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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?</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="#TBBCanIBlockJS">I'm an expert!  (No, really!)  Can I
70) configure NoScript to block JavaScript by default?</a></li>

71)     <li><a href="#TBBOtherBrowser">I want to use Chrome/IE/Opera/etc
72)     with Tor.</a></li>
73)     <li><a href="#TBBCloseBrowser">I want to leave Tor Browser Bundle
74)     running but close the browser.</a></li>
75) 

76)     <li><a href="#GoogleCaptcha">Google makes me solve a Captcha or
77) tells

78)     me I have spyware installed.</a></li>
79)     <li><a href="#GmailWarning">Gmail warns me that my account may have
80)     been compromised.</a></li>
81)     </ul>
82) 
83)     <p>Advanced Tor usage:</p>

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

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

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

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

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

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

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

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

98)     </ul>

99) 

100)     <p>Running a Tor relay:</p>
101)     <ul>

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

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

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

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

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

116)     </ul>

117) 

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

119) 

120)     <p>Anonymity and Security:</p>
121)     <ul>

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

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

125)     </ul>

126) 

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

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

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

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

136)     </ul>

137) 

138)     <p>Abuse:</p>

139)     <ul>

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

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

145) 

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

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

149) 

150)     <hr>

151) 

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

153) 

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

156) 

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

160) 

161)     <p>

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

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

167)     the world: it prevents somebody watching your Internet connection
168) from

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

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

174)     href="<page about/overview>">overview page</a>.
175)     </p>

176) 

177)     <p>

178)     The Tor Project is a non-profit (charity) organization that
179) maintains

180)     and develops the Tor software.
181)     </p>

182) 

183)     <hr>

184) 

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

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

209) free wifi Internet.
210)     </p>
211)     <p>

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

218) inside your

219) encrypted traffic as they relay it to your banking site or to ecommerce
220) stores.

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

222) watching your traffic, injecting their own advertisements into your
223) traffic

224) stream, and recording your personal details.

225)     </p>
226)     <p>

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

243) packets between themselves.</p>

244)     <p>
245)     <dl>

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

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

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

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

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

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

268)     </dl>
269)     </p>

270) 

271)     <hr>

272) 

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

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

276) 

277)     <p>

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

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

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

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

297) 

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

300)     bundles on the <a href="<page download/download>">download page</a>
301) automatically

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

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

307) 

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

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

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

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

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

319) 

320)     <hr>

321) 

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

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

325) 

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

335) 

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

339) 

340)     <p>

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

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

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

348)     spell it wrong.
349)     </p>

350) 

351)     <hr>

352) 

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

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

356) 

357)     <p>

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

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

365) 

366)     <p>
367)     We think that putting a backdoor in Tor would be tremendously

368)     irresponsible to our users, and a bad precedent for security
369) software

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

374) 

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

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

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

388) 

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

391)     anonymity. We periodically find and fix anonymity-related bugs, so
392) make

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

395) 

396)     <hr>

397) 

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

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

401) 

402)     <p>
403)     Yes.
404)     </p>

405) 

406)     <p>

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

413)     ask us for specific permission.
414)     </p>

415) 

416)     <p>

417)     However, if you want to redistribute the Tor software you must
418) follow our

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

420)     Essentially this means that you need to include our LICENSE file
421) along

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

424) 

425)     <p>

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

428)     Tor software, though. They want to distribute the <a
429)     href="https://www.torproject.org/projects/torbrowser.html.en">Tor
430)     Browser</a>. This includes <a
431)     href="https://www.mozilla.org/en-US/firefox/all-aurora.html">Mozilla
432)     Aurora</a> and <a href="<page projects/vidalia>">Vidalia</a>.

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

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

442)     </p>

443) 

444)     <p>

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

451)     </p>

452) 

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

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

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

462) 

463)     <hr>

464) 

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

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

468) 

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

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

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

474)     <li>Read through the <a

475) 
476) href="https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk">
477) tor-talk

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

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

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

482)     <li>Send an email to <a

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

487)     </ol>

488) 

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

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

492) 

493)     <hr>

494) 

495)     <a id="Forum"></a>
496)     <h3><a class="anchor" href="#Forum">Is there a Tor forum?</a></h3>
497) 
498)     <p>Not yet, but we're working on it. Most forum software is
499)     a disaster to maintain and keep secure, and at the same time
500)     too many of the Tor developers are spread too thin to be able
501)     to contribute enough to a forum. As of June 2012, we have a
502)     funder who wants to help us do it right. Stay tuned! (Tickets <a
503)     href="https://trac.torproject.org/projects/tor/ticket/3592">3592</a>
504)     and <a
505)     href="https://trac.torproject.org/projects/tor/ticket/5995">5995</a>
506)     relate to forums too.)
507)     </p>
508) 
509)     <hr>
510) 

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

513) 

514)     <p>
515)     There are many reasons why the Tor network is currently slow.
516)     </p>

517) 

518)     <p>

519)     Before we answer, though, you should realize that Tor is never going
520) to
521)     be blazing fast. Your traffic is bouncing through volunteers'
522) computers
523)     in various parts of the world, and some bottlenecks and network
524) latency

525)     will always be present. You shouldn't expect to see university-style
526)     bandwidth through Tor.
527)     </p>

528) 

529)     <p>

530)     But that doesn't mean that it can't be improved. The current Tor
531) network
532)     is quite small compared to the number of people trying to use it,
533) and
534)     many of these users don't understand or care that Tor can't
535) currently

536)     handle file-sharing traffic load.
537)     </p>

538) 

539)     <p>
540)     For the much more in-depth answer, see <a

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

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

544)     to go with it.
545)     </p>

546) 

547)     <p>
548)     What can you do to help?
549)     </p>

550) 

551)     <ul>

552) 

553)     <li>

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

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

560) 

561)     <li>

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

564)     especially need people to help make it easier to configure your Tor
565)     as a relay. Also, we need help with clear simple documentation to
566)     walk people through setting it up.
567)     </li>

568) 

569)     <li>

570)     There are some bottlenecks in the current Tor network. Help us
571) design
572)     experiments to track down and demonstrate where the problems are,
573) and

574)     then we can focus better on fixing them.
575)     </li>

576) 

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

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

583)     get to spend more time on it.
584)     </li>

585) 

586)     <li>

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

591)     getinvolved/volunteer>">look at our volunteer page</a>.
592)     </li>

593) 

594)     <li>

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

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

598)     competition's websites discreetly, or to connect back to the home
599) servers
600)     when on the road without revealing affiliations? If your
601) organization has
602)     an interest in keeping the Tor network working, please contact them
603) about
604)     supporting Tor. Without sponsors, Tor is going to become even
605) slower.

606)     </li>

607) 

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

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

612)     cause</a>. It adds up!
613)     </li>

614) 

615)     </ul>

616) 

617)     <hr>

618) 

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

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

622) 

623)     <p>

624)     The Tor network's <a

625) 
626) href="https://metrics.torproject.org/network.html#networksize">several

627)     thousand</a> relays push <a
628)     href="https://metrics.torproject.org/network.html#bandwidth">over
629)     1GB per second on average</a>. We have <a

630) 
631) href="https://metrics.torproject.org/users.html#direct-users">several

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

634)     </p>

635) 

636)     <p>

637)     There are six main development/maintenance pushes that need
638) attention:

639)     </p>

640) 

641)     <ul>

642) 

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

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

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

650) 

651)     <li>

652)     User support: With this many users, a lot of people are asking
653) questions
654)     all the time, offering to help out with things, and so on. We need
655) good
656)     clean docs, and we need to spend some effort coordinating
657) volunteers.

