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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 proxies?</a></li>
21)     <li><a href="#CompatibleApplications">What programs can I use with
22)     Tor?</a></li>
23)     <li><a href="#WhyCalledTor">Why is it called Tor?</a></li>
24)     <li><a href="#Backdoor">Is there a backdoor in Tor?</a></li>
25)     <li><a href="#DistributingTor">Can I distribute Tor on my magazine's
26)     CD?</a></li>

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

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

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

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

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

35)     </ul>

36) 

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

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

44)     <li><a href="#CompileTorWindows">How do I compile Tor under Windows?</a></li>
45)     <li><a href="#VirusFalsePositives">Why does my Tor executable appear to
46)     have a virus or spyware?</a></li>
47)     <li><a href="#LiveCD">Is there a LiveCD or other bundle that includes Tor?</a></li>
48)     </ul>

49) 

50)     <p>Tor Browser Bundle:</p>
51)     <ul>

52) 

53)     <li><a href="#TBBBrowserName">Why does TBB's browser window say
54)     Aurora?</a></li>
55)     <li><a href="#TBBFlash">Why can't I view videos on YouTube and other
56)     Flash-based sites?</a></li>

57)     <li><a href="#TBBSocksPort">I'm on OSX or Linux and I want to
58)     run another application through the Tor launched by Tor Browser

59)     Bundle. How do I predict my Socks port?</a></li>

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

62)     <li><a href="#TBBOtherExtensions">Can I install other Firefox
63)     extensions?</a></li>

64)     <li><a href="#TBBOtherBrowser">I want to use Chrome/IE/Opera/etc
65)     with Tor.</a></li>
66)     <li><a href="#TBBCloseBrowser">I want to leave Tor Browser Bundle
67)     running but close the browser.</a></li>
68) 

69)     <li><a href="#GoogleCaptcha">Google makes me solve a Captcha or tells
70)     me I have spyware installed.</a></li>
71)     <li><a href="#GmailWarning">Gmail warns me that my account may have
72)     been compromised.</a></li>
73)     </ul>
74) 
75)     <p>Advanced Tor usage:</p>

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

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

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

81)     <li><a href="#DoesntWork">I installed Tor and Polipo but it's not
82)     working.</a></li>
83)     <li><a href="#VidaliaPassword">Tor/Vidalia prompts for a password at
84)     start.</a></li>
85)     <li><a href="#ChooseEntryExit">Can I control which nodes (or country)
86)     are used for entry/exit?</a></li>

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

89)     </ul>

90) 

91)     <p>Running a Tor relay:</p>
92)     <ul>
93)     <li><a href="#RelayFlexible">How stable does my relay need to be?</a></li>
94)     <li><a href="#ExitPolicies">I'd run a relay, but I don't want to deal
95)     with abuse issues.</a></li>
96)     <li><a href="#RelayOrBridge">Should I be a normal relay or bridge
97)     relay?</a></li>

98)     <li><a href="#MultipleRelays">I want to run more than one relay.</a></li>

99)     <li><a href="#RelayMemory">Why is my Tor relay using so much memory?</a></li>
100)     <li><a href="#WhyNotNamed">Why is my Tor relay not named?</a></li>

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

103)     </ul>

104) 

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

106) 

107)     <p>Anonymity and Security:</p>
108)     <ul>
109)     <li><a href="#KeyManagement">Tell me about all the keys Tor uses.</a></li>

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

111)     </ul>

112) 

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

117)     <li><a href="#TransportIPnotTCP">You should transport all IP packets,
118)     not just TCP packets.</a></li>

119)     </ul>

120) 

121)     <p>Abuse:</p>

122)     <ul>
123)     <li><a href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></li>
124)     <li><a href="#RespondISP">How do I respond to my ISP about my exit
125)     relay?</a></li>
126)     </ul>

127) 

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

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

130) 

131)     <hr>

132) 

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

134) 

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

137) 

138)     <p>
139)     The name "Tor" can refer to several different components.
140)     </p>

141) 

142)     <p>
143)     The Tor software is a program you can run on your computer that helps keep
144)     you safe on the Internet. Tor protects you by bouncing your communications
145)     around a distributed network of relays run by volunteers all around
146)     the world: it prevents somebody watching your Internet connection from
147)     learning what sites you visit, and it prevents the sites you visit
148)     from learning your physical location. This set of volunteer relays is
149)     called the Tor network. You can read more about how Tor works on the <a
150)     href="<page about/overview>">overview page</a>.
151)     </p>

152) 

153)     <p>
154)     The Tor Project is a non-profit (charity) organization that maintains
155)     and develops the Tor software.
156)     </p>

157) 

158)     <hr>

159) 

160)     <a id="Torisdifferent"></a>
161)     <h3><a class="anchor" href="#Torisdifferent">How is Tor different from other proxies?</a></h3>
162)     <p>

163)     A typical proxy provider sets up a server somewhere on the Internet and
164) allows you to use it to relay your traffic.  This creates a simple, easy to
165) maintain architecture.  The users all enter and leave through the same server.
166) The provider may charge for use of the proxy, or fund their costs through
167) advertisements on the server.  In the simplest configuration, you don't have to
168) install anything.  You just have to point your browser at their proxy server.
169) Simple proxy providers are fine solutions if you do not want protections for
170) your privacy and anonymity online and you trust the provider from doing bad
171) things.  Some simple proxy providers use SSL to secure your connection to them.
172) This may protect you against local eavesdroppers, such as those at a cafe with
173) free wifi Internet.
174)     </p>
175)     <p>
176)     Simple proxy providers also create a single point of failure.  The provider
177) knows who you are and where you browse on the Internet.  They can see your

178) traffic as it passes through their server.  In some cases, they can even see
179) inside your

180) encrypted traffic as they relay it to your banking site or to ecommerce stores.
181) You have to trust the provider isn't doing any number of things, such as
182) watching your traffic, injecting their own advertisements into your traffic

183) stream, and recording your personal details.

184)     </p>
185)     <p>
186)     Tor passes your traffic through at least 3 different servers before sending

187) it on to the destination. Because there's a separate layer of encryption for
188) each of the three relays, Tor does not modify, or even know, what you are

189) sending into it.  It merely relays your traffic, completely encrypted through
190) the Tor network and has it pop out somewhere else in the world, completely
191) intact.  The Tor client is required because we assume you trust your local
192) computer.  The Tor client manages the encryption and the path chosen through
193) the network.  The relays located all over the world merely pass encrypted
194) packets between themselves.</p>

195)     <p>
196)     <dl>

197)     <dt>Doesn't the first server see who I am?</dt><dd>Possibly. A bad first of
198) three servers can see encrypted Tor traffic coming from your computer.  It
199) still doesn't know who you are and what you are doing over Tor.  It merely sees
200) "This IP address is using Tor".  Tor is not illegal anywhere in the world, so
201) using Tor by itself is fine.  You are still protected from this node figuring
202) out who you are and where you are going on the Internet.</dd>
203)     <dt>Can't the third server see my traffic?</dt><dd>Possibly.  A bad third
204) of three servers can see the traffic you sent into Tor.  It won't know who sent
205) this traffic.  If you're using encryption, such as visiting a bank or
206) e-commerce website, or encrypted mail connections, etc, it will only know the
207) destination.  It won't be able to see the data inside the traffic stream.  You
208) are still protected from this node figuring out who you are and if using
209) encryption, what data you're sending to the destination.</dd>

210)     </dl>
211)     </p>

212) 

213)     <hr>

214) 

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

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

217) 

218)     <p>
219)     There are two pieces to "Torifying" a program: connection-level anonymity
220)     and application-level anonymity. Connection-level anonymity focuses on
221)     making sure the application's Internet connections get sent through Tor.
222)     This step is normally done by configuring
223)     the program to use your Tor client as a "socks" proxy, but there are
224)     other ways to do it too. For application-level anonymity, you need to
225)     make sure that the information the application sends out doesn't hurt
226)     your privacy. (Even if the connections are being routed through Tor, you
227)     still don't want to include sensitive information like your name.) This
228)     second step needs to be done on a program-by-program basis, which is
229)     why we don't yet recommend very many programs for safe use with Tor.
230)     </p>

231) 

232)     <p>
233)     Most of our work so far has focused on the Firefox web browser. The
234)     bundles on the <a href="<page download/download>">download page</a> automatically

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

236)     extension</a> if you have Firefox installed. As of version 1.2.0,
237)     Torbutton now takes care of a lot of the connection-level and
238)     application-level worries.
239)     </p>

240) 

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

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

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

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

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

252) 

253)     <hr>

254) 

255)     <a id="WhyCalledTor"></a>
256)     <h3><a class="anchor" href="#WhyCalledTor">Why is it called Tor?</a></h3>

257) 

258)     <p>
259)     Because Tor is the onion routing network. When we were starting the
260)     new next-generation design and implementation of onion routing in
261)     2001-2002, we would tell people we were working on onion routing,
262)     and they would say "Neat. Which one?" Even if onion routing has
263)     become a standard household term, Tor was born out of the actual <a
264)     href="http://www.onion-router.net/">onion routing project</a> run by
265)     the Naval Research Lab.
266)     </p>

