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

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

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

15)     <hr>

16) 

17)     <p>General questions:</p>
18)     <ul>
19)     <li><a href="#WhatIsTor">What is Tor?</a></li>
20)     <li><a href="#Torisdifferent">How is Tor different from other proxies?</a></li>
21)     <li><a href="#CompatibleApplications">What programs can I use with
22)     Tor?</a></li>
23)     <li><a href="#WhyCalledTor">Why is it called Tor?</a></li>
24)     <li><a href="#Backdoor">Is there a backdoor in Tor?</a></li>
25)     <li><a href="#DistributingTor">Can I distribute Tor on my magazine's
26)     CD?</a></li>
27)     <li><a href="#SupportMail">How can I get an answer to my
28)     Tor support mail?</a></li>
29)     <li><a href="#WhySlow">Why is Tor so slow?</a></li>
30)     <li><a href="#Funding">What would The Tor Project do with more
31)     funding?</a></li>

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

34)     </ul>

35) 

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

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

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

48) 

49)     <p>Running Tor:</p>

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

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

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

55)     </ul>

56) 

57)     <p>Running a Tor client:</p>
58)     <ul>

59)     <li><a href="#DoesntWork">I installed Tor and Polipo but it's not
60)     working.</a></li>
61)     <li><a href="#VidaliaPassword">Tor/Vidalia prompts for a password at
62)     start.</a></li>
63)     <li><a href="#ChooseEntryExit">Can I control which nodes (or country)
64)     are used for entry/exit?</a></li>
65)     <li><a href="#GoogleCaptcha">Google makes me solve a Captcha or tells
66)     me I have spyware installed.</a></li>
67)     <li><a href="#GmailWarning">Gmail warns me that my account may have
68)     been compromised.</a></li>

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

71)     </ul>

72) 

73)     <p>Running a Tor relay:</p>
74)     <ul>
75)     <li><a href="#RelayFlexible">How stable does my relay need to be?</a></li>
76)     <li><a href="#ExitPolicies">I'd run a relay, but I don't want to deal
77)     with abuse issues.</a></li>
78)     <li><a href="#RelayOrBridge">Should I be a normal relay or bridge
79)     relay?</a></li>

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

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

84) 

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

86) 

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

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

91)     </ul>

92) 

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

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

99)     </ul>

100) 

101)     <p>Abuse:</p>

102)     <ul>
103)     <li><a href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></li>
104)     <li><a href="#RespondISP">How do I respond to my ISP about my exit
105)     relay?</a></li>
106)     </ul>

107) 

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

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

110) 

111)     <hr>

112) 

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

114) 

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

117) 

118)     <p>
119)     The name "Tor" can refer to several different components.
120)     </p>

121) 

122)     <p>
123)     The Tor software is a program you can run on your computer that helps keep
124)     you safe on the Internet. Tor protects you by bouncing your communications
125)     around a distributed network of relays run by volunteers all around
126)     the world: it prevents somebody watching your Internet connection from
127)     learning what sites you visit, and it prevents the sites you visit
128)     from learning your physical location. This set of volunteer relays is
129)     called the Tor network. You can read more about how Tor works on the <a
130)     href="<page about/overview>">overview page</a>.
131)     </p>

132) 

133)     <p>
134)     The Tor Project is a non-profit (charity) organization that maintains
135)     and develops the Tor software.
136)     </p>

137) 

138)     <hr>

139) 

140)     <a id="Torisdifferent"></a>
141)     <h3><a class="anchor" href="#Torisdifferent">How is Tor different from other proxies?</a></h3>
142)     <p>

143)     A typical proxy provider sets up a server somewhere on the Internet and
144) allows you to use it to relay your traffic.  This creates a simple, easy to
145) maintain architecture.  The users all enter and leave through the same server.
146) The provider may charge for use of the proxy, or fund their costs through
147) advertisements on the server.  In the simplest configuration, you don't have to
148) install anything.  You just have to point your browser at their proxy server.
149) Simple proxy providers are fine solutions if you do not want protections for
150) your privacy and anonymity online and you trust the provider from doing bad
151) things.  Some simple proxy providers use SSL to secure your connection to them.
152) This may protect you against local eavesdroppers, such as those at a cafe with
153) free wifi Internet.
154)     </p>
155)     <p>
156)     Simple proxy providers also create a single point of failure.  The provider
157) knows who you are and where you browse on the Internet.  They can see your
158) traffic as it passes through their server.  In some cases, they can see your
159) encrypted traffic as they relay it to your banking site or to ecommerce stores.
160) You have to trust the provider isn't doing any number of things, such as
161) watching your traffic, injecting their own advertisements into your traffic
162) stream, and isn't recording your personal details.
163)     </p>
164)     <p>
165)     Tor passes your traffic through at least 3 different servers before sending
166) it on to the destination.  Tor does not modify, or even know, what you are
167) sending into it.  It merely relays your traffic, completely encrypted through
168) the Tor network and has it pop out somewhere else in the world, completely
169) intact.  The Tor client is required because we assume you trust your local
170) computer.  The Tor client manages the encryption and the path chosen through
171) the network.  The relays located all over the world merely pass encrypted
172) packets between themselves.</p>

173)     <p>
174)     <dl>

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

188)     </dl>
189)     </p>

190) 

191)     <hr>

192) 

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

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

195) 

196)     <p>
197)     There are two pieces to "Torifying" a program: connection-level anonymity
198)     and application-level anonymity. Connection-level anonymity focuses on
199)     making sure the application's Internet connections get sent through Tor.
200)     This step is normally done by configuring
201)     the program to use your Tor client as a "socks" proxy, but there are
202)     other ways to do it too. For application-level anonymity, you need to
203)     make sure that the information the application sends out doesn't hurt
204)     your privacy. (Even if the connections are being routed through Tor, you
205)     still don't want to include sensitive information like your name.) This
206)     second step needs to be done on a program-by-program basis, which is
207)     why we don't yet recommend very many programs for safe use with Tor.
208)     </p>

209) 

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

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

214)     extension</a> if you have Firefox installed. As of version 1.2.0,
215)     Torbutton now takes care of a lot of the connection-level and
216)     application-level worries.
217)     </p>

218) 

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

224)     href="<wiki>TheOnionRouter/TorifyHOWTO">Torifying

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

226)     href="<wiki>TheOnionRouter/SupportPrograms">list

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

230) 

231)     <hr>

232) 

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

235) 

236)     <p>
237)     Because Tor is the onion routing network. When we were starting the
238)     new next-generation design and implementation of onion routing in
239)     2001-2002, we would tell people we were working on onion routing,
240)     and they would say "Neat. Which one?" Even if onion routing has
241)     become a standard household term, Tor was born out of the actual <a
242)     href="http://www.onion-router.net/">onion routing project</a> run by
243)     the Naval Research Lab.
244)     </p>

245) 

246)     <p>
247)     (It's also got a fine translation from German and Turkish.)
248)     </p>

249) 

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

257) 

258)     <hr>

259) 

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

262) 

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

269) 

270)     <p>
271)     We think that putting a backdoor in Tor would be tremendously
272)     irresponsible to our users, and a bad precedent for security software
273)     in general. If we ever put a deliberate backdoor in our security
274)     software, it would ruin our professional reputations. Nobody would
275)     trust our software ever again &mdash; for excellent reason!
276)     </p>

277) 

278)     <p>
279)     But that said, there are still plenty of subtle attacks
280)     people might try. Somebody might impersonate us, or break into our
281)     computers, or something like that. Tor is open source, and you should
282)     always check the source (or at least the diffs since the last release)
283)     for suspicious things. If we (or the distributors) don't give you
284)     source, that's a sure sign something funny might be going on. You
285)     should also check the <a href="<page docs/verifying-signatures>">PGP
286)     signatures</a> on the releases, to make sure nobody messed with the
287)     distribution sites.
288)     </p>

