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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 an answer to my
28)     Tor support mail?</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 Windows?</a></li>
46)     <li><a href="#VirusFalsePositives">Why does my Tor executable appear to
47)     have a virus or spyware?</a></li>
48)     <li><a href="#LiveCD">Is there a LiveCD or other bundle that includes Tor?</a></li>
49)     </ul>

50) 

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

53) 
54)     <li><a href="#TBBSocksPort">I'm on OSX or Linux and I want to
55)     run another application through the Tor launched by Tor Browser

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

57)     <li><a href="#TBBPolipo">I need an HTTP proxy. Where did Polipo
58)     go?</a></li>
59)     <li><a href="#TBBOtherBrowser">I want to use Chrome/IE/Opera/etc
60)     with Tor.</a></li>
61)     <li><a href="#TBBCloseBrowser">I want to leave Tor Browser Bundle
62)     running but close the browser.</a></li>
63) 

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

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

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

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

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

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

84)     </ul>

85) 

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

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

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

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

98)     </ul>

99) 

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

101) 

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

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

106)     </ul>

107) 

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

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

114)     </ul>

115) 

116)     <p>Abuse:</p>

117)     <ul>
118)     <li><a href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></li>
119)     <li><a href="#RespondISP">How do I respond to my ISP about my exit
120)     relay?</a></li>
121)     </ul>

122) 

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

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

125) 

126)     <hr>

127) 

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

129) 

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

132) 

133)     <p>
134)     The name "Tor" can refer to several different components.
135)     </p>

136) 

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

147) 

148)     <p>
149)     The Tor Project is a non-profit (charity) organization that maintains
150)     and develops the Tor software.
151)     </p>

152) 

153)     <hr>

154) 

155)     <a id="Torisdifferent"></a>
156)     <h3><a class="anchor" href="#Torisdifferent">How is Tor different from other proxies?</a></h3>
157)     <p>

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

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

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

178) stream, and recording your personal details.

179)     </p>
180)     <p>
181)     Tor passes your traffic through at least 3 different servers before sending

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

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

190)     <p>
191)     <dl>

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

205)     </dl>
206)     </p>

207) 

208)     <hr>

209) 

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

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

212) 

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

226) 

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

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

231)     extension</a> if you have Firefox installed. As of version 1.2.0,
232)     Torbutton now takes care of a lot of the connection-level and
233)     application-level worries.
234)     </p>

235) 

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

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

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

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

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

247) 

248)     <hr>

249) 

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

252) 

253)     <p>
254)     Because Tor is the onion routing network. When we were starting the
255)     new next-generation design and implementation of onion routing in
256)     2001-2002, we would tell people we were working on onion routing,
257)     and they would say "Neat. Which one?" Even if onion routing has
258)     become a standard household term, Tor was born out of the actual <a
259)     href="http://www.onion-router.net/">onion routing project</a> run by
260)     the Naval Research Lab.
261)     </p>

262) 

263)     <p>
264)     (It's also got a fine translation from German and Turkish.)
265)     </p>

266) 

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

274) 

275)     <hr>

276) 

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

279) 

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

286) 

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

294) 

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

306) 

307)     <p>
308)     Also, there might be accidental bugs in Tor that could affect your
309)     anonymity. We periodically find and fix anonymity-related bugs, so make
310)     sure you keep your Tor versions up-to-date.
311)     </p>

312) 

313)     <hr>

314) 

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

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

317) 

318)     <p>
319)     Yes.
320)     </p>

321) 

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

328) 

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

335) 

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

351) 

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

357) 

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

365) 

366)     <hr>

367) 

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

369)     <h3><a class="anchor" href="#SupportMail">How can I get an answer to my Tor support mail?</a></h3>

370) 

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

372)     <ol>
373)     <li>Read through this <a href="<page docs/faq>">FAQ</a>.</li>
374)     <li>Read through the <a href="<page docs/documentation>">documentation</a>.</li>
375)     <li>Read through the <a

376)     href="https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk">tor-talk
377)     archives</a> and

378)     see if your question is already answered.</li>
379)     <li>Join our <a href="irc://irc.oftc.net#tor">irc channel</a> and
380)     state the issue and wait for help.</li>
381)     <li>Send an email to tor-assistants at torproject.org. These are
382)     volunteers who may be able to help you but you may not get a response
383)     for days.</li>
384)     </ol>

385) 

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

388) 

389)     <hr>

390) 

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

393) 

394)     <p>
395)     There are many reasons why the Tor network is currently slow.
396)     </p>

397) 

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

405) 

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

412) 

413)     <p>
414)     For the much more in-depth answer, see <a

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

416)     post on the topic</a>, which includes both a detailed PDF and a video
417)     to go with it.
418)     </p>

419) 

420)     <p>
421)     What can you do to help?
422)     </p>

423) 

424)     <ul>

425) 

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

431) 

432)     <li>

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

434)     especially need people to help make it easier to configure your Tor
435)     as a relay. Also, we need help with clear simple documentation to
436)     walk people through setting it up.
437)     </li>

438) 

439)     <li>
440)     There are some bottlenecks in the current Tor network. Help us design
441)     experiments to track down and demonstrate where the problems are, and
442)     then we can focus better on fixing them.
443)     </li>

444) 

445)     <li>
446)     There are some steps that individuals
447)     can take to improve their Tor performance. <a

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

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

455) 

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

462) 

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

468) 

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

477) 

478)     <li>
479)     If you can't help out with any of the above, you can still help out
480)     individually by <a href="<page donate/donate>">donating a bit of money to the
481)     cause</a>. It adds up!
482)     </li>

483) 

484)     </ul>

485) 

486)     <hr>

487) 

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

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

490) 

491)     <p>

492)     The Tor network's <a
493)     href="https://metrics.torproject.org/network.html#networksize">several
494)     thousand</a> relays push <a
495)     href="https://metrics.torproject.org/network.html#bandwidth">over
496)     1GB per second on average</a>. We have <a
497)     href="https://metrics.torproject.org/users.html#direct-users">several
498)     hundred thousand daily users</a>. But the Tor network is not yet
499)     self-sustaining.