267) 

268)     <p>
269)     (It's also got a fine translation from German and Turkish.)
270)     </p>

271) 

272)     <p>
273)     Note: even though it originally came from an acronym, Tor is not spelled
274)     "TOR". Only the first letter is capitalized. In fact, we can usually
275)     spot people who haven't read any of our website (and have instead learned
276)     everything they know about Tor from news articles) by the fact that they
277)     spell it wrong.
278)     </p>

279) 

280)     <hr>

281) 

282)     <a id="Backdoor"></a>
283)     <h3><a class="anchor" href="#Backdoor">Is there a backdoor in Tor?</a></h3>

284) 

285)     <p>
286)     There is absolutely no backdoor in Tor. Nobody has asked us to put one
287)     in, and we know some smart lawyers who say that it's unlikely that anybody
288)     will try to make us add one in our jurisdiction (U.S.). If they do
289)     ask us, we will fight them, and (the lawyers say) probably win.
290)     </p>

291) 

292)     <p>
293)     We think that putting a backdoor in Tor would be tremendously
294)     irresponsible to our users, and a bad precedent for security software
295)     in general. If we ever put a deliberate backdoor in our security
296)     software, it would ruin our professional reputations. Nobody would
297)     trust our software ever again &mdash; for excellent reason!
298)     </p>

299) 

300)     <p>
301)     But that said, there are still plenty of subtle attacks
302)     people might try. Somebody might impersonate us, or break into our
303)     computers, or something like that. Tor is open source, and you should
304)     always check the source (or at least the diffs since the last release)
305)     for suspicious things. If we (or the distributors) don't give you
306)     source, that's a sure sign something funny might be going on. You
307)     should also check the <a href="<page docs/verifying-signatures>">PGP
308)     signatures</a> on the releases, to make sure nobody messed with the
309)     distribution sites.
310)     </p>

311) 

312)     <p>
313)     Also, there might be accidental bugs in Tor that could affect your
314)     anonymity. We periodically find and fix anonymity-related bugs, so make
315)     sure you keep your Tor versions up-to-date.
316)     </p>

317) 

318)     <hr>

319) 

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

321)     <h3><a class="anchor" href="#DistributingTor">Can I distribute Tor on my magazine's CD?</a></h3>

322) 

323)     <p>
324)     Yes.
325)     </p>

326) 

327)     <p>
328)     The Tor software is <a href="https://www.fsf.org/">free software</a>. This
329)     means we give you the rights to redistribute the Tor software, either
330)     modified or unmodified, either for a fee or gratis. You don't have to
331)     ask us for specific permission.
332)     </p>

333) 

334)     <p>
335)     However, if you want to redistribute the Tor software you must follow our
336)     <a href="<gitblob>LICENSE">LICENSE</a>.
337)     Essentially this means that you need to include our LICENSE file along
338)     with whatever part of the Tor software you're distributing.
339)     </p>

340) 

341)     <p>
342)     Most people who ask us this question don't want to distribute just the
343)     Tor software, though. They want to distribute the Tor bundles, which
344)     typically include <a href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a>
345)     and <a href="<page projects/vidalia>">Vidalia</a>.
346)     You will need to follow the licenses for those programs
347)     as well. Both of them are distributed under the <a
348)     href="https://www.fsf.org/licensing/licenses/gpl.html">GNU General
349)     Public License</a>. The simplest way to obey their licenses is to
350)     include the source code for these programs everywhere you include
351)     the bundles themselves. Look for "source" packages on the <a
352)     href="<page projects/vidalia>">Vidalia page</a> and the <a
353)     href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo
354)     download page</a>.
355)     </p>

356) 

357)     <p>
358)     Also, you should make sure not to confuse your readers about what Tor is,
359)     who makes it, and what properties it provides (and doesn't provide). See
360)     our <a href="<page docs/trademark-faq>">trademark FAQ</a> for details.
361)     </p>

362) 

363)     <p>
364)     Lastly, you should realize that we release new versions of the
365)     Tor software frequently, and sometimes we make backward incompatible
366)     changes. So if you distribute a particular version of the Tor software, it
367)     may not be supported &mdash; or even work &mdash; six months later. This
368)     is a fact of life for all security software under heavy development.
369)     </p>

370) 

371)     <hr>

372) 

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

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

375) 

376)     <p>There is no official support for Tor. Your best bet is to try the following:</p>

377)     <ol>
378)     <li>Read through this <a href="<page docs/faq>">FAQ</a>.</li>
379)     <li>Read through the <a href="<page docs/documentation>">documentation</a>.</li>
380)     <li>Read through the <a

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

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

383)     <li>Join our <a href="irc://irc.oftc.net#tor">irc channel</a> and
384)     state the issue and wait for help.</li>

385)     <li>Send an email to <a
386)     href="mailto:community-support@lists.torproject.org">community-support</a>.
387)     These are volunteers who may be able to help you but you may not
388)     get a response for days.</li>

389)     </ol>

390) 

391)     <p>If you find your answer, please stick around on the IRC channel or the
392)     mailing list and answer questions from others.</p>

393) 

394)     <hr>

395) 

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

398) 

399)     <p>
400)     There are many reasons why the Tor network is currently slow.
401)     </p>

402) 

403)     <p>
404)     Before we answer, though, you should realize that Tor is never going to
405)     be blazing fast. Your traffic is bouncing through volunteers' computers
406)     in various parts of the world, and some bottlenecks and network latency
407)     will always be present. You shouldn't expect to see university-style
408)     bandwidth through Tor.
409)     </p>

410) 

411)     <p>
412)     But that doesn't mean that it can't be improved. The current Tor network
413)     is quite small compared to the number of people trying to use it, and
414)     many of these users don't understand or care that Tor can't currently
415)     handle file-sharing traffic load.
416)     </p>

417) 

418)     <p>
419)     For the much more in-depth answer, see <a

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

421)     post on the topic</a>, which includes both a detailed PDF and a video
422)     to go with it.
423)     </p>

424) 

425)     <p>
426)     What can you do to help?
427)     </p>

428) 

429)     <ul>

430) 

431)     <li>
432)     <a href="<page docs/tor-doc-relay>">Configure your Tor to relay traffic
433)     for others</a>. Help make the Tor network large enough that we can handle
434)     all the users who want privacy and security on the Internet.
435)     </li>

436) 

437)     <li>

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

439)     especially need people to help make it easier to configure your Tor
440)     as a relay. Also, we need help with clear simple documentation to
441)     walk people through setting it up.
442)     </li>

443) 

444)     <li>
445)     There are some bottlenecks in the current Tor network. Help us design
446)     experiments to track down and demonstrate where the problems are, and
447)     then we can focus better on fixing them.
448)     </li>

449) 

450)     <li>
451)     There are some steps that individuals
452)     can take to improve their Tor performance. <a

453)     href="<wiki>doc/FireFoxTorPerf">You

454)     can configure your Firefox to handle Tor better</a>, <a
455)     href="http://www.pps.jussieu.fr/~jch/software/polipo/tor.html">you can use
456)     Polipo with Tor</a>, or you can try <a href="<page download/download>">upgrading
457)     to the latest version of Tor</a>.  If this works well, please help by
458)     documenting what you did, and letting us know about it.
459)     </li>

460) 

461)     <li>
462)     Tor needs some architectural changes too. One important change is to
463)     start providing <a href="#EverybodyARelay">better service to people who
464)     relay traffic</a>. We're working on this, and we'll finish faster if we
465)     get to spend more time on it.
466)     </li>

467) 

468)     <li>
469)     Help do other things so we can do the hard stuff. Please take a moment
470)     to figure out what your skills and interests are, and then <a href="<page
471)     getinvolved/volunteer>">look at our volunteer page</a>.
472)     </li>

473) 

474)     <li>
475)     Help find sponsors for Tor. Do you work at a company or government agency
476)     that uses Tor or has a use for Internet privacy, e.g. to browse the
477)     competition's websites discreetly, or to connect back to the home servers
478)     when on the road without revealing affiliations? If your organization has
479)     an interest in keeping the Tor network working, please contact them about
480)     supporting Tor. Without sponsors, Tor is going to become even slower.
481)     </li>

482) 

483)     <li>
484)     If you can't help out with any of the above, you can still help out
485)     individually by <a href="<page donate/donate>">donating a bit of money to the
486)     cause</a>. It adds up!
487)     </li>

488) 

489)     </ul>

490) 

491)     <hr>

492) 

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

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

495) 

496)     <p>

497)     The Tor network's <a
498)     href="https://metrics.torproject.org/network.html#networksize">several
499)     thousand</a> relays push <a
500)     href="https://metrics.torproject.org/network.html#bandwidth">over
501)     1GB per second on average</a>. We have <a
502)     href="https://metrics.torproject.org/users.html#direct-users">several
503)     hundred thousand daily users</a>. But the Tor network is not yet
504)     self-sustaining.

