) If your firewall works by blocking ports, then you can tell Tor to only

1523) use the ports that your firewall permits by adding "FascistFirewall 1"
1524) to

1525) your <a href="<page docs/faq>#torrc">torrc

1526) configuration file</a>, or by clicking "My firewall only lets me connect
1527) to certain ports" in Vidalia's Network Settings window.
1528) </p>
1529) 
1530) <p>
1531) By default, when you set this Tor assumes that your firewall allows only
1532) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1533) different set of ports with the FirewallPorts torrc option.
1534) </p>
1535) 
1536) <p>
1537) If you want to be more fine-grained with your controls, you can also
1538) use the ReachableAddresses config options, e.g.:
1539) </p>
1540) 
1541) <pre>
1542)   ReachableDirAddresses *:80
1543)   ReachableORAddresses *:443
1544) </pre>
1545) 
1546) <hr>

1547) 

1548)     <a id="RelayFlexible"></a>

1549)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay
1550) need to be?</a></h3>

1551) 

1552)     <p>
1553)     We aim to make setting up a Tor relay easy and convenient:
1554)     </p>

1555) 

1556)     <ul>
1557)     <li>Tor has built-in support for <a

1558)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1559)     rate limiting</a>. Further, if you have a fast
1560)     link but want to limit the number of bytes per
1561)     day (or week or month) that you donate, check out the <a

1562) 
1563) href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">
1564) hibernation

1565)     feature</a>.
1566)     </li>

1567)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a>
1568) that
1569)     specifies what sort of outbound connections are allowed or refused
1570) from
1571)     that relay. If you are uncomfortable allowing people to exit from
1572) your
1573)     relay, you can set it up to only allow connections to other Tor
1574) relays.

1575)     </li>
1576)     <li>It's fine if the relay goes offline sometimes. The directories
1577)     notice this quickly and stop advertising the relay. Just try to make
1578)     sure it's not too often, since connections using the relay when it
1579)     disconnects will break.
1580)     </li>
1581)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1582)     leave the Address config option blank, and Tor will try to guess.
1583)     </li>
1584)     <li>If your relay is behind a NAT and it doesn't know its public
1585)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1586)     forwarding. Forwarding TCP connections is system dependent but

1587)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1588)     offers some examples on how to do this.
1589)     </li>
1590)     <li>Your relay will passively estimate and advertise its recent

1591)     bandwidth capacity, so high-bandwidth relays will attract more users
1592) than
1593)     low-bandwidth ones. Therefore having low-bandwidth relays is useful
1594) too.

1595)     </li>
1596)     </ul>

1597) 

1598)     <hr>

1599) 

1600)     <a id="RunARelayBut"></a>
1601)     <a id="ExitPolicies"></a>

1602)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I
1603) don't want to deal with abuse issues.</a></h3>

1604) 

1605)     <p>
1606)     Great. That's exactly why we implemented exit policies.
1607)     </p>

1608) 

1609)     <p>
1610)     Each Tor relay has an exit policy that specifies what sort of

1611)     outbound connections are allowed or refused from that relay. The
1612) exit

1613)     policies are propagated to Tor clients via the directory, so clients
1614)     will automatically avoid picking exit relays that would refuse to
1615)     exit to their intended destination. This way each relay can decide
1616)     the services, hosts, and networks he wants to allow connections to,

1617)     based on abuse potential and his own situation. Read the FAQ entry
1618) on
1619)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might
1620) encounter</a>

1621)     if you use the default exit policy, and then read Mike Perry's

1622)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1623)     for running an exit node with minimal harassment</a>.
1624)     </p>

1625) 

1626)     <p>

1627)     The default exit policy allows access to many popular services

1628)     (e.g. web browsing), but <a
1629) href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1630)     some due to abuse potential (e.g. mail) and some since
1631)     the Tor network can't handle the load (e.g. default
1632)     file-sharing ports). You can change your exit policy

1633)     using Vidalia's "Sharing" tab, or by manually editing your

1634)     <a href="<page docs/faq>#torrc">torrc</a>

1635)     file. If you want to avoid most if not all abuse potential, set it
1636) to
1637)     "reject *:*" (or un-check all the boxes in Vidalia). This setting
1638) means
1639)     that your relay will be used for relaying traffic inside the Tor
1640) network,

1641)     but not for connections to external websites or other services.
1642)     </p>

1643) 

1644)     <p>

1645)     If you do allow any exit connections, make sure name resolution
1646) works

1647)     (that is, your computer can resolve Internet addresses correctly).