500)     </p>

501) 

502)     <p>
503)     There are six main development/maintenance pushes that need attention:
504)     </p>

505) 

506)     <ul>

507) 

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

514) 

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

520) 

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

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

528)     </li>

529) 

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

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

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

538) 

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

545) 

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

556) 

557)     </ul>

558) 

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

566) 

567)     <p>
568)     We are also excited about tackling related problems, such as
569)     censorship-resistance.
570)     </p>

571) 

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

578) 

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

585) 

586)     <hr>
587) 

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

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

590) 

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

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

593)     <hr>

594) 

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

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

599)     <pre>

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

601)     The serial number is: 02:DA:41:04:89:A5:FD:A2:B5:DB:DB:F8:ED:15:0D:BE
602)     The SHA-1 fingerprint is: a7e70f8a648fe04a9677f13eedf6f91b5f7f2e25
603)     The SHA-256 fingerprint is: 23b854af6b96co224fd173382c520b46fa94f2d4e7238893f63ad2d783e27b4b
604) 

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

606)     The serial number is: 00:EF:A3
607)     The SHA-1 fingerprint is: 50af43db8438e67f305a3257d8ef198e8c42f13f

608)     </pre>

609)     </p>
610)     <hr>
611) 

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

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

614) 

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

622) 

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

633) 

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

639) 

640)     <p>
641)     For Mac OS X, follow the <a
642)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
643)     </p>

644) 

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

650) 

651)     <hr>

652) 

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

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

655) 

656)     <p>
657)     These are PGP signatures, so you can verify that the file you've downloaded is
658)     exactly the one that we intended you to get.
659)     </p>

660) 

661)     <p>
662)     Please read the <a
663)     href="<page docs/verifying-signatures>">verifying signatures</a> page for details.
664)     </p>

665) 

666) <hr>
667) 
668) <a id="GetTor"></a>
669) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
670) country. How do I download Tor?</a></h3>
671) 
672) <p>
673) Some government or corporate firewalls censor connections to Tor's
674) website. In those cases, you have three options. First, get it from

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

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

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

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

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

691) </p>
692) 
693) <hr>

694) 

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

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

697) 

698)     <p>
699)     Try following the steps at <a href="<gitblob>doc/tor-win32-mingw-creation.txt">
700)     tor-win32-mingw-creation.txt</a>.
701)     </p>

702) 

703)     <p>
704)     (Note that you don't need to compile Tor yourself in order to use
705)     it. Most people just use the packages available on the <a href="<page
706)     download/download>">download page</a>.)
707)     </p>

708) 

709)     <hr>

710) 

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

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

713) 

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

721) 

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

727) 

728)     <hr>

729) 

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

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

732) 

733)     <p>

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

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

737)     </p>

738) 
739) <hr>
740) 

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

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

744) 
745) <p>
746) <a href="https://www.torproject.org/torbutton/torbutton-faq.html.en#noflash">Answer</a>
747) </p>
748) 
749) <hr>
750) 

751) <a id="TBBBrowserName"></a>
752) <h3><a class="anchor" href="#TBBBrowserName">Why does TBB's browser window
753) say Aurora?</a></h3>
754) 
755) <p>
756) We build Firefox from source in order to include our <a
757) href="https://gitweb.torproject.org/torbrowser.git/tree/maint-2.2:/src/current-patches">Firefox

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

759) browser "Aurora".
760) </p>
761) 
762) <p>
763) Don't be confused into thinking the browser you
764) see is the same as the Firefox pre-releases that
765) were also named Aurora. A future TBB release will <a
766) href="https://trac.torproject.org/projects/tor/ticket/2176">probably</a>
767) have a more recognizable name like "Tor Browser".
768) </p>
769) 
770) <hr>
771) 

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

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

776) 
777) <p>

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

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

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

787) here's a workaround:
788) </p>
789) 
790) <p>
791) In Vidalia, go to Settings-&gt;Advanced and uncheck the box that says
792) 'Configure ControlPort automatically'. Click OK and restart TBB. Your

793) Socks port will then be on 9050.

794) </p>
795) 
796) <hr>
797) 
798) <a id="TBBPolipo"></a>
799) <h3><a class="anchor" href="#TBBPolipo">I need an HTTP proxy. Where did
800) Polipo go?</a></h3>
801) 
802) <p>
803) In the past, Tor bundles included an HTTP proxy like Privoxy or Polipo,
804) solely to work around a bug in Firefox that was finally fixed in Firefox
805) 6. Now you don't need a separate HTTP proxy to use Tor, and in fact
806) leaving it out makes you safer because Torbutton has better control over
807) Firefox's interaction with websites.
808) </p>
809) 
810) <p>
811) If you are trying to use some external application with Tor, step zero

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

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

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

815) proxy on port 9050 on Windows, or <a href="#TBBSocksPort">see above</a>
816) for OSX and Linux.
817) </p>
818) 
819) <p>
820) If that fails, feel free to install privoxy or polipo. You can use <a
821) href="https://gitweb.torproject.org/torbrowser.git/blob_plain/HEAD:/build-scripts/config/polipo.conf">our
822) old polipo config file</a> if you like. However, please realize that
823) this approach is unsupported.
824) </p>
825) 
826) <hr>
827) 

828) <a id="TBBOtherExtensions"></a>
829) <h3><a class="anchor" href="#TBBOtherExtensions">Can I install other
830) Firefox extensions?</a></h3>
831) 
832) <p>
833) Yes. Just install them like normal. But be sure to avoid extensions like
834) Foxyproxy that screw up your proxy settings. Also, avoid privacy-invasive
835) extensions (for example, pretty much anything with the word Toolbar in
836) its name).
837) </p>
838) 
839) <hr>
840) 

841) <a id="TBBOtherBrowser"></a>
842) <h3><a class="anchor" href="#TBBOtherBrowser">I want to use
843) Chrome/IE/Opera/etc with Tor.</a></h3>
844) 
845) <p>
846) Unfortunately, Torbutton only works with Firefox right now, and without
847) <a href="https://www.torproject.org/torbutton/en/design/">Torbutton's
848) extensive privacy fixes</a> there are many ways for websites or other
849) attackers to recognize you, track you back to your IP address, and so on.
850) In short, using any browser besides Tor Browser Bundle with Tor is a
851) really bad idea.
852) </p>
853) 
854) <p>
855) We're working with the Chrome team to <a
856) href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-and-fingerprinting">fix
857) some bugs and missing APIs in Chrome</a> so it will be possible to write a
858) Torbutton for Chrome. No support for any other browser is on the horizon.
859) </p>
860) 
861) <hr>
862) 
863) <a id="TBBCloseBrowser"></a>
864) <h3><a class="anchor" href="#TBBCloseBrowser">I want to leave Tor Browser
865) Bundle running but close the browser.</a></h3>
866) 
867) <p>
868) We're working on a way to make this possible on all platforms. Please
869) be patient.
870) </p>
871) 
872) <hr>
873) 

