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

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

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

15)     <hr>

16) 

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

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

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

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

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

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

29)     <li><a href="#WhySlow">Why is Tor so slow?</a></li>

30)     <li><a href="#FileSharing">How can I share files anonymously through Tor?</a></li>
31)     <li><a href="#OutboundPorts">Do I have to open all these outbound ports on my firewall?</a></li>

32)     <li><a href="#Funding">What would The Tor Project do with more
33)     funding?</a></li>

34)     <li><a href="#IsItWorking">How can I tell if Tor is working, and that my connections really are anonymized?</a></li>
35)     <li><a href="#FTP">How do I use my browser for ftp with Tor?</a></li>

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

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

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

40)     </ul>

41) 

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

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

49)     <li><a href="#CompileTorWindows">How do I compile Tor under
50) Windows?</a></li>
51)     <li><a href="#VirusFalsePositives">Why does my Tor executable appear
52) to

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

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

56)     </ul>

57) 

58)     <p>Tor Browser Bundle:</p>
59)     <ul>

60) 

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

63)     <li><a href="#Ubuntu">I'm using Ubuntu and I can't start Tor Browser</a></li>

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

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

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

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

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

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

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

74)     <li><a href="#TBBOtherBrowser">I want to use Chrome/IE/Opera/etc
75)     with Tor.</a></li>
76)     <li><a href="#TBBCloseBrowser">I want to leave Tor Browser Bundle
77)     running but close the browser.</a></li>
78) 

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

80) tells

81)     me I have spyware installed.</a></li>

82)     <li><a href="#ForeignLanguages">Why does Google show up in foreign languages?</li></a>

83)     <li><a href="#GmailWarning">Gmail warns me that my account may have
84)     been compromised.</a></li>
85)     </ul>
86) 
87)     <p>Advanced Tor usage:</p>

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

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

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

93)     <li><a href="#LogLevel">What log level should I use?</a></li>

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

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

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

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

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

103)     <li><a href="#ExitPorts">Is there a list of default exit ports?</a></li>
104)     <li><a href="#SocksAndDNS">How do I check if my application that uses SOCKS is leaking DNS requests?</a></li>
105)     <li><a href="#DifferentComputer">I want to run my Tor client on a different computer than my applications.</a></li>
106)     <li><a href="#ServerClient">Can I install Tor on a central server, and have my clients connect to it?</a></li>

107)     <li><a href="#JoinTheNetwork">So I can just configure a nickname and ORPort and join the network?</a></li>

108)     </ul>

109) 

110)     <p>Running a Tor relay:</p>
111)     <ul>

112)     

113)     <li><a href="#RelayFlexible">How stable does my relay need to
114) be?</a></li>
115)     <li><a href="#ExitPolicies">I'd run a relay, but I don't want to
116) deal

117)     with abuse issues.</a></li>
118)     <li><a href="#RelayOrBridge">Should I be a normal relay or bridge
119)     relay?</a></li>

120)     <li><a href="#UpgradeOrMove">I want to upgrade/move my relay. How do I keep the same key?</a></li>

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

123)     <li><a href="#NTService">How do I run my Tor relay as an NT service?</a></li>
124)     <li><a href="#VirtualServer">Can I run a Tor relay from my virtual server account?</a></li>
125)     <li><a href="#WrongIP">My relay is picking the wrong IP address.</a></li>
126)     <li><a href="#BehindANAT">I'm behind a NAT/Firewall</a></li>
127)     <li><a href="#RelayMemory">Why is my Tor relay using so much memory?</a></li>
128)     <li><a href="#BetterAnonymity">Do I get better anonymity if I run a relay?</a></li>

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

131)     </ul>

132) 

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

134) 

135)     <p>Anonymity and Security:</p>
136)     <ul>

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

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

140)     <li><a href="#ChangePaths">How often does Tor change its paths?</a></li>
141)     <li><a href="#CellSize">Tor uses hundreds of bytes for every IRC line. I can't afford that!</a></li>
142)     <li><a href="#OutboundConnections">Why does netstat show these outbound connections?</a></li>

143)     <li><a href="#PowerfulBlockers">What about powerful blocking mechanisms</a></li>
144)     <li><a href="#RemotePhysicalDeviceFingerprinting">Does Tor resist "remote physical device fingerprinting"?</a></li>
145)     <li><a href="#AttacksOnOnionRouting">What attcks remain against onion routing?</a></li>

146)     </ul>

147) 

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

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

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

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

157)     <li><a href="#ChoosePathLength">You should let people choose their path length.</a></li>
158)     <li><a href="#SplitEachConnection">You should split each connection over many paths.</a></li>
159)     <li><a href="#UnallocatedNetBlocks">Your default exit policy should block unallocated net blocks too.</a></li>
160)     <li><a href="#BlockWebsites">Exit policies should be able to block websites, not just IP addresses.</a></li>
161)     <li><a href="#BlockContent">You should change Tor to prevent users from posting certain content.</a></li>
162)     <li><a href="#IPv6">Tor should support IPv6.</a></li>

163)     </ul>

164) 

165)     <p>Abuse:</p>

166)     <ul>

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

169)     <li><a href="#RespondISP">How do I respond to my ISP about my exit
170)     relay?</a></li>
171)     </ul>

172) 

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

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

176) 

177)     <hr>

178) 

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

180) 

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

183) 

184)     <p>
185)     The name "Tor" can refer to several different components.
186)     </p>

187) 

188)     <p>

189)     The Tor software is a program you can run on your computer that
190) helps keep
191)     you safe on the Internet. Tor protects you by bouncing your
192) communications

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

194)     the world: it prevents somebody watching your Internet connection
195) from

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

197)     from learning your physical location. This set of volunteer relays
198) is
199)     called the Tor network. You can read more about how Tor works on the
200) <a

201)     href="<page about/overview>">overview page</a>.
202)     </p>

203) 

204)     <p>

205)     The Tor Project is a non-profit (charity) organization that
206) maintains

207)     and develops the Tor software.
208)     </p>

209) 

210)     <hr>

211) 

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

213)     <h3><a class="anchor" href="#Torisdifferent">How is Tor different
214) from other proxies?</a></h3>
215)     <p>
216)     A typical proxy provider sets up a server somewhere on the Internet
217) and
218) allows you to use it to relay your traffic.  This creates a simple, easy
219) to
220) maintain architecture.  The users all enter and leave through the same
221) server.
222) The provider may charge for use of the proxy, or fund their costs
223) through
224) advertisements on the server.  In the simplest configuration, you don't
225) have to
226) install anything.  You just have to point your browser at their proxy
227) server.
228) Simple proxy providers are fine solutions if you do not want protections
229) for
230) your privacy and anonymity online and you trust the provider from doing
231) bad
232) things.  Some simple proxy providers use SSL to secure your connection
233) to them.
234) This may protect you against local eavesdroppers, such as those at a
235) cafe with

236) free wifi Internet.
237)     </p>
238)     <p>

239)     Simple proxy providers also create a single point of failure.  The
240) provider
241) knows who you are and where you browse on the Internet.  They can see
242) your
243) traffic as it passes through their server.  In some cases, they can even
244) see

245) inside your

246) encrypted traffic as they relay it to your banking site or to ecommerce
247) stores.

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

249) watching your traffic, injecting their own advertisements into your
250) traffic

251) stream, and recording your personal details.

252)     </p>
253)     <p>

254)     Tor passes your traffic through at least 3 different servers before
255) sending
256) it on to the destination. Because there's a separate layer of encryption
257) for
258) each of the three relays, Tor does not modify, or even know, what you
259) are
260) sending into it.  It merely relays your traffic, completely encrypted
261) through
262) the Tor network and has it pop out somewhere else in the world,
263) completely
264) intact.  The Tor client is required because we assume you trust your
265) local
266) computer.  The Tor client manages the encryption and the path chosen
267) through
268) the network.  The relays located all over the world merely pass
269) encrypted

270) packets between themselves.</p>

271)     <p>
272)     <dl>

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

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

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

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

289) e-commerce website, or encrypted mail connections, etc, it will only
290) know the
291) destination.  It won't be able to see the data inside the traffic
292) stream.  You

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

295)     </dl>
296)     </p>

297) 

298)     <hr>

299) 

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

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

303) 

304)     <p>

305)     If you want to use Tor with a web browser, we provide the Tor Browser Bundle, which includes everything you need to browse the web safely using Tor. If you want to use another web browser with Tor, see <a href="#TBBOtherBrowser">Other web browsers</a>. 

306)     </p>
307)     <p>
308)     There are plenty of other programs you can use with Tor,
309)     but we haven't researched the application-level anonymity

310)     issues on all of them well enough to be able to recommend a safe

311)     configuration. Our wiki has a list of instructions for <a

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

313)     specific applications</a>.

314)     Please add to these lists and help us keep them accurate!
315)     </p>

316) 

317)     <hr>

318) 

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

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

322) 

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

332) 

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

336) 

337)     <p>

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

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

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

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

347) 

348)     <hr>

349) 

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

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

353) 

354)     <p>

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

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

362) 

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

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

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

371) 

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

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

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

385) 

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

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

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

392) 

393)     <hr>

394) 

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

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

398) 

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

402) 

403)     <p>

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

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

412) 

413)     <p>

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

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

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

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

421) 

422)     <p>

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

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

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

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

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

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

438)     </p>

439) 

440)     <p>

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

447)     </p>

448) 

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

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

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

458) 

459)     <hr>

460) 

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

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

464) 

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

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

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

470)     <li>Read through the <a

471) 
472) href="https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk">
473) tor-talk

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

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

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

478)     <li>Send an email to <a

479) 
480) href="mailto:help@rt.torproject.org">help@rt.torproject.org</a>.</li>
481)     <li>If all else fails, try <a href="<page about/contact>">contacting
482) us</a> directly.</li>

483)     </ol>

484) 

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

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

488) 

489)     <hr>

490) 

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

497)     to contribute enough to a forum.

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

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

504) 

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

508) 

509)     <p>

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

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

519) 

520)     <p>

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

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

529) 

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

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

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

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

537) 

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

541) 

542)     <ul>

543) 

544)     <li>

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

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

551) 

552)     <li>

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

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

559) 

560)     <li>

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

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

567) 

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

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

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

576) 

577)     <li>

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

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

584) 

585)     <li>

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

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

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

597)     </li>

598) 

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

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

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

605) 

606)     </ul>

607) 

608)     <hr>

609) 

610)     <a id="FileSharing"></a>

611)     <h3><a class="anchor" href="#FileSharing">How can I share files anonymously through Tor?</a></h3>

612) 
613)     <p>

614)     File sharing (peer-to-peer/P2P) is widely unwanted in the Tor network, and exit nodes are configured to block file sharing traffic by default. Tor is not really designed for it, and file sharing through Tor slows down everyone's browsing. Also, Bittorrent over Tor <a href="https://blog.torproject.org/blog/bittorrent-over-tor-isnt-good-idea">is not anonymous</a>!

615)     </p>
616) 
617)     <hr>
618) 

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

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

622) 

623)     <p>

624)     The Tor network's <a

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

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

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

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

634)     </p>

635) 

636)     <p>

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

639)     </p>

640) 

641)     <ul>

642) 

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

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

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

650) 

651)     <li>

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

658)     </li>

659) 

660)     <li>

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

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

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

670)     Tor relays have problems on Win XP currently.

671)     </li>

672) 

673)     <li>

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

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

686) 

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

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

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

694) 

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

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

706)     behind these.
707)     </li>

708) 

709)     </ul>

710) 

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

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

715)     can keep up</a>.

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

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

720) 

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

725) 

726)     <p>

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

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

735) 

736)     <p>

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

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

745) 

746)     <hr>
747) 

748)      <a id="OutboundPorts"></a>
749)     <h3><a class="anchor" href="#OutboundPorts">Do I have to open all these outbound ports on my firewall?</a></h3>
750) 
751)     <p>
752)     Tor may attempt to connect to any port that is advertised in the directory as an ORPort (for making Tor connections) or a DirPort (for fetching updates to the directory). There are a variety of these ports, but many of them are running on 80, 443, 9001, and 9030.
753)     </p>
754)     <p>
755) So as a client, you could probably get away with opening only those four ports. Since Tor does all its connections in the background, it will retry ones that fail, and hopefully you'll never have to know that it failed, as long as it finds a working one often enough. However, to get the most diversity in your entry nodes -- and thus the most security -- as well as the most robustness in your connectivity, you'll want to let it connect to all of them.
756)     </p>
757)     <p>
758) If you really need to connect to only a small set of ports, see the FAQ entry on firewalled ports.
759)     </p>
760)     <p>

761) Note that if you're running Tor as a relay, you must allow outgoing connections to every other relay and to anywhere your exit policy advertises that you allow. The cleanest way to do that is simply to allow all outgoing connections at your firewall. If you don't, clients will try to use these connections and things won't work. 