658)     </li>

659) 

660)     <li>

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

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

664)     reminders to upgrade, and so on. The network itself is a commons,
665) and
666)     somebody needs to spend some energy making sure the relay operators
667) stay
668)     happy. We also need to work on stability on some platforms —
669) e.g.,

670)     Tor relays have problems on Win XP currently.

671)     </li>

672) 

673)     <li>

674)     Usability: Beyond documentation, we also need to work on usability
675) of the
676)     software itself. This includes installers, clean GUIs, easy
677) configuration
678)     to interface with other applications, and generally automating all
679) of
680)     the difficult and confusing steps inside Tor. We've got a start on
681) this
682)     with the <a href="<page projects/vidalia>">Vidalia GUI</a>, but much
683) more work

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

686) 

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

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

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

694) 

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

700)     critical <a href="<page getinvolved/volunteer>#Research">Tor
701) research questions</a>
702)     that will help us figure out how to make Tor secure against the
703) variety of
704)     attacks out there. Of course, there are more research questions
705) waiting

706)     behind these.
707)     </li>

708) 

709)     </ul>

710) 

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

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

715)     can keep up</a>.

716)     Now would be an excellent time to add a few more developers to the
717) effort

718)     so we can continue to grow the network.
719)     </p>

720) 

721)     <p>
722)     We are also excited about tackling related problems, such as
723)     censorship-resistance.
724)     </p>

725) 

726)     <p>

727)     We are proud to have <a href="<page about/sponsors>">sponsorship and
728) support</a>
729)     from the Omidyar Network, the International Broadcasting Bureau,
730) Bell
731)     Security Solutions, the Electronic Frontier Foundation, several
732) government

733)     agencies and research groups, and hundreds of private contributors.
734)     </p>

735) 

736)     <p>

737)     However, this support is not enough to keep Tor abreast of changes
738) in the
739)     Internet privacy landscape. Please <a href="<page
740) donate/donate>">donate</a>
741)     to the project, or <a href="<page about/contact>">contact</a> our
742) executive

743)     director for information on making grants or major donations.
744)     </p>

745) 

746)     <hr>
747) 

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

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

751) 

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

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

754)     <hr>

755) 

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

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

760)     <pre>

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

762)     The serial number is:

763) 06:DE:97:E5:1D:C3:9D:C2:64:8D:AC:72:DD:41:01:FC
764)     The SHA-1 fingerprint is: 1f9d306e8bfccfcb03981a71a27a9f5d1e0876ce

765)     The SHA-256 fingerprint is:

766) 3613d2b22a750094760c41ad19db52a4f05bdea80172e2578761ad967f7ed9aa

767) 

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

769)     The serial number is: 00:EF:A3
770)     The SHA-1 fingerprint is: 50af43db8438e67f305a3257d8ef198e8c42f13f

771)     </pre>

772)     </p>
773)     <hr>
774) 

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

776)     <h3><a class="anchor" href="#HowUninstallTor">How do I uninstall
777) Tor?</a></h3>
778) 
779)     <p>
780)     Tor Browser does not install itself in the classic sense of
781) applications. You just simply delete the folder or directory named "Tor
782) Browser" and it is removed from your system.
783)     </p>

784) 

785)     <p>

786)     If this is not related to Tor Browser, uninstallation depends
787) entirely on how you installed it and which operating system you
788)     have. If you installed a package, then hopefully your package has a
789) way to
790)     uninstall itself. The Windows packages include uninstallers. The
791) proper way to
792)     completely remove Tor, Vidalia, and Torbutton for Firefox on any
793) version of Windows is as follows:

794)     </p>

795) 

796)     <ol>

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

799)     and choose exit.</li>

800)     <li>Right click on the taskbar to bring up TaskManager. Look for
801) tor.exe in the
802)     Process List. If it's running, right click and choose End
803) Process.</li>
804)     <li>Click the Start button, go to Programs, go to Vidalia, choose
805) Uninstall.
806)     This will remove the Vidalia bundle, which includes Tor.</li>
807)     <li>Start Firefox. Go to the Tools menu, choose Add-ons. Select
808) Torbutton.

809)     Click the Uninstall button.</li>
810)     </ol>

811) 

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

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

817)     </p>

818) 

819)     <p>
820)     For Mac OS X, follow the <a
821)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
822)     </p>

823) 

824)     <p>

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

829)     be pretty easy to notice things there.
830)     </p>

831) 

832)     <hr>

833) 

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

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

837) 

838)     <p>

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

841)     exactly the one that we intended you to get.
842)     </p>

843) 

844)     <p>
845)     Please read the <a

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

848)     </p>

849) 

850) <hr>
851) 
852) <a id="GetTor"></a>
853) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
854) country. How do I download Tor?</a></h3>
855) 
856) <p>
857) Some government or corporate firewalls censor connections to Tor's
858) website. In those cases, you have three options. First, get it from

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

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

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

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

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

867) in the body of the email, it will reply with instructions. Note that
868) only a few webmail providers are supported, since they need to be able
869) to receive very large attachments.
870) </p>
871) 
872) <p>

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

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

877) </p>
878) 
879) <hr>

880) 

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

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

884) 

885)     <p>

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

888)     tor-win32-mingw-creation.txt</a>.
889)     </p>

890) 

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

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

895)     download/download>">download page</a>.)
896)     </p>

897) 

898)     <hr>

899) 

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

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

903) 

904)     <p>

905)     Sometimes, overzealous Windows virus and spyware detectors trigger
906) on some
907)     parts of the Tor Windows binary. Our best guess is that these are
908) false
909)     positives — after all, the anti-virus and anti-spyware
910) business is just a
911)     guessing game anyway. You should contact your vendor and explain
912) that you have
913)     a program that seems to be triggering false positives. Or pick a
914) better vendor.

915)     </p>

916) 

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

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

921)     href="#CompileTorWindows">recompile it yourself</a>.
922)     </p>

923) 

924)     <hr>

925) 

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

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

929) 

930)     <p>

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

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

934)     Bundle</a>.

935)     </p>

936) 
937) <hr>
938) 

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

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

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

943) 
944) <p>

945) <a
946) href="https://www.torproject.org/torbutton/torbutton-faq.html.
947) en#noflash">Answer</a>

948) </p>
949) 
950) <hr>
951) 

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

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

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

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

956) 
957) <p>

958) Typically Tor listens for Socks connections on port 9050. TBB listens
959) on port 9150. 
960) The goal is to avoid conflicting with a "system" Tor install,

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

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

965) </p>
966) 
967) <hr>
968) 
969) <a id="TBBPolipo"></a>
970) <h3><a class="anchor" href="#TBBPolipo">I need an HTTP proxy. Where did
971) Polipo go?</a></h3>
972) 
973) <p>
974) In the past, Tor bundles included an HTTP proxy like Privoxy or Polipo,
975) solely to work around a bug in Firefox that was finally fixed in Firefox
976) 6. Now you don't need a separate HTTP proxy to use Tor, and in fact
977) leaving it out makes you safer because Torbutton has better control over
978) Firefox's interaction with websites.
979) </p>
980) 
981) <p>
982) If you are trying to use some external application with Tor, step zero

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

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

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

986) proxy on port 9050 on Windows, or <a href="#TBBSocksPort">see above</a>
987) for OSX and Linux.
988) </p>
989) 
990) <p>

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

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

997) </p>
998) 
999) <hr>
1000) 

1001) <a id="TBBOtherExtensions"></a>
1002) <h3><a class="anchor" href="#TBBOtherExtensions">Can I install other
1003) Firefox extensions?</a></h3>
1004) 
1005) <p>
1006) Yes. Just install them like normal. But be sure to avoid extensions like