1648)     If there are any resources that your computer can't reach (for
1649) example,

1650)     you are behind a restrictive firewall or content filter), please

1651)     explicitly reject them in your exit policy — otherwise Tor
1652) users

1653)     will be impacted too.
1654)     </p>

1655) 

1656)     <hr>

1657) 

1658)     <a id="RelayOrBridge"></a>

1659)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal
1660) relay or bridge relay?</a></h3>

1661) 

1662)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for
1663) short)
1664)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't

1665)     listed in the public Tor directory.

1666)     That means that ISPs or governments trying to block access to the

1667)     Tor network can't simply block all bridges.

1668)     </p>

1669) 

1670)     <p>Being a normal relay vs being a bridge relay is almost the same
1671)     configuration: it's just a matter of whether your relay is listed

1672)     publicly or not.

1673)     </p>

1674) 

1675)     <p>

1676)     So bridges are useful a) for Tor users in oppressive regimes,

1677)     and b) for people who want an extra layer of security

1678)     because they're worried somebody will recognize that it's a public
1679)     Tor relay IP address they're contacting.

1680)     </p>

1681) 

1682)     <p>
1683)     Several countries, including China and Iran, have found ways to

1684)     detect and block connections to Tor bridges.

1685)     <a href="<page projects/obfsproxy>">Obfsproxy</a> bridges address

1686)     this by adding another layer of obfuscation.

1687)     </p>
1688) 

1689)     <p>So should you run a normal relay or bridge relay? If you have
1690) lots

1691)     of bandwidth, you should definitely run a normal relay.
1692)     If you're willing

1693)     to <a href="#ExitPolicies">be an exit</a>, you should definitely
1694)     run a normal relay, since we need more exits. If you can't be an
1695)     exit and only have a little bit of bandwidth, be a bridge. Thanks
1696)     for volunteering!

1697)     </p>

1698) 

1699)     <hr>

1700) 

1701) <a id="MultipleRelays"></a>

1702) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one
1703) relay.</a></h3>

1704) 
1705) <p>
1706) Great. If you want to run several relays to donate more to the network,
1707) we're happy with that. But please don't run more than a few dozen on
1708) the same network, since part of the goal of the Tor network is dispersal
1709) and diversity.
1710) </p>
1711) 
1712) <p>
1713) If you do decide to run more than one relay, please set the "MyFamily"

1714) config option in the <a href="#torrc">torrc</a> of each relay, listing
1715) all the relays (comma-separated) that are under your control:

1716) </p>
1717) 
1718) <pre>
1719)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
1720) </pre>
1721) 
1722) <p>
1723) where each fingerprint is the 40 character identity fingerprint (without

1724) spaces). You can also list them by nickname, but fingerprint is safer.
1725) Be

1726) sure to prefix the digest strings with a dollar sign ('$') so that the
1727) digest is not confused with a nickname in the config file.
1728) </p>
1729) 
1730) <p>
1731) That way clients will know to avoid using more than one of your relays
1732) in a single circuit. You should set MyFamily if you have administrative
1733) control of the computers or of their network, even if they're not all in
1734) the same geographic location.
1735) </p>
1736) 
1737)     <hr>
1738) 

1739)     <a id="RelayMemory"></a>

1740)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using
1741) so much memory?</a></h3>

1742) 

1743)     <p>If your Tor relay is using more memory than you'd like, here are
1744) some

1745)     tips for reducing its footprint:
1746)     </p>

1747) 