762)     </p>
763)     
764)     <hr>
765)     
766)     <a id="IsItWorking"></a>
767)     <h3><a class="anchor" href="#IsItWorking">How can I tell if Tor is working, and that my connections really are anonymized?</a></h3>
768) 
769)     <p>
770)     There are sites you can visit that will tell you if you appear to be coming through the Tor network. Try the <a href="https://check.torproject.org">Tor Check</a> site and see whether it thinks you are using Tor or not.
771)     </p>
772)     <p>

773) If that site is down, you can still test, but it will involve more effort. Sites like <a href="http://ipid.shat.net">http://ipid.shat.net</a> and <a href="http://www.showmyip.com/">http://www.showmyip.com/</a> will tell you what your IP address appears to be, but you'll need to know your current IP address so you can compare and decide whether you're using Tor correctly.

774)     </p>
775)     <p>
776) To learn your IP address on OS X, Linux, BSD, etc, run "ifconfig". On Windows, go to the Start menu, click Run and enter "cmd". At the command prompt, enter "ipconfig /a".
777)     </p>
778)     <p>
779) If you are behind a NAT or firewall, though, your IP address will be within the range of 10.XXX.XXX.XXX, 192.168.XXX.XXX, or 172.16.XXX.XXX - 172.31.XXX.XXX, which is not your public IP address. In this case, you should check your IP address with one of the sites above without using Tor, and then check again using Tor to see whether your IP address has changed. 
780)     </p>
781)     
782)     <hr>
783)     
784)     <a id="FTP"></a>
785)     <h3><a class="anchor" href="#FTP">How do I use my browser for ftp with Tor?
786)     </a></h3>
787) 
788)     <p>Use the Tor Browser Bundle. If you want a separate application for an ftp client, we've heard good things about  FileZilla for Windows. You can configure it to point to Tor as a "socks4a" proxy on "localhost" port "9050". </p>
789)     <hr>
790)     

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

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

794) 

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

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

798)     <hr>

799) 

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

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

804)     <pre>

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

806)     The serial number is:

807) 06:DE:97:E5:1D:C3:9D:C2:64:8D:AC:72:DD:41:01:FC
808)     The SHA-1 fingerprint is: 1f9d306e8bfccfcb03981a71a27a9f5d1e0876ce

809)     The SHA-256 fingerprint is:

810) 3613d2b22a750094760c41ad19db52a4f05bdea80172e2578761ad967f7ed9aa

811) 

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

813)     The serial number is: 00:EF:A3
814)     The SHA-1 fingerprint is: 50af43db8438e67f305a3257d8ef198e8c42f13f

815)     </pre>

816)     </p>
817)     <hr>
818) 

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

820)     <h3><a class="anchor" href="#HowUninstallTor">How do I uninstall
821) Tor?</a></h3>
822) 
823)     <p>
824)     Tor Browser does not install itself in the classic sense of
825) applications. You just simply delete the folder or directory named "Tor
826) Browser" and it is removed from your system.
827)     </p>

828) 

829)     <p>

830)     If this is not related to Tor Browser, uninstallation depends
831) entirely on how you installed it and which operating system you
832)     have. If you installed a package, then hopefully your package has a
833) way to

834)     uninstall itself. The Windows packages include uninstallers. 

835)     </p>

836) 

837)     <p>
838)     For Mac OS X, follow the <a
839)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
840)     </p>

841) 

842)     <p>

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

847)     be pretty easy to notice things there.
848)     </p>

849) 

850)     <hr>

851) 

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

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

855) 

856)     <p>

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

859)     exactly the one that we intended you to get.
860)     </p>

861) 

862)     <p>
863)     Please read the <a

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

866)     </p>

867) 

868) <hr>
869) 
870) <a id="GetTor"></a>
871) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
872) country. How do I download Tor?</a></h3>
873) 
874) <p>
875) Some government or corporate firewalls censor connections to Tor's
876) website. In those cases, you have three options. First, get it from

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

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

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

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

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

885) in the body of the email, it will reply with instructions. Note that
886) only a few webmail providers are supported, since they need to be able
887) to receive very large attachments.
888) </p>
889) 
890) <p>

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

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

895) </p>
896) 
897) <hr>

898) 

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

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

902) 

903)     <p>

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

906)     tor-win32-mingw-creation.txt</a>.
907)     </p>

908) 

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

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

913)     download/download>">download page</a>.)
914)     </p>

915) 

916)     <hr>

917) 

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

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

921) 

922)     <p>

923)     Sometimes, overzealous Windows virus and spyware detectors trigger
924) on some
925)     parts of the Tor Windows binary. Our best guess is that these are
926) false
927)     positives — after all, the anti-virus and anti-spyware
928) business is just a
929)     guessing game anyway. You should contact your vendor and explain
930) that you have
931)     a program that seems to be triggering false positives. Or pick a
932) better vendor.

933)     </p>

934) 

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

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

939)     href="#CompileTorWindows">recompile it yourself</a>.
940)     </p>

941) 

942)     <hr>

943) 

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

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

947) 

948)     <p>

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

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

952)     Bundle</a>.

953)     </p>

954) 
955) <hr>
956) 

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

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

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

961) 
962) <p>

963) YouTube and similar sites require third party browser plugins such as Flash.
964) Plugins operate independently from Firefox and can perform
965) activity on your computer that ruins your anonymity. This includes
966) but is not limited to: <a href="http://decloak.net">completely disregarding
967) proxy settings</a>, querying your <a
968) href="http://forums.sun.com/thread.jspa?threadID=5162138&amp;messageID=9618376">local
969) IP address</a>, and <a
970) href="http://epic.org/privacy/cookies/flash.html">storing their own
971) cookies</a>. It is possible to use a LiveCD solution such as
972) or <a href="https://tails.boum.org/">The Amnesic Incognito Live System</a> that creates a
973) secure, transparent proxy to protect you from proxy bypass, however issues
974) with local IP address discovery and Flash cookies still remain.  </p>
975) 
976) <p>

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

979) find HTML5 videos.
980) </p>
981) 

982) <hr>
983) 

984) <a id="Ubuntu"></a>
985) <h3><a class="anchor" href="#Ubuntu">
986) I'm using Ubuntu and I can't start Tor Browser</a></h3>
987) <p>
988) Ubuntu prevents its users from executing shell scripts by click-clicking them, even when the file permissions are set correctly. For now you need to start the Tor Browser from the command line by running </p>
989) <pre>
990) ./start-tor-browser
991) </pre>
992) <p>
993) from inside the Tor Browser directory.
994) </p>
995) 
996) <hr>
997) 

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

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

1000) I want to run another application through the Tor launched by Tor

1001) Browser Bundle.</a></h3>

1002) 
1003) <p>

1004) Typically Tor listens for Socks connections on port 9050. TBB listens

1005) on port 9150.

1006) The goal is to avoid conflicting with a "system" Tor install,

1007) so you can run a system Tor and TBB at the same time. We're <a
1008) href="https://trac.torproject.org/projects/tor/ticket/3948">working on
1009) a feature</a> where Tor will try the usual ports first and then back

1010) off to a random choice if they're already in use.

1011) </p>
1012) 
1013) <hr>
1014) 
1015) <a id="TBBPolipo"></a>
1016) <h3><a class="anchor" href="#TBBPolipo">I need an HTTP proxy. Where did
1017) Polipo go?</a></h3>
1018) 
1019) <p>
1020) In the past, Tor bundles included an HTTP proxy like Privoxy or Polipo,
1021) solely to work around a bug in Firefox that was finally fixed in Firefox
1022) 6. Now you don't need a separate HTTP proxy to use Tor, and in fact
1023) leaving it out makes you safer because Torbutton has better control over
1024) Firefox's interaction with websites.
1025) </p>
1026) 
1027) <p>
1028) If you are trying to use some external application with Tor, step zero

1029) should be to <a href="<page download/download>#warning">reread the set

1030) of warnings</a> for ways you can screw up. Step one should be to try

1031) to use a Socks proxy rather than an http proxy — Tor runs a Socks

1032) proxy on port 9050 on Windows, or <a href="#TBBSocksPort">see above</a>
1033) for OSX and Linux.
1034) </p>
1035) 
1036) <p>

1037) If that fails, feel free to install <a

1038) href="http://www.privoxy.org/">privoxy</a>.
1039) However, please realize that this approach is not recommended for novice
1040) users. Privoxy has an <a
1041) href="http://www.privoxy.org/faq/misc.html#TOR">example
1042) configuration</a> of Tor and Privoxy.

1043) </p>
1044) 
1045) <hr>
1046) 

1047) <a id="TBBOtherExtensions"></a>
1048) <h3><a class="anchor" href="#TBBOtherExtensions">Can I install other
1049) Firefox extensions?</a></h3>
1050) 
1051) <p>

1052) The Tor Browser is free software, so there is nothing preventing you from modifying it any way you like. However, we do not recommend installing any additional Firefox add-ons with the Tor Browser Bundle. Add-ons can break your anonymity in a number of ways, including browser fingerprinting and bypassing proxy settings.

1053) </p>

1054) <p>

1055) Some people have suggested we include ad-blocking software or anti-tracking software with the Tor Browser Bundle. Right now, we do not think that's such a good idea. The Tor Browser Bundle aims to provide sufficient privacy that additional add-ons to stop ads and trackers are not necessary. Using add-ons like these may cause some sites to break, which <a href="https://www.torproject.org/projects/torbrowser/design/#philosophy">we don't want to do</a>. Additionally, maintaining a list of "bad" sites that should be black-listed provides another opportunity to uniquely fingerprint users. 

1056) </p>

1057) 

1058) <hr>
1059) 

1060) <a id="TBBJavaScriptEnabled"></a>

1061) <a id="TBBCanIBlockJS"></a>

1062) <h3><a class="anchor" href="#TBBJavaScriptEnabled">Why is NoScript
1063) configured to allow JavaScript by default in the Tor Browser Bundle?
1064) Isn't that unsafe?</a></h3>

1065) 
1066) <p>
1067) We configure NoScript to allow JavaScript by default in the Tor
1068) Browser Bundle because many websites will not work with JavaScript
1069) disabled.  Most users would give up on Tor entirely if a website
1070) they want to use requires JavaScript, because they would not know
1071) how to allow a website to use JavaScript (or that enabling
1072) JavaScript might make a website work).
1073) </p>
1074) 

1075) <p>
1076) There's a tradeoff here. On the one hand, we should leave
1077) JavaScript enabled by default so websites work the way
1078) users expect. On the other hand, we should disable JavaScript
1079) by default to better protect against browser vulnerabilities (<a
1080) href="https://blog.torproject.org/blog/tor-security-advisory-old-tor-browser-bundles-vulnerable">not
1081) just a theoretical concern!</a>). But there's a third issue: websites
1082) can easily determine whether you have allowed JavaScript for them,
1083) and if you disable JavaScript by default but then allow a few websites
1084) to run scripts (the way most people use NoScript), then your choice of
1085) whitelisted websites acts as a sort of cookie that makes you recognizable
1086) (and distinguishable), thus harming your anonymity.
1087) </p>

1088) 
1089) <p>

1090) Ultimately, we want the default Tor bundles to use
1091) a combination of firewalls (like the iptables rules
1092) in <a href="https://tails.boum.org/">Tails</a>) and <a
1093) href="https://trac.torproject.org/projects/tor/ticket/7680">sandboxes</a>
1094) to make JavaScript not so scary. In
1095) the shorter term, TBB 3.0 will hopefully <a
1096) href="https://trac.torproject.org/projects/tor/ticket/9387">allow users
1097) to choose their JavaScript settings more easily</a> &mdash; but the
1098) partitioning concern will remain.