1007) Foxyproxy that screw up your proxy settings. Also, avoid
1008) privacy-invasive

1009) extensions (for example, pretty much anything with the word Toolbar in
1010) its name).
1011) </p>
1012) 
1013) <hr>
1014) 

1015) <a id="TBBJavaScriptEnabled"></a>

1016) <h3><a class="anchor" href="#TBBJavaScriptEnabled">Why is NoScript
1017) configured to allow JavaScript by default in the Tor Browser Bundle?
1018) Isn't that unsafe?</a></h3>

1019) 
1020) <p>
1021) We configure NoScript to allow JavaScript by default in the Tor
1022) Browser Bundle because many websites will not work with JavaScript
1023) disabled.  Most users would give up on Tor entirely if a website
1024) they want to use requires JavaScript, because they would not know
1025) how to allow a website to use JavaScript (or that enabling
1026) JavaScript might make a website work).
1027) </p>
1028) 
1029) <hr>
1030) 
1031) <a id="TBBCanIBlockJS"></a>

1032) <h3><a class="anchor" href="#CanIBlockJS">I'm an expert!  (No, really!)
1033) Can I configure NoScript to block JavaScript by default?</a></h3>

1034) 
1035) <p>
1036) You can configure your copies of Tor Browser Bundle however you want
1037) to.  However, we recommend that even users who know how to use
1038) NoScript leave JavaScript enabled if possible, because a website or
1039) exit node can easily distinguish users who disable JavaScript from
1040) users who use Tor Browser bundle with its default settings (thus
1041) users who disable JavaScript are less anonymous).
1042) </p>
1043) 
1044) <p>
1045) Disabling JavaScript by default, then allowing a few websites to run
1046) scripts, is especially bad for your anonymity: the set of websites
1047) which you allow to run scripts is very likely to <em>uniquely</em>
1048) identify your browser.
1049) </p>
1050) 
1051) <hr>
1052) 

1053) <a id="TBBOtherBrowser"></a>
1054) <h3><a class="anchor" href="#TBBOtherBrowser">I want to use
1055) Chrome/IE/Opera/etc with Tor.</a></h3>
1056) 
1057) <p>
1058) Unfortunately, Torbutton only works with Firefox right now, and without
1059) <a href="https://www.torproject.org/torbutton/en/design/">Torbutton's
1060) extensive privacy fixes</a> there are many ways for websites or other

1061) attackers to recognize you, track you back to your IP address, and so
1062) on.

1063) In short, using any browser besides Tor Browser Bundle with Tor is a
1064) really bad idea.
1065) </p>
1066) 
1067) <p>
1068) We're working with the Chrome team to <a

1069) href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-
1070) and-fingerprinting">fix
1071) some bugs and missing APIs in Chrome</a> so it will be possible to write
1072) a
1073) Torbutton for Chrome. No support for any other browser is on the
1074) horizon.

1075) </p>
1076) 
1077) <hr>
1078) 
1079) <a id="TBBCloseBrowser"></a>

1080) <h3><a class="anchor" href="#TBBCloseBrowser">I want to leave Tor
1081) Browser

1082) Bundle running but close the browser.</a></h3>
1083) 
1084) <p>
1085) We're working on a way to make this possible on all platforms. Please
1086) be patient.
1087) </p>
1088) 
1089) <hr>
1090) 

1091) <a id="GoogleCaptcha"></a>

1092) <h3><a class="anchor" href="#GoogleCaptcha">Google makes me solve a
1093) Captcha or tells me I have spyware installed.</a></h3>

1094) 
1095) <p>
1096) This is a known and intermittent problem; it does not mean that Google
1097) considers Tor to be spyware.
1098) </p>
1099) 
1100) <p>

1101) When you use Tor, you are sending queries through exit relays that are
1102) also

1103) shared by thousands of other users. Tor users typically see this message

1104) when many Tor users are querying Google in a short period of time.
1105) Google

1106) interprets the high volume of traffic from a single IP address (the exit
1107) relay you happened to pick) as somebody trying to "crawl" their website,
1108) so it slows down traffic from that IP address for a short time.
1109) </p>
1110) <p>
1111) An alternate explanation is that Google tries to detect certain
1112) kinds of spyware or viruses that send distinctive queries to Google
1113) Search. It notes the IP addresses from which those queries are received
1114) (not realizing that they are Tor exit relays), and tries to warn any
1115) connections coming from those IP addresses that recent queries indicate
1116) an infection.
1117) </p>
1118) 
1119) <p>

1120) To our knowledge, Google is not doing anything intentionally
1121) specifically

1122) to deter or block Tor use. The error message about an infected machine
1123) should clear up again after a short time.
1124) </p>
1125) 
1126) <p>
1127) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
1128) automatically redirect you to a more Tor-friendly search engine such as

1129) DuckDuckGo, ixquick, or Bing.

1130) </p>
1131) 
1132) <hr />
1133) 
1134) <a id="GmailWarning"></a>

1135) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my
1136) account

1137) may have been compromised.</a></h3>

1138) 
1139) <p>
1140) Sometimes, after you've used Gmail over Tor, Google presents a
1141) pop-up notification that your account may have been compromised.
1142) The notification window lists a series of IP addresses and locations
1143) throughout the world recently used to access your account.
1144) </p>
1145) 
1146) <p>
1147) In general this is a false alarm: Google saw a bunch of logins from

1148) different places, as a result of running the service via Tor, and
1149) decided

1150) it was a good idea to confirm the account was being accessed by it's
1151) rightful owner.
1152) </p>
1153) 
1154) <p>
1155) Even though this may be a biproduct of using the service via tor,
1156) that doesn't mean you can entirely ignore the warning. It is
1157) <i>probably</i> a false positive, but it might not be since it is
1158) possible for someone to hijack your Google cookie.
1159) </p>
1160) 
1161) <p>
1162) Cookie hijacking is possible by either physical access to your computer
1163) or by watching your network traffic.  In theory only physical access
1164) should compromise your system because Gmail and similar services
1165) should only send the cookie over an SSL link. In practice, alas, it's <a

1166) href="http://fscked.org/blog/fully-automated-active-https-cookie-
1167) hijacking">

1168) way more complex than that</a>.
1169) </p>
1170) 
1171) <p>
1172) And if somebody <i>did</i> steal your google cookie, they might end
1173) up logging in from unusual places (though of course they also might
1174) not). So the summary is that since you're using Tor, this security
1175) measure that Google uses isn't so useful for you, because it's full of
1176) false positives. You'll have to use other approaches, like seeing if
1177) anything looks weird on the account, or looking at the timestamps for
1178) recent logins and wondering if you actually logged in at those times.
1179) </p>
1180) 
1181) <hr>
1182) 

1183) <a id="torrc"></a>

1184) <h3><a class="anchor" href="#torrc">I'm supposed to "edit my torrc".
1185) What does that mean?</a></h3>

1186) 
1187) <p>
1188) Tor installs a text file called torrc that contains configuration
1189) instructions for how your Tor program should behave. The default
1190) configuration should work fine for most Tor users. Users of Vidalia can
1191) make common changes through the Vidalia interface &mdash; only advanced
1192) users should need to modify their torrc file directly.
1193) </p>

1194) <p>

1195) Tor Browser Bundle users should edit your torrc through Vidalia. Open
1196) the
1197) Vidalia Control Panel. Choose Settings. Choose Advanced. Click the
1198) button

1199) labelled "Edit current torrc". Remember to make sure the checkbox for
1200) "Save Settings." is checked. Hit the Ok button and you are done.
1201) </p>

1202) <p>

1203) Otherwise, you will need to edit the file manually.