505)     </p>

506) 

507)     <p>
508)     There are six main development/maintenance pushes that need attention:
509)     </p>

510) 

511)     <ul>

512) 

513)     <li>
514)     Scalability: We need to keep scaling and decentralizing the Tor
515)     architecture so it can handle thousands of relays and millions of
516)     users. The upcoming stable release is a major improvement, but there's
517)     lots more to be done next in terms of keeping Tor fast and stable.
518)     </li>

519) 

520)     <li>
521)     User support: With this many users, a lot of people are asking questions
522)     all the time, offering to help out with things, and so on. We need good
523)     clean docs, and we need to spend some effort coordinating volunteers.
524)     </li>

525) 

526)     <li>
527)     Relay support: the Tor network is run by volunteers, but they still need
528)     attention with prompt bug fixes, explanations when things go wrong,
529)     reminders to upgrade, and so on. The network itself is a commons, and
530)     somebody needs to spend some energy making sure the relay operators stay

531)     happy. We also need to work on stability on some platforms — e.g.,
532)     Tor relays have problems on Win XP currently.

533)     </li>

534) 

535)     <li>
536)     Usability: Beyond documentation, we also need to work on usability of the
537)     software itself. This includes installers, clean GUIs, easy configuration
538)     to interface with other applications, and generally automating all of
539)     the difficult and confusing steps inside Tor. We've got a start on this

540)     with the <a href="<page projects/vidalia>">Vidalia GUI</a>, but much more work

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

543) 

544)     <li>
545)     Incentives: We need to work on ways to encourage people to configure
546)     their Tors as relays and exit nodes rather than just clients.
547)     <a href="#EverybodyARelay">We need to make it easy to become a relay,
548)     and we need to give people incentives to do it.</a>
549)     </li>

550) 

551)     <li>
552)     Research: The anonymous communications field is full
553)     of surprises and gotchas. In our copious free time, we
554)     also help run top anonymity and privacy conferences like <a
555)     href="http://petsymposium.org/">PETS</a>. We've identified a set of
556)     critical <a href="<page getinvolved/volunteer>#Research">Tor research questions</a>
557)     that will help us figure out how to make Tor secure against the variety of
558)     attacks out there. Of course, there are more research questions waiting
559)     behind these.
560)     </li>

561) 

562)     </ul>

563) 

564)     <p>
565)     We're continuing to move forward on all of these, but at this rate
566)     <a href="#WhySlow">the Tor network is growing faster than the developers
567)     can keep up</a>.
568)     Now would be an excellent time to add a few more developers to the effort
569)     so we can continue to grow the network.
570)     </p>

571) 

572)     <p>
573)     We are also excited about tackling related problems, such as
574)     censorship-resistance.
575)     </p>

576) 

577)     <p>
578)     We are proud to have <a href="<page about/sponsors>">sponsorship and support</a>
579)     from the Omidyar Network, the International Broadcasting Bureau, Bell
580)     Security Solutions, the Electronic Frontier Foundation, several government
581)     agencies and research groups, and hundreds of private contributors.
582)     </p>

583) 

584)     <p>
585)     However, this support is not enough to keep Tor abreast of changes in the
586)     Internet privacy landscape. Please <a href="<page donate/donate>">donate</a>
587)     to the project, or <a href="<page about/contact>">contact</a> our executive
588)     director for information on making grants or major donations.
589)     </p>

590) 

591)     <hr>
592) 

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

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

595) 

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

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

598)     <hr>

599) 

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

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

604)     <pre>

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

606)     The serial number is: 02:DA:41:04:89:A5:FD:A2:B5:DB:DB:F8:ED:15:0D:BE
607)     The SHA-1 fingerprint is: a7e70f8a648fe04a9677f13eedf6f91b5f7f2e25
608)     The SHA-256 fingerprint is: 23b854af6b96co224fd173382c520b46fa94f2d4e7238893f63ad2d783e27b4b
609) 

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

611)     The serial number is: 00:EF:A3
612)     The SHA-1 fingerprint is: 50af43db8438e67f305a3257d8ef198e8c42f13f

613)     </pre>

614)     </p>
615)     <hr>
616) 

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

618)     <h3><a class="anchor" href="#HowUninstallTor">How do I uninstall Tor?</a></h3>

619) 

620)     <p>
621)     This depends entirely on how you installed it and which operating system you
622)     have. If you installed a package, then hopefully your package has a way to
623)     uninstall itself. The Windows packages include uninstallers. The proper way to
624)     completely remove Tor, Vidalia, Torbutton for Firefox, and Polipo on any
625)     version of Windows is as follows:
626)     </p>

627) 

628)     <ol>
629)     <li>In your taskbar, right click on Vidalia (the green onion or the black head)
630)     and choose exit.</li>
631)     <li>Right click on the taskbar to bring up TaskManager. Look for tor.exe in the
632)     Process List. If it's running, right click and choose End Process.</li>
633)     <li>Click the Start button, go to Programs, go to Vidalia, choose Uninstall.
634)     This will remove the Vidalia bundle, which includes Tor and Polipo.</li>
635)     <li>Start Firefox. Go to the Tools menu, choose Add-ons. Select Torbutton.
636)     Click the Uninstall button.</li>
637)     </ol>

638) 

639)     <p>
640)     If you do not follow these steps (for example by trying to uninstall
641)     Vidalia, Tor, and Polipo while they are still running), you will need to
642)     reboot and manually remove the directory "Program Files\Vidalia Bundle".
643)     </p>

644) 

645)     <p>
646)     For Mac OS X, follow the <a
647)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
648)     </p>

649) 

650)     <p>
651)     If you installed by source, I'm afraid there is no easy uninstall method. But
652)     on the bright side, by default it only installs into /usr/local/ and it should
653)     be pretty easy to notice things there.
654)     </p>

655) 

656)     <hr>

657) 

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

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

660) 

661)     <p>
662)     These are PGP signatures, so you can verify that the file you've downloaded is
663)     exactly the one that we intended you to get.
664)     </p>

665) 

666)     <p>
667)     Please read the <a
668)     href="<page docs/verifying-signatures>">verifying signatures</a> page for details.
669)     </p>

670) 

671) <hr>
672) 
673) <a id="GetTor"></a>
674) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
675) country. How do I download Tor?</a></h3>
676) 
677) <p>
678) Some government or corporate firewalls censor connections to Tor's
679) website. In those cases, you have three options. First, get it from

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

681) Bundle</a> fits nicely on a USB key. Second, find the <a
682) href="https://encrypted.google.com/search?q=tor+mirrors">google cache</a>

683) for the <a href="<page getinvolved/mirrors>">Tor mirrors</a> page
684) and see if any of those copies of our website work for you. Third,
685) you can download Tor via email: log in to your Gmail account and mail
686) '<tt>gettor AT torproject.org</tt>'. If you include the word 'help'
687) in the body of the email, it will reply with instructions. Note that
688) only a few webmail providers are supported, since they need to be able
689) to receive very large attachments.
690) </p>
691) 
692) <p>

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

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

696) </p>
697) 
698) <hr>

699) 

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

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

702) 

703)     <p>
704)     Try following the steps at <a href="<gitblob>doc/tor-win32-mingw-creation.txt">
705)     tor-win32-mingw-creation.txt</a>.
706)     </p>

707) 

708)     <p>
709)     (Note that you don't need to compile Tor yourself in order to use
710)     it. Most people just use the packages available on the <a href="<page
711)     download/download>">download page</a>.)
712)     </p>

713) 

714)     <hr>

715) 

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

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

718) 

719)     <p>
720)     Sometimes, overzealous Windows virus and spyware detectors trigger on some
721)     parts of the Tor Windows binary. Our best guess is that these are false
722)     positives &mdash; after all, the anti-virus and anti-spyware business is just a
723)     guessing game anyway. You should contact your vendor and explain that you have
724)     a program that seems to be triggering false positives. Or pick a better vendor.
725)     </p>

726) 

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

732) 

733)     <hr>

734) 

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

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

737) 

738)     <p>

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

740)     Live System</a> or <a href="<page projects/torbrowser>">the Tor Browser
741)     Bundle</a>.