1748)     <ol>
1749)     <li>If you're on Linux, you may be encountering memory fragmentation

1750)     bugs in glibc's malloc implementation. That is, when Tor releases
1751) memory
1752)     back to the system, the pieces of memory are fragmented so they're
1753) hard
1754)     to reuse. The Tor tarball ships with OpenBSD's malloc
1755) implementation,
1756)     which doesn't have as many fragmentation bugs (but the tradeoff is
1757) higher
1758)     CPU load). You can tell Tor to use this malloc implementation
1759) instead:

1760)     <tt>./configure --enable-openbsd-malloc</tt></li>

1761) 

1762)     <li>If you're running a fast relay, meaning you have many TLS
1763) connections

1764)     open, you are probably losing a lot of memory to OpenSSL's internal
1765)     buffers (38KB+ per socket). We've patched OpenSSL to <a

1766) 
1767) href="https://lists.torproject.org/pipermail/tor-dev/2008-June/001519.
1768) html">release

1769)     unused buffer memory more aggressively</a>. If you update to OpenSSL

1770)     1.0.0 or newer, Tor's build process will automatically recognize and
1771) use

1772)     this feature.</li>

1773) 

1774)     <li>If you're running on Solaris, Tor is probably
1775)     forking separate processes for each CPUWorker rather
1776)     than using threads. Try explicitly configuring Tor with
1777)     <tt>--enable-threads</tt>, but be ready for the lockups some
1778)     people reported back in 2005. Also consider running your relay on <a
1779)     href="https://trac.torproject.org/projects/tor/wiki/doc/TorFAQ#WhydoesntmyWindowsorotherOSTorrelayrunwell">an
1780)     operating system where Tor works better</a>.</li>

1781) 

1782)     <li>If you still can't handle the memory load, consider reducing the

1783)     amount of bandwidth your relay advertises. Advertising less
1784) bandwidth

1785)     means you will attract fewer users, so your relay shouldn't grow
1786)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1787)     page.</li>

1788) 

1789)     </ol>

1790) 

1791)     <p>

1792)     All of this said, fast Tor relays do use a lot of ram. It is not
1793) unusual

1794)     for a fast exit relay to use 500-1000 MB of memory.
1795)     </p>

1796) 

1797)     <hr>

1798) 

1799)     <a id="WhyNotNamed"></a>

1800)     <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not
1801) named?</a></h3>

1802) 

1803)     <p>

1804)     We currently use these metrics to determine if your relay should be
1805) named:<br>

1806)     </p>
1807)     <ul>

1808)     <li>The name is not currently mapped to a different key. Existing
1809) mappings

1810)     are removed after 6 months of inactivity from a relay.</li>
1811)     <li>The relay must have been around for at least two weeks.</li>

1812)     <li>No other router may have wanted the same name in the past
1813) month.</li>

1814)     </ul>

1815) 

1816)     <hr>

1817) 

1818)     <a id="RelayDonations"></a>

1819)     <h3><a class="anchor" href="#RelayDonations">Can I donate for a
1820)     relay rather than run my own?</a></h3>

1821) 
1822)     <p>

1823)     Sure! We recommend these non-profit charities that are happy to turn

1824)     your donations into better speed and anonymity for the Tor network:
1825)     </p>
1826)     <ul>
1827)     <li><a href="https://www.torservers.net/">torservers.net</a>
1828)     is a German charitable non-profit that runs a wide variety of

1829)     exit relays worldwide. They also like donations of bandwidth from
1830)     ISPs.</li>

1831)     <li><a

1832) href="https://www.noisebridge.net/wiki/Noisebridge_Tor">Noisebridge</a>

1833)     is a US-based 501(c)(3) non-profit that collects donations and turns

1834)     them into more US-based exit relay capacity.</li>
1835)     <li><a href="https://nos-oignons.net/">Nos Oignons</a> is a French
1836)     charitable non-profit that runs fast exit relays in France.</li>

1837)     </ul>
1838) 
1839)     <p>
1840)     These organizations are not the same as <a href="<page
1841)     donate/donate>">The Tor Project, Inc</a>, but we consider that a

1842)     good thing. They're both run by nice people who are part of the
1843)     Tor community.