874) <a id="GoogleCaptcha"></a>
875) <h3><a class="anchor" href="#GoogleCaptcha">Google makes me solve a Captcha or tells me I have spyware installed.</a></h3>
876) 
877) <p>
878) This is a known and intermittent problem; it does not mean that Google
879) considers Tor to be spyware.
880) </p>
881) 
882) <p>
883) When you use Tor, you are sending queries through exit relays that are also
884) shared by thousands of other users. Tor users typically see this message
885) when many Tor users are querying Google in a short period of time. Google
886) interprets the high volume of traffic from a single IP address (the exit
887) relay you happened to pick) as somebody trying to "crawl" their website,
888) so it slows down traffic from that IP address for a short time.
889) </p>
890) <p>
891) An alternate explanation is that Google tries to detect certain
892) kinds of spyware or viruses that send distinctive queries to Google
893) Search. It notes the IP addresses from which those queries are received
894) (not realizing that they are Tor exit relays), and tries to warn any
895) connections coming from those IP addresses that recent queries indicate
896) an infection.
897) </p>
898) 
899) <p>
900) To our knowledge, Google is not doing anything intentionally specifically
901) to deter or block Tor use. The error message about an infected machine
902) should clear up again after a short time.
903) </p>
904) 
905) <p>
906) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
907) automatically redirect you to a more Tor-friendly search engine such as
908) Ixquick or Bing.
909) </p>
910) 
911) <hr />
912) 
913) <a id="GmailWarning"></a>
914) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my account may have been compromised.</a></h3>
915) 
916) <p>
917) Sometimes, after you've used Gmail over Tor, Google presents a
918) pop-up notification that your account may have been compromised.
919) The notification window lists a series of IP addresses and locations
920) throughout the world recently used to access your account.
921) </p>
922) 
923) <p>
924) In general this is a false alarm: Google saw a bunch of logins from
925) different places, as a result of running the service via Tor, and decided
926) it was a good idea to confirm the account was being accessed by it's
927) rightful owner.
928) </p>
929) 
930) <p>
931) Even though this may be a biproduct of using the service via tor,
932) that doesn't mean you can entirely ignore the warning. It is
933) <i>probably</i> a false positive, but it might not be since it is
934) possible for someone to hijack your Google cookie.
935) </p>
936) 
937) <p>
938) Cookie hijacking is possible by either physical access to your computer
939) or by watching your network traffic.  In theory only physical access
940) should compromise your system because Gmail and similar services
941) should only send the cookie over an SSL link. In practice, alas, it's <a
942) href="http://fscked.org/blog/fully-automated-active-https-cookie-hijacking">
943) way more complex than that</a>.
944) </p>
945) 
946) <p>
947) And if somebody <i>did</i> steal your google cookie, they might end
948) up logging in from unusual places (though of course they also might
949) not). So the summary is that since you're using Tor, this security
950) measure that Google uses isn't so useful for you, because it's full of
951) false positives. You'll have to use other approaches, like seeing if
952) anything looks weird on the account, or looking at the timestamps for
953) recent logins and wondering if you actually logged in at those times.
954) </p>
955) 
956) <hr>
957) 

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

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

960) 
961) <p>
962) Tor installs a text file called torrc that contains configuration
963) instructions for how your Tor program should behave. The default
964) configuration should work fine for most Tor users. Users of Vidalia can
965) make common changes through the Vidalia interface &mdash; only advanced
966) users should need to modify their torrc file directly.
967) </p>
968) 
969) <p>
970) The location of your torrc file depends on the way you installed Tor:
971) </p>
972) 
973) <ul>
974) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
975) find your torrc file in the Start menu under Programs -&gt; Vidalia
976) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
977) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
978) installed Tor without Vidalia, you can find your torrc in the Start
979) menu under Programs -&gt; Tor, or manually in either <code>\Documents
980) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
981) Settings\<i>username</i>\Application Data\tor\torrc</code>.
982) </li>
983) <li>On OS X, if you use Vidalia, edit
984) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
985) and load <code>/Library/Tor/torrc</code>.
986) </li>
987) <li>On Unix, if you installed a pre-built package, look for
988) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
989) package's documentation.
990) </li>
991) <li>Finally, if you installed from source, you may not have a torrc
992) installed yet: look in <code>/usr/local/etc/</code> and note that you
993) may need to manually copy <code>torrc.sample</code> to <code>torrc</code>.
994) </li>
995) </ul>
996) 
997) <p>
998) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit
999) your torrc file. Otherwise Vidalia might overwrite your changes.
1000) </p>
1001) 
1002) <p>
1003) Once you've changed your torrc, you will need to restart Tor for the
1004) changes to take effect. (For advanced users on OS X and Unix, note that
1005) you actually only need to send Tor a HUP signal, not actually restart it.)
1006) </p>
1007) 
1008) <p>
1009) For other configuration options you can use, look at the <a href="<page
1010) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
1011) with # in torrc are treated as comments and have no effect on Tor's
1012) configuration.
1013) </p>
1014) 
1015) <hr>
1016) 

1017) <a id="Logs"></a>

1018) <h3><a class="anchor" href="#Logs">How do I set up logging, or see Tor's logs?</a></h3>

1019) 
1020) <p>

1021) If you installed a Tor bundle that includes Vidalia, then Vidalia has a
1022) window called "Message Log" that will show you Tor's log messages. You
1023) can click on "Settings" to see more details, or to save the messages to
1024) a file. You're all set.

1025) </p>
1026) 
1027) <p>
1028) If you're not using Vidalia, you'll have to go find the log files by

1029) hand. Here are some likely places for your logs to be:

1030) </p>
1031) 
1032) <ul>
1033) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
1034) </li>

1035) <li>On Windows, there are no default log files currently. If you enable
1036) logs in your torrc file, they default to <code>\username\Application
1037) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
1038) </li>
1039) <li>If you compiled Tor from source, by default your Tor logs to <a
1040) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
1041) at log-level notice. If you enable logs in your torrc file, they
1042) default to <code>/usr/local/var/log/tor/</code>.

1043) </li>
1044) </ul>
1045) 
1046) <p>

1047) To change your logging setup by hand, <a href="#torrc">edit your torrc</a>
1048) and find the section (near the top of the file) which contains the
1049) following line:

1050) </p>
1051) 
1052) <pre>

1053) \## Logs go to stdout at level "notice" unless redirected by something
1054) \## else, like one of the below lines.

1055) </pre>

1056) 
1057) <p>

1058) For example, if you want Tor to send complete debug, info, notice, warn,

1059) and err level messages to a file, append the following line to the end
1060) of the section:
1061) </p>
1062) 
1063) <pre>
1064) Log debug file c:/program files/tor/debug.log
1065) </pre>
1066) 
1067) <p>

1068) Replace <code>c:/program files/tor/debug.log</code> with a directory
1069) and filename for your Tor log.