742)     </p>

743) 
744) <hr>
745) 

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

747) <h3><a class="anchor" href="#TBBFlash">Why can't I view videos on YouTube
748) and other Flash-based sites?</a></h3>

749) 
750) <p>
751) <a href="https://www.torproject.org/torbutton/torbutton-faq.html.en#noflash">Answer</a>
752) </p>
753) 
754) <hr>
755) 

756) <a id="TBBBrowserName"></a>
757) <h3><a class="anchor" href="#TBBBrowserName">Why does TBB's browser window
758) say Aurora?</a></h3>
759) 
760) <p>
761) We build Firefox from source in order to include our <a
762) href="https://gitweb.torproject.org/torbrowser.git/tree/maint-2.2:/src/current-patches">Firefox

763) privacy fixes</a>. The default Firefox build process calls the resulting

764) browser "Aurora".
765) </p>
766) 
767) <p>
768) Don't be confused into thinking the browser you
769) see is the same as the Firefox pre-releases that
770) were also named Aurora. A future TBB release will <a
771) href="https://trac.torproject.org/projects/tor/ticket/2176">probably</a>
772) have a more recognizable name like "Tor Browser".
773) </p>
774) 
775) <hr>
776) 

777) <a id="TBBSocksPort"></a>
778) <h3><a class="anchor" href="#TBBSocksPort">I'm on OSX or Linux and
779) I want to run another application through the Tor launched by Tor

780) Browser Bundle. How do I predict my Socks port?</a></h3>

781) 
782) <p>

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

784) on OSX and Linux has an experimental feature where Tor listens
785) on random unused ports rather than a fixed port each time. The
786) goal is to avoid conflicting with a "system" Tor install,
787) so you can run a system Tor and TBB at the same time. We're <a
788) href="https://trac.torproject.org/projects/tor/ticket/3948">working on
789) a feature</a> where Tor will try the usual ports first and then back
790) off to a random choice if they're already in use. Until then, if you

791) want to configure some other application to use Tor as a Socks proxy,

792) here's a workaround:
793) </p>
794) 
795) <p>
796) In Vidalia, go to Settings-&gt;Advanced and uncheck the box that says
797) 'Configure ControlPort automatically'. Click OK and restart TBB. Your

798) Socks port will then be on 9050.

799) </p>
800) 
801) <hr>
802) 
803) <a id="TBBPolipo"></a>
804) <h3><a class="anchor" href="#TBBPolipo">I need an HTTP proxy. Where did
805) Polipo go?</a></h3>
806) 
807) <p>
808) In the past, Tor bundles included an HTTP proxy like Privoxy or Polipo,
809) solely to work around a bug in Firefox that was finally fixed in Firefox
810) 6. Now you don't need a separate HTTP proxy to use Tor, and in fact
811) leaving it out makes you safer because Torbutton has better control over
812) Firefox's interaction with websites.
813) </p>
814) 
815) <p>
816) If you are trying to use some external application with Tor, step zero

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

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

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

820) proxy on port 9050 on Windows, or <a href="#TBBSocksPort">see above</a>
821) for OSX and Linux.
822) </p>
823) 
824) <p>

825) If that fails, feel free to install <a
826) href="http://www.privoxy.org/">privoxy</a> or <a
827) href="https://archive.torproject.org/tor-package-archive/polipo/">polipo</a>.
828) You can use <a

829) href="https://gitweb.torproject.org/torbrowser.git/blob_plain/HEAD:/build-scripts/config/polipo.conf">our
830) old polipo config file</a> if you like. However, please realize that
831) this approach is unsupported.
832) </p>
833) 
834) <hr>
835) 

836) <a id="TBBOtherExtensions"></a>
837) <h3><a class="anchor" href="#TBBOtherExtensions">Can I install other
838) Firefox extensions?</a></h3>
839) 
840) <p>
841) Yes. Just install them like normal. But be sure to avoid extensions like
842) Foxyproxy that screw up your proxy settings. Also, avoid privacy-invasive
843) extensions (for example, pretty much anything with the word Toolbar in
844) its name).
845) </p>
846) 
847) <hr>
848) 

849) <a id="TBBOtherBrowser"></a>
850) <h3><a class="anchor" href="#TBBOtherBrowser">I want to use
851) Chrome/IE/Opera/etc with Tor.</a></h3>
852) 
853) <p>
854) Unfortunately, Torbutton only works with Firefox right now, and without
855) <a href="https://www.torproject.org/torbutton/en/design/">Torbutton's
856) extensive privacy fixes</a> there are many ways for websites or other
857) attackers to recognize you, track you back to your IP address, and so on.
858) In short, using any browser besides Tor Browser Bundle with Tor is a
859) really bad idea.
860) </p>
861) 
862) <p>
863) We're working with the Chrome team to <a
864) href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-and-fingerprinting">fix
865) some bugs and missing APIs in Chrome</a> so it will be possible to write a
866) Torbutton for Chrome. No support for any other browser is on the horizon.
867) </p>
868) 
869) <hr>
870) 
871) <a id="TBBCloseBrowser"></a>
872) <h3><a class="anchor" href="#TBBCloseBrowser">I want to leave Tor Browser
873) Bundle running but close the browser.</a></h3>
874) 
875) <p>
876) We're working on a way to make this possible on all platforms. Please
877) be patient.
878) </p>
879) 
880) <hr>
881) 

882) <a id="GoogleCaptcha"></a>
883) <h3><a class="anchor" href="#GoogleCaptcha">Google makes me solve a Captcha or tells me I have spyware installed.</a></h3>
884) 
885) <p>
886) This is a known and intermittent problem; it does not mean that Google
887) considers Tor to be spyware.
888) </p>
889) 
890) <p>
891) When you use Tor, you are sending queries through exit relays that are also
892) shared by thousands of other users. Tor users typically see this message
893) when many Tor users are querying Google in a short period of time. Google
894) interprets the high volume of traffic from a single IP address (the exit
895) relay you happened to pick) as somebody trying to "crawl" their website,
896) so it slows down traffic from that IP address for a short time.
897) </p>
898) <p>
899) An alternate explanation is that Google tries to detect certain
900) kinds of spyware or viruses that send distinctive queries to Google
901) Search. It notes the IP addresses from which those queries are received
902) (not realizing that they are Tor exit relays), and tries to warn any
903) connections coming from those IP addresses that recent queries indicate
904) an infection.
905) </p>
906) 
907) <p>
908) To our knowledge, Google is not doing anything intentionally specifically
909) to deter or block Tor use. The error message about an infected machine
910) should clear up again after a short time.
911) </p>
912) 
913) <p>
914) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
915) automatically redirect you to a more Tor-friendly search engine such as

916) DuckDuckGo, ixquick, or Bing.

917) </p>
918) 
919) <hr />
920) 
921) <a id="GmailWarning"></a>

922) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my account
923) may have been compromised.</a></h3>

924) 
925) <p>
926) Sometimes, after you've used Gmail over Tor, Google presents a
927) pop-up notification that your account may have been compromised.
928) The notification window lists a series of IP addresses and locations
929) throughout the world recently used to access your account.
930) </p>
931) 
932) <p>
933) In general this is a false alarm: Google saw a bunch of logins from
934) different places, as a result of running the service via Tor, and decided
935) it was a good idea to confirm the account was being accessed by it's
936) rightful owner.
937) </p>
938) 
939) <p>
940) Even though this may be a biproduct of using the service via tor,
941) that doesn't mean you can entirely ignore the warning. It is
942) <i>probably</i> a false positive, but it might not be since it is
943) possible for someone to hijack your Google cookie.
944) </p>
945) 
946) <p>
947) Cookie hijacking is possible by either physical access to your computer
948) or by watching your network traffic.  In theory only physical access
949) should compromise your system because Gmail and similar services
950) should only send the cookie over an SSL link. In practice, alas, it's <a
951) href="http://fscked.org/blog/fully-automated-active-https-cookie-hijacking">
952) way more complex than that</a>.
953) </p>
954) 
955) <p>
956) And if somebody <i>did</i> steal your google cookie, they might end
957) up logging in from unusual places (though of course they also might
958) not). So the summary is that since you're using Tor, this security
959) measure that Google uses isn't so useful for you, because it's full of
960) false positives. You'll have to use other approaches, like seeing if
961) anything looks weird on the account, or looking at the timestamps for
962) recent logins and wondering if you actually logged in at those times.
963) </p>
964) 
965) <hr>
966) 

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

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

969) 
970) <p>
971) Tor installs a text file called torrc that contains configuration
972) instructions for how your Tor program should behave. The default
973) configuration should work fine for most Tor users. Users of Vidalia can
974) make common changes through the Vidalia interface &mdash; only advanced
975) users should need to modify their torrc file directly.
976) </p>
977) 
978) <p>
979) The location of your torrc file depends on the way you installed Tor:
980) </p>
981) 
982) <ul>
983) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
984) find your torrc file in the Start menu under Programs -&gt; Vidalia
985) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
986) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
987) installed Tor without Vidalia, you can find your torrc in the Start
988) menu under Programs -&gt; Tor, or manually in either <code>\Documents
989) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
990) Settings\<i>username</i>\Application Data\tor\torrc</code>.
991) </li>
992) <li>On OS X, if you use Vidalia, edit
993) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
994) and load <code>/Library/Tor/torrc</code>.
995) </li>
996) <li>On Unix, if you installed a pre-built package, look for
997) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
998) package's documentation.
999) </li>
1000) <li>Finally, if you installed from source, you may not have a torrc
1001) installed yet: look in <code>/usr/local/etc/</code> and note that you
1002) may need to manually copy <code>torrc.sample</code> to <code>torrc</code>.
1003) </li>
1004) </ul>
1005) 
1006) <p>
1007) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit
1008) your torrc file. Otherwise Vidalia might overwrite your changes.
1009) </p>
1010) 
1011) <p>
1012) Once you've changed your torrc, you will need to restart Tor for the
1013) changes to take effect. (For advanced users on OS X and Unix, note that
1014) you actually only need to send Tor a HUP signal, not actually restart it.)
1015) </p>
1016) 
1017) <p>
1018) For other configuration options you can use, look at the <a href="<page
1019) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
1020) with # in torrc are treated as comments and have no effect on Tor's
1021) configuration.
1022) </p>
1023) 
1024) <hr>
1025) 

1026) <a id="Logs"></a>

1027) <h3><a class="anchor" href="#Logs">How do I set up logging, or see Tor's logs?</a></h3>

1028) 
1029) <p>

1030) If you installed a Tor bundle that includes Vidalia, then Vidalia has a
1031) window called "Message Log" that will show you Tor's log messages. You
1032) can click on "Settings" to see more details, or to save the messages to
1033) a file. You're all set.