1204) The location of your torrc file depends on the way you installed Tor:
1205) </p>
1206) <ul>

1207) <li>If you installed Tor Browser Bundle, look for
1208) <code>Data/Tor/torrc</code> inside your Tor Browser Bundle directory.
1209) </li>

1210) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
1211) find your torrc file in the Start menu under Programs -&gt; Vidalia
1212) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
1213) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
1214) installed Tor without Vidalia, you can find your torrc in the Start
1215) menu under Programs -&gt; Tor, or manually in either <code>\Documents
1216) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
1217) Settings\<i>username</i>\Application Data\tor\torrc</code>.
1218) </li>
1219) <li>On OS X, if you use Vidalia, edit
1220) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
1221) and load <code>/Library/Tor/torrc</code>.
1222) </li>
1223) <li>On Unix, if you installed a pre-built package, look for
1224) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
1225) package's documentation.
1226) </li>
1227) <li>Finally, if you installed from source, you may not have a torrc
1228) installed yet: look in <code>/usr/local/etc/</code> and note that you

1229) may need to manually copy <code>torrc.sample</code> to
1230) <code>torrc</code>.

1231) </li>
1232) </ul>
1233) 
1234) <p>
1235) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit

1236) your torrc file manually. Otherwise Vidalia might overwrite your
1237) changes.

1238) </p>
1239) 
1240) <p>
1241) Once you've changed your torrc, you will need to restart Tor for the
1242) changes to take effect. (For advanced users on OS X and Unix, note that

1243) you actually only need to send Tor a HUP signal, not actually restart
1244) it.)

1245) </p>
1246) 
1247) <p>
1248) For other configuration options you can use, look at the <a href="<page
1249) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
1250) with # in torrc are treated as comments and have no effect on Tor's
1251) configuration.
1252) </p>
1253) 
1254) <hr>
1255) 

1256) <a id="Logs"></a>

1257) <h3><a class="anchor" href="#Logs">How do I set up logging, or see Tor's
1258) logs?</a></h3>

1259) 
1260) <p>

1261) If you installed a Tor bundle that includes Vidalia, then Vidalia has a

1262) window called "Message Log" that will show you Tor's log messages. Click
1263) on "Advanced" to see more details. You can click on "Settings" to change
1264) your log verbosity or save the messages to a file. You're all set.

1265) </p>
1266) 
1267) <p>
1268) If you're not using Vidalia, you'll have to go find the log files by

1269) hand. Here are some likely places for your logs to be:

1270) </p>
1271) 
1272) <ul>
1273) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
1274) </li>

1275) <li>On Windows, there are no default log files currently. If you enable
1276) logs in your torrc file, they default to <code>\username\Application
1277) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
1278) </li>
1279) <li>If you compiled Tor from source, by default your Tor logs to <a
1280) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
1281) at log-level notice. If you enable logs in your torrc file, they
1282) default to <code>/usr/local/var/log/tor/</code>.

1283) </li>
1284) </ul>
1285) 
1286) <p>

1287) To change your logging setup by hand, <a href="#torrc">edit your
1288) torrc</a>

1289) and find the section (near the top of the file) which contains the
1290) following line:

1291) </p>
1292) 
1293) <pre>

1294) \## Logs go to stdout at level "notice" unless redirected by something
1295) \## else, like one of the below lines.

1296) </pre>

1297) 
1298) <p>

1299) For example, if you want Tor to send complete debug, info, notice, warn,

1300) and err level messages to a file, append the following line to the end
1301) of the section:
1302) </p>
1303) 
1304) <pre>
1305) Log debug file c:/program files/tor/debug.log
1306) </pre>
1307) 
1308) <p>

1309) Replace <code>c:/program files/tor/debug.log</code> with a directory
1310) and filename for your Tor log.

1311) </p>
1312) 
1313) <hr>
1314) 

1315) <a id="DoesntWork"></a>

1316) <h3><a class="anchor" href="#DoesntWork">I installed Tor but it's not
1317) working.</a></h3>

1318) 
1319) <p>

1320) Once you've got the Tor bundle up and running, the first question to
1321) ask is whether your Tor client is able to establish a circuit.

1322) </p>
1323) 
1324) <p>If Tor can establish a circuit, the onion icon in

1325) Vidalia will turn green (and if you're running Tor Browser Bundle, it
1326) will
1327) automatically launch a browser for you). You can also check in the
1328) Vidalia

1329) Control Panel to make sure it says "Connected to the Tor
1330) network!" under Status. For those not using Vidalia, check your <a

1331) href="#Logs">Tor logs</a> for

1332) a line saying that Tor "has successfully opened a circuit. Looks like
1333) client functionality is working."
1334) </p>
1335) 
1336) <p>
1337) If Tor can't establish a circuit, here are some hints:
1338) </p>
1339) 
1340) <ol>
1341) <li>Are you sure Tor is running? If you're using Vidalia, you may have
1342) to click on the onion and select "Start" to launch Tor.</li>
1343) <li>Check your system clock. If it's more than a few hours off, Tor will

1344) refuse to build circuits. For Microsoft Windows users, synchronize your
1345) clock under the clock -> Internet time tab. In addition, correct the

1346) day and date under the 'Date & Time' Tab. Also make sure your time
1347) zone is correct.</li>

1348) <li>Is your Internet connection <a href="#FirewallPorts">firewalled
1349) by port</a>, or do you normally need to use a <a

1350) href="<wikifaq>#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</
1351) a>?

1352) </li>

1353) <li>Are you running programs like Norton Internet Security or SELinux
1354) that

1355) block certain connections, even though you don't realize they do? They
1356) could be preventing Tor from making network connections.</li>
1357) <li>Are you in China, or behind a restrictive corporate network firewall
1358) that blocks the public Tor relays? If so, you should learn about <a

1359) href="<page docs/bridges>">Tor bridges</a>.</li>

1360) <li>Check your <a href="#Logs">Tor logs</a>. Do they give you any hints
1361) about what's going wrong?</li>

1362) </ol>
1363) 
1364) <hr />
1365) 
1366) <a id="VidaliaPassword"></a>

1367) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for a
1368) password at start.</a></h3>

1369) 
1370) <p>
1371) Vidalia interacts with the Tor software via Tor's "control port". The
1372) control port lets Vidalia receive status updates from Tor, request a new
1373) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
1374) Vidalia sets a random password for Tor's control port to prevent other
1375) applications from also connecting to the control port and potentially
1376) compromising your anonymity.
1377) </p>
1378) 
1379) <p>
1380) Usually this process of generating and setting a random control password
1381) happens in the background. There are three common situations, though,
1382) where Vidalia may prompt you for a password:
1383) </p>
1384) 
1385) <ol>
1386) <li>You're already running Vidalia and Tor. For example, this situation
1387) can happen if you installed the Vidalia bundle and now you're trying to
1388) run the Tor Browser Bundle. In that case, you'll need to close the old
1389) Vidalia and Tor before you can run this one.
1390) </li>
1391) <li>Vidalia crashed, but left Tor running with the last known random
1392) password. After you restart Vidalia, it generates a new random password,

1393) but Vidalia can't talk to Tor, because the random passwords are
1394) different.