1070) </p>
1071) 
1072) <hr>
1073) 

1074) <a id="DoesntWork"></a>

1075) <h3><a class="anchor" href="#DoesntWork">I installed Tor and Polipo but it's not working.</a></h3>

1076) 
1077) <p>
1078) Once you've installed the Tor bundle, there are two questions to ask:
1079) first, is your Tor able to establish a circuit? Second, is your
1080) Firefox correctly configured to send its traffic through Tor?
1081) </p>
1082) 
1083) <p>If Tor can establish a circuit, the onion icon in
1084) Vidalia will turn green. You can also check in the Vidalia
1085) Control Panel to make sure it says "Connected to the Tor
1086) network!" under Status. For those not using Vidalia, check your <a

1087) href="#Logs">Tor logs</a> for

1088) a line saying that Tor "has successfully opened a circuit. Looks like
1089) client functionality is working."
1090) </p>
1091) 
1092) <p>
1093) If Tor can't establish a circuit, here are some hints:
1094) </p>
1095) 
1096) <ol>
1097) <li>Are you sure Tor is running? If you're using Vidalia, you may have
1098) to click on the onion and select "Start" to launch Tor.</li>
1099) <li>Check your system clock. If it's more than a few hours off, Tor will
1100) refuse to build circuits. For XP users, synchronize your clock under
1101) the clock -&gt; Internet time tab. In addition, correct the day and date
1102) under the 'Date &amp; Time' Tab.</li>
1103) <li>Is your Internet connection <a

1104) href="#FirewallPorts">firewalled by port</a>,

1105) or do you normally need to use a <a

1106) href="<wikifaq>#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</a>?

1107) </li>
1108) <li>Are you running programs like Norton Internet Security or SELinux that
1109) block certain connections, even though you don't realize they do? They
1110) could be preventing Tor from making network connections.</li>
1111) <li>Are you in China, or behind a restrictive corporate network firewall
1112) that blocks the public Tor relays? If so, you should learn about <a

1113) href="<page docs/bridges>">Tor bridges</a>.</li>

1114) <li>Check your <a href="#Logs">Tor logs</a>. Do they give you any hints
1115) about what's going wrong?</li>

1116) </ol>
1117) 
1118) <p>
1119) Step two is to confirm that Firefox is correctly configured to send its
1120) traffic through Tor. Try the <a href="https://check.torproject.org/">Tor
1121) Check</a> site and see whether it thinks you are using Tor. See <a

1122) href="<wikifaq>#HowcanItellifTorisworkingandthatmyconnectionsreallyareanonymizedArethereexternalserversthatwilltestmyconnection">the

1123) Tor Check FAQ entry</a> for details.

1124) </p>

1125) 
1126) <p>
1127) If it thinks you're not using Tor, here are some hints:
1128) </p>
1129) 
1130) <ol>
1131) <li>Did you install the Torbutton extension for Firefox? The installation
1132) bundles include it, but sometimes people forget to install it. Make sure
1133) it says "Tor enabled" at the bottom right of your Firefox window. (For
1134) expert users, make sure your http proxy is set to localhost port
1135) 8118.)</li>
1136) <li>Do you have incompatible Firefox extensions like FoxyProxy
1137) installed? If so, uninstall them. (Note that using FoxyProxy is NOT
1138) a sufficient substitute for Torbutton. There are many known attacks
1139) against a browser setup that does not include Torbutton. Read more

1140) in the <a href="<page torbutton/torbutton-faq>">Torbutton FAQ</a> and the <a

1141) href="https://www.torproject.org/torbutton/design/">Torbutton design</a>
1142) specification.)</li>
1143) <li>If your browser says "The proxy server is refusing connections.",
1144) check that Polipo (the http proxy that passes traffic between Firefox
1145) and Tor) is running. On Windows, look in the task manager and check for
1146) a polipo.exe. On OS X, open the utilities folder in your applications
1147) folder, and open Terminal.app. Then run "ps aux|grep polipo".</li>
1148) <li>If you're upgrading from OS X, some of the earlier OS X installers
1149) were broken in really unfortunate ways. You may find that <a href="<page
1150) docs/tor-doc-osx>#uninstall">uninstalling everything</a> and then
1151) installing a fresh bundle helps. Alas, the current uninstall instructions
1152) may not apply anymore to your old bundle. Sorry.</li>
1153) <li>If you're on Linux, make sure Privoxy isn't running, since it will
1154) conflict with the port that our Polipo configuration file picks.</li>
1155) <li>If you installed Polipo yourself (not from a bundle), did you edit the

1156) config file as described? Did you restart Polipo after this change? Are
1157) you sure?</li>

1158) <li>For Red Hat Linux and related systems, do you have SELinux enabled? If
1159) so, it might be preventing Polipo from talking to Tor. We also run across
1160) BSD users periodically who have local firewall rules that prevent some
1161) connections to localhost.</li>
1162) </ol>
1163) 
1164) <hr />
1165) 
1166) <a id="VidaliaPassword"></a>

1167) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for a password at start.</a></h3>

1168) 
1169) <p>
1170) Vidalia interacts with the Tor software via Tor's "control port". The
1171) control port lets Vidalia receive status updates from Tor, request a new
1172) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
1173) Vidalia sets a random password for Tor's control port to prevent other
1174) applications from also connecting to the control port and potentially
1175) compromising your anonymity.
1176) </p>
1177) 
1178) <p>
1179) Usually this process of generating and setting a random control password
1180) happens in the background. There are three common situations, though,
1181) where Vidalia may prompt you for a password:
1182) </p>
1183) 
1184) <ol>
1185) <li>You're already running Vidalia and Tor. For example, this situation
1186) can happen if you installed the Vidalia bundle and now you're trying to
1187) run the Tor Browser Bundle. In that case, you'll need to close the old
1188) Vidalia and Tor before you can run this one.
1189) </li>
1190) <li>Vidalia crashed, but left Tor running with the last known random
1191) password. After you restart Vidalia, it generates a new random password,
1192) but Vidalia can't talk to Tor, because the random passwords are different.
1193) <br />
1194) If the dialog that prompts you for a control password has a Reset button,
1195) you can click the button and Vidalia will restart Tor with a new random
1196) control password.
1197) <br />
1198) If you do not see a Reset button, or if Vidalia is unable to restart
1199) Tor for you, you can still fix the problem manually. Simply go into your
1200) process or task manager, and terminate the Tor process. Then use Vidalia
1201) to restart Tor and all will work again.
1202) </li>
1203) <li>You had previously set Tor to run as a Windows NT service. When Tor
1204) is set to
1205) run as a service, it starts up when the system boots. If you configured
1206) Tor to start as a service through Vidalia, a random password was set
1207) and saved in Tor. When you reboot, Tor starts up and uses the random
1208) password it saved. You login and start up Vidalia. Vidalia attempts to
1209) talk to the already running Tor. Vidalia generates a random password,
1210) but it is different than the saved password in the Tor service.
1211) <br />
1212) You need to reconfigure Tor to not be a service. See the FAQ entry on

1213) <a href="<wikifaq>#HowdoIrunmyTorrelayasanNTservice">running Tor as a Windows NT service</a>

1214) for more information on how to remove the Tor service.
1215) </li>
1216) </ol>
1217) 

1218)     <hr>

1219) 

1220)     <a id="ChooseEntryExit"></a>
1221)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which nodes (or country) are used for entry/exit?</a></h3>

1222) 

1223)     <p>

1224)     Yes. You can set preferred entry and exit nodes as well as
1225)     inform Tor which nodes you do not want to use.