1034) </p>
1035) 
1036) <p>
1037) If you're not using Vidalia, you'll have to go find the log files by

1038) hand. Here are some likely places for your logs to be:

1039) </p>
1040) 
1041) <ul>
1042) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
1043) </li>

1044) <li>On Windows, there are no default log files currently. If you enable
1045) logs in your torrc file, they default to <code>\username\Application
1046) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
1047) </li>
1048) <li>If you compiled Tor from source, by default your Tor logs to <a
1049) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
1050) at log-level notice. If you enable logs in your torrc file, they
1051) default to <code>/usr/local/var/log/tor/</code>.

1052) </li>
1053) </ul>
1054) 
1055) <p>

1056) To change your logging setup by hand, <a href="#torrc">edit your torrc</a>
1057) and find the section (near the top of the file) which contains the
1058) following line:

1059) </p>
1060) 
1061) <pre>

1062) \## Logs go to stdout at level "notice" unless redirected by something
1063) \## else, like one of the below lines.

1064) </pre>

1065) 
1066) <p>

1067) For example, if you want Tor to send complete debug, info, notice, warn,

1068) and err level messages to a file, append the following line to the end
1069) of the section:
1070) </p>
1071) 
1072) <pre>
1073) Log debug file c:/program files/tor/debug.log
1074) </pre>
1075) 
1076) <p>

1077) Replace <code>c:/program files/tor/debug.log</code> with a directory
1078) and filename for your Tor log.

1079) </p>
1080) 
1081) <hr>
1082) 

1083) <a id="DoesntWork"></a>

1084) <h3><a class="anchor" href="#DoesntWork">I installed Tor and Polipo but it's not working.</a></h3>

1085) 
1086) <p>
1087) Once you've installed the Tor bundle, there are two questions to ask:
1088) first, is your Tor able to establish a circuit? Second, is your
1089) Firefox correctly configured to send its traffic through Tor?
1090) </p>
1091) 
1092) <p>If Tor can establish a circuit, the onion icon in
1093) Vidalia will turn green. You can also check in the Vidalia
1094) Control Panel to make sure it says "Connected to the Tor
1095) network!" under Status. For those not using Vidalia, check your <a

1096) href="#Logs">Tor logs</a> for

1097) a line saying that Tor "has successfully opened a circuit. Looks like
1098) client functionality is working."
1099) </p>
1100) 
1101) <p>
1102) If Tor can't establish a circuit, here are some hints:
1103) </p>
1104) 
1105) <ol>
1106) <li>Are you sure Tor is running? If you're using Vidalia, you may have
1107) to click on the onion and select "Start" to launch Tor.</li>
1108) <li>Check your system clock. If it's more than a few hours off, Tor will
1109) refuse to build circuits. For XP users, synchronize your clock under
1110) the clock -&gt; Internet time tab. In addition, correct the day and date
1111) under the 'Date &amp; Time' Tab.</li>
1112) <li>Is your Internet connection <a

1113) href="#FirewallPorts">firewalled by port</a>,

1114) or do you normally need to use a <a

1115) href="<wikifaq>#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</a>?

1116) </li>
1117) <li>Are you running programs like Norton Internet Security or SELinux that
1118) block certain connections, even though you don't realize they do? They
1119) could be preventing Tor from making network connections.</li>
1120) <li>Are you in China, or behind a restrictive corporate network firewall
1121) that blocks the public Tor relays? If so, you should learn about <a

1122) href="<page docs/bridges>">Tor bridges</a>.</li>

1123) <li>Check your <a href="#Logs">Tor logs</a>. Do they give you any hints
1124) about what's going wrong?</li>

1125) </ol>
1126) 
1127) <p>
1128) Step two is to confirm that Firefox is correctly configured to send its
1129) traffic through Tor. Try the <a href="https://check.torproject.org/">Tor
1130) Check</a> site and see whether it thinks you are using Tor. See <a

1131) href="<wikifaq>#HowcanItellifTorisworkingandthatmyconnectionsreallyareanonymizedArethereexternalserversthatwilltestmyconnection">the

1132) Tor Check FAQ entry</a> for details.

1133) </p>

1134) 
1135) <p>
1136) If it thinks you're not using Tor, here are some hints:
1137) </p>
1138) 
1139) <ol>
1140) <li>Did you install the Torbutton extension for Firefox? The installation
1141) bundles include it, but sometimes people forget to install it. Make sure
1142) it says "Tor enabled" at the bottom right of your Firefox window. (For
1143) expert users, make sure your http proxy is set to localhost port
1144) 8118.)</li>
1145) <li>Do you have incompatible Firefox extensions like FoxyProxy
1146) installed? If so, uninstall them. (Note that using FoxyProxy is NOT
1147) a sufficient substitute for Torbutton. There are many known attacks
1148) against a browser setup that does not include Torbutton. Read more

1149) in the <a href="<page torbutton/torbutton-faq>">Torbutton FAQ</a> and the <a

1150) href="https://www.torproject.org/torbutton/design/">Torbutton design</a>
1151) specification.)</li>
1152) <li>If your browser says "The proxy server is refusing connections.",
1153) check that Polipo (the http proxy that passes traffic between Firefox
1154) and Tor) is running. On Windows, look in the task manager and check for
1155) a polipo.exe. On OS X, open the utilities folder in your applications
1156) folder, and open Terminal.app. Then run "ps aux|grep polipo".</li>
1157) <li>If you're upgrading from OS X, some of the earlier OS X installers
1158) were broken in really unfortunate ways. You may find that <a href="<page
1159) docs/tor-doc-osx>#uninstall">uninstalling everything</a> and then
1160) installing a fresh bundle helps. Alas, the current uninstall instructions
1161) may not apply anymore to your old bundle. Sorry.</li>
1162) <li>If you're on Linux, make sure Privoxy isn't running, since it will
1163) conflict with the port that our Polipo configuration file picks.</li>
1164) <li>If you installed Polipo yourself (not from a bundle), did you edit the

1165) config file as described? Did you restart Polipo after this change? Are
1166) you sure?</li>

1167) <li>For Red Hat Linux and related systems, do you have SELinux enabled? If
1168) so, it might be preventing Polipo from talking to Tor. We also run across
1169) BSD users periodically who have local firewall rules that prevent some
1170) connections to localhost.</li>
1171) </ol>
1172) 
1173) <hr />
1174) 
1175) <a id="VidaliaPassword"></a>

1176) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for a password at start.</a></h3>

1177) 
1178) <p>
1179) Vidalia interacts with the Tor software via Tor's "control port". The
1180) control port lets Vidalia receive status updates from Tor, request a new
1181) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
1182) Vidalia sets a random password for Tor's control port to prevent other
1183) applications from also connecting to the control port and potentially
1184) compromising your anonymity.
1185) </p>
1186) 
1187) <p>
1188) Usually this process of generating and setting a random control password
1189) happens in the background. There are three common situations, though,
1190) where Vidalia may prompt you for a password:
1191) </p>
1192) 
1193) <ol>
1194) <li>You're already running Vidalia and Tor. For example, this situation
1195) can happen if you installed the Vidalia bundle and now you're trying to
1196) run the Tor Browser Bundle. In that case, you'll need to close the old
1197) Vidalia and Tor before you can run this one.
1198) </li>
1199) <li>Vidalia crashed, but left Tor running with the last known random
1200) password. After you restart Vidalia, it generates a new random password,
1201) but Vidalia can't talk to Tor, because the random passwords are different.
1202) <br />
1203) If the dialog that prompts you for a control password has a Reset button,
1204) you can click the button and Vidalia will restart Tor with a new random
1205) control password.
1206) <br />
1207) If you do not see a Reset button, or if Vidalia is unable to restart
1208) Tor for you, you can still fix the problem manually. Simply go into your
1209) process or task manager, and terminate the Tor process. Then use Vidalia
1210) to restart Tor and all will work again.
1211) </li>
1212) <li>You had previously set Tor to run as a Windows NT service. When Tor
1213) is set to
1214) run as a service, it starts up when the system boots. If you configured
1215) Tor to start as a service through Vidalia, a random password was set
1216) and saved in Tor. When you reboot, Tor starts up and uses the random
1217) password it saved. You login and start up Vidalia. Vidalia attempts to
1218) talk to the already running Tor. Vidalia generates a random password,
1219) but it is different than the saved password in the Tor service.
1220) <br />
1221) You need to reconfigure Tor to not be a service. See the FAQ entry on

1222) <a href="<wikifaq>#HowdoIrunmyTorrelayasanNTservice">running Tor as a Windows NT service</a>

1223) for more information on how to remove the Tor service.
1224) </li>
1225) </ol>
1226) 

1227)     <hr>

1228) 

1229)     <a id="ChooseEntryExit"></a>
1230)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which nodes (or country) are used for entry/exit?</a></h3>

1231) 

1232)     <p>

1233)     Yes. You can set preferred entry and exit nodes as well as
1234)     inform Tor which nodes you do not want to use.