289) 

290)     <p>
291)     Also, there might be accidental bugs in Tor that could affect your
292)     anonymity. We periodically find and fix anonymity-related bugs, so make
293)     sure you keep your Tor versions up-to-date.
294)     </p>

295) 

296)     <hr>

297) 

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

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

300) 

301)     <p>
302)     Yes.
303)     </p>

304) 

305)     <p>
306)     The Tor software is <a href="https://www.fsf.org/">free software</a>. This
307)     means we give you the rights to redistribute the Tor software, either
308)     modified or unmodified, either for a fee or gratis. You don't have to
309)     ask us for specific permission.
310)     </p>

311) 

312)     <p>
313)     However, if you want to redistribute the Tor software you must follow our
314)     <a href="<gitblob>LICENSE">LICENSE</a>.
315)     Essentially this means that you need to include our LICENSE file along
316)     with whatever part of the Tor software you're distributing.
317)     </p>

318) 

319)     <p>
320)     Most people who ask us this question don't want to distribute just the
321)     Tor software, though. They want to distribute the Tor bundles, which
322)     typically include <a href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a>
323)     and <a href="<page projects/vidalia>">Vidalia</a>.
324)     You will need to follow the licenses for those programs
325)     as well. Both of them are distributed under the <a
326)     href="https://www.fsf.org/licensing/licenses/gpl.html">GNU General
327)     Public License</a>. The simplest way to obey their licenses is to
328)     include the source code for these programs everywhere you include
329)     the bundles themselves. Look for "source" packages on the <a
330)     href="<page projects/vidalia>">Vidalia page</a> and the <a
331)     href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo
332)     download page</a>.
333)     </p>

334) 

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

340) 

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

348) 

349)     <hr>

350) 

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

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

353) 

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

355)     <ol>
356)     <li>Read through this <a href="<page docs/faq>">FAQ</a>.</li>
357)     <li>Read through the <a href="<page docs/documentation>">documentation</a>.</li>
358)     <li>Read through the <a
359)     href="http://archives.seul.org/or/talk">OR-TALK Archives</a> and
360)     see if your question is already answered.</li>
361)     <li>Join our <a href="irc://irc.oftc.net#tor">irc channel</a> and
362)     state the issue and wait for help.</li>
363)     <li>Send an email to tor-assistants at torproject.org. These are
364)     volunteers who may be able to help you but you may not get a response
365)     for days.</li>
366)     </ol>

367) 

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

370) 

371)     <hr>

372) 

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

375) 

376)     <p>
377)     There are many reasons why the Tor network is currently slow.
378)     </p>

379) 

380)     <p>
381)     Before we answer, though, you should realize that Tor is never going to
382)     be blazing fast. Your traffic is bouncing through volunteers' computers
383)     in various parts of the world, and some bottlenecks and network latency
384)     will always be present. You shouldn't expect to see university-style
385)     bandwidth through Tor.
386)     </p>

387) 

388)     <p>
389)     But that doesn't mean that it can't be improved. The current Tor network
390)     is quite small compared to the number of people trying to use it, and
391)     many of these users don't understand or care that Tor can't currently
392)     handle file-sharing traffic load.
393)     </p>

394) 

395)     <p>
396)     For the much more in-depth answer, see <a

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

398)     post on the topic</a>, which includes both a detailed PDF and a video
399)     to go with it.
400)     </p>

401) 

402)     <p>
403)     What can you do to help?
404)     </p>

405) 

406)     <ul>

407) 

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

413) 

414)     <li>

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

416)     especially need people to help make it easier to configure your Tor
417)     as a relay. Also, we need help with clear simple documentation to
418)     walk people through setting it up.
419)     </li>

420) 

421)     <li>
422)     There are some bottlenecks in the current Tor network. Help us design
423)     experiments to track down and demonstrate where the problems are, and
424)     then we can focus better on fixing them.
425)     </li>

426) 

427)     <li>
428)     There are some steps that individuals
429)     can take to improve their Tor performance. <a

430)     href="<wiki>TheOnionRouter/FireFoxTorPerf">You

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

437) 

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

444) 

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

450) 

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

459) 

460)     <li>
461)     If you can't help out with any of the above, you can still help out
462)     individually by <a href="<page donate/donate>">donating a bit of money to the
463)     cause</a>. It adds up!
464)     </li>

465) 

466)     </ul>

467) 

468)     <hr>

469) 

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

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

472) 

473)     <p>
474)     We have about 1800 relays right now, pushing over 150 MB/s average
475)     traffic. We have several hundred thousand active users. But the Tor
476)     network is not yet self-sustaining.
477)     </p>

478) 

479)     <p>
480)     There are six main development/maintenance pushes that need attention:
481)     </p>

482) 

483)     <ul>

484) 

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

491) 

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

497) 

498)     <li>
499)     Relay support: the Tor network is run by volunteers, but they still need
500)     attention with prompt bug fixes, explanations when things go wrong,
501)     reminders to upgrade, and so on. The network itself is a commons, and
502)     somebody needs to spend some energy making sure the relay operators stay
503)     happy. We also need to work on <a href="#RelayOS">stability</a> on some
504)     platforms &mdash; e.g., Tor relays have problems on Win XP currently.
505)     </li>

506) 

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

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

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

515) 

516)     <li>
517)     Incentives: We need to work on ways to encourage people to configure
518)     their Tors as relays and exit nodes rather than just clients.
519)     <a href="#EverybodyARelay">We need to make it easy to become a relay,
520)     and we need to give people incentives to do it.</a>
521)     </li>

522) 

523)     <li>
524)     Research: The anonymous communications field is full
525)     of surprises and gotchas. In our copious free time, we
526)     also help run top anonymity and privacy conferences like <a
527)     href="http://petsymposium.org/">PETS</a>. We've identified a set of
528)     critical <a href="<page getinvolved/volunteer>#Research">Tor research questions</a>
529)     that will help us figure out how to make Tor secure against the variety of
530)     attacks out there. Of course, there are more research questions waiting
531)     behind these.
532)     </li>

533) 

534)     </ul>

535) 

536)     <p>
537)     We're continuing to move forward on all of these, but at this rate
538)     <a href="#WhySlow">the Tor network is growing faster than the developers
539)     can keep up</a>.
540)     Now would be an excellent time to add a few more developers to the effort
541)     so we can continue to grow the network.
542)     </p>

543) 

544)     <p>
545)     We are also excited about tackling related problems, such as
546)     censorship-resistance.
547)     </p>

548) 

549)     <p>
550)     We are proud to have <a href="<page about/sponsors>">sponsorship and support</a>
551)     from the Omidyar Network, the International Broadcasting Bureau, Bell
552)     Security Solutions, the Electronic Frontier Foundation, several government
553)     agencies and research groups, and hundreds of private contributors.
554)     </p>

555) 

556)     <p>
557)     However, this support is not enough to keep Tor abreast of changes in the
558)     Internet privacy landscape. Please <a href="<page donate/donate>">donate</a>
559)     to the project, or <a href="<page about/contact>">contact</a> our executive
560)     director for information on making grants or major donations.
561)     </p>

562) 

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

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

565) 

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

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

568)     <hr>

569) 

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

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

572) 

573)     <p>
574)     This depends entirely on how you installed it and which operating system you
575)     have. If you installed a package, then hopefully your package has a way to
576)     uninstall itself. The Windows packages include uninstallers. The proper way to
577)     completely remove Tor, Vidalia, Torbutton for Firefox, and Polipo on any
578)     version of Windows is as follows:
579)     </p>

580) 