1099) </p>
1100) 
1101) <p>

1102) Until we get there, feel free to leave JavaScript on or off depending
1103) on your security, anonymity, and usability priorities.

1104) </p>
1105) 
1106) <hr>
1107) 

1108) <a id="TBBOtherBrowser"></a>
1109) <h3><a class="anchor" href="#TBBOtherBrowser">I want to use
1110) Chrome/IE/Opera/etc with Tor.</a></h3>
1111) 
1112) <p>
1113) Unfortunately, Torbutton only works with Firefox right now, and without
1114) <a href="https://www.torproject.org/torbutton/en/design/">Torbutton's
1115) extensive privacy fixes</a> there are many ways for websites or other

1116) attackers to recognize you, track you back to your IP address, and so
1117) on.

1118) In short, using any browser besides Tor Browser Bundle with Tor is a
1119) really bad idea.
1120) </p>
1121) 
1122) <p>
1123) We're working with the Chrome team to <a

1124) href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-
1125) and-fingerprinting">fix
1126) some bugs and missing APIs in Chrome</a> so it will be possible to write
1127) a
1128) Torbutton for Chrome. No support for any other browser is on the
1129) horizon.

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

1135) <h3><a class="anchor" href="#TBBCloseBrowser">I want to leave Tor
1136) Browser

1137) Bundle running but close the browser.</a></h3>
1138) 
1139) <p>
1140) We're working on a way to make this possible on all platforms. Please
1141) be patient.
1142) </p>
1143) 
1144) <hr>
1145) 

1146) <a id="GoogleCAPTCHA"></a>
1147) <h3><a class="anchor" href="#GoogleCAPTCHA">Google makes me solve a
1148) CAPTCHA or tells me I have spyware installed.</a></h3>

1149) 
1150) <p>
1151) This is a known and intermittent problem; it does not mean that Google
1152) considers Tor to be spyware.
1153) </p>
1154) 
1155) <p>

1156) When you use Tor, you are sending queries through exit relays that are
1157) also

1158) shared by thousands of other users. Tor users typically see this message

1159) when many Tor users are querying Google in a short period of time.
1160) Google

1161) interprets the high volume of traffic from a single IP address (the exit
1162) relay you happened to pick) as somebody trying to "crawl" their website,
1163) so it slows down traffic from that IP address for a short time.
1164) </p>
1165) <p>
1166) An alternate explanation is that Google tries to detect certain
1167) kinds of spyware or viruses that send distinctive queries to Google
1168) Search. It notes the IP addresses from which those queries are received
1169) (not realizing that they are Tor exit relays), and tries to warn any
1170) connections coming from those IP addresses that recent queries indicate
1171) an infection.
1172) </p>
1173) 
1174) <p>

1175) To our knowledge, Google is not doing anything intentionally
1176) specifically

1177) to deter or block Tor use. The error message about an infected machine
1178) should clear up again after a short time.
1179) </p>
1180) 
1181) <p>
1182) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
1183) automatically redirect you to a more Tor-friendly search engine such as

1184) DuckDuckGo, ixquick, or Bing.

1185) </p>
1186) 
1187) <hr />
1188) 

1189) <a id="ForeignLanguages"></a>
1190) <h3><a class="anchor" href="#ForeignLanguages">
1191) Why does Google show up in foreign languages?</a></h3>
1192) 
1193) <p>
1194)  Google uses "geolocation" to determine where in the world you are, so it can give you a personalized experience. This includes using the language it thinks you prefer, and it also includes giving you different results on your queries.
1195) </p>
1196) <p>

1197) If you really want to see Google in English you can click the link that provides that. But we consider this a feature with Tor, not a bug --- the Internet is not flat, and it in fact does look different depending on where you are. This feature reminds people of this fact. The easy way to avoid this "feature" is to use <a href="http://google.com/ncr">http://google.com/ncr</a>.

1198) </p>
1199) <p>

1200) Note that Google search URLs take name/value pairs as arguments and one of those names is "hl". If you set "hl" to "en" then Google will return search results in English regardless of what Google server you have been sent to. On a query this looks like: </p><pre>https://encrypted.google.com/search?q=online%20anonymity&hl=en
1201) </pre>

1202) <p>

1203) Another method is to simply use your country code for accessing Google. This can be google.be, google.de, google.us and so on. 
1204) </p>
1205) <hr />

1206) <a id="GmailWarning"></a>

1207) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my
1208) account

1209) may have been compromised.</a></h3>

1210) 
1211) <p>
1212) Sometimes, after you've used Gmail over Tor, Google presents a
1213) pop-up notification that your account may have been compromised.
1214) The notification window lists a series of IP addresses and locations
1215) throughout the world recently used to access your account.
1216) </p>
1217) 
1218) <p>
1219) In general this is a false alarm: Google saw a bunch of logins from

1220) different places, as a result of running the service via Tor, and
1221) decided

1222) it was a good idea to confirm the account was being accessed by it's
1223) rightful owner.
1224) </p>
1225) 
1226) <p>
1227) Even though this may be a biproduct of using the service via tor,
1228) that doesn't mean you can entirely ignore the warning. It is
1229) <i>probably</i> a false positive, but it might not be since it is
1230) possible for someone to hijack your Google cookie.
1231) </p>
1232) 
1233) <p>
1234) Cookie hijacking is possible by either physical access to your computer
1235) or by watching your network traffic.  In theory only physical access
1236) should compromise your system because Gmail and similar services
1237) should only send the cookie over an SSL link. In practice, alas, it's <a

1238) href="http://fscked.org/blog/fully-automated-active-https-cookie-
1239) hijacking">

1240) way more complex than that</a>.
1241) </p>
1242) 
1243) <p>
1244) And if somebody <i>did</i> steal your google cookie, they might end
1245) up logging in from unusual places (though of course they also might
1246) not). So the summary is that since you're using Tor, this security
1247) measure that Google uses isn't so useful for you, because it's full of
1248) false positives. You'll have to use other approaches, like seeing if
1249) anything looks weird on the account, or looking at the timestamps for
1250) recent logins and wondering if you actually logged in at those times.
1251) </p>
1252) 
1253) <hr>
1254) 

1255) <a id="torrc"></a>

1256) <h3><a class="anchor" href="#torrc">I'm supposed to "edit my torrc".
1257) What does that mean?</a></h3>

1258) 
1259) <p>
1260) Tor installs a text file called torrc that contains configuration
1261) instructions for how your Tor program should behave. The default
1262) configuration should work fine for most Tor users. Users of Vidalia can
1263) make common changes through the Vidalia interface &mdash; only advanced
1264) users should need to modify their torrc file directly.
1265) </p>

1266) <p>

1267) Tor Browser Bundle users should edit your torrc through Vidalia. Open
1268) the
1269) Vidalia Control Panel. Choose Settings. Choose Advanced. Click the
1270) button

1271) labelled "Edit current torrc". Remember to make sure the checkbox for
1272) "Save Settings." is checked. Hit the Ok button and you are done.
1273) </p>

1274) <p>

1275) Otherwise, you will need to edit the file manually.

1276) The location of your torrc file depends on the way you installed Tor:
1277) </p>
1278) <ul>

1279) <li>If you installed Tor Browser Bundle, look for
1280) <code>Data/Tor/torrc</code> inside your Tor Browser Bundle directory.
1281) </li>

1282) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
1283) find your torrc file in the Start menu under Programs -&gt; Vidalia
1284) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
1285) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
1286) installed Tor without Vidalia, you can find your torrc in the Start
1287) menu under Programs -&gt; Tor, or manually in either <code>\Documents
1288) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
1289) Settings\<i>username</i>\Application Data\tor\torrc</code>.
1290) </li>
1291) <li>On OS X, if you use Vidalia, edit
1292) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
1293) and load <code>/Library/Tor/torrc</code>.
1294) </li>
1295) <li>On Unix, if you installed a pre-built package, look for
1296) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
1297) package's documentation.
1298) </li>
1299) <li>Finally, if you installed from source, you may not have a torrc
1300) installed yet: look in <code>/usr/local/etc/</code> and note that you

1301) may need to manually copy <code>torrc.sample</code> to
1302) <code>torrc</code>.

1303) </li>
1304) </ul>
1305) 
1306) <p>
1307) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit

1308) your torrc file manually. Otherwise Vidalia might overwrite your
1309) changes.

1310) </p>
1311) 
1312) <p>
1313) Once you've changed your torrc, you will need to restart Tor for the
1314) changes to take effect. (For advanced users on OS X and Unix, note that

1315) you actually only need to send Tor a HUP signal, not actually restart
1316) it.)

1317) </p>
1318) 
1319) <p>
1320) For other configuration options you can use, look at the <a href="<page
1321) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
1322) with # in torrc are treated as comments and have no effect on Tor's
1323) configuration.
1324) </p>
1325) 
1326) <hr>
1327) 

1328) <a id="Logs"></a>

1329) <h3><a class="anchor" href="#Logs">How do I set up logging, or see Tor's
1330) logs?</a></h3>

1331) 
1332) <p>

1333) If you installed a Tor bundle that includes Vidalia, then Vidalia has a

1334) window called "Message Log" that will show you Tor's log messages. Click
1335) on "Advanced" to see more details. You can click on "Settings" to change
1336) your log verbosity or save the messages to a file. You're all set.

1337) </p>
1338) 
1339) <p>
1340) If you're not using Vidalia, you'll have to go find the log files by

1341) hand. Here are some likely places for your logs to be:

1342) </p>
1343) 
1344) <ul>
1345) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
1346) </li>

1347) <li>On Windows, there are no default log files currently. If you enable
1348) logs in your torrc file, they default to <code>\username\Application
1349) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
1350) </li>
1351) <li>If you compiled Tor from source, by default your Tor logs to <a
1352) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
1353) at log-level notice. If you enable logs in your torrc file, they
1354) default to <code>/usr/local/var/log/tor/</code>.

1355) </li>
1356) </ul>
1357) 
1358) <p>

1359) To change your logging setup by hand, <a href="#torrc">edit your
1360) torrc</a>

1361) and find the section (near the top of the file) which contains the
1362) following line:

1363) </p>
1364) 
1365) <pre>

1366) \## Logs go to stdout at level "notice" unless redirected by something
1367) \## else, like one of the below lines.

1368) </pre>

1369) 
1370) <p>

1371) For example, if you want Tor to send complete debug, info, notice, warn,

1372) and err level messages to a file, append the following line to the end
1373) of the section:
1374) </p>
1375) 
1376) <pre>
1377) Log debug file c:/program files/tor/debug.log
1378) </pre>
1379) 
1380) <p>

1381) Replace <code>c:/program files/tor/debug.log</code> with a directory
1382) and filename for your Tor log.

1383) </p>
1384) 
1385) <hr>
1386) 

1387) 
1388) <a id="LogLevel"></a>
1389) <h3><a class="anchor" href="#LogLevel">What log level should I use?</a></h3>
1390) 
1391) <p>
1392) There are five log levels (also called "log severities") you might see in Tor's logs:
1393) </p>
1394) 
1395) <ul>
1396)     <li>"err": something bad just happened, and we can't recover. Tor will exit.</li>
1397)     <li>"warn": something bad happened, but we're still running. The bad thing might be a bug in the code, some other Tor process doing something unexpected, etc. The operator should examine the message and try to correct the problem.</li>
1398)     <li>"notice": something the operator will want to know about.</li>
1399)     <li>"info": something happened (maybe bad, maybe ok), but there's nothing you need to (or can) do about it.</li>
1400)     <li>"debug": for everything louder than info. It is quite loud indeed.</li> 
1401) </ul>
1402) 
1403) <p>
1404) Alas, some of the warn messages are hard for ordinary users to correct -- the developers are slowly making progress at making Tor automatically react correctly for each situation.
1405) </p>
1406) 
1407) <p>
1408) We recommend running at the default, which is "notice". You will hear about important things, and you won't hear about unimportant things.
1409) </p>
1410) 
1411) <p>
1412) Tor relays in particular should avoid logging at info or debug in normal operation, since they might end up recording sensitive information in their logs. 
1413) </p>
1414) 

1415) <a id="DoesntWork"></a>

1416) <h3><a class="anchor" href="#DoesntWork">I installed Tor but it's not
1417) working.</a></h3>

1418) 
1419) <p>

1420) Once you've got the Tor bundle up and running, the first question to
1421) ask is whether your Tor client is able to establish a circuit.