1844)     </p>
1845) 
1846)     <p>
1847)     Note that there can be a tradeoff here between anonymity and

1848)     performance. The Tor network's anonymity comes in part from
1849) diversity,

1850)     so if you are in a position to run your own relay, you will be

1851)     improving Tor's anonymity more than by donating. At the same time
1852)     though, economies

1853)     of scale for bandwidth mean that combining many small donations into

1854)     several larger relays is more efficient at improving network

1855)     performance. Improving anonymity and improving performance are both
1856)     worthwhile goals, so however you can help is great!
1857)     </p>
1858) 
1859)     <hr>
1860) 

1861)     <a id="KeyManagement"></a>

1862)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the
1863) keys Tor uses.</a></h3>

1864) 

1865)     <p>
1866)     Tor uses a variety of different keys, with three goals in mind: 1)
1867)     encryption to ensure privacy of data within the Tor network, 2)
1868)     authentication so clients know they're

1869)     talking to the relays they meant to talk to, and 3) signatures to
1870) make

1871)     sure all clients know the same set of relays.
1872)     </p>

1873) 

1874)     <p>

1875)     <b>Encryption</b>: first, all connections in Tor use TLS link
1876) encryption,

1877)     so observers can't look inside to see which circuit a given cell is

1878)     intended for. Further, the Tor client establishes an ephemeral
1879) encryption

1880)     key with each relay in the circuit; these extra layers of encryption
1881)     mean that only the exit relay can read

1882)     the cells. Both sides discard the circuit key when the circuit ends,

1883)     so logging traffic and then breaking into the relay to discover the
1884) key

1885)     won't work.
1886)     </p>

1887) 

1888)     <p>
1889)     <b>Authentication</b>:
1890)     Every Tor relay has a public decryption key called the "onion key".

1891)     Each relay rotates its onion key once a week.

1892)     When the Tor client establishes circuits, at each step it <a

1893) 
1894) href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands

1895)     that the Tor relay prove knowledge of its onion key</a>. That way
1896)     the first node in the path can't just spoof the rest of the path.

1897)     Because the Tor client chooses the path, it can make sure to get
1898)     Tor's "distributed trust" property: no single relay in the path can
1899)     know about both the client and what the client is doing.

1900)     </p>

1901) 

1902)     <p>
1903)     <b>Coordination</b>:

1904)     How do clients know what the relays are, and how do they know that
1905) they
1906)     have the right keys for them? Each relay has a long-term public
1907) signing
1908)     key called the "identity key". Each directory authority additionally
1909) has a

1910)     "directory signing key". The directory authorities <a

1911)     href="<specblob>dir-spec.txt">provide a signed list</a>

1912)     of all the known relays, and in that list are a set of certificates
1913) from
1914)     each relay (self-signed by their identity key) specifying their
1915) keys,
1916)     locations, exit policies, and so on. So unless the adversary can
1917) control

1918)     a majority of the directory authorities (as of 2012 there are 8

1919)     directory authorities), he can't trick the Tor client into using
1920)     other Tor relays.

1921)     </p>

1922) 

1923)     <p>

1924)     How do clients know what the directory authorities are? The Tor
1925) software
1926)     comes with a built-in list of location and public key for each
1927) directory
1928)     authority. So the only way to trick users into using a fake Tor
1929) network

1930)     is to give them a specially modified version of the software.
1931)     </p>

1932) 

1933)     <p>
1934)     How do users know they've got the right software? When we distribute
1935)     the source code or a package, we digitally sign it with <a
1936)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
1937)     href="<page docs/verifying-signatures>">instructions
1938)     on how to check Tor's signatures</a>.
1939)     </p>

1940) 

1941)     <p>

1942)     In order to be certain that it's really signed by us, you need to
1943) have
1944)     met us in person and gotten a copy of our GPG key fingerprint, or
1945) you
1946)     need to know somebody who has. If you're concerned about an attack
1947) on
1948)     this level, we recommend you get involved with the security
1949) community