581)     <ol>
582)     <li>In your taskbar, right click on Vidalia (the green onion or the black head)
583)     and choose exit.</li>
584)     <li>Right click on the taskbar to bring up TaskManager. Look for tor.exe in the
585)     Process List. If it's running, right click and choose End Process.</li>
586)     <li>Click the Start button, go to Programs, go to Vidalia, choose Uninstall.
587)     This will remove the Vidalia bundle, which includes Tor and Polipo.</li>
588)     <li>Start Firefox. Go to the Tools menu, choose Add-ons. Select Torbutton.
589)     Click the Uninstall button.</li>
590)     </ol>

591) 

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

597) 

598)     <p>
599)     For Mac OS X, follow the <a
600)     href="<page docs/tor-doc-osx>#uninstall">uninstall directions</a>.
601)     </p>

602) 

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

608) 

609)     <hr>

610) 

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

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

613) 

614)     <p>
615)     These are PGP signatures, so you can verify that the file you've downloaded is
616)     exactly the one that we intended you to get.
617)     </p>

618) 

619)     <p>
620)     Please read the <a
621)     href="<page docs/verifying-signatures>">verifying signatures</a> page for details.
622)     </p>

623) 

624) <hr>
625) 
626) <a id="GetTor"></a>
627) <h3><a class="anchor" href="#GetTor">Your website is blocked in my
628) country. How do I download Tor?</a></h3>
629) 
630) <p>
631) Some government or corporate firewalls censor connections to Tor's
632) website. In those cases, you have three options. First, get it from

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

634) Bundle</a> fits nicely on a USB key. Second, find the google cache
635) for the <a href="<page getinvolved/mirrors>">Tor mirrors</a> page
636) and see if any of those copies of our website work for you. Third,
637) you can download Tor via email: log in to your Gmail account and mail
638) '<tt>gettor AT torproject.org</tt>'. If you include the word 'help'
639) in the body of the email, it will reply with instructions. Note that
640) only a few webmail providers are supported, since they need to be able
641) to receive very large attachments.
642) </p>
643) 
644) <p>

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

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

648) </p>
649) 
650) <hr>

651) 

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

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

654) 

655)     <p>
656)     Try following the steps at <a href="<gitblob>doc/tor-win32-mingw-creation.txt">
657)     tor-win32-mingw-creation.txt</a>.
658)     </p>

659) 

660)     <p>
661)     (Note that you don't need to compile Tor yourself in order to use
662)     it. Most people just use the packages available on the <a href="<page
663)     download/download>">download page</a>.)
664)     </p>

665) 

666)     <hr>

667) 

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

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

670) 

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

678) 

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

684) 

685)     <hr>

686) 

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

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

689) 

690)     <p>
691)     There isn't any official LiveCD at this point. We're still trying to find good
692)     solutions and trying to understand the security and anonymity implications of
693)     the various options. In the mean time, feel free to check out the list below
694)     and use your best judgement:
695)     </p>

696) 

697)     <p>
698)     LiveCDs:
699)     </p>

700) 

701)     <ol>
702)     <li><a href="https://amnesia.boum.org/">The (Amnesic) Incognito Live
703)     System</a> is a Live System aimed at preserving your privacy and
704)     anonymity:
705)     <ul>
706)     <li> All outgoing connections to the Internet are forced to go through
707)     the Tor network.</li>
708)     <li> No trace is left on local storage devices unless explicitely asked.</li>
709)     <li> It includes Firefox, Tor, Torbutton, Vidalia graphical Tor
710)     controller, Pidgin Instant Messaging client, and lots of other
711)     software.</li>
712)     <li> It's based upon Debian gnu/linux and comes with the GNOME desktop
713)     environment.</li>
714)     </ul>
715)     <li><a href="http://tork.sourceforge.net/wiki/index.php/LiveCD">TorK LiveCD</a>
716)     is Knoppix-based with an emphasis on user-friendliness. You can work
717)     anonymously or non-anonymously while TorK tries to keep you informed of the
718)     consequences of your activity. The TorK LiveCD is experimental, so the aim is
719)     to provide regular releases through 2007 and beyond.</li>
720)     <li><a href="http://mandalka.name/privatix/">Privatix LiveCD/USB</a> is a
721)     debian based live-system including tor, firefox and torbutton which can save
722)     bookmarks and other settings or data on an encrypted usb-key</li>
723)     </li>
724)     </ol>

725) 

726)     <p>
727)     Windows bundles:
728)     </p>

729) 

730)     <ol>
731)     <li><a href="<page projects/torbrowser>">Tor Browser Bundle</a>
732)     for Windows comes with a pre-configured web browser and is self contained
733)     so you can run it from a USB stick.</li>
734)     <li><a href="http://www.janusvm.com/tor_vm/">Tor VM</a> is a successor
735)     to JanusVM. It needs testing from you!</li>
736)     <li><a href="http://janusvm.com/">JanusVM</a> is a Linux kernel and software
737)     running in VMWare that sits between your Windows computer and the Internet,
738)     making sure that your Internet traffic is scrubbed and anonymized.</li>
739)     <li><a href="http://www.xerobank.com/xB_browser.html">xB Browser</a>,
740)     previously known as Torpark, is a Firefox+Tor package for Win32 that can
741)     installed on a USB key. It needs a host Win32 operating system.</li>
742)     </ol>

743) 

744)     <p>
745)     Not currently maintained as far as we know:
746)     </p>

747) 

748)     <ol>
749)     <li>Polippix / Privatlivets Fred is a Danish Knoppix-based LiveCD with Tor
750)     and utilities to encrypt IP-telephony. <a href="http://polippix.org/">Info and
751)     download</a>.</li>
752)     <li>ELE is a Linux LiveCD which is focused on privacy related
753)     software. It includes Tor and you can download it at
754)     <a
755)     href="http://www.northernsecurity.net/download/ele/">http://www.northernsecurity.net/download/ele/</a>.</li>
756)     <li>Virtual Privacy Machine is a Linux LiveCD that includes Firefox, Privoxy,
757)     Tor, some IRC and IM applications, and a set of ipchains rules aimed to prevent
758)     non-Tor traffic from accidentally leaving your computer. More information at

759)     <a href="<wiki>VirtualPrivacyMachine"><wiki>VirtualPrivacyMachine</a>.</li>

760)     <li>Anonym.OS is a LiveCD similar to the above but is based on OpenBSD rather
761)     than Linux for maximum security. It was designed to be anonymous and secure
762)     from the ground up, and thus has some features and limitations not found in
763)     other LiveCDs (Tor related or otherwise). You can obtain more information and
764)     download Anonym.OS from <a href="http://theory.kaos.to/projects.html">Kaos.Theory</a>.</li>
765)     <li>Phantomix is a LiveCD for anonymous surfing and chatting based on the most
766)     recent KNOPPIX release. It comes preconfigured with Privoxy, Tor and Polipo. You can
767)     get it from the <a href="http://phantomix.ytternhagen.de/">Phantomix
768)     Website</a>.</li>
769)     </ol>

770) 

771)     <p>
772)     Please contact us if you know any others.
773)     </p>

774) 
775) <hr>
776) 