1395) <br />

1396) If the dialog that prompts you for a control password has a Reset
1397) button,

1398) you can click the button and Vidalia will restart Tor with a new random
1399) control password.
1400) <br />
1401) If you do not see a Reset button, or if Vidalia is unable to restart
1402) Tor for you, you can still fix the problem manually. Simply go into your
1403) process or task manager, and terminate the Tor process. Then use Vidalia
1404) to restart Tor and all will work again.
1405) </li>
1406) <li>You had previously set Tor to run as a Windows NT service. When Tor
1407) is set to
1408) run as a service, it starts up when the system boots. If you configured
1409) Tor to start as a service through Vidalia, a random password was set
1410) and saved in Tor. When you reboot, Tor starts up and uses the random
1411) password it saved. You login and start up Vidalia. Vidalia attempts to
1412) talk to the already running Tor. Vidalia generates a random password,
1413) but it is different than the saved password in the Tor service.
1414) <br />
1415) You need to reconfigure Tor to not be a service. See the FAQ entry on

1416) <a href="<wikifaq>#HowdoIrunmyTorrelayasanNTservice">running Tor as a
1417) Windows NT service</a>

1418) for more information on how to remove the Tor service.
1419) </li>
1420) </ol>
1421) 

1422)     <hr>

1423) 

1424)     <a id="ChooseEntryExit"></a>

1425)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which
1426) nodes (or country) are used for entry/exit?</a></h3>

1427) 

1428)     <p>

1429)     Yes. You can set preferred entry and exit nodes as well as
1430)     inform Tor which nodes you do not want to use.

1431)     The following options can be added to your config file <a
1432)     href="#torrc">"torrc"</a> or specified on the command line:

1433)     </p>
1434)     <dl>
1435)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>

1436)         <dd>A list of preferred nodes to use for the first hop in the
1437) circuit, if possible.

1438)         </dd>
1439)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1440)         <dd>A list of preferred nodes to use for the last hop in the
1441) circuit, if possible.

1442)         </dd>
1443)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1444)         <dd>A list of nodes to never use when building a circuit.

1445)         </dd>
1446)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1447)         <dd>A list of nodes to never use when picking an exit.

1448)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in
1449) this list.

1450)         </dd>
1451)     </dl>
1452)     <p>

1453)     <em>We recommend you do not use these</em>

1454)     — they are intended for testing and may disappear in future
1455) versions.

1456)     You get the best security that Tor can provide when you leave the
1457)     route selection to Tor; overriding the entry / exit nodes can mess
1458)     up your anonymity in ways we don't understand.

1459)     </p>
1460)     <p>

1461)     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>.

1462)     </p>
1463)     <p>

1464)     Instead of <tt>$fingerprint</tt> you can also specify a <a

1465) 
1466) href="https://secure.wikimedia.org/wikipedia/en/wiki/ISO_3166-1_alpha-2"
1467) >2

1468)     letter ISO3166 country code</a> in curly braces (for example <tt>{de}</tt>),

1469)     or an ip address pattern (for example 255.254.0.0/8), or a node
1470)     nickname. Make sure there are no spaces between the commas and the
1471)     list items.

1472)     </p>
1473)     <p>

1474)     If you want to access a service directly through Tor's Socks
1475) interface

1476)     (eg. using ssh via connect.c), another option is to set up an

1477)     internal mapping in your configuration file using
1478) <tt>MapAddress</tt>.

1479)     See the manual page for details.
1480)     </p>

1481) 

1482)     <hr>

1483) 

1484) <a id="FirewallPorts"></a>

1485) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a
1486) few outgoing ports.</a></h3>

1487) 
1488) <p>
1489) If your firewall works by blocking ports, then you can tell Tor to only

1490) use the ports that your firewall permits by adding "FascistFirewall 1"
1491) to

1492) your <a href="<page docs/faq>#torrc">torrc

1493) configuration file</a>, or by clicking "My firewall only lets me connect
1494) to certain ports" in Vidalia's Network Settings window.
1495) </p>
1496) 
1497) <p>
1498) By default, when you set this Tor assumes that your firewall allows only
1499) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1500) different set of ports with the FirewallPorts torrc option.
1501) </p>
1502) 
1503) <p>
1504) If you want to be more fine-grained with your controls, you can also
1505) use the ReachableAddresses config options, e.g.:
1506) </p>
1507) 
1508) <pre>
1509)   ReachableDirAddresses *:80
1510)   ReachableORAddresses *:443
1511) </pre>
1512) 
1513) <hr>

1514) 

1515)     <a id="RelayFlexible"></a>

1516)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay
1517) need to be?</a></h3>

1518) 

1519)     <p>
1520)     We aim to make setting up a Tor relay easy and convenient:
1521)     </p>

1522) 

1523)     <ul>
1524)     <li>Tor has built-in support for <a

1525)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1526)     rate limiting</a>. Further, if you have a fast
1527)     link but want to limit the number of bytes per
1528)     day (or week or month) that you donate, check out the <a

1529) 
1530) href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">
1531) hibernation

1532)     feature</a>.
1533)     </li>

1534)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a>
1535) that
1536)     specifies what sort of outbound connections are allowed or refused
1537) from
1538)     that relay. If you are uncomfortable allowing people to exit from
1539) your
1540)     relay, you can set it up to only allow connections to other Tor
1541) relays.

1542)     </li>
1543)     <li>It's fine if the relay goes offline sometimes. The directories
1544)     notice this quickly and stop advertising the relay. Just try to make
1545)     sure it's not too often, since connections using the relay when it
1546)     disconnects will break.
1547)     </li>
1548)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1549)     leave the Address config option blank, and Tor will try to guess.
1550)     </li>
1551)     <li>If your relay is behind a NAT and it doesn't know its public
1552)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1553)     forwarding. Forwarding TCP connections is system dependent but

1554)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1555)     offers some examples on how to do this.
1556)     </li>
1557)     <li>Your relay will passively estimate and advertise its recent

1558)     bandwidth capacity, so high-bandwidth relays will attract more users
1559) than
1560)     low-bandwidth ones. Therefore having low-bandwidth relays is useful
1561) too.

1562)     </li>
1563)     </ul>

1564) 

1565)     <hr>

1566) 

1567)     <a id="RunARelayBut"></a>
1568)     <a id="ExitPolicies"></a>

1569)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I
1570) don't want to deal with abuse issues.</a></h3>

1571) 

1572)     <p>
1573)     Great. That's exactly why we implemented exit policies.
1574)     </p>

1575) 

1576)     <p>
1577)     Each Tor relay has an exit policy that specifies what sort of

1578)     outbound connections are allowed or refused from that relay. The
1579) exit

1580)     policies are propagated to Tor clients via the directory, so clients
1581)     will automatically avoid picking exit relays that would refuse to
1582)     exit to their intended destination. This way each relay can decide
1583)     the services, hosts, and networks he wants to allow connections to,

1584)     based on abuse potential and his own situation. Read the FAQ entry
1585) on
1586)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might
1587) encounter</a>

1588)     if you use the default exit policy, and then read Mike Perry's

1589)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1590)     for running an exit node with minimal harassment</a>.
1591)     </p>

1592) 

1593)     <p>

1594)     The default exit policy allows access to many popular services

1595)     (e.g. web browsing), but <a
1596) href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1597)     some due to abuse potential (e.g. mail) and some since
1598)     the Tor network can't handle the load (e.g. default
1599)     file-sharing ports). You can change your exit policy

1600)     using Vidalia's "Sharing" tab, or by manually editing your

1601)     <a href="<page docs/faq>#torrc">torrc</a>

1602)     file. If you want to avoid most if not all abuse potential, set it
1603) to
1604)     "reject *:*" (or un-check all the boxes in Vidalia). This setting
1605) means
1606)     that your relay will be used for relaying traffic inside the Tor
1607) network,

1608)     but not for connections to external websites or other services.
1609)     </p>

1610) 

1611)     <p>

1612)     If you do allow any exit connections, make sure name resolution
1613) works

1614)     (that is, your computer can resolve Internet addresses correctly).