1235)     The following options can be added to your config file <a
1236)     href="#torrc">"torrc"</a> or specified on the command line:

1237)     </p>
1238)     <dl>
1239)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>
1240)         <dd>A list of preferred nodes to use for the first hop in the circuit, if possible.
1241)         </dd>
1242)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1243)         <dd>A list of preferred nodes to use for the last hop in the circuit, if possible.

1244)         </dd>
1245)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1246)         <dd>A list of nodes to never use when building a circuit.

1247)         </dd>
1248)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1249)         <dd>A list of nodes to never use when picking an exit.
1250)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in this list.

1251)         </dd>
1252)     </dl>
1253)     <p>

1254)     <em>We recommend you do not use these</em>
1255)     &mdash; they are intended for testing and may disappear in future versions.
1256)     You get the best security that Tor can provide when you leave the
1257)     route selection to Tor; overriding the entry / exit nodes can mess
1258)     up your anonymity in ways we don't understand.

1259)     </p>
1260)     <p>

1261)     The <tt>EntryNodes</tt> and <tt>ExitNodes</tt> config options are
1262)     treated as a request, meaning if the nodes are down or seem slow,
1263)     Tor will still avoid them. You can make the option mandatory by
1264)     setting <tt>StrictExitNodes 1</tt> or <tt>StrictEntryNodes 1</tt>
1265)     &mdash; but if you do, your Tor connections will stop working
1266)     if all of the nodes you have specified become unreachable.
1267)     See the <a href="<page docs/documentation>#NeatLinks">Tor status pages</a>

1268)     for some nodes you might pick.
1269)     </p>
1270)     <p>

1271)     Instead of <tt>$fingerprint</tt> you can also specify a 2 letter
1272)     ISO3166 country code in curly braces (for example {de}), or an ip
1273)     address pattern (for example 255.254.0.0/8), or a node nickname. Make
1274)     sure there are no spaces between the commas and the list items.

1275)     </p>
1276)     <p>

1277)     If you want to access a service directly through Tor's Socks interface

1278)     (eg. using ssh via connect.c), another option is to set up an
1279)     internal mapping in your configuration file using <tt>MapAddress</tt>.

1280)     See the manual page for details.
1281)     </p>

1282) 

1283)     <hr>

1284) 

1285) <a id="FirewallPorts"></a>

1286) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a few outgoing ports.</a></h3>

1287) 
1288) <p>
1289) If your firewall works by blocking ports, then you can tell Tor to only
1290) use the ports that your firewall permits by adding "FascistFirewall 1" to

1291) your <a href="<page docs/faq>#torrc">torrc

1292) configuration file</a>, or by clicking "My firewall only lets me connect
1293) to certain ports" in Vidalia's Network Settings window.
1294) </p>
1295) 
1296) <p>
1297) By default, when you set this Tor assumes that your firewall allows only
1298) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1299) different set of ports with the FirewallPorts torrc option.
1300) </p>
1301) 
1302) <p>
1303) If you want to be more fine-grained with your controls, you can also
1304) use the ReachableAddresses config options, e.g.:
1305) </p>
1306) 
1307) <pre>
1308)   ReachableDirAddresses *:80
1309)   ReachableORAddresses *:443
1310) </pre>
1311) 
1312) <hr>

1313) 

1314)     <a id="RelayFlexible"></a>

1315)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay need to be?</a></h3>

1316) 

1317)     <p>
1318)     We aim to make setting up a Tor relay easy and convenient:
1319)     </p>

1320) 

1321)     <ul>
1322)     <li>Tor has built-in support for <a

1323)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1324)     rate limiting</a>. Further, if you have a fast
1325)     link but want to limit the number of bytes per
1326)     day (or week or month) that you donate, check out the <a

1327)     href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">hibernation

1328)     feature</a>.
1329)     </li>
1330)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a> that
1331)     specifies what sort of outbound connections are allowed or refused from
1332)     that relay. If you are uncomfortable allowing people to exit from your
1333)     relay, you can set it up to only allow connections to other Tor relays.
1334)     </li>
1335)     <li>It's fine if the relay goes offline sometimes. The directories
1336)     notice this quickly and stop advertising the relay. Just try to make
1337)     sure it's not too often, since connections using the relay when it
1338)     disconnects will break.
1339)     </li>
1340)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1341)     leave the Address config option blank, and Tor will try to guess.
1342)     </li>
1343)     <li>If your relay is behind a NAT and it doesn't know its public
1344)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1345)     forwarding. Forwarding TCP connections is system dependent but

1346)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1347)     offers some examples on how to do this.
1348)     </li>
1349)     <li>Your relay will passively estimate and advertise its recent
1350)     bandwidth capacity, so high-bandwidth relays will attract more users than
1351)     low-bandwidth ones. Therefore having low-bandwidth relays is useful too.
1352)     </li>
1353)     </ul>

1354) 

1355)     <hr>

1356) 

1357)     <a id="RunARelayBut"></a>
1358)     <a id="ExitPolicies"></a>

1359)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I don't want to deal with abuse issues.</a></h3>

1360) 

1361)     <p>
1362)     Great. That's exactly why we implemented exit policies.
1363)     </p>

1364) 

1365)     <p>
1366)     Each Tor relay has an exit policy that specifies what sort of
1367)     outbound connections are allowed or refused from that relay. The exit
1368)     policies are propagated to Tor clients via the directory, so clients
1369)     will automatically avoid picking exit relays that would refuse to
1370)     exit to their intended destination. This way each relay can decide
1371)     the services, hosts, and networks he wants to allow connections to,

1372)     based on abuse potential and his own situation. Read the FAQ entry on
1373)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might encounter</a>
1374)     if you use the default exit policy, and then read Mike Perry's

1375)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1376)     for running an exit node with minimal harassment</a>.
1377)     </p>

1378) 

1379)     <p>

1380)     The default exit policy allows access to many popular services

1381)     (e.g. web browsing), but <a href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1382)     some due to abuse potential (e.g. mail) and some since
1383)     the Tor network can't handle the load (e.g. default
1384)     file-sharing ports). You can change your exit policy

1385)     using Vidalia's "Sharing" tab, or by manually editing your

1386)     <a href="<page docs/faq>#torrc">torrc</a>

1387)     file. If you want to avoid most if not all abuse potential, set it to
1388)     "reject *:*" (or un-check all the boxes in Vidalia). This setting means
1389)     that your relay will be used for relaying traffic inside the Tor network,
1390)     but not for connections to external websites or other services.
1391)     </p>

1392) 

1393)     <p>
1394)     If you do allow any exit connections, make sure name resolution works
1395)     (that is, your computer can resolve Internet addresses correctly).
1396)     If there are any resources that your computer can't reach (for example,
1397)     you are behind a restrictive firewall or content filter), please
1398)     explicitly reject them in your exit policy &mdash; otherwise Tor users
1399)     will be impacted too.
1400)     </p>

1401) 

1402)     <hr>

1403) 

1404)     <a id="RelayOrBridge"></a>

1405)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal relay or bridge relay?</a></h3>

1406) 

1407)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for short)
1408)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't listed
1409)     in the main Tor directory. That means
1410)     that even an ISP or government trying to filter connections to the Tor
1411)     network probably won't be able to block all the bridges.
1412)     </p>

1413) 

1414)     <p>Being a normal relay vs being a bridge relay is almost the same
1415)     configuration: it's just a matter of whether your relay is listed
1416)     publically or not.
1417)     </p>

1418) 

1419)     <p>Right now, China is the main place in the world that filters
1420)     connections to the Tor network. So bridges are useful a) for users in
1421)     China, b) as a backup measure in case the Tor network gets blocked in
1422)     more places, and c) for people who want an extra layer of security
1423)     because they're worried somebody will recognize that it's a public
1424)     Tor relay IP address they're contacting.

1425)     </p>

1426) 

1427)     <p>So should you run a normal relay or bridge relay? If you have lots
1428)     of bandwidth, you should definitely run a normal relay &mdash; the
1429)     average bridge doesn't see much load these days. If you're willing
1430)     to <a href="#ExitPolicies">be an exit</a>, you should definitely
1431)     run a normal relay, since we need more exits. If you can't be an
1432)     exit and only have a little bit of bandwidth, be a bridge. Thanks
1433)     for volunteering!