1422) </p>
1423) 
1424) <p>If Tor can establish a circuit, the onion icon in

1425) Vidalia will turn green (and if you're running Tor Browser Bundle, it
1426) will
1427) automatically launch a browser for you). You can also check in the
1428) Vidalia

1429) Control Panel to make sure it says "Connected to the Tor
1430) network!" under Status. For those not using Vidalia, check your <a

1431) href="#Logs">Tor logs</a> for

1432) a line saying that Tor "has successfully opened a circuit. Looks like
1433) client functionality is working."
1434) </p>
1435) 
1436) <p>
1437) If Tor can't establish a circuit, here are some hints:
1438) </p>
1439) 
1440) <ol>
1441) <li>Are you sure Tor is running? If you're using Vidalia, you may have
1442) to click on the onion and select "Start" to launch Tor.</li>
1443) <li>Check your system clock. If it's more than a few hours off, Tor will

1444) refuse to build circuits. For Microsoft Windows users, synchronize your
1445) clock under the clock -> Internet time tab. In addition, correct the

1446) day and date under the 'Date & Time' Tab. Also make sure your time
1447) zone is correct.</li>

1448) <li>Is your Internet connection <a href="#FirewallPorts">firewalled
1449) by port</a>, or do you normally need to use a <a

1450) href="<wikifaq>#MyInternetconnectionrequiresanHTTPorSOCKSproxy.">proxy</a>?

1451) </li>

1452) <li>Are you running programs like Norton Internet Security or SELinux
1453) that

1454) block certain connections, even though you don't realize they do? They
1455) could be preventing Tor from making network connections.</li>
1456) <li>Are you in China, or behind a restrictive corporate network firewall
1457) that blocks the public Tor relays? If so, you should learn about <a

1458) href="<page docs/bridges>">Tor bridges</a>.</li>

1459) <li>Check your <a href="#Logs">Tor logs</a>. Do they give you any hints
1460) about what's going wrong?</li>

1461) </ol>
1462) 
1463) <hr />
1464) 
1465) <a id="VidaliaPassword"></a>

1466) <h3><a class="anchor" href="#VidaliaPassword">Tor/Vidalia prompts for a
1467) password at start.</a></h3>

1468) 
1469) <p>
1470) Vidalia interacts with the Tor software via Tor's "control port". The
1471) control port lets Vidalia receive status updates from Tor, request a new
1472) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
1473) Vidalia sets a random password for Tor's control port to prevent other
1474) applications from also connecting to the control port and potentially
1475) compromising your anonymity.
1476) </p>
1477) 
1478) <p>
1479) Usually this process of generating and setting a random control password
1480) happens in the background. There are three common situations, though,
1481) where Vidalia may prompt you for a password:
1482) </p>
1483) 
1484) <ol>
1485) <li>You're already running Vidalia and Tor. For example, this situation
1486) can happen if you installed the Vidalia bundle and now you're trying to
1487) run the Tor Browser Bundle. In that case, you'll need to close the old
1488) Vidalia and Tor before you can run this one.
1489) </li>
1490) <li>Vidalia crashed, but left Tor running with the last known random
1491) password. After you restart Vidalia, it generates a new random password,

1492) but Vidalia can't talk to Tor, because the random passwords are
1493) different.

1494) <br />

1495) If the dialog that prompts you for a control password has a Reset
1496) button,

1497) you can click the button and Vidalia will restart Tor with a new random
1498) control password.
1499) <br />
1500) If you do not see a Reset button, or if Vidalia is unable to restart
1501) Tor for you, you can still fix the problem manually. Simply go into your
1502) process or task manager, and terminate the Tor process. Then use Vidalia
1503) to restart Tor and all will work again.
1504) </li>
1505) <li>You had previously set Tor to run as a Windows NT service. When Tor
1506) is set to
1507) run as a service, it starts up when the system boots. If you configured
1508) Tor to start as a service through Vidalia, a random password was set
1509) and saved in Tor. When you reboot, Tor starts up and uses the random
1510) password it saved. You login and start up Vidalia. Vidalia attempts to
1511) talk to the already running Tor. Vidalia generates a random password,
1512) but it is different than the saved password in the Tor service.
1513) <br />
1514) You need to reconfigure Tor to not be a service. See the FAQ entry on

1515) <a href="#NTservice">running Tor as a

1516) Windows NT service</a>

1517) for more information on how to remove the Tor service.
1518) </li>
1519) </ol>
1520) 

1521)     <hr>

1522) 

1523)     <a id="ChooseEntryExit"></a>

1524)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which
1525) nodes (or country) are used for entry/exit?</a></h3>

1526) 

1527)     <p>

1528)     Yes. You can set preferred entry and exit nodes as well as
1529)     inform Tor which nodes you do not want to use.

1530)     The following options can be added to your config file <a
1531)     href="#torrc">"torrc"</a> or specified on the command line:

1532)     </p>
1533)     <dl>
1534)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>

1535)         <dd>A list of preferred nodes to use for the first hop in the
1536) circuit, if possible.

1537)         </dd>
1538)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1539)         <dd>A list of preferred nodes to use for the last hop in the
1540) circuit, if possible.

1541)         </dd>
1542)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1543)         <dd>A list of nodes to never use when building a circuit.

1544)         </dd>
1545)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1546)         <dd>A list of nodes to never use when picking an exit.

1547)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in
1548) this list.

1549)         </dd>
1550)     </dl>
1551)     <p>

1552)     <em>We recommend you do not use these</em>

1553)     — they are intended for testing and may disappear in future
1554) versions.

1555)     You get the best security that Tor can provide when you leave the
1556)     route selection to Tor; overriding the entry / exit nodes can mess
1557)     up your anonymity in ways we don't understand.

1558)     </p>
1559)     <p>

1560)     Note also that not every circuit is used to deliver traffic outside of the Tor network. It is normal to see non-exit circuits (such as those used to connect to hidden services, those that do directory fetches, those used for relay reachability self-tests, and so on) that end at a non-exit node. To keep a node from being used entirely, see <tt>ExcludeNodes</tt> and <tt>StrictNodes</tt> in the <a href="<page docs/tor-manual>">manual</a>.

1561)     </p>
1562)     <p>

1563)     Instead of <tt>$fingerprint</tt> you can also specify a <a

1564) 
1565) href="https://secure.wikimedia.org/wikipedia/en/wiki/ISO_3166-1_alpha-2"
1566) >2

1567)     letter ISO3166 country code</a> in curly braces (for example <tt>{de}</tt>),

1568)     or an ip address pattern (for example 255.254.0.0/8), or a node
1569)     nickname. Make sure there are no spaces between the commas and the
1570)     list items.

1571)     </p>
1572)     <p>

1573)     If you want to access a service directly through Tor's Socks
1574) interface

1575)     (eg. using ssh via connect.c), another option is to set up an

1576)     internal mapping in your configuration file using
1577) <tt>MapAddress</tt>.

1578)     See the manual page for details.
1579)     </p>

1580) 

1581)     <hr>

1582) 

1583) <a id="FirewallPorts"></a>

1584) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a
1585) few outgoing ports.</a></h3>

1586) 
1587) <p>
1588) If your firewall works by blocking ports, then you can tell Tor to only

1589) use the ports that your firewall permits by adding "FascistFirewall 1"
1590) to

1591) your <a href="<page docs/faq>#torrc">torrc

1592) configuration file</a>, or by clicking "My firewall only lets me connect
1593) to certain ports" in Vidalia's Network Settings window.
1594) </p>
1595) 
1596) <p>
1597) By default, when you set this Tor assumes that your firewall allows only
1598) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1599) different set of ports with the FirewallPorts torrc option.
1600) </p>
1601) 
1602) <p>
1603) If you want to be more fine-grained with your controls, you can also
1604) use the ReachableAddresses config options, e.g.:
1605) </p>
1606) 
1607) <pre>
1608)   ReachableDirAddresses *:80
1609)   ReachableORAddresses *:443
1610) </pre>
1611) 
1612) <hr>

1613) 

1614)     <a id="ExitPorts"></a>
1615)     <h3><a class="anchor" href="#ExitPorts">Is there a list of default exit ports?</a></h3>
1616)     <p>
1617) The default open ports are listed below but keep in mind that, any port or ports can be opened by the relay operator by configuring it in torrc or modifying the source code. But the default according to src/or/policies.c from the source code release tor-0.2.4.16-rc is: 
1618)     </p>
1619)     <pre>
1620)   reject 0.0.0.0/8
1621)   reject 169.254.0.0/16
1622)   reject 127.0.0.0/8
1623)   reject 192.168.0.0/16
1624)   reject 10.0.0.0/8
1625)   reject 172.16.0.0/12
1626)   reject *:25
1627)   reject *:119
1628)   reject *:135-139
1629)   reject *:445
1630)   reject *:563
1631)   reject *:1214
1632)   reject *:4661-4666
1633)   reject *:6346-6429
1634)   reject *:6699
1635)   reject *:6881-6999
1636)   accept *:*
1637)     </pre>
1638)     <p>
1639)     A relay will block access to its own IP address, as well local network IP addresses. A relay always blocks itself by default. This prevents Tor users from accidentally accessing any of the exit operator's local services. 
1640)     </p>
1641) 
1642)     <hr>
1643) 

1644)     <a id="RelayFlexible"></a>

1645)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay
1646) need to be?</a></h3>

1647) 

1648)     <p>
1649)     We aim to make setting up a Tor relay easy and convenient:
1650)     </p>

1651) 

1652)     <ul>
1653)     <li>Tor has built-in support for <a

1654)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1655)     rate limiting</a>. Further, if you have a fast
1656)     link but want to limit the number of bytes per
1657)     day (or week or month) that you donate, check out the <a

1658) 
1659) href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">
1660) hibernation

1661)     feature</a>.
1662)     </li>

1663)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a>
1664) that
1665)     specifies what sort of outbound connections are allowed or refused
1666) from
1667)     that relay. If you are uncomfortable allowing people to exit from
1668) your
1669)     relay, you can set it up to only allow connections to other Tor
1670) relays.

1671)     </li>
1672)     <li>It's fine if the relay goes offline sometimes. The directories
1673)     notice this quickly and stop advertising the relay. Just try to make
1674)     sure it's not too often, since connections using the relay when it
1675)     disconnects will break.
1676)     </li>
1677)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1678)     leave the Address config option blank, and Tor will try to guess.
1679)     </li>
1680)     <li>If your relay is behind a NAT and it doesn't know its public
1681)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1682)     forwarding. Forwarding TCP connections is system dependent but

1683)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1684)     offers some examples on how to do this.
1685)     </li>
1686)     <li>Your relay will passively estimate and advertise its recent

1687)     bandwidth capacity, so high-bandwidth relays will attract more users
1688) than
1689)     low-bandwidth ones. Therefore having low-bandwidth relays is useful
1690) too.

1691)     </li>
1692)     </ul>

1693) 

1694)     <hr>

1695) 

1696)        <a id="RunARelayBut"></a>

1697)     <a id="ExitPolicies"></a>

1698)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I
1699) don't want to deal with abuse issues.</a></h3>

1700) 

1701)     <p>
1702)     Great. That's exactly why we implemented exit policies.
1703)     </p>

1704) 

1705)     <p>
1706)     Each Tor relay has an exit policy that specifies what sort of

1707)     outbound connections are allowed or refused from that relay. The
1708) exit

1709)     policies are propagated to Tor clients via the directory, so clients
1710)     will automatically avoid picking exit relays that would refuse to
1711)     exit to their intended destination. This way each relay can decide
1712)     the services, hosts, and networks he wants to allow connections to,

1713)     based on abuse potential and his own situation. Read the FAQ entry
1714) on
1715)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might
1716) encounter</a>

1717)     if you use the default exit policy, and then read Mike Perry's

1718)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1719)     for running an exit node with minimal harassment</a>.
1720)     </p>

1721) 

1722)     <p>

1723)     The default exit policy allows access to many popular services

1724)     (e.g. web browsing), but <a
1725) href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1726)     some due to abuse potential (e.g. mail) and some since
1727)     the Tor network can't handle the load (e.g. default
1728)     file-sharing ports). You can change your exit policy

1729)     using Vidalia's "Sharing" tab, or by manually editing your

1730)     <a href="<page docs/faq>#torrc">torrc</a>

1731)     file. If you want to avoid most if not all abuse potential, set it
1732) to
1733)     "reject *:*" (or un-check all the boxes in Vidalia). This setting
1734) means
1735)     that your relay will be used for relaying traffic inside the Tor
1736) network,

1737)     but not for connections to external websites or other services.
1738)     </p>

1739) 

1740)     <p>

1741)     If you do allow any exit connections, make sure name resolution
1742) works

1743)     (that is, your computer can resolve Internet addresses correctly).