1615)     If there are any resources that your computer can't reach (for
1616) example,

1617)     you are behind a restrictive firewall or content filter), please

1618)     explicitly reject them in your exit policy — otherwise Tor
1619) users

1620)     will be impacted too.
1621)     </p>

1622) 

1623)     <hr>

1624) 

1625)     <a id="RelayOrBridge"></a>

1626)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal
1627) relay or bridge relay?</a></h3>

1628) 

1629)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for
1630) short)
1631)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't

1632)     listed in the public Tor directory.
1633)     That means that ISPs or governments trying to block access to the 
1634)     Tor network can't simply block all bridges.

1635)     </p>

1636) 

1637)     <p>Being a normal relay vs being a bridge relay is almost the same
1638)     configuration: it's just a matter of whether your relay is listed

1639)     publicly or not.

1640)     </p>

1641) 

1642)     <p>
1643)     So bridges are useful a) for Tor users in oppressive regimes, 
1644)     and b) for people who want an extra layer of security

1645)     because they're worried somebody will recognize that it's a public
1646)     Tor relay IP address they're contacting.

1647)     </p>

1648) 

1649)     <p>
1650)     Several countries, including China and Iran, have found ways to
1651)     detect and block connections to Tor bridges. 
1652)     <a href="<page projects/obfsproxy>">Obfsproxy</a> bridges address
1653)     this by adding another layer of obfuscation. 
1654)     </p>
1655) 

1656)     <p>So should you run a normal relay or bridge relay? If you have
1657) lots

1658)     of bandwidth, you should definitely run a normal relay.
1659)     If you're willing

1660)     to <a href="#ExitPolicies">be an exit</a>, you should definitely
1661)     run a normal relay, since we need more exits. If you can't be an
1662)     exit and only have a little bit of bandwidth, be a bridge. Thanks
1663)     for volunteering!

1664)     </p>

1665) 

1666)     <hr>

1667) 

1668) <a id="MultipleRelays"></a>

1669) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one
1670) relay.</a></h3>

1671) 
1672) <p>
1673) Great. If you want to run several relays to donate more to the network,
1674) we're happy with that. But please don't run more than a few dozen on
1675) the same network, since part of the goal of the Tor network is dispersal
1676) and diversity.
1677) </p>
1678) 
1679) <p>
1680) If you do decide to run more than one relay, please set the "MyFamily"

1681) config option in the <a href="#torrc">torrc</a> of each relay, listing
1682) all the relays (comma-separated) that are under your control:

1683) </p>
1684) 
1685) <pre>
1686)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
1687) </pre>
1688) 
1689) <p>
1690) where each fingerprint is the 40 character identity fingerprint (without

1691) spaces). You can also list them by nickname, but fingerprint is safer.
1692) Be

1693) sure to prefix the digest strings with a dollar sign ('$') so that the
1694) digest is not confused with a nickname in the config file.
1695) </p>
1696) 
1697) <p>
1698) That way clients will know to avoid using more than one of your relays
1699) in a single circuit. You should set MyFamily if you have administrative
1700) control of the computers or of their network, even if they're not all in
1701) the same geographic location.
1702) </p>
1703) 
1704)     <hr>
1705) 

1706)     <a id="RelayMemory"></a>

1707)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using
1708) so much memory?</a></h3>

1709) 

1710)     <p>If your Tor relay is using more memory than you'd like, here are
1711) some

1712)     tips for reducing its footprint:
1713)     </p>

1714) 

1715)     <ol>
1716)     <li>If you're on Linux, you may be encountering memory fragmentation

1717)     bugs in glibc's malloc implementation. That is, when Tor releases
1718) memory
1719)     back to the system, the pieces of memory are fragmented so they're
1720) hard
1721)     to reuse. The Tor tarball ships with OpenBSD's malloc
1722) implementation,
1723)     which doesn't have as many fragmentation bugs (but the tradeoff is
1724) higher
1725)     CPU load). You can tell Tor to use this malloc implementation
1726) instead:

1727)     <tt>./configure --enable-openbsd-malloc</tt></li>

1728) 

1729)     <li>If you're running a fast relay, meaning you have many TLS
1730) connections

1731)     open, you are probably losing a lot of memory to OpenSSL's internal
1732)     buffers (38KB+ per socket). We've patched OpenSSL to <a

1733) 
1734) href="https://lists.torproject.org/pipermail/tor-dev/2008-June/001519.
1735) html">release

1736)     unused buffer memory more aggressively</a>. If you update to OpenSSL

1737)     1.0.0 or newer, Tor's build process will automatically recognize and
1738) use

1739)     this feature.</li>

1740) 

1741)     <li>If you're running on Solaris, OpenBSD, NetBSD, or
1742)     old FreeBSD, Tor is probably forking separate processes
1743)     rather than using threads. Consider switching to a <a

1744)     href="<wikifaq>#WhydoesntmyWindowsorotherOSTorrelayrunwell">better

1745)     operating system</a>.</li>

1746) 

1747)     <li>If you still can't handle the memory load, consider reducing the

1748)     amount of bandwidth your relay advertises. Advertising less
1749) bandwidth

1750)     means you will attract fewer users, so your relay shouldn't grow
1751)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1752)     page.</li>

1753) 

1754)     </ol>

1755) 

1756)     <p>

1757)     All of this said, fast Tor relays do use a lot of ram. It is not
1758) unusual

1759)     for a fast exit relay to use 500-1000 MB of memory.
1760)     </p>

1761) 

1762)     <hr>

1763) 

1764)     <a id="WhyNotNamed"></a>

1765)     <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not
1766) named?</a></h3>

1767) 

1768)     <p>

1769)     We currently use these metrics to determine if your relay should be
1770) named:<br>

1771)     </p>
1772)     <ul>

1773)     <li>The name is not currently mapped to a different key. Existing
1774) mappings

1775)     are removed after 6 months of inactivity from a relay.</li>
1776)     <li>The relay must have been around for at least two weeks.</li>

1777)     <li>No other router may have wanted the same name in the past
1778) month.</li>

1779)     </ul>

1780) 

1781)     <hr>

1782) 

1783)     <a id="RelayDonations"></a>

1784)     <h3><a class="anchor" href="#RelayDonations">Can I donate for a
1785)     relay rather than run my own?</a></h3>

1786) 
1787)     <p>
1788)     Sure! We recommend two non-profit charities that are happy to turn
1789)     your donations into better speed and anonymity for the Tor network:
1790)     </p>
1791)     <ul>
1792)     <li><a href="https://www.torservers.net/">torservers.net</a>
1793)     is a German charitable non-profit that runs a wide variety of

1794)     exit relays. They also like donations of bandwidth from ISPs.</li>

1795)     <li><a

1796) 
1797) href="https://www.noisebridge.net/wiki/Noisebridge_Tor">Noisebridge</a>

1798)     is a US-based 501(c)(3) non-profit that collects donations and turns
1799)     them into more exit relay capacity.</li>
1800)     </ul>
1801) 
1802)     <p>
1803)     These organizations are not the same as <a href="<page
1804)     donate/donate>">The Tor Project, Inc</a>, but we consider that a

1805)     good thing. They're both run by nice people who are part of the
1806)     Tor community.