1434)     </p>

1435) 

1436)     <hr>

1437) 

1438) <a id="MultipleRelays"></a>
1439) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one relay.</a></h3>

1440) 
1441) <p>
1442) Great. If you want to run several relays to donate more to the network,
1443) we're happy with that. But please don't run more than a few dozen on
1444) the same network, since part of the goal of the Tor network is dispersal
1445) and diversity.
1446) </p>
1447) 
1448) <p>
1449) If you do decide to run more than one relay, please set the "MyFamily"

1450) config option in the <a href="#torrc">torrc</a> of each relay, listing
1451) all the relays (comma-separated) that are under your control:

1452) </p>
1453) 
1454) <pre>
1455)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
1456) </pre>
1457) 
1458) <p>
1459) where each fingerprint is the 40 character identity fingerprint (without
1460) spaces). You can also list them by nickname, but fingerprint is safer. Be
1461) sure to prefix the digest strings with a dollar sign ('$') so that the
1462) digest is not confused with a nickname in the config file.
1463) </p>
1464) 
1465) <p>
1466) That way clients will know to avoid using more than one of your relays
1467) in a single circuit. You should set MyFamily if you have administrative
1468) control of the computers or of their network, even if they're not all in
1469) the same geographic location.
1470) </p>
1471) 
1472)     <hr>
1473) 

1474)     <a id="RelayMemory"></a>

1475)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using so much memory?</a></h3>

1476) 

1477)     <p>If your Tor relay is using more memory than you'd like, here are some
1478)     tips for reducing its footprint:
1479)     </p>

1480) 

1481)     <ol>
1482)     <li>If you're on Linux, you may be encountering memory fragmentation
1483)     bugs in glibc's malloc implementation. That is, when Tor releases memory
1484)     back to the system, the pieces of memory are fragmented so they're hard
1485)     to reuse. The Tor tarball ships with OpenBSD's malloc implementation,
1486)     which doesn't have as many fragmentation bugs (but the tradeoff is higher
1487)     CPU load). You can tell Tor to use this malloc implementation instead:
1488)     <tt>./configure --enable-openbsd-malloc</tt></li>

1489) 

1490)     <li>If you're running a fast relay, meaning you have many TLS connections
1491)     open, you are probably losing a lot of memory to OpenSSL's internal
1492)     buffers (38KB+ per socket). We've patched OpenSSL to <a

1493)     href="https://lists.torproject.org/pipermail/tor-dev/2008-June/001519.html">release

1494)     unused buffer memory more aggressively</a>. If you update to OpenSSL
1495)     1.0.0-beta5, Tor's build process will automatically recognize and use
1496)     this feature.</li>

1497) 

1498)     <li>If you're running on Solaris, OpenBSD, NetBSD, or
1499)     old FreeBSD, Tor is probably forking separate processes
1500)     rather than using threads. Consider switching to a <a

1501)     href="<wikifaq>#WhydoesntmyWindowsorotherOSTorrelayrunwell">better

1502)     operating system</a>.</li>

1503) 

1504)     <li>If you still can't handle the memory load, consider reducing the
1505)     amount of bandwidth your relay advertises. Advertising less bandwidth
1506)     means you will attract fewer users, so your relay shouldn't grow
1507)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1508)     page.</li>

1509) 

1510)     </ol>

1511) 

1512)     <p>
1513)     All of this said, fast Tor relays do use a lot of ram. It is not unusual
1514)     for a fast exit relay to use 500-1000 MB of memory.
1515)     </p>

1516) 

1517)     <hr>

1518) 

1519)     <a id="WhyNotNamed"></a>

1520)     <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not named?</a></h3>

1521) 

1522)     <p>

1523)     We currently use these metrics to determine if your relay should be named:<br>

1524)     </p>
1525)     <ul>
1526)     <li>The name is not currently mapped to a different key. Existing mappings
1527)     are removed after 6 months of inactivity from a relay.</li>
1528)     <li>The relay must have been around for at least two weeks.</li>
1529)     <li>No other router may have wanted the same name in the past month.</li>
1530)     </ul>

1531) 

1532)     <hr>

1533) 

1534)     <a id="RelayDonations"></a>

1535)     <h3><a class="anchor" href="#RelayDonations">Can I donate for a
1536)     relay rather than run my own?</a></h3>

1537) 
1538)     <p>
1539)     Sure! We recommend two non-profit charities that are happy to turn
1540)     your donations into better speed and anonymity for the Tor network:
1541)     </p>
1542)     <ul>
1543)     <li><a href="https://www.torservers.net/">torservers.net</a>
1544)     is a German charitable non-profit that runs a wide variety of

1545)     exit relays. They also like donations of bandwidth from ISPs.</li>

1546)     <li><a
1547)     href="https://www.noisebridge.net/wiki/Noisebridge_Tor">Noisebridge</a>
1548)     is a US-based 501(c)(3) non-profit that collects donations and turns
1549)     them into more exit relay capacity.</li>
1550)     </ul>
1551) 
1552)     <p>
1553)     These organizations are not the same as <a href="<page
1554)     donate/donate>">The Tor Project, Inc</a>, but we consider that a

1555)     good thing. They're both run by nice people who are part of the
1556)     Tor community.

1557)     </p>
1558) 
1559)     <p>
1560)     Note that there can be a tradeoff here between anonymity and
1561)     performance. The Tor network's anonymity comes in part from diversity,
1562)     so if you are in a position to run your own relay, you will be

1563)     improving Tor's anonymity more than by donating. At the same time
1564)     though, economies

1565)     of scale for bandwidth mean that combining many small donations into

1566)     several larger relays is more efficient at improving network

1567)     performance. Improving anonymity and improving performance are both
1568)     worthwhile goals, so however you can help is great!
1569)     </p>
1570) 
1571)     <hr>
1572) 

1573)     <a id="KeyManagement"></a>

1574)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the keys Tor uses.</a></h3>

1575) 

1576)     <p>
1577)     Tor uses a variety of different keys, with three goals in mind: 1)
1578)     encryption to ensure privacy of data within the Tor network, 2)
1579)     authentication so clients know they're
1580)     talking to the relays they meant to talk to, and 3) signatures to make
1581)     sure all clients know the same set of relays.
1582)     </p>

1583) 

1584)     <p>
1585)     <b>Encryption</b>: first, all connections in Tor use TLS link encryption,
1586)     so observers can't look inside to see which circuit a given cell is
1587)     intended for. Further, the Tor client establishes an ephemeral encryption
1588)     key with each relay in the circuit, so only the exit relay can read
1589)     the cells. Both sides discard the circuit key when the circuit ends,
1590)     so logging traffic and then breaking into the relay to discover the key
1591)     won't work.
1592)     </p>

1593) 

1594)     <p>
1595)     <b>Authentication</b>:
1596)     Every Tor relay has a public decryption key called the "onion key".
1597)     When the Tor client establishes circuits, at each step it <a
1598)     href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands
1599)     that the Tor relay prove knowledge of its onion key</a>. That way
1600)     the first node in the path can't just spoof the rest of the path.
1601)     Each relay rotates its onion key once a week.
1602)     </p>

1603) 

1604)     <p>
1605)     <b>Coordination</b>:
1606)     How do clients know what the relays are, and how do they know that they
1607)     have the right keys for them? Each relay has a long-term public signing
1608)     key called the "identity key". Each directory authority additionally has a
1609)     "directory signing key". The directory authorities <a

1610)     href="<specblob>dir-spec.txt">provide a signed list</a>

1611)     of all the known relays, and in that list are a set of certificates from
1612)     each relay (self-signed by their identity key) specifying their keys,
1613)     locations, exit policies, and so on. So unless the adversary can control
1614)     a threshold of the directory authorities, he can't trick the Tor client
1615)     into using other Tor relays.
1616)     </p>

1617) 

1618)     <p>
1619)     How do clients know what the directory authorities are? The Tor software
1620)     comes with a built-in list of location and public key for each directory
1621)     authority. So the only way to trick users into using a fake Tor network
1622)     is to give them a specially modified version of the software.
1623)     </p>

1624) 

1625)     <p>
1626)     How do users know they've got the right software? When we distribute
1627)     the source code or a package, we digitally sign it with <a
1628)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
1629)     href="<page docs/verifying-signatures>">instructions
1630)     on how to check Tor's signatures</a>.
1631)     </p>

1632) 

1633)     <p>
1634)     In order to be certain that it's really signed by us, you need to have
1635)     met us in person and gotten a copy of our GPG key fingerprint, or you
1636)     need to know somebody who has. If you're concerned about an attack on
1637)     this level, we recommend you get involved with the security community
1638)     and start meeting people.
1639)     </p>

1640) 

1641)     <hr>

1642) 

1643) <a id="EntryGuards"></a>
1644) <h3><a class="anchor" href="#EntryGuards">What are Entry Guards?</a></h3>
1645) 
1646) <p>
1647) Tor (like all current practical low-latency anonymity designs) fails
1648) when the attacker can see both ends of the communications channel. For

1649) example, suppose the attacker controls or watches the Tor relay you choose
1650) to enter the network, and also controls or watches the website you visit. In

1651) this case, the research community knows no practical low-latency design
1652) that can reliably stop the attacker from correlating volume and timing
1653) information on the two sides.
1654) </p>
1655) 
1656) <p>
1657) So, what should we do? Suppose the attacker controls, or can observe,

1658) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
1659) new entry and exit relays each time you use the network, the attacker
1660) will be able to correlate all traffic you send with probability
1661) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
1662) as being traced all the time: they want to do something often without
1663) an attacker noticing, and the attacker noticing once is as bad as the
1664) attacker noticing more often. Thus, choosing many random entries and exits
1665) gives the user no chance of escaping profiling by this kind of attacker.