1744)     If there are any resources that your computer can't reach (for
1745) example,

1746)     you are behind a restrictive firewall or content filter), please

1747)     explicitly reject them in your exit policy — otherwise Tor
1748) users

1749)     will be impacted too.
1750)     </p>

1751) 

1752)     <hr>

1753) 

1754)     <a id="DifferentComputer"></a>
1755)     <h3><a class="anchor" href="#DifferentComputer">I want to run my Tor client on a different computer than my applications.</a></h3>
1756)     <p>
1757)     By default, your Tor client only listens for applications that connect from localhost. Connections from other computers are refused. If you want to torify applications on different computers than the Tor client, you should edit your torrc to define SocksListenAddress 0.0.0.0 g and then restart (or hup) Tor. If you want to get more advanced, you can configure your Tor client on a firewall to bind to your internal IP but not your external IP.  
1758)     </p>
1759) 
1760)     <hr>
1761) 
1762)     <a id="ServerClient"></a>
1763)     <h3><a class="anchor" href="#ServerClient">Can I install Tor on a central server, and have my clients connect to it?</a></h3>
1764)     <p>
1765)      Yes. Tor can be configured as a client or a relay on another machine, and allow other machines to be able to connect to it for anonymity. This is most useful in an environment where many computers want a gateway of anonymity to the rest of the world. However, be forwarned that with this configuration, anyone within your private network (existing between you and the Tor client/relay) can see what traffic you are sending in clear text. The anonymity doesn't start until you get to the Tor relay. Because of this, if you are the controller of your domain and you know everything's locked down, you will be OK, but this configuration may not be suitable for large private networks where security is key all around.
1766)     </p>
1767)     <p>
1768) Configuration is simple, editing your torrc file's SocksListenAddress according to the following examples:
1769)     </p>
1770)     <pre>

1771) 
1772)   #This provides local interface access only, 
1773)   #needs SocksPort to be greater than 0
1774)   SocksListenAddress 127.0.0.1 
1775) 
1776)   #This provides access to Tor on a specified interface
1777)   SocksListenAddress 192.168.x.x:9100 
1778) 
1779)   #Accept from all interfaces
1780)   SocksListenAddress 0.0.0.0:9100
1781)    </pre>

1782)     <p>
1783) You can state multiple listen addresses, in the case that you are part of several networks or subnets.
1784)     </p>
1785)     <pre>
1786)   SocksListenAddress 192.168.x.x:9100 #eth0
1787)   SocksListenAddress 10.x.x.x:9100 #eth1
1788)     </pre>
1789)     <p>
1790) After this, your clients on their respective networks/subnets would specify a socks proxy with the address and port you specified SocksListenAddress to be. 
1791)     </p>
1792)     <p>
1793) Please note that the SocksPort configuration option gives the port ONLY for localhost (127.0.0.1). When setting up your SocksListenAddress(es), you need to give the port with the address, as shown above.
1794)     <p>
1795) If you are interested in forcing all outgoing data through the central Tor client/relay, instead of the server only being an optional proxy, you may find the program iptables (for *nix) useful. 
1796)     </p>
1797) 
1798)     <hr>
1799) 

1800)     <a id="JoinTheNetwork"></a>
1801)     <h3><a class="anchor" href="#JoinTheNetwork">So I can just configure a nickname and ORPort and join the network?</a></h3>
1802) 
1803)     <p>
1804)      Yes. You can join the network and be a useful relay just by configuring your Tor to be a relay and making sure it's reachable from the outside.
1805)     </p>
1806)     <p>
1807) 30 Seconds to a Tor Relay:
1808)     </p>
1809)     <ul><li>
1810)     Configure a Nickname: 
1811)     </li></ul>
1812)     <pre>
1813) Nickname ididnteditheconfig
1814)     </pre>

1815)     <ul><li>

1816)     Configure ORPort: 

1817)     </li></ul>

1818)     <pre>
1819) ORPort 9001
1820)     </pre>

1821)     <ul><li>

1822)     Configure Contact Info: 

1823)     </li></ul>

1824) 
1825)     <pre>
1826) ContactInfo human@…

1827)     </pre>
1828)     <ul><li>

1829)     Start Tor. Watch the log file for a log entry that states: "Self-testing indicates your ORPort is reachable from the outside. Excellent. Publishing server descriptor."

1830)     </li></ul>

1831) 
1832)     <hr />

1833) 

1834)     <a id="RelayOrBridge"></a>

1835)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal
1836) relay or bridge relay?</a></h3>

1837) 

1838)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for
1839) short)
1840)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't

1841)     listed in the public Tor directory.

1842)     That means that ISPs or governments trying to block access to the

1843)     Tor network can't simply block all bridges.

1844)     </p>

1845) 

1846)     <p>Being a normal relay vs being a bridge relay is almost the same
1847)     configuration: it's just a matter of whether your relay is listed

1848)     publicly or not.

1849)     </p>

1850) 

1851)     <p>

1852)     So bridges are useful a) for Tor users in oppressive regimes,

1853)     and b) for people who want an extra layer of security

1854)     because they're worried somebody will recognize that it's a public
1855)     Tor relay IP address they're contacting.

1856)     </p>

1857) 

1858)     <p>
1859)     Several countries, including China and Iran, have found ways to

1860)     detect and block connections to Tor bridges.

1861)     <a href="<page projects/obfsproxy>">Obfsproxy</a> bridges address

1862)     this by adding another layer of obfuscation.

1863)     </p>
1864) 

1865)     <p>So should you run a normal relay or bridge relay? If you have
1866) lots

1867)     of bandwidth, you should definitely run a normal relay.
1868)     If you're willing

1869)     to <a href="#ExitPolicies">be an exit</a>, you should definitely
1870)     run a normal relay, since we need more exits. If you can't be an
1871)     exit and only have a little bit of bandwidth, be a bridge. Thanks
1872)     for volunteering!

1873)     </p>

1874) 

1875)     <hr>

1876) 

1877) <a id="UpgradeOrMove"></a>
1878) <h3><a class="anchor" href="#UpgradeOrMove">I want to upgrade/move my relay. How do I keep the same key?</a></h3>
1879) 
1880) <p>

1881)  When upgrading your Tor relay, or running it on a different computer, the important part is to keep the same nickname (defined in your torrc file) and the same identity key (stored in "keys/secret_id_key" in your DataDirectory).

1882) </p>
1883) <p>
1884) This means that if you're upgrading your Tor relay and you keep the same torrc and the same DataDirectory, then the upgrade should just work and your relay will keep using the same key. If you need to pick a new DataDirectory, be sure to copy your old keys/secret_id_key over. 
1885) </p>
1886) 
1887)     <hr>
1888) 
1889) <a id="NTService"></a>
1890) <h3><a class="anchor" href="#NTService">How do I run my Tor relay as an NT service?</a></h3>
1891) 
1892) <p>
1893)  You can run Tor as a service on all versions of Windows except Windows 95/98/ME. This way you can run a Tor relay without needing to always have Vidalia running.
1894) </p>
1895) <p>
1896) If you've already configured your Tor to be a relay, please note that when you enable Tor as a service, it will use a different DatagDirectory, and thus will generate a different key. If you want to keep using the old key, see the Upgrading your Tor relay FAQ entry for how to restore the old identity key.
1897) </p>
1898) <p>
1899) To install Tor as a service, you can simply run:
1900) </p>
1901) <pre>
1902) tor --service install
1903) </pre>
1904) <p>
1905) A service called Tor Win32 Service will be installed and started. This service will also automatically start every time Windows boots, unless you change the Start-up type. An easy way to check the status of Tor, start or stop the service, and change the start-up type is by running services.msc and finding the Tor service in the list of currently installed services.
1906) </p>
1907) <p>
1908) Optionally, you can specify additional options for the Tor service using the -options argument. For example, if you want Tor to use C:\tor\torrc, instead of the default torrc, and open a control port on port 9151, you would run:
1909) </p>
1910) <pre>
1911) tor --service install -options -f C:\tor\torrc ControlPort 9151
1912) </pre>
1913) <p>
1914) You can also start or stop the Tor service from the command line by typing:
1915) </p>
1916) <pre>
1917)  tor --service start
1918) </pre>
1919) <p>
1920) or
1921) </p>
1922) <pre>
1923)  tor --service stop
1924) </pre>
1925) <p>
1926) To remove the Tor service, you can run the following command:
1927) </p>
1928) <pre>
1929) tor --service remove
1930) </pre>
1931) <p>
1932) If you are running Tor as a service and you want to uninstall Tor entirely, be sure to run the service removal command (shown above) first before running the uninstaller from "Add/Remove Programs". The uninstaller is currently not capable of removing the active service.
1933) </p>
1934) 
1935) <hr>
1936) 
1937) <a id="VirtualServer"></a>
1938) <h3><a class="anchor" href="#VirtualServer">Can I run a Tor relay from my virtual server account?</a></h3>
1939) 
1940) <p>
1941) Some ISPs are selling "vserver" accounts that provide what they call a virtual server -- you can't actually interact with the hardware, and they can artificially limit certain resources such as the number of file descriptors you can open at once. Competent vserver admins are able to configure your server to not hit these limits. For example, in SWSoft's Virtuozzo, investigate /proc/user_beancounters. Look for "failcnt" in tcpsndbuf, tcprecvbuf, numothersock, and othersockbuf. Ask for these to be increased accordingly. Some users have seen settings work well as follows: 
1942) <p>

1943) <table border="1">

1944) <tr>
1945) <td>
1946) <i>resource</i>
1947) </td>
1948) <td>
1949) <i>held</i>
1950) </td>
1951) <td>
1952) <i>maxheld</i>
1953) </td>
1954) <td>
1955) <i>barrier</i>
1956) </td>
1957) <td>
1958) <i>limit</i>
1959) </td>
1960) <td>
1961) <i>failcnt</i>
1962) </td>
1963) </tr>
1964) <tr>
1965) <td>
1966) tcpsndbuf
1967) </td>
1968) <td>
1969) 46620
1970) </td>
1971) <td>
1972) 48840
1973) </td>
1974) <td>
1975) 3440640
1976) </td>
1977) <td>
1978) 5406720
1979) </td>
1980) <td>
1981) 0
1982) </td>
1983) </tr>
1984) <tr>
1985) <td>
1986) tcprcvbuf
1987) </td>
1988) <td>
1989) 0
1990) </td>
1991) <td>
1992) 2220
1993) </td>
1994) <td>
1995) 3440640
1996) </td>
1997) <td>
1998) 5406720
1999) </td>
2000) <td>
2001) 0
2002) </td>
2003) </tr>
2004) <tr>
2005) <td>
2006) othersockbuf
2007) </td>
2008) <td>
2009) 243516
2010) </td>
2011) <td>
2012) 260072
2013) </td>
2014) <td>
2015) 2252160
2016) </td>
2017) <td>
2018) 4194304
2019) </td>
2020) <td>
2021) 0
2022) </td>
2023) </tr>
2024) <tr>
2025) <td>
2026) numothersock
2027) </td>
2028) <td>
2029) 151
2030) </td>
2031) <td>
2032) 153
2033) </td>
2034) <td>
2035) 720
2036) </td>
2037) <td>
2038) 720
2039) </td>
2040) <td>
2041) 0
2042) </td>
2043) </tr>
2044) </table>
2045) <p>
2046)  Xen, Virtual Box and VMware virtual servers have no such limits normally.
2047) </p>
2048) <p>
2049) If the vserver admin will not increase system limits another option is to reduce the memory allocated to the send and receive buffers on TCP connections Tor uses. An experimental feature to constrain socket buffers has recently been added. If your version of Tor supports it, set "ConstrainedSockets 1" in your configuration. See the tor man page for additional details about this option.
2050) </p>
2051) <p>
2052) Unfortunately, since Tor currently requires you to be able to connect to all the other Tor relays, we need you to be able to use at least 1024 file descriptors. This means we can't make use of Tor relays that are crippled in this way.
2053) </p>
2054) <p>
2055) We hope to fix this in the future, once we know how to build a Tor network with restricted topologies -- that is, where each node connects to only a few other nodes. But this is still a long way off.
2056) </p>
2057) 