1950)     and start meeting people.
1951)     </p>

1952) 

1953)     <hr>

1954) 

1955) <a id="EntryGuards"></a>

1956) <h3><a class="anchor" href="#EntryGuards">What are Entry
1957) Guards?</a></h3>

1958) 
1959) <p>
1960) Tor (like all current practical low-latency anonymity designs) fails
1961) when the attacker can see both ends of the communications channel. For

1962) example, suppose the attacker controls or watches the Tor relay you
1963) choose
1964) to enter the network, and also controls or watches the website you
1965) visit. In

1966) this case, the research community knows no practical low-latency design
1967) that can reliably stop the attacker from correlating volume and timing
1968) information on the two sides.
1969) </p>
1970) 
1971) <p>
1972) So, what should we do? Suppose the attacker controls, or can observe,

1973) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
1974) new entry and exit relays each time you use the network, the attacker
1975) will be able to correlate all traffic you send with probability
1976) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
1977) as being traced all the time: they want to do something often without
1978) an attacker noticing, and the attacker noticing once is as bad as the

1979) attacker noticing more often. Thus, choosing many random entries and
1980) exits

1981) gives the user no chance of escaping profiling by this kind of attacker.

1982) </p>
1983) 
1984) <p>

1985) The solution is "entry guards": each Tor client selects a few relays at
1986) random

1987) to use as entry points, and uses only those relays for her first hop. If
1988) those relays are not controlled or observed, the attacker can't win,
1989) ever, and the user is secure. If those relays <i>are</i> observed or
1990) controlled by the attacker, the attacker sees a larger <i>fraction</i>

1991) of the user's traffic — but still the user is no more profiled
1992) than

1993) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
1994) of avoiding profiling, whereas she had none before.

1995) </p>
1996) 
1997) <p>

1998) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
1999) Analysis of the Degradation of Anonymous Protocols</a>, <a
2000) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
2001) Communication Against Passive Logging Attacks</a>, and especially
2002) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
2003) Servers</a>.

2004) </p>
2005) 
2006) <p>
2007) Restricting your entry nodes may also help against attackers who want
2008) to run a few Tor nodes and easily enumerate all of the Tor user IP
2009) addresses. (Even though they can't learn what destinations the users
2010) are talking to, they still might be able to do bad things with just a

2011) list of users.) However, that feature won't really become useful until
2012) we move to a "directory guard" design as well.

2013) </p>
2014) 
2015)     <hr>
2016) 

2017)     <a id="EverybodyARelay"></a>

2018)     <h3><a class="anchor" href="#EverybodyARelay">You should make every
2019) Tor user be a relay.</a></h3>

2020) 

2021)     <p>
2022)     Requiring every Tor user to be a relay would help with scaling the

2023)     network to handle all our users, and <a
2024)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

2025)     relay may help your anonymity</a>. However, many Tor users cannot be
2026) good
2027)     relays &mdash; for example, some Tor clients operate from behind
2028) restrictive
2029)     firewalls, connect via modem, or otherwise aren't in a position
2030) where they

2031)     can relay traffic. Providing service to these clients is a critical

2032)     part of providing effective anonymity for everyone, since many Tor
2033) users
2034)     are subject to these or similar constraints and including these
2035) clients

2036)     increases the size of the anonymity set.
2037)     </p>

2038) 

2039)     <p>

2040)     That said, we do want to encourage Tor users to run relays, so what
2041) we
2042)     really want to do is simplify the process of setting up and
2043) maintaining
2044)     a relay. We've made a lot of progress with easy configuration in the
2045) past
2046)     few years: Vidalia has an easy relay configuration interface, and
2047) supports
2048)     uPnP too. Tor is good at automatically detecting whether it's
2049) reachable and

2050)     how much bandwidth it can offer.
2051)     </p>

2052) 

2053)     <p>

2054)     There are five steps we need to address before we can do this
2055) though:

2056)     </p>

2057) 

2058)     <p>
2059)     First, we need to make Tor stable as a relay on all common
2060)     operating systems. The main remaining platform is Windows,

2061)     and we're mostly there. See Section 4.1 of <a

2062) 
2063) href="https://www.torproject.org/press/2008-12-19-roadmap-press-release"
2064) >our

2065)     development roadmap</a>.
2066)     </p>

2067) 

2068)     <p>
2069)     Second, we still need to get better at automatically estimating
2070)     the right amount of bandwidth to allow. See item #7 on the

2071)     <a href="<page getinvolved/volunteer>#Research">research section of
2072) the

2073)     volunteer page</a>: "Tor doesn't work very well when relays
2074)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

2075)     href="<page docs/faq>#TransportIPnotTCP">switching

2076)     to UDP transport</a> is the simplest answer here &mdash; which alas
2077) is

2078)     not a very simple answer at all.
2079)     </p>

2080) 

2081)     <p>
2082)     Third, we need to work on scalability, both of the network (how to
2083)     stop requiring that all Tor relays be able to connect to all Tor
2084)     relays) and of the directory (how to stop requiring that all Tor
2085)     users know about all Tor relays). Changes like this can have large
2086)     impact on potential and actual anonymity. See Section 5 of the <a
2087)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
2088)     for details. Again, UDP transport would help here.
2089)     </p>

2090) 

2091)     <p>
2092)     Fourth, we need to better understand the risks from
2093)     letting the attacker send traffic through your relay while
2094)     you're also initiating your own anonymized traffic. <a
2095)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
2096)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
2097)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
2098)     describe ways to identify the relays in a circuit by running traffic

2099)     through candidate relays and looking for dips in the traffic while
2100) the
2101)     circuit is active. These clogging attacks are not that scary in the
2102) Tor
2103)     context so long as relays are never clients too. But if we're trying
2104) to
2105)     encourage more clients to turn on relay functionality too (whether
2106) as
2107)     <a href="<page docs/bridges>">bridge relays</a> or as normal
2108) relays), then
2109)     we need to understand this threat better and learn how to mitigate
2110) it.
2111)     </p>
2112) 
2113)     <p>
2114)     Fifth, we might need some sort of incentive scheme to encourage
2115) people
2116)     to relay traffic for others, and/or to become exit nodes. Here are
2117) our

2118)     <a href="<blog>two-incentive-designs-tor">current

2119)     thoughts on Tor incentives</a>.
2120)     </p>

2121) 

2122)     <p>
2123)     Please help on all of these!
2124)     </p>

2125) 

2126) <hr>
2127) 
2128) <a id="TransportIPnotTCP"></a>

2129) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all
2130) IP packets, not just TCP packets.</a></h3>

2131) 
2132) <p>

2133) This would be handy, because it would make Tor better able to handle
2134) new protocols like VoIP, it could solve the whole need to socksify
2135) applications, and it would solve the fact that exit relays need to

2136) allocate a lot of file descriptors to hold open all the exit
2137) connections.

2138) </p>
2139) 
2140) <p>

2141) We're heading in this direction: see <a
2142) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
2143) ticket</a> for directions we should investigate. Some of the hard
2144) problems are:

2145) </p>
2146) 

2147) <ol>

2148) <li>IP packets reveal OS characteristics. We would still need to do
2149) IP-level packet normalization, to stop things like TCP fingerprinting
2150) attacks. Given the diversity and complexity of TCP stacks, along with <a

2151) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

2152) fingerprinting attacks</a>, it looks like our best bet is shipping our
2153) own user-space TCP stack.

2154) </li>

2155) <li>Application-level streams still need scrubbing. We will still need
2156) user-side applications like Torbutton. So it won't become just a matter
2157) of capturing packets and anonymizing them at the IP layer.