1226)     The following options can be added to your config file <a
1227)     href="#torrc">"torrc"</a> or specified on the command line:

1228)     </p>
1229)     <dl>
1230)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>
1231)         <dd>A list of preferred nodes to use for the first hop in the circuit, if possible.
1232)         </dd>
1233)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1234)         <dd>A list of preferred nodes to use for the last hop in the circuit, if possible.

1235)         </dd>
1236)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1237)         <dd>A list of nodes to never use when building a circuit.

1238)         </dd>
1239)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1240)         <dd>A list of nodes to never use when picking an exit.
1241)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in this list.

1242)         </dd>
1243)     </dl>
1244)     <p>

1245)     <em>We recommend you do not use these</em>
1246)     &mdash; they are intended for testing and may disappear in future versions.
1247)     You get the best security that Tor can provide when you leave the
1248)     route selection to Tor; overriding the entry / exit nodes can mess
1249)     up your anonymity in ways we don't understand.

1250)     </p>
1251)     <p>

1252)     The <tt>EntryNodes</tt> and <tt>ExitNodes</tt> config options are
1253)     treated as a request, meaning if the nodes are down or seem slow,
1254)     Tor will still avoid them. You can make the option mandatory by
1255)     setting <tt>StrictExitNodes 1</tt> or <tt>StrictEntryNodes 1</tt>
1256)     &mdash; but if you do, your Tor connections will stop working
1257)     if all of the nodes you have specified become unreachable.
1258)     See the <a href="<page docs/documentation>#NeatLinks">Tor status pages</a>

1259)     for some nodes you might pick.
1260)     </p>
1261)     <p>

1262)     Instead of <tt>$fingerprint</tt> you can also specify a 2 letter
1263)     ISO3166 country code in curly braces (for example {de}), or an ip
1264)     address pattern (for example 255.254.0.0/8), or a node nickname. Make
1265)     sure there are no spaces between the commas and the list items.

1266)     </p>
1267)     <p>

1268)     If you want to access a service directly through Tor's Socks interface

1269)     (eg. using ssh via connect.c), another option is to set up an
1270)     internal mapping in your configuration file using <tt>MapAddress</tt>.

1271)     See the manual page for details.
1272)     </p>

1273) 

1274)     <hr>

1275) 

1276) <a id="FirewallPorts"></a>

1277) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a few outgoing ports.</a></h3>

1278) 
1279) <p>
1280) If your firewall works by blocking ports, then you can tell Tor to only
1281) use the ports that your firewall permits by adding "FascistFirewall 1" to

1282) your <a href="<page docs/faq>#torrc">torrc

1283) configuration file</a>, or by clicking "My firewall only lets me connect
1284) to certain ports" in Vidalia's Network Settings window.
1285) </p>
1286) 
1287) <p>
1288) By default, when you set this Tor assumes that your firewall allows only
1289) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1290) different set of ports with the FirewallPorts torrc option.
1291) </p>
1292) 
1293) <p>
1294) If you want to be more fine-grained with your controls, you can also
1295) use the ReachableAddresses config options, e.g.:
1296) </p>
1297) 
1298) <pre>
1299)   ReachableDirAddresses *:80
1300)   ReachableORAddresses *:443
1301) </pre>
1302) 
1303) <hr>

1304) 

1305)     <a id="RelayFlexible"></a>

1306)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay need to be?</a></h3>

1307) 

1308)     <p>
1309)     We aim to make setting up a Tor relay easy and convenient:
1310)     </p>

1311) 

1312)     <ul>
1313)     <li>Tor has built-in support for <a

1314)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1315)     rate limiting</a>. Further, if you have a fast
1316)     link but want to limit the number of bytes per
1317)     day (or week or month) that you donate, check out the <a

1318)     href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">hibernation

1319)     feature</a>.
1320)     </li>
1321)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a> that
1322)     specifies what sort of outbound connections are allowed or refused from
1323)     that relay. If you are uncomfortable allowing people to exit from your
1324)     relay, you can set it up to only allow connections to other Tor relays.
1325)     </li>
1326)     <li>It's fine if the relay goes offline sometimes. The directories
1327)     notice this quickly and stop advertising the relay. Just try to make
1328)     sure it's not too often, since connections using the relay when it
1329)     disconnects will break.
1330)     </li>
1331)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1332)     leave the Address config option blank, and Tor will try to guess.
1333)     </li>
1334)     <li>If your relay is behind a NAT and it doesn't know its public
1335)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1336)     forwarding. Forwarding TCP connections is system dependent but

1337)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1338)     offers some examples on how to do this.
1339)     </li>
1340)     <li>Your relay will passively estimate and advertise its recent
1341)     bandwidth capacity, so high-bandwidth relays will attract more users than
1342)     low-bandwidth ones. Therefore having low-bandwidth relays is useful too.
1343)     </li>
1344)     </ul>

1345) 

1346)     <hr>

1347) 

1348)     <a id="RunARelayBut"></a>
1349)     <a id="ExitPolicies"></a>

1350)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I don't want to deal with abuse issues.</a></h3>

1351) 

1352)     <p>
1353)     Great. That's exactly why we implemented exit policies.
1354)     </p>

1355) 

1356)     <p>
1357)     Each Tor relay has an exit policy that specifies what sort of
1358)     outbound connections are allowed or refused from that relay. The exit
1359)     policies are propagated to Tor clients via the directory, so clients
1360)     will automatically avoid picking exit relays that would refuse to
1361)     exit to their intended destination. This way each relay can decide
1362)     the services, hosts, and networks he wants to allow connections to,

1363)     based on abuse potential and his own situation. Read the FAQ entry on
1364)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might encounter</a>
1365)     if you use the default exit policy, and then read Mike Perry's

1366)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1367)     for running an exit node with minimal harassment</a>.
1368)     </p>

1369) 

1370)     <p>

1371)     The default exit policy allows access to many popular services

1372)     (e.g. web browsing), but <a href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1373)     some due to abuse potential (e.g. mail) and some since
1374)     the Tor network can't handle the load (e.g. default
1375)     file-sharing ports). You can change your exit policy

1376)     using Vidalia's "Sharing" tab, or by manually editing your

1377)     <a href="<page docs/faq>#torrc">torrc</a>

1378)     file. If you want to avoid most if not all abuse potential, set it to
1379)     "reject *:*" (or un-check all the boxes in Vidalia). This setting means
1380)     that your relay will be used for relaying traffic inside the Tor network,
1381)     but not for connections to external websites or other services.
1382)     </p>