1807)     </p>
1808) 
1809)     <p>
1810)     Note that there can be a tradeoff here between anonymity and

1811)     performance. The Tor network's anonymity comes in part from
1812) diversity,

1813)     so if you are in a position to run your own relay, you will be

1814)     improving Tor's anonymity more than by donating. At the same time
1815)     though, economies

1816)     of scale for bandwidth mean that combining many small donations into

1817)     several larger relays is more efficient at improving network

1818)     performance. Improving anonymity and improving performance are both
1819)     worthwhile goals, so however you can help is great!
1820)     </p>
1821) 
1822)     <hr>
1823) 

1824)     <a id="KeyManagement"></a>

1825)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the
1826) keys Tor uses.</a></h3>

1827) 

1828)     <p>
1829)     Tor uses a variety of different keys, with three goals in mind: 1)
1830)     encryption to ensure privacy of data within the Tor network, 2)
1831)     authentication so clients know they're

1832)     talking to the relays they meant to talk to, and 3) signatures to
1833) make

1834)     sure all clients know the same set of relays.
1835)     </p>

1836) 

1837)     <p>

1838)     <b>Encryption</b>: first, all connections in Tor use TLS link
1839) encryption,

1840)     so observers can't look inside to see which circuit a given cell is

1841)     intended for. Further, the Tor client establishes an ephemeral
1842) encryption

1843)     key with each relay in the circuit; these extra layers of encryption
1844)     mean that only the exit relay can read

1845)     the cells. Both sides discard the circuit key when the circuit ends,

1846)     so logging traffic and then breaking into the relay to discover the
1847) key

1848)     won't work.
1849)     </p>

1850) 

1851)     <p>
1852)     <b>Authentication</b>:
1853)     Every Tor relay has a public decryption key called the "onion key".

1854)     Each relay rotates its onion key once a week.

1855)     When the Tor client establishes circuits, at each step it <a

1856) 
1857) href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands

1858)     that the Tor relay prove knowledge of its onion key</a>. That way
1859)     the first node in the path can't just spoof the rest of the path.

1860)     Because the Tor client chooses the path, it can make sure to get
1861)     Tor's "distributed trust" property: no single relay in the path can
1862)     know about both the client and what the client is doing.

1863)     </p>

1864) 

1865)     <p>
1866)     <b>Coordination</b>:

1867)     How do clients know what the relays are, and how do they know that
1868) they
1869)     have the right keys for them? Each relay has a long-term public
1870) signing
1871)     key called the "identity key". Each directory authority additionally
1872) has a

1873)     "directory signing key". The directory authorities <a

1874)     href="<specblob>dir-spec.txt">provide a signed list</a>

1875)     of all the known relays, and in that list are a set of certificates
1876) from
1877)     each relay (self-signed by their identity key) specifying their
1878) keys,
1879)     locations, exit policies, and so on. So unless the adversary can
1880) control

1881)     a majority of the directory authorities (as of 2012 there are 8

1882)     directory authorities), he can't trick the Tor client into using
1883)     other Tor relays.

1884)     </p>

1885) 

1886)     <p>

1887)     How do clients know what the directory authorities are? The Tor
1888) software
1889)     comes with a built-in list of location and public key for each
1890) directory
1891)     authority. So the only way to trick users into using a fake Tor
1892) network

1893)     is to give them a specially modified version of the software.
1894)     </p>

1895) 

1896)     <p>
1897)     How do users know they've got the right software? When we distribute
1898)     the source code or a package, we digitally sign it with <a
1899)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
1900)     href="<page docs/verifying-signatures>">instructions
1901)     on how to check Tor's signatures</a>.
1902)     </p>

1903) 

1904)     <p>

1905)     In order to be certain that it's really signed by us, you need to
1906) have
1907)     met us in person and gotten a copy of our GPG key fingerprint, or
1908) you
1909)     need to know somebody who has. If you're concerned about an attack
1910) on
1911)     this level, we recommend you get involved with the security
1912) community

1913)     and start meeting people.
1914)     </p>

1915) 

1916)     <hr>

1917) 

1918) <a id="EntryGuards"></a>

1919) <h3><a class="anchor" href="#EntryGuards">What are Entry
1920) Guards?</a></h3>

1921) 
1922) <p>
1923) Tor (like all current practical low-latency anonymity designs) fails
1924) when the attacker can see both ends of the communications channel. For

1925) example, suppose the attacker controls or watches the Tor relay you
1926) choose
1927) to enter the network, and also controls or watches the website you
1928) visit. In

1929) this case, the research community knows no practical low-latency design
1930) that can reliably stop the attacker from correlating volume and timing
1931) information on the two sides.
1932) </p>
1933) 
1934) <p>
1935) So, what should we do? Suppose the attacker controls, or can observe,

1936) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
1937) new entry and exit relays each time you use the network, the attacker
1938) will be able to correlate all traffic you send with probability
1939) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
1940) as being traced all the time: they want to do something often without
1941) an attacker noticing, and the attacker noticing once is as bad as the

1942) attacker noticing more often. Thus, choosing many random entries and
1943) exits

1944) gives the user no chance of escaping profiling by this kind of attacker.

1945) </p>
1946) 
1947) <p>

1948) The solution is "entry guards": each Tor client selects a few relays at
1949) random

1950) to use as entry points, and uses only those relays for her first hop. If
1951) those relays are not controlled or observed, the attacker can't win,
1952) ever, and the user is secure. If those relays <i>are</i> observed or
1953) controlled by the attacker, the attacker sees a larger <i>fraction</i>

1954) of the user's traffic — but still the user is no more profiled
1955) than

1956) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
1957) of avoiding profiling, whereas she had none before.

1958) </p>
1959) 
1960) <p>

1961) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
1962) Analysis of the Degradation of Anonymous Protocols</a>, <a
1963) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
1964) Communication Against Passive Logging Attacks</a>, and especially
1965) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
1966) Servers</a>.

1967) </p>
1968) 
1969) <p>
1970) Restricting your entry nodes may also help against attackers who want
1971) to run a few Tor nodes and easily enumerate all of the Tor user IP
1972) addresses. (Even though they can't learn what destinations the users
1973) are talking to, they still might be able to do bad things with just a

1974) list of users.) However, that feature won't really become useful until
1975) we move to a "directory guard" design as well.

1976) </p>
1977) 
1978)     <hr>
1979) 

1980)     <a id="EverybodyARelay"></a>

1981)     <h3><a class="anchor" href="#EverybodyARelay">You should make every
1982) Tor user be a relay.</a></h3>

1983) 

1984)     <p>
1985)     Requiring every Tor user to be a relay would help with scaling the

1986)     network to handle all our users, and <a
1987)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

1988)     relay may help your anonymity</a>. However, many Tor users cannot be
1989) good
1990)     relays &mdash; for example, some Tor clients operate from behind
1991) restrictive
1992)     firewalls, connect via modem, or otherwise aren't in a position
1993) where they

1994)     can relay traffic. Providing service to these clients is a critical

1995)     part of providing effective anonymity for everyone, since many Tor
1996) users
1997)     are subject to these or similar constraints and including these
1998) clients

1999)     increases the size of the anonymity set.
2000)     </p>

2001) 

2002)     <p>

2003)     That said, we do want to encourage Tor users to run relays, so what
2004) we
2005)     really want to do is simplify the process of setting up and
2006) maintaining
2007)     a relay. We've made a lot of progress with easy configuration in the
2008) past
2009)     few years: Vidalia has an easy relay configuration interface, and
2010) supports
2011)     uPnP too. Tor is good at automatically detecting whether it's
2012) reachable and

2013)     how much bandwidth it can offer.
2014)     </p>

2015) 

2016)     <p>

2017)     There are five steps we need to address before we can do this
2018) though:

2019)     </p>

2020) 

2021)     <p>
2022)     First, we need to make Tor stable as a relay on all common
2023)     operating systems. The main remaining platform is Windows,

2024)     and we're mostly there. See Section 4.1 of <a

2025) 
2026) href="https://www.torproject.org/press/2008-12-19-roadmap-press-release"
2027) >our