2158) </li>
2159) <li>Certain protocols will still leak information. For example, we must
2160) rewrite DNS requests so they are delivered to an unlinkable DNS server
2161) rather than the DNS server at a user's ISP; thus, we must understand
2162) the protocols we are transporting.
2163) </li>
2164) <li><a

2165) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS
2166) </a>

2167) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
2168) picked a transport mechanism, we need to design a new end-to-end Tor
2169) protocol for avoiding tagging attacks and other potential anonymity and
2170) integrity issues now that we allow drops, resends, et cetera.

2171) </li>
2172) <li>Exit policies for arbitrary IP packets mean building a secure
2173) IDS. Our node operators tell us that exit policies are one of the main
2174) reasons they're willing to run Tor. Adding an Intrusion Detection System
2175) to handle exit policies would increase the security complexity of Tor,

2176) and would likely not work anyway, as evidenced by the entire field of
2177) IDS

2178) and counter-IDS papers. Many potential abuse issues are resolved by the
2179) fact that Tor only transports valid TCP streams (as opposed to arbitrary
2180) IP including malformed packets and IP floods), so exit policies become
2181) even <i>more</i> important as we become able to transport IP packets. We
2182) also need to compactly describe exit policies in the Tor directory,

2183) so clients can predict which nodes will allow their packets to exit
2184) —

2185) and clients need to predict all the packets they will want to send in
2186) a session before picking their exit node!
2187) </li>

2188) <li>The Tor-internal name spaces would need to be redesigned. We support
2189) hidden service ".onion" addresses by intercepting the addresses when
2190) they are passed to the Tor client. Doing so at the IP level will require
2191) a more complex interface between Tor and the local DNS resolver.

2192) </li>

2193) </ol>
2194) 
2195) <hr>
2196) 
2197) <a id="HideExits"></a>
2198) <h3><a class="anchor" href="#HideExits">You should hide the list of Tor
2199) relays, so people can't block the exits.</a></h3>
2200) 
2201) <p>
2202) There are a few reasons we don't:
2203) </p>
2204) 
2205) <ol>
2206) <li>We can't help but make the information available, since Tor clients
2207) need to use it to pick their paths. So if the "blockers" want it, they
2208) can get it anyway. Further, even if we didn't tell clients about the
2209) list of relays directly, somebody could still make a lot of connections
2210) through Tor to a test site and build a list of the addresses they see.
2211) </li>
2212) 

2213) <li>If people want to block us, we believe that they should be allowed
2214) to

2215) do so.  Obviously, we would prefer for everybody to allow Tor users to
2216) connect to them, but people have the right to decide who their services

2217) should allow connections from, and if they want to block anonymous
2218) users,

2219) they can.
2220) </li>
2221) 
2222) <li>Being blockable also has tactical advantages: it may be a persuasive

2223) response to website maintainers who feel threatened by Tor. Giving them
2224) the option may inspire them to <a href="<page docs/faq-abuse>#Bans">stop
2225) and think</a> about whether they really want to eliminate private access
2226) to their system, and if not, what other options they might have. The
2227) time they might otherwise have spent blocking Tor, they may instead
2228) spend rethinking their overall approach to privacy and anonymity.

2229) </li>

2230) </ol>
2231) 

2232)     <hr>

2233) 

2234)     <a id="Criminals"></a>

2235)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals
2236) to do bad things?</a></h3>

2237) 

2238)     <p>
2239)     For the answer to this question and others, please see our <a
2240)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
2241)     </p>

2242) 

2243)     <hr>

2244) 

2245)     <a id="RespondISP"></a>

2246)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP
2247) about my exit relay?</a></h3>

2248) 

2249)     <p>
2250)     A collection of templates for successfully responding to ISPs is <a

2251)     href="<wiki>doc/TorAbuseTemplates">collected

2252)     here</a>.
2253)     </p>

2254) 

2255)     <hr>

2256) 

2257)   </div>
2258)   <!-- END MAINCOL -->
2259)   <div id = "sidecol">
2260) #include "side.wmi"
2261) #include "info.wmi"
2262)   </div>
2263)   <!-- END SIDECOL -->
2264) </div>
2265) <!-- END CONTENT -->

2266) #include <foot.wmi>