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

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

779) 
780) <p>
781) Tor installs a text file called torrc that contains configuration
782) instructions for how your Tor program should behave. The default
783) configuration should work fine for most Tor users. Users of Vidalia can
784) make common changes through the Vidalia interface &mdash; only advanced
785) users should need to modify their torrc file directly.
786) </p>
787) 
788) <p>
789) The location of your torrc file depends on the way you installed Tor:
790) </p>
791) 
792) <ul>
793) <li>On Windows, if you installed a Tor bundle with Vidalia, you can
794) find your torrc file in the Start menu under Programs -&gt; Vidalia
795) Bundle -&gt; Tor, or you can find it by hand in <code>\Documents and
796) Settings\<i>username</i>\Application Data\Vidalia\torrc</code>. If you
797) installed Tor without Vidalia, you can find your torrc in the Start
798) menu under Programs -&gt; Tor, or manually in either <code>\Documents
799) and Settings\Application Data\tor\torrc</code> or <code>\Documents and
800) Settings\<i>username</i>\Application Data\tor\torrc</code>.
801) </li>
802) <li>On OS X, if you use Vidalia, edit
803) <code>~/.vidalia/torrc</code>. Otherwise, open your favorite text editor
804) and load <code>/Library/Tor/torrc</code>.
805) </li>
806) <li>On Unix, if you installed a pre-built package, look for
807) <code>/etc/tor/torrc</code> or <code>/etc/torrc</code> or consult your
808) package's documentation.
809) </li>
810) <li>Finally, if you installed from source, you may not have a torrc
811) installed yet: look in <code>/usr/local/etc/</code> and note that you
812) may need to manually copy <code>torrc.sample</code> to <code>torrc</code>.
813) </li>
814) </ul>
815) 
816) <p>
817) If you use Vidalia, be sure to exit both Tor and Vidalia before you edit
818) your torrc file. Otherwise Vidalia might overwrite your changes.
819) </p>
820) 
821) <p>
822) Once you've changed your torrc, you will need to restart Tor for the
823) changes to take effect. (For advanced users on OS X and Unix, note that
824) you actually only need to send Tor a HUP signal, not actually restart it.)
825) </p>
826) 
827) <p>
828) For other configuration options you can use, look at the <a href="<page
829) docs/tor-manual>">Tor manual page</a>. Remember, all lines beginning
830) with # in torrc are treated as comments and have no effect on Tor's
831) configuration.
832) </p>
833) 
834) <hr>
835) 

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

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

838) 
839) <p>

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

844) </p>
845) 
846) <p>
847) If you're not using Vidalia, you'll have to go find the log files by

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

849) </p>
850) 
851) <ul>
852) <li>On OS X, Debian, Red Hat, etc, the logs are in /var/log/tor/
853) </li>

854) <li>On Windows, there are no default log files currently. If you enable
855) logs in your torrc file, they default to <code>\username\Application
856) Data\tor\log\</code> or <code>\Application Data\tor\log\</code>
857) </li>
858) <li>If you compiled Tor from source, by default your Tor logs to <a
859) href="http://en.wikipedia.org/wiki/Standard_streams">"stdout"</a>
860) at log-level notice. If you enable logs in your torrc file, they
861) default to <code>/usr/local/var/log/tor/</code>.

862) </li>
863) </ul>
864) 
865) <p>

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

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

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

874) </pre>

875) 
876) <p>

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

878) and err level messages to a file, append the following line to the end
879) of the section:
880) </p>
881) 
882) <pre>
883) Log debug file c:/program files/tor/debug.log
884) </pre>
885) 
886) <p>

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

889) </p>
890) 
891) <hr>
892) 

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

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

895) 
896) <p>
897) Once you've installed the Tor bundle, there are two questions to ask:
898) first, is your Tor able to establish a circuit? Second, is your
899) Firefox correctly configured to send its traffic through Tor?
900) </p>
901) 
902) <p>If Tor can establish a circuit, the onion icon in
903) Vidalia will turn green. You can also check in the Vidalia
904) Control Panel to make sure it says "Connected to the Tor
905) network!" under Status. For those not using Vidalia, check your <a

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

907) a line saying that Tor "has successfully opened a circuit. Looks like
908) client functionality is working."
909) </p>
910) 
911) <p>
912) If Tor can't establish a circuit, here are some hints:
913) </p>
914) 
915) <ol>
916) <li>Are you sure Tor is running? If you're using Vidalia, you may have
917) to click on the onion and select "Start" to launch Tor.</li>
918) <li>Check your system clock. If it's more than a few hours off, Tor will
919) refuse to build circuits. For XP users, synchronize your clock under
920) the clock -&gt; Internet time tab. In addition, correct the day and date
921) under the 'Date &amp; Time' Tab.</li>
922) <li>Is your Internet connection <a

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

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

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

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

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

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

935) </ol>
936) 
937) <p>
938) Step two is to confirm that Firefox is correctly configured to send its
939) traffic through Tor. Try the <a href="https://check.torproject.org/">Tor
940) Check</a> site and see whether it thinks you are using Tor. See <a

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

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

943) </p>

944) 
945) <p>
946) If it thinks you're not using Tor, here are some hints:
947) </p>
948) 
949) <ol>
950) <li>Did you install the Torbutton extension for Firefox? The installation
951) bundles include it, but sometimes people forget to install it. Make sure
952) it says "Tor enabled" at the bottom right of your Firefox window. (For
953) expert users, make sure your http proxy is set to localhost port
954) 8118.)</li>
955) <li>Do you have incompatible Firefox extensions like FoxyProxy
956) installed? If so, uninstall them. (Note that using FoxyProxy is NOT
957) a sufficient substitute for Torbutton. There are many known attacks
958) against a browser setup that does not include Torbutton. Read more

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

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

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

977) <li>For Red Hat Linux and related systems, do you have SELinux enabled? If
978) so, it might be preventing Polipo from talking to Tor. We also run across
979) BSD users periodically who have local firewall rules that prevent some
980) connections to localhost.</li>
981) </ol>
982) 
983) <hr />
984) 
985) <a id="VidaliaPassword"></a>

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

987) 
988) <p>
989) Vidalia interacts with the Tor software via Tor's "control port". The
990) control port lets Vidalia receive status updates from Tor, request a new
991) identity, configure Tor's settings, etc. Each time Vidalia starts Tor,
992) Vidalia sets a random password for Tor's control port to prevent other
993) applications from also connecting to the control port and potentially
994) compromising your anonymity.
995) </p>
996) 
997) <p>
998) Usually this process of generating and setting a random control password
999) happens in the background. There are three common situations, though,
1000) where Vidalia may prompt you for a password:
1001) </p>
1002) 
1003) <ol>
1004) <li>You're already running Vidalia and Tor. For example, this situation
1005) can happen if you installed the Vidalia bundle and now you're trying to
1006) run the Tor Browser Bundle. In that case, you'll need to close the old
1007) Vidalia and Tor before you can run this one.
1008) </li>
1009) <li>Vidalia crashed, but left Tor running with the last known random
1010) password. After you restart Vidalia, it generates a new random password,
1011) but Vidalia can't talk to Tor, because the random passwords are different.
1012) <br />
1013) If the dialog that prompts you for a control password has a Reset button,
1014) you can click the button and Vidalia will restart Tor with a new random
1015) control password.
1016) <br />
1017) If you do not see a Reset button, or if Vidalia is unable to restart
1018) Tor for you, you can still fix the problem manually. Simply go into your
1019) process or task manager, and terminate the Tor process. Then use Vidalia
1020) to restart Tor and all will work again.
1021) </li>
1022) <li>You had previously set Tor to run as a Windows NT service. When Tor
1023) is set to
1024) run as a service, it starts up when the system boots. If you configured
1025) Tor to start as a service through Vidalia, a random password was set
1026) and saved in Tor. When you reboot, Tor starts up and uses the random
1027) password it saved. You login and start up Vidalia. Vidalia attempts to
1028) talk to the already running Tor. Vidalia generates a random password,
1029) but it is different than the saved password in the Tor service.
1030) <br />
1031) You need to reconfigure Tor to not be a service. See the FAQ entry on

1032) <a href="<wikifaq>#HowdoIrunmyTorrelayasanNTservice">running Tor as a Windows NT service</a>

1033) for more information on how to remove the Tor service.
1034) </li>
1035) </ol>
1036) 

1037)     <hr>

1038) 

1039)     <a id="ChooseEntryExit"></a>
1040)     <h3><a class="anchor" href="#ChooseEntryExit">Can I control which nodes (or country) are used for entry/exit?</a></h3>

1041) 

1042)     <p>

1043)     Yes. You can set preferred entry and exit nodes as well as
1044)     inform Tor which nodes you do not want to use.