1383) 

1384)     <p>
1385)     If you do allow any exit connections, make sure name resolution works
1386)     (that is, your computer can resolve Internet addresses correctly).
1387)     If there are any resources that your computer can't reach (for example,
1388)     you are behind a restrictive firewall or content filter), please
1389)     explicitly reject them in your exit policy &mdash; otherwise Tor users
1390)     will be impacted too.
1391)     </p>

1392) 

1393)     <hr>

1394) 

1395)     <a id="RelayOrBridge"></a>

1396)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal relay or bridge relay?</a></h3>

1397) 

1398)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for short)
1399)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't listed
1400)     in the main Tor directory. That means
1401)     that even an ISP or government trying to filter connections to the Tor
1402)     network probably won't be able to block all the bridges.
1403)     </p>

1404) 

1405)     <p>Being a normal relay vs being a bridge relay is almost the same
1406)     configuration: it's just a matter of whether your relay is listed
1407)     publically or not.
1408)     </p>

1409) 

1410)     <p>Right now, China is the main place in the world that filters
1411)     connections to the Tor network. So bridges are useful a) for users in
1412)     China, b) as a backup measure in case the Tor network gets blocked in
1413)     more places, and c) for people who want an extra layer of security
1414)     because they're worried somebody will recognize that it's a public
1415)     Tor relay IP address they're contacting.

1416)     </p>

1417) 

1418)     <p>So should you run a normal relay or bridge relay? If you have lots
1419)     of bandwidth, you should definitely run a normal relay &mdash; the
1420)     average bridge doesn't see much load these days. If you're willing
1421)     to <a href="#ExitPolicies">be an exit</a>, you should definitely
1422)     run a normal relay, since we need more exits. If you can't be an
1423)     exit and only have a little bit of bandwidth, be a bridge. Thanks
1424)     for volunteering!

1425)     </p>

1426) 

1427)     <hr>

1428) 

1429) <a id="MultipleRelays"></a>
1430) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one relay.</a></h3>

1431) 
1432) <p>
1433) Great. If you want to run several relays to donate more to the network,
1434) we're happy with that. But please don't run more than a few dozen on
1435) the same network, since part of the goal of the Tor network is dispersal
1436) and diversity.
1437) </p>
1438) 
1439) <p>
1440) If you do decide to run more than one relay, please set the "MyFamily"

1441) config option in the <a href="#torrc">torrc</a> of each relay, listing
1442) all the relays (comma-separated) that are under your control:

1443) </p>
1444) 
1445) <pre>
1446)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
1447) </pre>
1448) 
1449) <p>
1450) where each fingerprint is the 40 character identity fingerprint (without
1451) spaces). You can also list them by nickname, but fingerprint is safer. Be
1452) sure to prefix the digest strings with a dollar sign ('$') so that the
1453) digest is not confused with a nickname in the config file.
1454) </p>
1455) 
1456) <p>
1457) That way clients will know to avoid using more than one of your relays
1458) in a single circuit. You should set MyFamily if you have administrative
1459) control of the computers or of their network, even if they're not all in
1460) the same geographic location.
1461) </p>
1462) 
1463)     <hr>
1464) 

1465)     <a id="RelayMemory"></a>

1466)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using so much memory?</a></h3>

1467) 

1468)     <p>If your Tor relay is using more memory than you'd like, here are some
1469)     tips for reducing its footprint:
1470)     </p>

1471) 

1472)     <ol>
1473)     <li>If you're on Linux, you may be encountering memory fragmentation
1474)     bugs in glibc's malloc implementation. That is, when Tor releases memory
1475)     back to the system, the pieces of memory are fragmented so they're hard
1476)     to reuse. The Tor tarball ships with OpenBSD's malloc implementation,
1477)     which doesn't have as many fragmentation bugs (but the tradeoff is higher
1478)     CPU load). You can tell Tor to use this malloc implementation instead:
1479)     <tt>./configure --enable-openbsd-malloc</tt></li>

1480) 

1481)     <li>If you're running a fast relay, meaning you have many TLS connections
1482)     open, you are probably losing a lot of memory to OpenSSL's internal
1483)     buffers (38KB+ per socket). We've patched OpenSSL to <a

1484)     href="https://lists.torproject.org/pipermail/tor-dev/2008-June/001519.html">release

1485)     unused buffer memory more aggressively</a>. If you update to OpenSSL
1486)     1.0.0-beta5, Tor's build process will automatically recognize and use
1487)     this feature.</li>

1488) 

1489)     <li>If you're running on Solaris, OpenBSD, NetBSD, or
1490)     old FreeBSD, Tor is probably forking separate processes
1491)     rather than using threads. Consider switching to a <a

1492)     href="<wikifaq>#WhydoesntmyWindowsorotherOSTorrelayrunwell">better

1493)     operating system</a>.</li>

1494) 

1495)     <li>If you still can't handle the memory load, consider reducing the
1496)     amount of bandwidth your relay advertises. Advertising less bandwidth
1497)     means you will attract fewer users, so your relay shouldn't grow
1498)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1499)     page.</li>

1500) 

1501)     </ol>

1502) 

1503)     <p>
1504)     All of this said, fast Tor relays do use a lot of ram. It is not unusual
1505)     for a fast exit relay to use 500-1000 MB of memory.
1506)     </p>

1507) 

1508)     <hr>

1509) 

1510)     <a id="WhyNotNamed"></a>

1511)     <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not named?</a></h3>

1512) 

1513)     <p>

1514)     We currently use these metrics to determine if your relay should be named:<br>

1515)     </p>
1516)     <ul>
1517)     <li>The name is not currently mapped to a different key. Existing mappings
1518)     are removed after 6 months of inactivity from a relay.</li>
1519)     <li>The relay must have been around for at least two weeks.</li>
1520)     <li>No other router may have wanted the same name in the past month.</li>
1521)     </ul>

1522) 

1523)     <hr>

1524) 

1525)     <a id="RelayDonations"></a>

1526)     <h3><a class="anchor" href="#RelayDonations">Can I donate for a
1527)     relay rather than run my own?</a></h3>

1528) 
1529)     <p>
1530)     Sure! We recommend two non-profit charities that are happy to turn
1531)     your donations into better speed and anonymity for the Tor network:
1532)     </p>
1533)     <ul>
1534)     <li><a href="https://www.torservers.net/">torservers.net</a>
1535)     is a German charitable non-profit that runs a wide variety of

1536)     exit relays. They also like donations of bandwidth from ISPs.</li>

1537)     <li><a
1538)     href="https://www.noisebridge.net/wiki/Noisebridge_Tor">Noisebridge</a>
1539)     is a US-based 501(c)(3) non-profit that collects donations and turns
1540)     them into more exit relay capacity.</li>
1541)     </ul>
1542) 
1543)     <p>
1544)     These organizations are not the same as <a href="<page
1545)     donate/donate>">The Tor Project, Inc</a>, but we consider that a

1546)     good thing. They're both run by nice people who are part of the
1547)     Tor community.