2028)     development roadmap</a>.
2029)     </p>

2030) 

2031)     <p>
2032)     Second, we still need to get better at automatically estimating
2033)     the right amount of bandwidth to allow. See item #7 on the

2034)     <a href="<page getinvolved/volunteer>#Research">research section of
2035) the

2036)     volunteer page</a>: "Tor doesn't work very well when relays
2037)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

2038)     href="<page docs/faq>#TransportIPnotTCP">switching

2039)     to UDP transport</a> is the simplest answer here &mdash; which alas
2040) is

2041)     not a very simple answer at all.
2042)     </p>

2043) 

2044)     <p>
2045)     Third, we need to work on scalability, both of the network (how to
2046)     stop requiring that all Tor relays be able to connect to all Tor
2047)     relays) and of the directory (how to stop requiring that all Tor
2048)     users know about all Tor relays). Changes like this can have large
2049)     impact on potential and actual anonymity. See Section 5 of the <a
2050)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
2051)     for details. Again, UDP transport would help here.
2052)     </p>

2053) 

2054)     <p>
2055)     Fourth, we need to better understand the risks from
2056)     letting the attacker send traffic through your relay while
2057)     you're also initiating your own anonymized traffic. <a
2058)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
2059)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
2060)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
2061)     describe ways to identify the relays in a circuit by running traffic

2062)     through candidate relays and looking for dips in the traffic while
2063) the
2064)     circuit is active. These clogging attacks are not that scary in the
2065) Tor
2066)     context so long as relays are never clients too. But if we're trying
2067) to
2068)     encourage more clients to turn on relay functionality too (whether
2069) as
2070)     <a href="<page docs/bridges>">bridge relays</a> or as normal
2071) relays), then
2072)     we need to understand this threat better and learn how to mitigate
2073) it.
2074)     </p>
2075) 
2076)     <p>
2077)     Fifth, we might need some sort of incentive scheme to encourage
2078) people
2079)     to relay traffic for others, and/or to become exit nodes. Here are
2080) our

2081)     <a href="<blog>two-incentive-designs-tor">current

2082)     thoughts on Tor incentives</a>.
2083)     </p>

2084) 

2085)     <p>
2086)     Please help on all of these!
2087)     </p>

2088) 

2089) <hr>
2090) 
2091) <a id="TransportIPnotTCP"></a>

2092) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all
2093) IP packets, not just TCP packets.</a></h3>

2094) 
2095) <p>

2096) This would be handy, because it would make Tor better able to handle
2097) new protocols like VoIP, it could solve the whole need to socksify
2098) applications, and it would solve the fact that exit relays need to

2099) allocate a lot of file descriptors to hold open all the exit
2100) connections.

2101) </p>
2102) 
2103) <p>

2104) We're heading in this direction: see <a
2105) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
2106) ticket</a> for directions we should investigate. Some of the hard
2107) problems are:

2108) </p>
2109) 

2110) <ol>

2111) <li>IP packets reveal OS characteristics. We would still need to do
2112) IP-level packet normalization, to stop things like TCP fingerprinting
2113) attacks. Given the diversity and complexity of TCP stacks, along with <a

2114) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

2115) fingerprinting attacks</a>, it looks like our best bet is shipping our
2116) own user-space TCP stack.

2117) </li>

2118) <li>Application-level streams still need scrubbing. We will still need
2119) user-side applications like Torbutton. So it won't become just a matter
2120) of capturing packets and anonymizing them at the IP layer.

2121) </li>
2122) <li>Certain protocols will still leak information. For example, we must
2123) rewrite DNS requests so they are delivered to an unlinkable DNS server
2124) rather than the DNS server at a user's ISP; thus, we must understand
2125) the protocols we are transporting.
2126) </li>
2127) <li><a

2128) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS
2129) </a>

2130) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
2131) picked a transport mechanism, we need to design a new end-to-end Tor
2132) protocol for avoiding tagging attacks and other potential anonymity and
2133) integrity issues now that we allow drops, resends, et cetera.

2134) </li>
2135) <li>Exit policies for arbitrary IP packets mean building a secure
2136) IDS. Our node operators tell us that exit policies are one of the main
2137) reasons they're willing to run Tor. Adding an Intrusion Detection System
2138) to handle exit policies would increase the security complexity of Tor,

2139) and would likely not work anyway, as evidenced by the entire field of
2140) IDS

2141) and counter-IDS papers. Many potential abuse issues are resolved by the
2142) fact that Tor only transports valid TCP streams (as opposed to arbitrary
2143) IP including malformed packets and IP floods), so exit policies become
2144) even <i>more</i> important as we become able to transport IP packets. We
2145) also need to compactly describe exit policies in the Tor directory,

2146) so clients can predict which nodes will allow their packets to exit
2147) —

2148) and clients need to predict all the packets they will want to send in
2149) a session before picking their exit node!
2150) </li>

2151) <li>The Tor-internal name spaces would need to be redesigned. We support
2152) hidden service ".onion" addresses by intercepting the addresses when
2153) they are passed to the Tor client. Doing so at the IP level will require
2154) a more complex interface between Tor and the local DNS resolver.

2155) </li>

2156) </ol>
2157) 
2158) <hr>
2159) 
2160) <a id="HideExits"></a>
2161) <h3><a class="anchor" href="#HideExits">You should hide the list of Tor
2162) relays, so people can't block the exits.</a></h3>
2163) 
2164) <p>
2165) There are a few reasons we don't:
2166) </p>
2167) 
2168) <ol>
2169) <li>We can't help but make the information available, since Tor clients
2170) need to use it to pick their paths. So if the "blockers" want it, they
2171) can get it anyway. Further, even if we didn't tell clients about the
2172) list of relays directly, somebody could still make a lot of connections
2173) through Tor to a test site and build a list of the addresses they see.
2174) </li>
2175) 

2176) <li>If people want to block us, we believe that they should be allowed
2177) to

2178) do so.  Obviously, we would prefer for everybody to allow Tor users to
2179) connect to them, but people have the right to decide who their services

2180) should allow connections from, and if they want to block anonymous
2181) users,

2182) they can.
2183) </li>
2184) 
2185) <li>Being blockable also has tactical advantages: it may be a persuasive

2186) response to website maintainers who feel threatened by Tor. Giving them
2187) the option may inspire them to <a href="<page docs/faq-abuse>#Bans">stop
2188) and think</a> about whether they really want to eliminate private access
2189) to their system, and if not, what other options they might have. The
2190) time they might otherwise have spent blocking Tor, they may instead
2191) spend rethinking their overall approach to privacy and anonymity.

2192) </li>

2193) </ol>
2194) 

2195)     <hr>

2196) 

2197)     <a id="Criminals"></a>

2198)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals
2199) to do bad things?</a></h3>

2200) 

2201)     <p>
2202)     For the answer to this question and others, please see our <a
2203)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
2204)     </p>

2205) 

2206)     <hr>

2207) 

2208)     <a id="RespondISP"></a>

2209)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP
2210) about my exit relay?</a></h3>

2211) 

2212)     <p>
2213)     A collection of templates for successfully responding to ISPs is <a

2214)     href="<wiki>doc/TorAbuseTemplates">collected

2215)     here</a>.
2216)     </p>

2217) 

2218)     <hr>

2219) 

2220)   </div>
2221)   <!-- END MAINCOL -->
2222)   <div id = "sidecol">
2223) #include "side.wmi"
2224) #include "info.wmi"
2225)   </div>
2226)   <!-- END SIDECOL -->
2227) </div>
2228) <!-- END CONTENT -->