1045)     The following options can be added to your config file <a
1046)     href="#torrc">"torrc"</a> or specified on the command line:

1047)     </p>
1048)     <dl>
1049)       <dt><tt>EntryNodes $fingerprint,$fingerprint,...</tt></dt>
1050)         <dd>A list of preferred nodes to use for the first hop in the circuit, if possible.
1051)         </dd>
1052)       <dt><tt>ExitNodes $fingerprint,$fingerprint,...</tt></dt>

1053)         <dd>A list of preferred nodes to use for the last hop in the circuit, if possible.

1054)         </dd>
1055)       <dt><tt>ExcludeNodes $fingerprint,$fingerprint,...</tt></dt>

1056)         <dd>A list of nodes to never use when building a circuit.

1057)         </dd>
1058)       <dt><tt>ExcludeExitNodes $fingerprint,$fingerprint,...</tt></dt>

1059)         <dd>A list of nodes to never use when picking an exit.
1060)             Nodes listed in <tt>ExcludeNodes</tt> are automatically in this list.

1061)         </dd>
1062)     </dl>
1063)     <p>

1064)     <em>We recommend you do not use these</em>
1065)     &mdash; they are intended for testing and may disappear in future versions.
1066)     You get the best security that Tor can provide when you leave the
1067)     route selection to Tor; overriding the entry / exit nodes can mess
1068)     up your anonymity in ways we don't understand.

1069)     </p>
1070)     <p>

1071)     The <tt>EntryNodes</tt> and <tt>ExitNodes</tt> config options are
1072)     treated as a request, meaning if the nodes are down or seem slow,
1073)     Tor will still avoid them. You can make the option mandatory by
1074)     setting <tt>StrictExitNodes 1</tt> or <tt>StrictEntryNodes 1</tt>
1075)     &mdash; but if you do, your Tor connections will stop working
1076)     if all of the nodes you have specified become unreachable.
1077)     See the <a href="<page docs/documentation>#NeatLinks">Tor status pages</a>

1078)     for some nodes you might pick.
1079)     </p>
1080)     <p>

1081)     Instead of <tt>$fingerprint</tt> you can also specify a 2 letter
1082)     ISO3166 country code in curly braces (for example {de}), or an ip
1083)     address pattern (for example 255.254.0.0/8), or a node nickname. Make
1084)     sure there are no spaces between the commas and the list items.

1085)     </p>
1086)     <p>

1087)     If you want to access a service directly through Tor's SOCKS interface
1088)     (eg. using ssh via connect.c), another option is to set up an
1089)     internal mapping in your configuration file using <tt>MapAddress</tt>.

1090)     See the manual page for details.
1091)     </p>

1092) 

1093)     <hr>

1094) 
1095) <a id="GoogleCaptcha"></a>

1096) <h3><a class="anchor" href="#GoogleCaptcha">Google makes me solve a Captcha or tells me I have spyware installed.</a></h3>

1097) 
1098) <p>
1099) This is a known and intermittent problem; it does not mean that Google
1100) considers Tor to be spyware.
1101) </p>
1102) 
1103) <p>
1104) When you use Tor, you are sending queries through exit relays that are also
1105) shared by thousands of other users. Tor users typically see this message
1106) when many Tor users are querying Google in a short period of time. Google
1107) interprets the high volume of traffic from a single IP address (the exit
1108) relay you happened to pick) as somebody trying to "crawl" their website,
1109) so it slows down traffic from that IP address for a short time.
1110) </p>
1111) <p>
1112) An alternate explanation is that Google tries to detect certain
1113) kinds of spyware or viruses that send distinctive queries to Google
1114) Search. It notes the IP addresses from which those queries are received
1115) (not realizing that they are Tor exit relays), and tries to warn any
1116) connections coming from those IP addresses that recent queries indicate
1117) an infection.
1118) </p>
1119) 
1120) <p>
1121) To our knowledge, Google is not doing anything intentionally specifically
1122) to deter or block Tor use. The error message about an infected machine
1123) should clear up again after a short time.
1124) </p>
1125) 
1126) <p>
1127) Torbutton 1.2.5 (released in mid 2010) detects Google captchas and can
1128) automatically redirect you to a more Tor-friendly search engine such as
1129) Ixquick or Bing.
1130) </p>
1131) 
1132) <hr />
1133) 
1134) <a id="GmailWarning"></a>

1135) <h3><a class="anchor" href="#GmailWarning">Gmail warns me that my account may have been compromised.</a></h3>

1136) 
1137) <p>
1138) Sometimes, after you've used Gmail over Tor, Google presents a

1139) pop-up notification that your account may have been compromised.
1140) The notification window lists a series of IP addresses and locations
1141) throughout the world recently used to access your account.

1142) </p>
1143) 
1144) <p>
1145) In general this is a false alarm: Google saw a bunch of logins from

1146) different places, as a result of running the service via Tor, and decided
1147) it was a good idea to confirm the account was being accessed by it's
1148) rightful owner.

1149) </p>
1150) 
1151) <p>

1152) Even though this may be a biproduct of using the service via tor,
1153) that doesn't mean you can entirely ignore the warning. It is
1154) <i>probably</i> a false positive, but it might not be since it is
1155) possible for someone to hijack your Google cookie.
1156) </p>
1157) 
1158) <p>
1159) Cookie hijacking is possible by either physical access to your computer
1160) or by watching your network traffic.  In theory only physical access
1161) should compromise your system because Gmail and similar services
1162) should only send the cookie over an SSL link. In practice, alas, it's <a
1163) href="http://fscked.org/blog/fully-automated-active-https-cookie-hijacking">
1164) way more complex than that</a>.

1165) </p>
1166) 
1167) <p>
1168) And if somebody <i>did</i> steal your google cookie, they might end
1169) up logging in from unusual places (though of course they also might
1170) not). So the summary is that since you're using Tor, this security
1171) measure that Google uses isn't so useful for you, because it's full of
1172) false positives. You'll have to use other approaches, like seeing if
1173) anything looks weird on the account, or looking at the timestamps for
1174) recent logins and wondering if you actually logged in at those times.
1175) </p>
1176) 

1177) <hr>
1178) 
1179) <a id="FirewallPorts"></a>

1180) <h3><a class="anchor" href="#FirewallPorts">My firewall only allows a few outgoing ports.</a></h3>

1181) 
1182) <p>
1183) If your firewall works by blocking ports, then you can tell Tor to only
1184) use the ports that your firewall permits by adding "FascistFirewall 1" to

1185) your <a href="<page docs/faq>#torrc">torrc

1186) configuration file</a>, or by clicking "My firewall only lets me connect
1187) to certain ports" in Vidalia's Network Settings window.
1188) </p>
1189) 
1190) <p>
1191) By default, when you set this Tor assumes that your firewall allows only
1192) port 80 and port 443 (HTTP and HTTPS respectively). You can select a
1193) different set of ports with the FirewallPorts torrc option.
1194) </p>
1195) 
1196) <p>
1197) If you want to be more fine-grained with your controls, you can also
1198) use the ReachableAddresses config options, e.g.:
1199) </p>
1200) 
1201) <pre>
1202)   ReachableDirAddresses *:80
1203)   ReachableORAddresses *:443
1204) </pre>
1205) 
1206) <hr>

1207) 

1208)     <a id="RelayFlexible"></a>

1209)     <h3><a class="anchor" href="#RelayFlexible">How stable does my relay need to be?</a></h3>