2058) <hr>
2059) 

2060) <a id="MultipleRelays"></a>

2061) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one
2062) relay.</a></h3>

2063) 
2064) <p>
2065) Great. If you want to run several relays to donate more to the network,
2066) we're happy with that. But please don't run more than a few dozen on
2067) the same network, since part of the goal of the Tor network is dispersal
2068) and diversity.
2069) </p>
2070) 
2071) <p>
2072) If you do decide to run more than one relay, please set the "MyFamily"

2073) config option in the <a href="#torrc">torrc</a> of each relay, listing
2074) all the relays (comma-separated) that are under your control:

2075) </p>
2076) 
2077) <pre>
2078)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
2079) </pre>
2080) 
2081) <p>
2082) where each fingerprint is the 40 character identity fingerprint (without

2083) spaces). You can also list them by nickname, but fingerprint is safer.
2084) Be

2085) sure to prefix the digest strings with a dollar sign ('$') so that the
2086) digest is not confused with a nickname in the config file.
2087) </p>
2088) 
2089) <p>
2090) That way clients will know to avoid using more than one of your relays
2091) in a single circuit. You should set MyFamily if you have administrative
2092) control of the computers or of their network, even if they're not all in
2093) the same geographic location.
2094) </p>
2095) 
2096)     <hr>
2097) 

2098)     <a id="WrongIP"></a>
2099)     <h3><a class="anchor" href="#WrongIP">My relay is picking the wrong IP address.</a></h3>
2100)     <p>
2101)  Tor guesses its IP address by asking the computer for its hostname, and then resolving that hostname. Often people have old entries in their /etc/hosts file that point to old IP addresses.
2102)     </p>
2103)     <p>
2104) If that doesn't fix it, you should use the "Address" config option to specify the IP you want it to pick. If your computer is behind a NAT and it only has an internal IP address, see the following FAQ entry on <a href="https://www.torproject.org/docs/faq.html.en#RelayFlexible">dynamic IP addresses</a>.
2105)     </p>
2106)     <p>
2107) Also, if you have many addresses, you might also want to set "OutboundBindAddress" so external connections come from the IP you intend to present to the world. 
2108)     </p>
2109) 
2110)     <hr>
2111) 
2112)     <a id="BehindANAT"></a>
2113)     <h3><a class="anchor" href="#BehindANAT">I'm behind a NAT/Firewall.</a></h3>
2114) 
2115)     <p>
2116) See <a>​http://portforward.com/</a> for directions on how to port forward with your NAT/router device.
2117) </p>
2118) <p>
2119) If your relay is running on a internal net you need to setup port forwarding. Forwarding TCP connections is system dependent but the firewalled-clients FAQ entry offers some examples on how to do this.
2120) </p>
2121) <p>
2122) Also, here's an example of how you would do this on GNU/Linux if you're using iptables:
2123) </p>
2124) <pre>
2125) /sbin/iptables -A INPUT -i eth0 -p tcp --destination-port 9001 -j ACCEPT
2126) </pre>
2127) <p>
2128) You may have to change "eth0" if you have a different external interface (the one connected to the Internet). Chances are you have only one (except the loopback) so it shouldn't be too hard to figure out. 
2129)     </p>
2130)     <hr>
2131) 

2132)     <a id="RelayMemory"></a>

2133)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using
2134) so much memory?</a></h3>

2135) 

2136)     <p>If your Tor relay is using more memory than you'd like, here are
2137) some

2138)     tips for reducing its footprint:
2139)     </p>

2140) 

2141)     <ol>
2142)     <li>If you're on Linux, you may be encountering memory fragmentation

2143)     bugs in glibc's malloc implementation. That is, when Tor releases
2144) memory
2145)     back to the system, the pieces of memory are fragmented so they're
2146) hard
2147)     to reuse. The Tor tarball ships with OpenBSD's malloc
2148) implementation,
2149)     which doesn't have as many fragmentation bugs (but the tradeoff is
2150) higher
2151)     CPU load). You can tell Tor to use this malloc implementation
2152) instead:

2153)     <tt>./configure --enable-openbsd-malloc</tt></li>

2154) 

2155)     <li>If you're running a fast relay, meaning you have many TLS
2156) connections

2157)     open, you are probably losing a lot of memory to OpenSSL's internal
2158)     buffers (38KB+ per socket). We've patched OpenSSL to <a

2159) 
2160) href="https://lists.torproject.org/pipermail/tor-dev/2008-June/001519.
2161) html">release

2162)     unused buffer memory more aggressively</a>. If you update to OpenSSL

2163)     1.0.0 or newer, Tor's build process will automatically recognize and
2164) use

2165)     this feature.</li>

2166) 

2167)     <li>If you're running on Solaris, OpenBSD, NetBSD, or
2168)     old FreeBSD, Tor is probably forking separate processes
2169)     rather than using threads. Consider switching to a <a
2170)     href="<wikifaq>#WhydoesntmyWindowsorotherOSTorrelayrunwell">better
2171)     operating system</a>.</li>

2172) 

2173)     <li>If you still can't handle the memory load, consider reducing the

2174)     amount of bandwidth your relay advertises. Advertising less
2175) bandwidth

2176)     means you will attract fewer users, so your relay shouldn't grow
2177)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
2178)     page.</li>

2179) 

2180)     </ol>

2181) 

2182)     <p>

2183)     All of this said, fast Tor relays do use a lot of ram. It is not
2184) unusual

2185)     for a fast exit relay to use 500-1000 MB of memory.
2186)     </p>

2187) 

2188)     <hr>

2189) 

2190)     <a id="BetterAnonymity"></a>
2191)     <h3><a class="anchor" href="#BetterAnonymity">Do I get better anonymity if I run a relay?</a></h3>

2192) 

2193)     <p>

2194) Yes, you do get better anonymity against some attacks.
2195)     </p>
2196)     <p>
2197) The simplest example is an attacker who owns a small number of Tor relays. He will see a connection from you, but he won't be able to know whether the connection originated at your computer or was relayed from somebody else.
2198)     </p>
2199)     <p>
2200) There are some cases where it doesn't seem to help: if an attacker can watch all of your incoming and outgoing traffic, then it's easy for him to learn which connections were relayed and which started at you. (In this case he still doesn't know your destinations unless he is watching them too, but you're no better off than if you were an ordinary client.)
2201)     </p>
2202)     <p>
2203) There are also some downsides to running a Tor relay. First, while we only have a few hundred relays, the fact that you're running one might signal to an attacker that you place a high value on your anonymity. Second, there are some more esoteric attacks that are not as well-understood or well-tested that involve making use of the knowledge that you're running a relay -- for example, an attacker may be able to "observe" whether you're sending traffic even if he can't actually watch your network, by relaying traffic through your Tor relay and noticing changes in traffic timing.
2204)     </p>
2205)     <p>
2206) It is an open research question whether the benefits outweigh the risks. A lot of that depends on the attacks you are most worried about. For most users, we think it's a smart move. 

2207)     </p>

2208) 

2209)     <hr>

2210) 

2211)     <a id="RelayDonations"></a>

2212)     <h3><a class="anchor" href="#RelayDonations">Can I donate for a
2213)     relay rather than run my own?</a></h3>

2214) 
2215)     <p>

2216)     Sure! We recommend these non-profit charities that are happy to turn

2217)     your donations into better speed and anonymity for the Tor network:
2218)     </p>
2219)     <ul>
2220)     <li><a href="https://www.torservers.net/">torservers.net</a>
2221)     is a German charitable non-profit that runs a wide variety of

2222)     exit relays worldwide. They also like donations of bandwidth from
2223)     ISPs.</li>

2224)     <li><a

2225) href="https://www.noisebridge.net/wiki/Noisebridge_Tor">Noisebridge</a>

2226)     is a US-based 501(c)(3) non-profit that collects donations and turns

2227)     them into more US-based exit relay capacity.</li>
2228)     <li><a href="https://nos-oignons.net/">Nos Oignons</a> is a French
2229)     charitable non-profit that runs fast exit relays in France.</li>

2230)     </ul>
2231) 
2232)     <p>
2233)     These organizations are not the same as <a href="<page
2234)     donate/donate>">The Tor Project, Inc</a>, but we consider that a

2235)     good thing. They're both run by nice people who are part of the
2236)     Tor community.

2237)     </p>
2238) 
2239)     <p>
2240)     Note that there can be a tradeoff here between anonymity and

2241)     performance. The Tor network's anonymity comes in part from
2242) diversity,

2243)     so if you are in a position to run your own relay, you will be

2244)     improving Tor's anonymity more than by donating. At the same time
2245)     though, economies

2246)     of scale for bandwidth mean that combining many small donations into

2247)     several larger relays is more efficient at improving network

2248)     performance. Improving anonymity and improving performance are both
2249)     worthwhile goals, so however you can help is great!
2250)     </p>
2251) 
2252)     <hr>
2253) 

2254)     <a id="KeyManagement"></a>

2255)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the
2256) keys Tor uses.</a></h3>

2257) 

2258)     <p>
2259)     Tor uses a variety of different keys, with three goals in mind: 1)
2260)     encryption to ensure privacy of data within the Tor network, 2)
2261)     authentication so clients know they're

2262)     talking to the relays they meant to talk to, and 3) signatures to
2263) make

2264)     sure all clients know the same set of relays.
2265)     </p>

2266) 

2267)     <p>

2268)     <b>Encryption</b>: first, all connections in Tor use TLS link
2269) encryption,

2270)     so observers can't look inside to see which circuit a given cell is

2271)     intended for. Further, the Tor client establishes an ephemeral
2272) encryption

2273)     key with each relay in the circuit; these extra layers of encryption
2274)     mean that only the exit relay can read

2275)     the cells. Both sides discard the circuit key when the circuit ends,

2276)     so logging traffic and then breaking into the relay to discover the
2277) key

2278)     won't work.
2279)     </p>

2280) 

2281)     <p>
2282)     <b>Authentication</b>:
2283)     Every Tor relay has a public decryption key called the "onion key".

2284)     Each relay rotates its onion key once a week.

2285)     When the Tor client establishes circuits, at each step it <a

2286) 
2287) href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands

2288)     that the Tor relay prove knowledge of its onion key</a>. That way
2289)     the first node in the path can't just spoof the rest of the path.

2290)     Because the Tor client chooses the path, it can make sure to get
2291)     Tor's "distributed trust" property: no single relay in the path can
2292)     know about both the client and what the client is doing.

2293)     </p>

2294) 

2295)     <p>
2296)     <b>Coordination</b>:

2297)     How do clients know what the relays are, and how do they know that
2298) they
2299)     have the right keys for them? Each relay has a long-term public
2300) signing
2301)     key called the "identity key". Each directory authority additionally
2302) has a

2303)     "directory signing key". The directory authorities <a

2304)     href="<specblob>dir-spec.txt">provide a signed list</a>

2305)     of all the known relays, and in that list are a set of certificates
2306) from
2307)     each relay (self-signed by their identity key) specifying their
2308) keys,
2309)     locations, exit policies, and so on. So unless the adversary can
2310) control

2311)     a majority of the directory authorities (as of 2012 there are 8

2312)     directory authorities), he can't trick the Tor client into using
2313)     other Tor relays.