1666) </p>
1667) 
1668) <p>

1669) The solution is "entry guards": each Tor client selects a few relays at random

1670) to use as entry points, and uses only those relays for her first hop. If
1671) those relays are not controlled or observed, the attacker can't win,
1672) ever, and the user is secure. If those relays <i>are</i> observed or
1673) controlled by the attacker, the attacker sees a larger <i>fraction</i>
1674) of the user's traffic &mdash; but still the user is no more profiled than
1675) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
1676) of avoiding profiling, whereas she had none before.

1677) </p>
1678) 
1679) <p>

1680) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
1681) Analysis of the Degradation of Anonymous Protocols</a>, <a
1682) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
1683) Communication Against Passive Logging Attacks</a>, and especially
1684) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
1685) Servers</a>.

1686) </p>
1687) 
1688) <p>
1689) Restricting your entry nodes may also help against attackers who want
1690) to run a few Tor nodes and easily enumerate all of the Tor user IP
1691) addresses. (Even though they can't learn what destinations the users
1692) are talking to, they still might be able to do bad things with just a

1693) list of users.) However, that feature won't really become useful until
1694) we move to a "directory guard" design as well.

1695) </p>
1696) 
1697)     <hr>
1698) 

1699)     <a id="EverybodyARelay"></a>

1700)     <h3><a class="anchor" href="#EverybodyARelay">You should make every Tor user be a relay.</a></h3>

1701) 

1702)     <p>
1703)     Requiring every Tor user to be a relay would help with scaling the

1704)     network to handle all our users, and <a
1705)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

1706)     relay may help your anonymity</a>. However, many Tor users cannot be good
1707)     relays &mdash; for example, some Tor clients operate from behind restrictive
1708)     firewalls, connect via modem, or otherwise aren't in a position where they
1709)     can relay traffic. Providing service to these clients is a critical
1710)     part of providing effective anonymity for everyone, since many Tor users
1711)     are subject to these or similar constraints and including these clients
1712)     increases the size of the anonymity set.
1713)     </p>

1714) 

1715)     <p>
1716)     That said, we do want to encourage Tor users to run relays, so what we
1717)     really want to do is simplify the process of setting up and maintaining
1718)     a relay. We've made a lot of progress with easy configuration in the past
1719)     few years: Vidalia has an easy relay configuration interface, and supports
1720)     uPnP too. Tor is good at automatically detecting whether it's reachable and
1721)     how much bandwidth it can offer.
1722)     </p>

1723) 

1724)     <p>
1725)     There are five steps we need to address before we can do this though:
1726)     </p>

1727) 

1728)     <p>
1729)     First, we need to make Tor stable as a relay on all common
1730)     operating systems. The main remaining platform is Windows,
1731)     and we plan to finally address that in 2009. See Section 4.1 of <a
1732)     href="https://www.torproject.org/press/2008-12-19-roadmap-press-release">our
1733)     development roadmap</a>.
1734)     </p>

1735) 

1736)     <p>
1737)     Second, we still need to get better at automatically estimating
1738)     the right amount of bandwidth to allow. See item #7 on the
1739)     <a href="<page getinvolved/volunteer>#Research">research section of the
1740)     volunteer page</a>: "Tor doesn't work very well when relays
1741)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

1742)     href="<page docs/faq>#TransportIPnotTCP">switching

1743)     to UDP transport</a> is the simplest answer here &mdash; which alas is
1744)     not a very simple answer at all.
1745)     </p>

1746) 

1747)     <p>
1748)     Third, we need to work on scalability, both of the network (how to
1749)     stop requiring that all Tor relays be able to connect to all Tor
1750)     relays) and of the directory (how to stop requiring that all Tor
1751)     users know about all Tor relays). Changes like this can have large
1752)     impact on potential and actual anonymity. See Section 5 of the <a
1753)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
1754)     for details. Again, UDP transport would help here.
1755)     </p>

1756) 

1757)     <p>
1758)     Fourth, we need to better understand the risks from
1759)     letting the attacker send traffic through your relay while
1760)     you're also initiating your own anonymized traffic. <a
1761)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
1762)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
1763)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
1764)     describe ways to identify the relays in a circuit by running traffic
1765)     through candidate relays and looking for dips in the traffic while the
1766)     circuit is active. These clogging attacks are not that scary in the Tor
1767)     context so long as relays are never clients too. But if we're trying to
1768)     encourage more clients to turn on relay functionality too (whether as
1769)     <a href="<page docs/bridges>">bridge relays</a> or as normal relays), then
1770)     we need to understand this threat better and learn how to mitigate it.
1771)     </p>

1772) 

1773)     <p>
1774)     Fifth, we might need some sort of incentive scheme to encourage people
1775)     to relay traffic for others, and/or to become exit nodes. Here are our

1776)     <a href="<blog>two-incentive-designs-tor">current

1777)     thoughts on Tor incentives</a>.
1778)     </p>

1779) 

1780)     <p>
1781)     Please help on all of these!
1782)     </p>

1783) 

1784) <hr>
1785) 
1786) <a id="TransportIPnotTCP"></a>

1787) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all IP packets, not just TCP packets.</a></h3>

1788) 
1789) <p>

1790) This would be handy, because it would make Tor better able to handle
1791) new protocols like VoIP, it could solve the whole need to socksify
1792) applications, and it would solve the fact that exit relays need to
1793) allocate a lot of file descriptors to hold open all the exit connections.

1794) </p>
1795) 
1796) <p>

1797) We're heading in this direction: see <a
1798) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
1799) ticket</a> for directions we should investigate. Some of the hard
1800) problems are:

1801) </p>
1802) 

1803) <ol>

1804) <li>IP packets reveal OS characteristics. We would still need to do
1805) IP-level packet normalization, to stop things like TCP fingerprinting
1806) attacks. Given the diversity and complexity of TCP stacks, along with <a

1807) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

1808) fingerprinting attacks</a>, it looks like our best bet is shipping our
1809) own user-space TCP stack.

1810) </li>

1811) <li>Application-level streams still need scrubbing. We will still need
1812) user-side applications like Torbutton. So it won't become just a matter
1813) of capturing packets and anonymizing them at the IP layer.

1814) </li>
1815) <li>Certain protocols will still leak information. For example, we must
1816) rewrite DNS requests so they are delivered to an unlinkable DNS server
1817) rather than the DNS server at a user's ISP; thus, we must understand
1818) the protocols we are transporting.
1819) </li>
1820) <li><a
1821) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS</a>

1822) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
1823) picked a transport mechanism, we need to design a new end-to-end Tor
1824) protocol for avoiding tagging attacks and other potential anonymity and
1825) integrity issues now that we allow drops, resends, et cetera.

1826) </li>
1827) <li>Exit policies for arbitrary IP packets mean building a secure
1828) IDS. Our node operators tell us that exit policies are one of the main
1829) reasons they're willing to run Tor. Adding an Intrusion Detection System
1830) to handle exit policies would increase the security complexity of Tor,
1831) and would likely not work anyway, as evidenced by the entire field of IDS
1832) and counter-IDS papers. Many potential abuse issues are resolved by the
1833) fact that Tor only transports valid TCP streams (as opposed to arbitrary
1834) IP including malformed packets and IP floods), so exit policies become
1835) even <i>more</i> important as we become able to transport IP packets. We
1836) also need to compactly describe exit policies in the Tor directory,
1837) so clients can predict which nodes will allow their packets to exit &mdash;
1838) and clients need to predict all the packets they will want to send in
1839) a session before picking their exit node!
1840) </li>

1841) <li>The Tor-internal name spaces would need to be redesigned. We support
1842) hidden service ".onion" addresses by intercepting the addresses when
1843) they are passed to the Tor client. Doing so at the IP level will require
1844) a more complex interface between Tor and the local DNS resolver.

1845) </li>
1846) </ol>
1847) 

1848)     <hr>

1849) 

1850)     <a id="Criminals"></a>

1851)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></h3>

1852) 

1853)     <p>
1854)     For the answer to this question and others, please see our <a
1855)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
1856)     </p>

1857) 

1858)     <hr>

1859) 

1860)     <a id="RespondISP"></a>

1861)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP about my exit relay?</a></h3>

1862) 

1863)     <p>
1864)     A collection of templates for successfully responding to ISPs is <a

1865)     href="<wiki>doc/TorAbuseTemplates">collected

1866)     here</a>.
1867)     </p>

1868) 

1869)     <hr>

1870) 

1871)   </div>
1872)   <!-- END MAINCOL -->
1873)   <div id = "sidecol">
1874) #include "side.wmi"
1875) #include "info.wmi"
1876)   </div>
1877)   <!-- END SIDECOL -->
1878) </div>
1879) <!-- END CONTENT -->