1210) 

1211)     <p>
1212)     We aim to make setting up a Tor relay easy and convenient:
1213)     </p>

1214) 

1215)     <ul>
1216)     <li>Tor has built-in support for <a

1217)     href="<wikifaq>#WhatbandwidthshapingoptionsareavailabletoTorrelays">

1218)     rate limiting</a>. Further, if you have a fast
1219)     link but want to limit the number of bytes per
1220)     day (or week or month) that you donate, check out the <a

1221)     href="<wikifaq>#HowcanIlimitthetotalamountofbandwidthusedbymyTorrelay">hibernation

1222)     feature</a>.
1223)     </li>
1224)     <li>Each Tor relay has an <a href="#ExitPolicies">exit policy</a> that
1225)     specifies what sort of outbound connections are allowed or refused from
1226)     that relay. If you are uncomfortable allowing people to exit from your
1227)     relay, you can set it up to only allow connections to other Tor relays.
1228)     </li>
1229)     <li>It's fine if the relay goes offline sometimes. The directories
1230)     notice this quickly and stop advertising the relay. Just try to make
1231)     sure it's not too often, since connections using the relay when it
1232)     disconnects will break.
1233)     </li>
1234)     <li>We can handle relays with dynamic IPs just fine &mdash; simply
1235)     leave the Address config option blank, and Tor will try to guess.
1236)     </li>
1237)     <li>If your relay is behind a NAT and it doesn't know its public
1238)     IP (e.g. it has an IP of 192.168.x.y), you'll need to set up port

1239)     forwarding. Forwarding TCP connections is system dependent but

1240)     <a href="<wikifaq>#ImbehindaNATFirewall">this FAQ entry</a>

1241)     offers some examples on how to do this.
1242)     </li>
1243)     <li>Your relay will passively estimate and advertise its recent
1244)     bandwidth capacity, so high-bandwidth relays will attract more users than
1245)     low-bandwidth ones. Therefore having low-bandwidth relays is useful too.
1246)     </li>
1247)     </ul>

1248) 

1249)     <hr>

1250) 

1251)     <a id="RunARelayBut"></a>
1252)     <a id="ExitPolicies"></a>

1253)     <h3><a class="anchor" href="#ExitPolicies">I'd run a relay, but I don't want to deal with abuse issues.</a></h3>

1254) 

1255)     <p>
1256)     Great. That's exactly why we implemented exit policies.
1257)     </p>

1258) 

1259)     <p>
1260)     Each Tor relay has an exit policy that specifies what sort of
1261)     outbound connections are allowed or refused from that relay. The exit
1262)     policies are propagated to Tor clients via the directory, so clients
1263)     will automatically avoid picking exit relays that would refuse to
1264)     exit to their intended destination. This way each relay can decide
1265)     the services, hosts, and networks he wants to allow connections to,

1266)     based on abuse potential and his own situation. Read the FAQ entry on
1267)     <a href="<page docs/faq-abuse>#TypicalAbuses">issues you might encounter</a>
1268)     if you use the default exit policy, and then read Mike Perry's

1269)     <a href="<blog>tips-running-exit-node-minimal-harassment">tips

1270)     for running an exit node with minimal harassment</a>.
1271)     </p>

1272) 

1273)     <p>

1274)     The default exit policy allows access to many popular services

1275)     (e.g. web browsing), but <a href="<wikifaq>#Istherealistofdefaultexitports">restricts</a>

1276)     some due to abuse potential (e.g. mail) and some since
1277)     the Tor network can't handle the load (e.g. default
1278)     file-sharing ports). You can change your exit policy

1279)     using Vidalia's "Sharing" tab, or by manually editing your

1280)     <a href="<page docs/faq>#torrc">torrc</a>

1281)     file. If you want to avoid most if not all abuse potential, set it to
1282)     "reject *:*" (or un-check all the boxes in Vidalia). This setting means
1283)     that your relay will be used for relaying traffic inside the Tor network,
1284)     but not for connections to external websites or other services.
1285)     </p>

1286) 

1287)     <p>
1288)     If you do allow any exit connections, make sure name resolution works
1289)     (that is, your computer can resolve Internet addresses correctly).
1290)     If there are any resources that your computer can't reach (for example,
1291)     you are behind a restrictive firewall or content filter), please
1292)     explicitly reject them in your exit policy &mdash; otherwise Tor users
1293)     will be impacted too.
1294)     </p>

1295) 

1296)     <hr>

1297) 

1298)     <a id="RelayOrBridge"></a>

1299)     <h3><a class="anchor" href="#RelayOrBridge">Should I be a normal relay or bridge relay?</a></h3>

1300) 

1301)     <p><a href="<page docs/bridges>">Bridge relays</a> (or "bridges" for short)
1302)     are <a href="<page docs/tor-doc-relay>">Tor relays</a> that aren't listed
1303)     in the main Tor directory. That means
1304)     that even an ISP or government trying to filter connections to the Tor
1305)     network probably won't be able to block all the bridges.
1306)     </p>

1307) 

1308)     <p>Being a normal relay vs being a bridge relay is almost the same
1309)     configuration: it's just a matter of whether your relay is listed
1310)     publically or not.
1311)     </p>

1312) 

1313)     <p>Right now, there are a small number of places in the world that filter

1314)     connections to the Tor network. So getting a lot of bridges running
1315)     right now is mostly a backup measure, a) in case the Tor network does
1316)     get blocked somewhere, and b) for people who want an extra layer of
1317)     security because they're worried somebody will recognize that it's a
1318)     public Tor relay IP address they're contacting.
1319)     </p>

1320) 

1321)     <p>So should you run a normal relay or bridge relay? If you have
1322)     lots of bandwidth, you should definitely run a normal relay &mdash;

1323)     bridge relays see very little use these days. If you're willing to

1324)     <a href="#ExitPolicies">be an exit</a>, you should definitely run a normal
1325)     relay, since we need more exits. If you can't be an exit and only have
1326)     a little bit of bandwidth, then flip a coin. Thanks for volunteering!
1327)     </p>

1328) 

1329)     <hr>

1330) 

1331) <a id="MultipleRelays"></a>
1332) <h3><a class="anchor" href="#MultipleRelays">I want to run more than one relay.</a></h3>

1333) 
1334) <p>
1335) Great. If you want to run several relays to donate more to the network,
1336) we're happy with that. But please don't run more than a few dozen on
1337) the same network, since part of the goal of the Tor network is dispersal
1338) and diversity.
1339) </p>
1340) 
1341) <p>
1342) If you do decide to run more than one relay, please set the "MyFamily"

1343) config option in the <a href="#torrc">torrc</a> of each relay, listing
1344) all the relays (comma-separated) that are under your control:

1345) </p>
1346) 
1347) <pre>
1348)     MyFamily $fingerprint1,$fingerprint2,$fingerprint3
1349) </pre>
1350) 
1351) <p>
1352) where each fingerprint is the 40 character identity fingerprint (without
1353) spaces). You can also list them by nickname, but fingerprint is safer. Be
1354) sure to prefix the digest strings with a dollar sign ('$') so that the
1355) digest is not confused with a nickname in the config file.
1356) </p>
1357) 
1358) <p>
1359) That way clients will know to avoid using more than one of your relays
1360) in a single circuit. You should set MyFamily if you have administrative
1361) control of the computers or of their network, even if they're not all in
1362) the same geographic location.
1363) </p>
1364) 
1365)     <hr>
1366) 

1367)     <a id="RelayMemory"></a>

1368)     <h3><a class="anchor" href="#RelayMemory">Why is my Tor relay using so much memory?</a></h3>

1369) 

1370)     <p>If your Tor relay is using more memory than you'd like, here are some
1371)     tips for reducing its footprint:
1372)     </p>