2314)     </p>

2315) 

2316)     <p>

2317)     How do clients know what the directory authorities are? The Tor
2318) software
2319)     comes with a built-in list of location and public key for each
2320) directory
2321)     authority. So the only way to trick users into using a fake Tor
2322) network

2323)     is to give them a specially modified version of the software.
2324)     </p>

2325) 

2326)     <p>
2327)     How do users know they've got the right software? When we distribute
2328)     the source code or a package, we digitally sign it with <a
2329)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
2330)     href="<page docs/verifying-signatures>">instructions
2331)     on how to check Tor's signatures</a>.
2332)     </p>

2333) 

2334)     <p>

2335)     In order to be certain that it's really signed by us, you need to
2336) have
2337)     met us in person and gotten a copy of our GPG key fingerprint, or
2338) you
2339)     need to know somebody who has. If you're concerned about an attack
2340) on
2341)     this level, we recommend you get involved with the security
2342) community

2343)     and start meeting people.
2344)     </p>

2345) 

2346)     <hr>

2347) 

2348) <a id="EntryGuards"></a>

2349) <h3><a class="anchor" href="#EntryGuards">What are Entry
2350) Guards?</a></h3>

2351) 
2352) <p>
2353) Tor (like all current practical low-latency anonymity designs) fails
2354) when the attacker can see both ends of the communications channel. For

2355) example, suppose the attacker controls or watches the Tor relay you
2356) choose
2357) to enter the network, and also controls or watches the website you
2358) visit. In

2359) this case, the research community knows no practical low-latency design
2360) that can reliably stop the attacker from correlating volume and timing
2361) information on the two sides.
2362) </p>
2363) 
2364) <p>
2365) So, what should we do? Suppose the attacker controls, or can observe,

2366) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
2367) new entry and exit relays each time you use the network, the attacker
2368) will be able to correlate all traffic you send with probability
2369) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
2370) as being traced all the time: they want to do something often without
2371) an attacker noticing, and the attacker noticing once is as bad as the

2372) attacker noticing more often. Thus, choosing many random entries and
2373) exits

2374) gives the user no chance of escaping profiling by this kind of attacker.

2375) </p>
2376) 
2377) <p>

2378) The solution is "entry guards": each Tor client selects a few relays at
2379) random

2380) to use as entry points, and uses only those relays for her first hop. If
2381) those relays are not controlled or observed, the attacker can't win,
2382) ever, and the user is secure. If those relays <i>are</i> observed or
2383) controlled by the attacker, the attacker sees a larger <i>fraction</i>

2384) of the user's traffic — but still the user is no more profiled
2385) than

2386) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
2387) of avoiding profiling, whereas she had none before.

2388) </p>
2389) 
2390) <p>

2391) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
2392) Analysis of the Degradation of Anonymous Protocols</a>, <a
2393) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
2394) Communication Against Passive Logging Attacks</a>, and especially
2395) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
2396) Servers</a>.

2397) </p>
2398) 
2399) <p>
2400) Restricting your entry nodes may also help against attackers who want
2401) to run a few Tor nodes and easily enumerate all of the Tor user IP
2402) addresses. (Even though they can't learn what destinations the users
2403) are talking to, they still might be able to do bad things with just a

2404) list of users.) However, that feature won't really become useful until
2405) we move to a "directory guard" design as well.

2406) </p>
2407) 
2408)     <hr>
2409) 

2410)     <a id="ChangePaths"></a>
2411)     <h3><a class="anchor" href="#ChangePaths">How often does Tor change its paths?</a></h3>
2412)     <p>
2413)      Tor will reuse the same circuit for new TCP streams for 10 minutes, as long as the circuit is working fine. (If the circuit fails, Tor will switch to a new circuit immediately.)
2414)     </p>
2415)     <p>
2416) But note that a single TCP stream (e.g. a long IRC connection) will stay on the same circuit forever -- we don't rotate individual streams from one circuit to the next. Otherwise an adversary with a partial view of the network would be given many chances over time to link you to your destination, rather than just one chance.
2417)     </p>
2418) 
2419)     <a id="OutboundConnections"></a>
2420)     <h3><a class="anchor" href="#OutboundConnections">Why does netstat show these outbound connections?</a></h3>
2421)     <p>
2422)     Because that's how Tor works. It holds open a handful of connections so there will be one available when you need one. 
2423)     </p>
2424) 
2425)     <hr>
2426) 

2427)     <a id="PowerfulBlockers"></a>
2428)     <h3><a class="anchor" href="#PowerfulBlockers">What about powerful blocking mechanisms?</a></h3>
2429)     <p>
2430)  An adversary with a great deal of manpower and money, and severe real-world penalties to discourage people from trying to evade detection, is a difficult test for an anonymity and anti-censorship system.
2431)     </p>
2432)     <p>
2433) The original Tor design was easy to block if the attacker controls Alice's connection to the Tor network --- by blocking the directory authorities, by blocking all the relay IP addresses in the directory, or by filtering based on the fingerprint of the Tor TLS handshake. After seeing these attacks and others first-hand, more effort was put into researching new circumvention techniques. Pluggable transports are protocols designed to allow users behind government firewalls to access the Tor network.
2434)     </p>
2435)     <p>
2436) We've made quite a bit of progress on this problem lately. You can read more details on the <a href="https://www.torproject.org/docs/pluggable-transports.html.en">pluggable transports page</a>. You may also be interested in <a href="https://www.youtube.com/watch?v=GwMr8Xl7JMQ">Roger and Jake's ​talk at 28C3</a>, or <a href="https://www.youtube.com/watch?v=JZg1nqs793M">​Runa's talk at 44con</a>.
2437)     </p>
2438) 
2439)     <hr>
2440)  
2441)     <a id="RemotePhysicalDeviceFingerprinting"></a>
2442)     <h3><a class="anchor" href="#RemotePhysicalDeviceFingerprinting">Does Tor resist "remote physical device fingerprinting"?</a></h3>
2443)     <p>
2444)  Yes, we resist all of these attacks as far as we know.
2445)     </p>
2446)     <p>
2447) These attacks come from examining characteristics of the IP headers or TCP headers and looking for information leaks based on individual hardware signatures. One example is the ​<a href="http://www.caida.org/outreach/papers/2005/fingerprinting/">Oakland 2005 paper</a> that lets you learn if two packet streams originated from the same hardware, but only if you can see the original TCP timestamps.
2448) </p>
2449) <p>
2450) Tor transports TCP streams, not IP packets, so we end up automatically scrubbing a lot of the potential information leaks. Because Tor relays use their own (new) IP and TCP headers at each hop, this information isn't relayed from hop to hop. Of course, this also means that we're limited in the protocols we can transport (only correctly-formed TCP, not all IP like ZKS's Freedom network could) -- but maybe that's a good thing at this stage. </p>
2451) 
2452)     <hr>
2453) 
2454) <a id="AttacksOnOnionRouting"></a>
2455)     <h3><a class="anchor" href="#AttacksOnOnionRouting">What attacks remain against onion routing?</a></h3>
2456)     <p>
2457) As mentioned above, it is possible for an observer who can view both you and either the destination website or your Tor exit node to correlate timings of your traffic as it enters the Tor network and also as it exits. Tor does not defend against such a threat model.
2458)     </p>
2459)     <p>
2460) In a more limited sense, note that if a censor or law enforcement agency has the ability to obtain specific observation of parts of the network, it is possible for them to verify a suspicion that you talk regularly to your friend by observing traffic at both ends and correlating the timing of only that traffic. Again, this is only useful to verify that parties already suspected of communicating with one another are doing so. In most countries, the suspicion required to obtain a warrant already carries more weight than timing correlation would provide.
2461)     </p>
2462)     <p>
2463) Furthermore, since Tor reuses circuits for multiple TCP connections, it is possible to ​associate non anonymous and anonymous traffic at a given exit node, so be careful about what applications you run concurrently over Tor. Perhaps even run separate Tor clients for these applications. 
2464)     </p>
2465) 
2466)     <hr>
2467) 

2468)     <a id="CellSize"></a>
2469)     <h3><a class="anchor" href="#CellSize">Tor uses hundreds of bytes for every IRC line. I can't afford that!</a></h3>
2470)     <p>
2471)      Tor sends data in chunks of 512 bytes (called "cells"), to make it harder for intermediaries to guess exactly how many bytes you're communicating at each step. This is unlikely to change in the near future -- if this increased bandwidth use is prohibitive for you, I'm afraid Tor is not useful for you right now.
2472)     </p>
2473)     <p>
2474) The actual content of these fixed size cells is <a href="https://gitweb.torproject.org/torspec.git/blob/HEAD:/tor-spec.txt">documented in the main Tor spec</a>, section 3.
2475)     </p>
2476)     <p>
2477) We have been considering one day adding two classes of cells -- maybe a 64 byte cell and a 1024 byte cell. This would allow less overhead for interactive streams while still allowing good throughput for bulk streams. But since we want to do a lot of work on quality-of-service and better queuing approaches first, you shouldn't expect this change anytime soon (if ever). However if you are keen, there are a couple of <a href="https://www.torproject.org/getinvolved/volunteer.html.en#Research">research ideas</a> that may involve changing the cell size. 
2478)     </p>
2479) 
2480)     <hr>
2481) 

2482)     <a id="EverybodyARelay"></a>

2483)     <h3><a class="anchor" href="#EverybodyARelay">You should make every
2484) Tor user be a relay.</a></h3>

2485) 

2486)     <p>
2487)     Requiring every Tor user to be a relay would help with scaling the

2488)     network to handle all our users, and <a
2489)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

2490)     relay may help your anonymity</a>. However, many Tor users cannot be
2491) good
2492)     relays &mdash; for example, some Tor clients operate from behind
2493) restrictive
2494)     firewalls, connect via modem, or otherwise aren't in a position
2495) where they

2496)     can relay traffic. Providing service to these clients is a critical

2497)     part of providing effective anonymity for everyone, since many Tor
2498) users
2499)     are subject to these or similar constraints and including these
2500) clients

2501)     increases the size of the anonymity set.
2502)     </p>

2503) 

2504)     <p>

2505)     That said, we do want to encourage Tor users to run relays, so what
2506) we
2507)     really want to do is simplify the process of setting up and
2508) maintaining
2509)     a relay. We've made a lot of progress with easy configuration in the
2510) past
2511)     few years: Vidalia has an easy relay configuration interface, and
2512) supports
2513)     uPnP too. Tor is good at automatically detecting whether it's
2514) reachable and

2515)     how much bandwidth it can offer.
2516)     </p>

2517) 

2518)     <p>

2519)     There are five steps we need to address before we can do this
2520) though:

2521)     </p>

2522) 

2523)     <p>
2524)     First, we need to make Tor stable as a relay on all common
2525)     operating systems. The main remaining platform is Windows,

2526)     and we're mostly there. See Section 4.1 of <a href="https://www.torproject.org/press/2008-12-19-roadmap-press-release"

2527) >our

2528)     development roadmap</a>.
2529)     </p>

2530) 

2531)     <p>
2532)     Second, we still need to get better at automatically estimating
2533)     the right amount of bandwidth to allow. See item #7 on the

2534)     <a href="<page getinvolved/volunteer>#Research">research section of
2535) the

2536)     volunteer page</a>: "Tor doesn't work very well when relays
2537)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

2538)     href="<page docs/faq>#TransportIPnotTCP">switching

2539)     to UDP transport</a> is the simplest answer here &mdash; which alas
2540) is

2541)     not a very simple answer at all.
2542)     </p>

2543) 

2544)     <p>
2545)     Third, we need to work on scalability, both of the network (how to
2546)     stop requiring that all Tor relays be able to connect to all Tor
2547)     relays) and of the directory (how to stop requiring that all Tor
2548)     users know about all Tor relays). Changes like this can have large
2549)     impact on potential and actual anonymity. See Section 5 of the <a
2550)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
2551)     for details. Again, UDP transport would help here.
2552)     </p>

2553) 

2554)     <p>
2555)     Fourth, we need to better understand the risks from
2556)     letting the attacker send traffic through your relay while
2557)     you're also initiating your own anonymized traffic. <a
2558)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
2559)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
2560)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
2561)     describe ways to identify the relays in a circuit by running traffic

2562)     through candidate relays and looking for dips in the traffic while
2563) the
2564)     circuit is active. These clogging attacks are not that scary in the
2565) Tor
2566)     context so long as relays are never clients too. But if we're trying
2567) to
2568)     encourage more clients to turn on relay functionality too (whether
2569) as
2570)     <a href="<page docs/bridges>">bridge relays</a> or as normal
2571) relays), then
2572)     we need to understand this threat better and learn how to mitigate
2573) it.
2574)     </p>
2575) 
2576)     <p>
2577)     Fifth, we might need some sort of incentive scheme to encourage
2578) people
2579)     to relay traffic for others, and/or to become exit nodes. Here are
2580) our

2581)     <a href="<blog>two-incentive-designs-tor">current

2582)     thoughts on Tor incentives</a>.
2583)     </p>

2584) 

2585)     <p>
2586)     Please help on all of these!
2587)     </p>

2588) 

2589) <hr>
2590) 
2591) <a id="TransportIPnotTCP"></a>

2592) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all
2593) IP packets, not just TCP packets.</a></h3>

2594) 
2595) <p>

2596) This would be handy, because it would make Tor better able to handle
2597) new protocols like VoIP, it could solve the whole need to socksify
2598) applications, and it would solve the fact that exit relays need to

2599) allocate a lot of file descriptors to hold open all the exit
2600) connections.