1548)     </p>
1549) 
1550)     <p>
1551)     Note that there can be a tradeoff here between anonymity and
1552)     performance. The Tor network's anonymity comes in part from diversity,
1553)     so if you are in a position to run your own relay, you will be

1554)     improving Tor's anonymity more than by donating. At the same time
1555)     though, economies

1556)     of scale for bandwidth mean that combining many small donations into

1557)     several larger relays is more efficient at improving network

1558)     performance. Improving anonymity and improving performance are both
1559)     worthwhile goals, so however you can help is great!
1560)     </p>
1561) 
1562)     <hr>
1563) 

1564)     <a id="KeyManagement"></a>

1565)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the keys Tor uses.</a></h3>

1566) 

1567)     <p>
1568)     Tor uses a variety of different keys, with three goals in mind: 1)
1569)     encryption to ensure privacy of data within the Tor network, 2)
1570)     authentication so clients know they're
1571)     talking to the relays they meant to talk to, and 3) signatures to make
1572)     sure all clients know the same set of relays.
1573)     </p>

1574) 

1575)     <p>
1576)     <b>Encryption</b>: first, all connections in Tor use TLS link encryption,
1577)     so observers can't look inside to see which circuit a given cell is
1578)     intended for. Further, the Tor client establishes an ephemeral encryption
1579)     key with each relay in the circuit, so only the exit relay can read
1580)     the cells. Both sides discard the circuit key when the circuit ends,
1581)     so logging traffic and then breaking into the relay to discover the key
1582)     won't work.
1583)     </p>

1584) 

1585)     <p>
1586)     <b>Authentication</b>:
1587)     Every Tor relay has a public decryption key called the "onion key".
1588)     When the Tor client establishes circuits, at each step it <a
1589)     href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands
1590)     that the Tor relay prove knowledge of its onion key</a>. That way
1591)     the first node in the path can't just spoof the rest of the path.
1592)     Each relay rotates its onion key once a week.
1593)     </p>

1594) 

1595)     <p>
1596)     <b>Coordination</b>:
1597)     How do clients know what the relays are, and how do they know that they
1598)     have the right keys for them? Each relay has a long-term public signing
1599)     key called the "identity key". Each directory authority additionally has a
1600)     "directory signing key". The directory authorities <a

1601)     href="<specblob>dir-spec.txt">provide a signed list</a>

1602)     of all the known relays, and in that list are a set of certificates from
1603)     each relay (self-signed by their identity key) specifying their keys,
1604)     locations, exit policies, and so on. So unless the adversary can control
1605)     a threshold of the directory authorities, he can't trick the Tor client
1606)     into using other Tor relays.
1607)     </p>

1608) 

1609)     <p>
1610)     How do clients know what the directory authorities are? The Tor software
1611)     comes with a built-in list of location and public key for each directory
1612)     authority. So the only way to trick users into using a fake Tor network
1613)     is to give them a specially modified version of the software.
1614)     </p>

1615) 

1616)     <p>
1617)     How do users know they've got the right software? When we distribute
1618)     the source code or a package, we digitally sign it with <a
1619)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
1620)     href="<page docs/verifying-signatures>">instructions
1621)     on how to check Tor's signatures</a>.
1622)     </p>

1623) 

1624)     <p>
1625)     In order to be certain that it's really signed by us, you need to have
1626)     met us in person and gotten a copy of our GPG key fingerprint, or you
1627)     need to know somebody who has. If you're concerned about an attack on
1628)     this level, we recommend you get involved with the security community
1629)     and start meeting people.
1630)     </p>

1631) 

1632)     <hr>

1633) 

1634) <a id="EntryGuards"></a>
1635) <h3><a class="anchor" href="#EntryGuards">What are Entry Guards?</a></h3>
1636) 
1637) <p>
1638) Tor (like all current practical low-latency anonymity designs) fails
1639) when the attacker can see both ends of the communications channel. For

1640) example, suppose the attacker controls or watches the Tor relay you choose
1641) to enter the network, and also controls or watches the website you visit. In

1642) this case, the research community knows no practical low-latency design
1643) that can reliably stop the attacker from correlating volume and timing
1644) information on the two sides.
1645) </p>
1646) 
1647) <p>
1648) So, what should we do? Suppose the attacker controls, or can observe,

1649) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
1650) new entry and exit relays each time you use the network, the attacker
1651) will be able to correlate all traffic you send with probability
1652) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
1653) as being traced all the time: they want to do something often without
1654) an attacker noticing, and the attacker noticing once is as bad as the
1655) attacker noticing more often. Thus, choosing many random entries and exits
1656) gives the user no chance of escaping profiling by this kind of attacker.

1657) </p>
1658) 
1659) <p>

1660) The solution is "entry guards": each Tor client selects a few relays at random

1661) to use as entry points, and uses only those relays for her first hop. If
1662) those relays are not controlled or observed, the attacker can't win,
1663) ever, and the user is secure. If those relays <i>are</i> observed or
1664) controlled by the attacker, the attacker sees a larger <i>fraction</i>
1665) of the user's traffic &mdash; but still the user is no more profiled than
1666) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
1667) of avoiding profiling, whereas she had none before.

1668) </p>
1669) 
1670) <p>

1671) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
1672) Analysis of the Degradation of Anonymous Protocols</a>, <a
1673) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
1674) Communication Against Passive Logging Attacks</a>, and especially
1675) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
1676) Servers</a>.

1677) </p>
1678) 
1679) <p>
1680) Restricting your entry nodes may also help against attackers who want
1681) to run a few Tor nodes and easily enumerate all of the Tor user IP
1682) addresses. (Even though they can't learn what destinations the users
1683) are talking to, they still might be able to do bad things with just a

1684) list of users.) However, that feature won't really become useful until
1685) we move to a "directory guard" design as well.