1373) 

1374)     <ol>
1375)     <li>If you're on Linux, you may be encountering memory fragmentation
1376)     bugs in glibc's malloc implementation. That is, when Tor releases memory
1377)     back to the system, the pieces of memory are fragmented so they're hard
1378)     to reuse. The Tor tarball ships with OpenBSD's malloc implementation,
1379)     which doesn't have as many fragmentation bugs (but the tradeoff is higher
1380)     CPU load). You can tell Tor to use this malloc implementation instead:
1381)     <tt>./configure --enable-openbsd-malloc</tt></li>

1382) 

1383)     <li>If you're running a fast relay, meaning you have many TLS connections
1384)     open, you are probably losing a lot of memory to OpenSSL's internal
1385)     buffers (38KB+ per socket). We've patched OpenSSL to <a
1386)     href="http://archives.seul.org/or/dev/Jun-2008/msg00001.html">release
1387)     unused buffer memory more aggressively</a>. If you update to OpenSSL
1388)     1.0.0-beta5, Tor's build process will automatically recognize and use
1389)     this feature.</li>

1390) 

1391)     <li>If you're running on Solaris, OpenBSD, NetBSD, or
1392)     old FreeBSD, Tor is probably forking separate processes
1393)     rather than using threads. Consider switching to a <a

1394)     href="<wikifaq>#WhydoesntmyWindowsorotherOSTorrelayrunwell">better

1395)     operating system</a>.</li>

1396) 

1397)     <li>If you still can't handle the memory load, consider reducing the
1398)     amount of bandwidth your relay advertises. Advertising less bandwidth
1399)     means you will attract fewer users, so your relay shouldn't grow
1400)     as large. See the <tt>MaxAdvertisedBandwidth</tt> option in the man
1401)     page.</li>

1402) 

1403)     </ol>

1404) 

1405)     <p>
1406)     All of this said, fast Tor relays do use a lot of ram. It is not unusual
1407)     for a fast exit relay to use 500-1000 MB of memory.
1408)     </p>

1409) 

1410)     <hr>

1411) 

1412)     <a id="WhyNotNamed"></a>

1413)     <h3><a class="anchor" href="#WhyNotNamed">Why is my Tor relay not named?</a></h3>

1414) 

1415)     <p>

1416)     We currently use these metrics to determine if your relay should be named:<br>

1417)     </p>
1418)     <ul>
1419)     <li>The name is not currently mapped to a different key. Existing mappings
1420)     are removed after 6 months of inactivity from a relay.</li>
1421)     <li>The relay must have been around for at least two weeks.</li>
1422)     <li>No other router may have wanted the same name in the past month.</li>
1423)     </ul>

1424) 

1425)     <hr>

1426) 

1427)     <a id="KeyManagement"></a>

1428)     <h3><a class="anchor" href="#KeyManagement">Tell me about all the keys Tor uses.</a></h3>

1429) 

1430)     <p>
1431)     Tor uses a variety of different keys, with three goals in mind: 1)
1432)     encryption to ensure privacy of data within the Tor network, 2)
1433)     authentication so clients know they're
1434)     talking to the relays they meant to talk to, and 3) signatures to make
1435)     sure all clients know the same set of relays.
1436)     </p>

1437) 

1438)     <p>
1439)     <b>Encryption</b>: first, all connections in Tor use TLS link encryption,
1440)     so observers can't look inside to see which circuit a given cell is
1441)     intended for. Further, the Tor client establishes an ephemeral encryption
1442)     key with each relay in the circuit, so only the exit relay can read
1443)     the cells. Both sides discard the circuit key when the circuit ends,
1444)     so logging traffic and then breaking into the relay to discover the key
1445)     won't work.
1446)     </p>

1447) 

1448)     <p>
1449)     <b>Authentication</b>:
1450)     Every Tor relay has a public decryption key called the "onion key".
1451)     When the Tor client establishes circuits, at each step it <a
1452)     href="<svnprojects>design-paper/tor-design.html#subsec:circuits">demands
1453)     that the Tor relay prove knowledge of its onion key</a>. That way
1454)     the first node in the path can't just spoof the rest of the path.
1455)     Each relay rotates its onion key once a week.
1456)     </p>

1457) 

1458)     <p>
1459)     <b>Coordination</b>:
1460)     How do clients know what the relays are, and how do they know that they
1461)     have the right keys for them? Each relay has a long-term public signing
1462)     key called the "identity key". Each directory authority additionally has a
1463)     "directory signing key". The directory authorities <a
1464)     href="<gitblob>doc/spec/dir-spec.txt">provide a signed list</a>
1465)     of all the known relays, and in that list are a set of certificates from
1466)     each relay (self-signed by their identity key) specifying their keys,
1467)     locations, exit policies, and so on. So unless the adversary can control
1468)     a threshold of the directory authorities, he can't trick the Tor client
1469)     into using other Tor relays.
1470)     </p>

1471) 

1472)     <p>
1473)     How do clients know what the directory authorities are? The Tor software
1474)     comes with a built-in list of location and public key for each directory
1475)     authority. So the only way to trick users into using a fake Tor network
1476)     is to give them a specially modified version of the software.
1477)     </p>

1478) 

1479)     <p>
1480)     How do users know they've got the right software? When we distribute
1481)     the source code or a package, we digitally sign it with <a
1482)     href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a
1483)     href="<page docs/verifying-signatures>">instructions
1484)     on how to check Tor's signatures</a>.
1485)     </p>

1486) 

1487)     <p>
1488)     In order to be certain that it's really signed by us, you need to have
1489)     met us in person and gotten a copy of our GPG key fingerprint, or you
1490)     need to know somebody who has. If you're concerned about an attack on
1491)     this level, we recommend you get involved with the security community
1492)     and start meeting people.
1493)     </p>

1494) 

1495)     <hr>

1496) 

1497) [https://www.torproject.org/docs/faq#EntryGuards Answer moved to our new FAQ page]
1498) 
1499) <a id="EntryGuards"></a>
1500) <h3><a class="anchor" href="#EntryGuards">What are Entry Guards?</a></h3>
1501) 
1502) <p>
1503) Tor (like all current practical low-latency anonymity designs) fails
1504) when the attacker can see both ends of the communications channel. For

1505) example, suppose the attacker controls or watches the Tor relay you choose
1506) to enter the network, and also controls or watches the website you visit. In

1507) this case, the research community knows no practical low-latency design
1508) that can reliably stop the attacker from correlating volume and timing
1509) information on the two sides.
1510) </p>
1511) 
1512) <p>
1513) So, what should we do? Suppose the attacker controls, or can observe,

1514) <i>C</i> relays. Suppose there are <i>N</i> relays total. If you select
1515) new entry and exit relays each time you use the network, the attacker
1516) will be able to correlate all traffic you send with probability
1517) <i>(c/n)<sup>2</sup></i>. But profiling is, for most users, as bad
1518) as being traced all the time: they want to do something often without
1519) an attacker noticing, and the attacker noticing once is as bad as the
1520) attacker noticing more often. Thus, choosing many random entries and exits
1521) gives the user no chance of escaping profiling by this kind of attacker.

1522) </p>
1523) 
1524) <p>
1525) The solution is "entry guards": each user selects a few relays at random

1526) to use as entry points, and uses only those relays for her first hop. If
1527) those relays are not controlled or observed, the attacker can't win,
1528) ever, and the user is secure. If those relays <i>are</i> observed or
1529) controlled by the attacker, the attacker sees a larger <i>fraction</i>
1530) of the user's traffic &mdash; but still the user is no more profiled than
1531) before. Thus, the user has some chance (on the order of <i>(n-c)/n</i>)
1532) of avoiding profiling, whereas she had none before.