2601) </p>
2602) 
2603) <p>

2604) We're heading in this direction: see <a
2605) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
2606) ticket</a> for directions we should investigate. Some of the hard
2607) problems are:

2608) </p>
2609) 

2610) <ol>

2611) <li>IP packets reveal OS characteristics. We would still need to do
2612) IP-level packet normalization, to stop things like TCP fingerprinting
2613) attacks. Given the diversity and complexity of TCP stacks, along with <a

2614) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

2615) fingerprinting attacks</a>, it looks like our best bet is shipping our
2616) own user-space TCP stack.

2617) </li>

2618) <li>Application-level streams still need scrubbing. We will still need
2619) user-side applications like Torbutton. So it won't become just a matter
2620) of capturing packets and anonymizing them at the IP layer.

2621) </li>
2622) <li>Certain protocols will still leak information. For example, we must
2623) rewrite DNS requests so they are delivered to an unlinkable DNS server
2624) rather than the DNS server at a user's ISP; thus, we must understand
2625) the protocols we are transporting.
2626) </li>
2627) <li><a

2628) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS
2629) </a>

2630) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
2631) picked a transport mechanism, we need to design a new end-to-end Tor
2632) protocol for avoiding tagging attacks and other potential anonymity and
2633) integrity issues now that we allow drops, resends, et cetera.

2634) </li>
2635) <li>Exit policies for arbitrary IP packets mean building a secure
2636) IDS. Our node operators tell us that exit policies are one of the main
2637) reasons they're willing to run Tor. Adding an Intrusion Detection System
2638) to handle exit policies would increase the security complexity of Tor,

2639) and would likely not work anyway, as evidenced by the entire field of
2640) IDS

2641) and counter-IDS papers. Many potential abuse issues are resolved by the
2642) fact that Tor only transports valid TCP streams (as opposed to arbitrary
2643) IP including malformed packets and IP floods), so exit policies become
2644) even <i>more</i> important as we become able to transport IP packets. We
2645) also need to compactly describe exit policies in the Tor directory,

2646) so clients can predict which nodes will allow their packets to exit
2647) —

2648) and clients need to predict all the packets they will want to send in
2649) a session before picking their exit node!
2650) </li>

2651) <li>The Tor-internal name spaces would need to be redesigned. We support
2652) hidden service ".onion" addresses by intercepting the addresses when
2653) they are passed to the Tor client. Doing so at the IP level will require
2654) a more complex interface between Tor and the local DNS resolver.

2655) </li>

2656) </ol>
2657) 
2658) <hr>
2659) 
2660) <a id="HideExits"></a>
2661) <h3><a class="anchor" href="#HideExits">You should hide the list of Tor
2662) relays, so people can't block the exits.</a></h3>
2663) 
2664) <p>
2665) There are a few reasons we don't:
2666) </p>
2667) 
2668) <ol>
2669) <li>We can't help but make the information available, since Tor clients
2670) need to use it to pick their paths. So if the "blockers" want it, they
2671) can get it anyway. Further, even if we didn't tell clients about the
2672) list of relays directly, somebody could still make a lot of connections
2673) through Tor to a test site and build a list of the addresses they see.
2674) </li>
2675) 

2676) <li>If people want to block us, we believe that they should be allowed
2677) to

2678) do so.  Obviously, we would prefer for everybody to allow Tor users to
2679) connect to them, but people have the right to decide who their services

2680) should allow connections from, and if they want to block anonymous
2681) users,

2682) they can.
2683) </li>
2684) 
2685) <li>Being blockable also has tactical advantages: it may be a persuasive

2686) response to website maintainers who feel threatened by Tor. Giving them
2687) the option may inspire them to <a href="<page docs/faq-abuse>#Bans">stop
2688) and think</a> about whether they really want to eliminate private access
2689) to their system, and if not, what other options they might have. The
2690) time they might otherwise have spent blocking Tor, they may instead
2691) spend rethinking their overall approach to privacy and anonymity.

2692) </li>

2693) </ol>
2694) 

2695)     <hr>

2696) 

2697) <a id="ChoosePathLength"></a>
2698) <h3><a class="anchor" href="#ChoosePathLength">You should let people choose their path length.</a></h3>
2699) <p>
2700)  Right now the path length is hard-coded at 3 plus the number of nodes in your path that are sensitive. That is, in normal cases it's 3, but for example if you're accessing a hidden service or a ".exit" address it could be 4.
2701) </p>
2702) <p>
2703)  We don't want to encourage people to use paths longer than this -- it increases load on the network without (as far as we can tell) providing any more security. Remember that <a href="https://svn.torproject.org/svn/tor/trunk/doc/design-paper/tor-design.html#subsec:threat-model">the best way to attack Tor is to attack the endpoints and ignore the middle of the path</a>.
2704) </p>
2705) <p>
2706)  And we don't want to encourage people to use paths of length 1 either. Currently there is no reason to suspect that investigating a single relay will yield user-destination pairs, but if many people are using only a single hop, we make it more likely that attackers will seize or break into relays in hopes of tracing users.
2707) </p>
2708) <p>
2709)  Now, there is a good argument for making the number of hops in a path unpredictable. For example, somebody who happens to control the last two hops in your path still doesn't know who you are, but they know for sure which entry node you used. Choosing path length from, say, a geometric distribution will turn this into a statistical attack, which seems to be an improvement. On the other hand, a longer path length is bad for usability. We're not sure of the right trade-offs here. Please write a research paper that tells us what to do. 
2710) </p>
2711) 
2712)     <hr>
2713) 
2714) <a id="SplitEachConnection"></a>
2715)     <h3><a class="anchor" href="#SplitEachConnection">You should split each connection over many paths.</a></h3>
2716) 
2717)     <p>
2718)  We don't currently think this is a good idea. You see, the attacks we're worried about are at the endpoints: the adversary watches Alice (or the first hop in the path) and Bob (or the last hop in the path) and learns that they are communicating.
2719)     </p>
2720)     <p>
2721) If we make the assumption that timing attacks work well on even a few packets end-to-end, then having *more* possible ways for the adversary to observe the connection seems to hurt anonymity, not help it.
2722)     </p>
2723)     <p>
2724) Now, it's possible that we could make ourselves more resistant to end-to-end attacks with a little bit of padding and by making each circuit send and receive a fixed number of cells. This approach is more well-understood in the context of high-latency systems. See e.g. <a href="http://freehaven.net/anonbib/#pet05-serjantov">Message Splitting Against the Partial Adversary by Andrei Serjantov and Steven J. Murdoch</a>.
2725)     </p>
2726)     <p>
2727) But since we don't currently understand what network and padding parameters, if any, could provide increased end-to-end security, our current strategy is to minimize the number of places that the adversary could possibly see.
2728)     </p>
2729) 
2730)     <hr>
2731) 
2732)     <a id="UnallocatedNetBlocks"></a>
2733)     <h3><a class="anchor" href="#UnallocatedNetBlocks">Your default exit policy should block unallocated net blocks too.</a></h3>
2734) 
2735)     <p>
2736)  No, it shouldn't. The default exit policy blocks certain private net blocks, like 10.0.0.0/8, because they might actively be in use by Tor relays and we don't want to cause any surprises by bridging to internal networks. Some overzealous firewall configs suggest that you also block all the parts of the Internet that IANA has not currently allocated. First, this turns into a problem for them when those addresses *are* allocated. Second, why should we default-reject something that might one day be useful?
2737)     </p>
2738)     <p>
2739) Tor's default exit policy is chosen to be flexible and useful in the future: we allow everything except the specific addresses and ports that we anticipate will lead to problems. 
2740)     </p>
2741) 
2742)     <hr>
2743) 
2744)     <a id="BlockWebsites"></a>
2745)     <h3><a class="anchor" href="#BlockWebsites">Exit policies should be able to block websites, not just IP addresses.</a></h3>
2746) 
2747)     <p>
2748)  It would be nice to let relay operators say things like "reject www.slashdot.org" in their exit policies, rather than requiring them to learn all the IP address space that could be covered by the site (and then also blocking other sites at those IP addresses).
2749)     </p>
2750)     <p>
2751) There are two problems, though. First, users could still get around these blocks. For example, they could request the IP address rather than the hostname when they exit from the Tor network. This means operators would still need to learn all the IP addresses for the destinations in question.
2752)     </p>
2753)     <p>
2754) The second problem is that it would allow remote attackers to censor arbitrary sites. For example, if a Tor operator blocks www1.slashdot.org, and then some attacker poisons the Tor relay's DNS or otherwise changes that hostname to resolve to the IP address for a major news site, then suddenly that Tor relay is blocking the news site. 
2755)     </p>
2756) 
2757)     <hr>
2758) 
2759)     <a id="BlockContent"></a>
2760)     <h3><a class="anchor" href="#BlockContent">You should change Tor to prevent users from posting certain content.</a></h3>
2761) 
2762)     <p> Tor only transports data, it does not inspect the contents of the connections which are sent over it. In general it's a very hard problem for a computer to determine what is objectionable content with good true positive/false positive rates and we are not interested in addressing this problem.
2763)     </p>
2764)     <p>
2765) Further, and more importantly, which definition of "certain content" could we use? Every choice would lead to a quagmire of conflicting personal morals. The only solution is to have no opinion. 
2766)     </p>
2767) 
2768)     <hr>
2769) 
2770)     <a id="IPv6"></a>
2771)     <h3><a class="anchor" href="#IPv6">Tor should support IPv6.</a></h3>
2772) 
2773)     <p>
2774)      That's a great idea! There are two aspects for IPv6 support that Tor needs. First, Tor needs to support exit to hosts that only have IPv6 addresses. Second, Tor needs to support Tor relays that only have IPv6 addresses.
2775)     </p>
2776)     <p>
2777) The first is far easier: the protocol changes are relatively simple and isolated. It would be like another kind of exit policy.
2778)     </p>
2779)     <p>
2780) The second is a little harder: right now, we assume that (mostly) every Tor relay can connect to every other. This has problems of its own, and adding IPv6-address-only relays adds problems too: it means that only relays with IPv6 abilities can connect to IPv6-address-only relays. This makes it possible for the attacker to make some inferences about client paths that it would not be able to make otherwise.
2781)     </p>
2782)     <p>
2783) There is an  IPv6 exit proposal to address the first step for anonymous access to IPv6 resources on the Internet.
2784)     </p>
2785)     <p>
2786) Full IPv6 support is definitely on our "someday" list; it will come along faster if somebody who wants it does some of the work.
2787)     </p>
2788) 
2789)     <hr>
2790) 

2791)     <a id="Criminals"></a>

2792)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals
2793) to do bad things?</a></h3>

2794) 

2795)     <p>
2796)     For the answer to this question and others, please see our <a
2797)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
2798)     </p>

2799) 

2800)     <hr>

2801) 

2802)     <a id="RespondISP"></a>

2803)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP
2804) about my exit relay?</a></h3>

2805) 

2806)     <p>
2807)     A collection of templates for successfully responding to ISPs is <a

2808)     href="<wiki>doc/TorAbuseTemplates">collected

2809)     here</a>.
2810)     </p>

2811) 

2812)     <hr>

2813) 

2814)   </div>
2815)   <!-- END MAINCOL -->
2816)   <div id = "sidecol">
2817) #include "side.wmi"
2818) #include "info.wmi"
2819)   </div>
2820)   <!-- END SIDECOL -->
2821) </div>
2822) <!-- END CONTENT -->

2823) #include <foot.wmi>