1686) </p>
1687) 
1688)     <hr>
1689) 

1690)     <a id="EverybodyARelay"></a>

1691)     <h3><a class="anchor" href="#EverybodyARelay">You should make every Tor user be a relay.</a></h3>

1692) 

1693)     <p>
1694)     Requiring every Tor user to be a relay would help with scaling the

1695)     network to handle all our users, and <a
1696)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

1697)     relay may help your anonymity</a>. However, many Tor users cannot be good
1698)     relays &mdash; for example, some Tor clients operate from behind restrictive
1699)     firewalls, connect via modem, or otherwise aren't in a position where they
1700)     can relay traffic. Providing service to these clients is a critical
1701)     part of providing effective anonymity for everyone, since many Tor users
1702)     are subject to these or similar constraints and including these clients
1703)     increases the size of the anonymity set.
1704)     </p>

1705) 

1706)     <p>
1707)     That said, we do want to encourage Tor users to run relays, so what we
1708)     really want to do is simplify the process of setting up and maintaining
1709)     a relay. We've made a lot of progress with easy configuration in the past
1710)     few years: Vidalia has an easy relay configuration interface, and supports
1711)     uPnP too. Tor is good at automatically detecting whether it's reachable and
1712)     how much bandwidth it can offer.
1713)     </p>

1714) 

1715)     <p>
1716)     There are five steps we need to address before we can do this though:
1717)     </p>

1718) 

1719)     <p>
1720)     First, we need to make Tor stable as a relay on all common
1721)     operating systems. The main remaining platform is Windows,
1722)     and we plan to finally address that in 2009. See Section 4.1 of <a
1723)     href="https://www.torproject.org/press/2008-12-19-roadmap-press-release">our
1724)     development roadmap</a>.
1725)     </p>

1726) 

1727)     <p>
1728)     Second, we still need to get better at automatically estimating
1729)     the right amount of bandwidth to allow. See item #7 on the
1730)     <a href="<page getinvolved/volunteer>#Research">research section of the
1731)     volunteer page</a>: "Tor doesn't work very well when relays
1732)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

1733)     href="<page docs/faq>#TransportIPnotTCP">switching

1734)     to UDP transport</a> is the simplest answer here &mdash; which alas is
1735)     not a very simple answer at all.
1736)     </p>

1737) 

1738)     <p>
1739)     Third, we need to work on scalability, both of the network (how to
1740)     stop requiring that all Tor relays be able to connect to all Tor
1741)     relays) and of the directory (how to stop requiring that all Tor
1742)     users know about all Tor relays). Changes like this can have large
1743)     impact on potential and actual anonymity. See Section 5 of the <a
1744)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
1745)     for details. Again, UDP transport would help here.
1746)     </p>

1747) 

1748)     <p>
1749)     Fourth, we need to better understand the risks from
1750)     letting the attacker send traffic through your relay while
1751)     you're also initiating your own anonymized traffic. <a
1752)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
1753)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
1754)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
1755)     describe ways to identify the relays in a circuit by running traffic
1756)     through candidate relays and looking for dips in the traffic while the
1757)     circuit is active. These clogging attacks are not that scary in the Tor
1758)     context so long as relays are never clients too. But if we're trying to
1759)     encourage more clients to turn on relay functionality too (whether as
1760)     <a href="<page docs/bridges>">bridge relays</a> or as normal relays), then
1761)     we need to understand this threat better and learn how to mitigate it.
1762)     </p>

1763) 

1764)     <p>
1765)     Fifth, we might need some sort of incentive scheme to encourage people
1766)     to relay traffic for others, and/or to become exit nodes. Here are our

1767)     <a href="<blog>two-incentive-designs-tor">current

1768)     thoughts on Tor incentives</a>.
1769)     </p>

1770) 

1771)     <p>
1772)     Please help on all of these!
1773)     </p>

1774) 

1775) <hr>
1776) 
1777) <a id="TransportIPnotTCP"></a>

1778) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all IP packets, not just TCP packets.</a></h3>

1779) 
1780) <p>

1781) This would be handy, because it would make Tor better able to handle
1782) new protocols like VoIP, it could solve the whole need to socksify
1783) applications, and it would solve the fact that exit relays need to
1784) allocate a lot of file descriptors to hold open all the exit connections.

1785) </p>
1786) 
1787) <p>

1788) We're heading in this direction: see <a
1789) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
1790) ticket</a> for directions we should investigate. Some of the hard
1791) problems are:

1792) </p>
1793) 

1794) <ol>

1795) <li>IP packets reveal OS characteristics. We would still need to do
1796) IP-level packet normalization, to stop things like TCP fingerprinting
1797) attacks. Given the diversity and complexity of TCP stacks, along with <a

1798) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

1799) fingerprinting attacks</a>, it looks like our best bet is shipping our
1800) own user-space TCP stack.

1801) </li>

1802) <li>Application-level streams still need scrubbing. We will still need
1803) user-side applications like Torbutton. So it won't become just a matter
1804) of capturing packets and anonymizing them at the IP layer.

1805) </li>
1806) <li>Certain protocols will still leak information. For example, we must
1807) rewrite DNS requests so they are delivered to an unlinkable DNS server
1808) rather than the DNS server at a user's ISP; thus, we must understand
1809) the protocols we are transporting.
1810) </li>
1811) <li><a
1812) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS</a>

1813) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
1814) picked a transport mechanism, we need to design a new end-to-end Tor
1815) protocol for avoiding tagging attacks and other potential anonymity and
1816) integrity issues now that we allow drops, resends, et cetera.

1817) </li>
1818) <li>Exit policies for arbitrary IP packets mean building a secure
1819) IDS. Our node operators tell us that exit policies are one of the main
1820) reasons they're willing to run Tor. Adding an Intrusion Detection System
1821) to handle exit policies would increase the security complexity of Tor,
1822) and would likely not work anyway, as evidenced by the entire field of IDS
1823) and counter-IDS papers. Many potential abuse issues are resolved by the
1824) fact that Tor only transports valid TCP streams (as opposed to arbitrary
1825) IP including malformed packets and IP floods), so exit policies become
1826) even <i>more</i> important as we become able to transport IP packets. We
1827) also need to compactly describe exit policies in the Tor directory,
1828) so clients can predict which nodes will allow their packets to exit &mdash;
1829) and clients need to predict all the packets they will want to send in
1830) a session before picking their exit node!
1831) </li>

1832) <li>The Tor-internal name spaces would need to be redesigned. We support
1833) hidden service ".onion" addresses by intercepting the addresses when
1834) they are passed to the Tor client. Doing so at the IP level will require
1835) a more complex interface between Tor and the local DNS resolver.

1836) </li>
1837) </ol>
1838) 

1839)     <hr>

1840) 

1841)     <a id="Criminals"></a>

1842)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></h3>

1843) 

1844)     <p>
1845)     For the answer to this question and others, please see our <a
1846)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
1847)     </p>

1848) 

1849)     <hr>

1850) 

1851)     <a id="RespondISP"></a>

1852)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP about my exit relay?</a></h3>

1853) 

1854)     <p>
1855)     A collection of templates for successfully responding to ISPs is <a

1856)     href="<wiki>doc/TorAbuseTemplates">collected

1857)     here</a>.
1858)     </p>

1859) 

1860)     <hr>

1861) 

1862)   </div>
1863)   <!-- END MAINCOL -->
1864)   <div id = "sidecol">
1865) #include "side.wmi"
1866) #include "info.wmi"
1867)   </div>
1868)   <!-- END SIDECOL -->
1869) </div>
1870) <!-- END CONTENT -->