1533) </p>
1534) 
1535) <p>

1536) You can read more at <a href="http://freehaven.net/anonbib/#wright02">An
1537) Analysis of the Degradation of Anonymous Protocols</a>, <a
1538) href="http://freehaven.net/anonbib/#wright03">Defending Anonymous
1539) Communication Against Passive Logging Attacks</a>, and especially
1540) <a href="http://freehaven.net/anonbib/#hs-attack06">Locating Hidden
1541) Servers</a>.

1542) </p>
1543) 
1544) <p>
1545) Restricting your entry nodes may also help against attackers who want
1546) to run a few Tor nodes and easily enumerate all of the Tor user IP
1547) addresses. (Even though they can't learn what destinations the users
1548) are talking to, they still might be able to do bad things with just a

1549) list of users.) However, that feature won't really become useful until
1550) we move to a "directory guard" design as well.

1551) </p>
1552) 
1553)     <hr>
1554) 

1555)     <a id="EverybodyARelay"></a>

1556)     <h3><a class="anchor" href="#EverybodyARelay">You should make every Tor user be a relay.</a></h3>

1557) 

1558)     <p>
1559)     Requiring every Tor user to be a relay would help with scaling the

1560)     network to handle all our users, and <a
1561)     href="<wikifaq>#DoIgetbetteranonymityifIrunarelay">running a Tor

1562)     relay may help your anonymity</a>. However, many Tor users cannot be good
1563)     relays &mdash; for example, some Tor clients operate from behind restrictive
1564)     firewalls, connect via modem, or otherwise aren't in a position where they
1565)     can relay traffic. Providing service to these clients is a critical
1566)     part of providing effective anonymity for everyone, since many Tor users
1567)     are subject to these or similar constraints and including these clients
1568)     increases the size of the anonymity set.
1569)     </p>

1570) 

1571)     <p>
1572)     That said, we do want to encourage Tor users to run relays, so what we
1573)     really want to do is simplify the process of setting up and maintaining
1574)     a relay. We've made a lot of progress with easy configuration in the past
1575)     few years: Vidalia has an easy relay configuration interface, and supports
1576)     uPnP too. Tor is good at automatically detecting whether it's reachable and
1577)     how much bandwidth it can offer.
1578)     </p>

1579) 

1580)     <p>
1581)     There are five steps we need to address before we can do this though:
1582)     </p>

1583) 

1584)     <p>
1585)     First, we need to make Tor stable as a relay on all common
1586)     operating systems. The main remaining platform is Windows,
1587)     and we plan to finally address that in 2009. See Section 4.1 of <a
1588)     href="https://www.torproject.org/press/2008-12-19-roadmap-press-release">our
1589)     development roadmap</a>.
1590)     </p>

1591) 

1592)     <p>
1593)     Second, we still need to get better at automatically estimating
1594)     the right amount of bandwidth to allow. See item #7 on the
1595)     <a href="<page getinvolved/volunteer>#Research">research section of the
1596)     volunteer page</a>: "Tor doesn't work very well when relays
1597)     have asymmetric bandwidth (e.g. cable or DSL)". It might be that <a

1598)     href="<page docs/faq>#TransportIPnotTCP">switching

1599)     to UDP transport</a> is the simplest answer here &mdash; which alas is
1600)     not a very simple answer at all.
1601)     </p>

1602) 

1603)     <p>
1604)     Third, we need to work on scalability, both of the network (how to
1605)     stop requiring that all Tor relays be able to connect to all Tor
1606)     relays) and of the directory (how to stop requiring that all Tor
1607)     users know about all Tor relays). Changes like this can have large
1608)     impact on potential and actual anonymity. See Section 5 of the <a
1609)     href="<svnprojects>design-paper/challenges.pdf">Challenges</a> paper
1610)     for details. Again, UDP transport would help here.
1611)     </p>

1612) 

1613)     <p>
1614)     Fourth, we need to better understand the risks from
1615)     letting the attacker send traffic through your relay while
1616)     you're also initiating your own anonymized traffic. <a
1617)     href="http://freehaven.net/anonbib/#back01">Three</a> <a
1618)     href="http://freehaven.net/anonbib/#clog-the-queue">different</a>
1619)     <a href="http://freehaven.net/anonbib/#torta05">research</a> papers
1620)     describe ways to identify the relays in a circuit by running traffic
1621)     through candidate relays and looking for dips in the traffic while the
1622)     circuit is active. These clogging attacks are not that scary in the Tor
1623)     context so long as relays are never clients too. But if we're trying to
1624)     encourage more clients to turn on relay functionality too (whether as
1625)     <a href="<page docs/bridges>">bridge relays</a> or as normal relays), then
1626)     we need to understand this threat better and learn how to mitigate it.
1627)     </p>

1628) 

1629)     <p>
1630)     Fifth, we might need some sort of incentive scheme to encourage people
1631)     to relay traffic for others, and/or to become exit nodes. Here are our

1632)     <a href="<blog>two-incentive-designs-tor">current

1633)     thoughts on Tor incentives</a>.
1634)     </p>

1635) 

1636)     <p>
1637)     Please help on all of these!
1638)     </p>

1639) 

1640) <hr>
1641) 
1642) <a id="TransportIPnotTCP"></a>

1643) <h3><a class="anchor" href="#TransportIPnotTCP">You should transport all IP packets, not just TCP packets.</a></h3>

1644) 
1645) <p>

1646) This would be handy, because it would make Tor better able to handle
1647) new protocols like VoIP, it could solve the whole need to socksify
1648) applications, and it would solve the fact that exit relays need to
1649) allocate a lot of file descriptors to hold open all the exit connections.

1650) </p>
1651) 
1652) <p>

1653) We're heading in this direction: see <a
1654) href="https://trac.torproject.org/projects/tor/ticket/1855">this trac
1655) ticket</a> for directions we should investigate. Some of the hard
1656) problems are:

1657) </p>
1658) 

1659) <li>IP packets reveal OS characteristics. We would still need to do
1660) IP-level packet normalization, to stop things like TCP fingerprinting
1661) attacks. Given the diversity and complexity of TCP stacks, along with <a

1662) href="<wikifaq>#DoesTorresistremotephysicaldevicefingerprinting">device

1663) fingerprinting attacks</a>, it looks like our best bet is shipping our
1664) own user-space TCP stack.

1665) </li>

1666) <li>Application-level streams still need scrubbing. We will still need
1667) user-side applications like Torbutton. So it won't become just a matter
1668) of capturing packets and anonymizing them at the IP layer.

1669) </li>
1670) <li>Certain protocols will still leak information. For example, we must
1671) rewrite DNS requests so they are delivered to an unlinkable DNS server
1672) rather than the DNS server at a user's ISP; thus, we must understand
1673) the protocols we are transporting.
1674) </li>
1675) <li><a
1676) href="http://crypto.stanford.edu/~nagendra/projects/dtls/dtls.html">DTLS</a>

1677) (datagram TLS) basically has no users, and IPsec sure is big. Once we've
1678) picked a transport mechanism, we need to design a new end-to-end Tor
1679) protocol for avoiding tagging attacks and other potential anonymity and
1680) integrity issues now that we allow drops, resends, et cetera.

1681) </li>
1682) <li>Exit policies for arbitrary IP packets mean building a secure
1683) IDS. Our node operators tell us that exit policies are one of the main
1684) reasons they're willing to run Tor. Adding an Intrusion Detection System
1685) to handle exit policies would increase the security complexity of Tor,
1686) and would likely not work anyway, as evidenced by the entire field of IDS
1687) and counter-IDS papers. Many potential abuse issues are resolved by the
1688) fact that Tor only transports valid TCP streams (as opposed to arbitrary
1689) IP including malformed packets and IP floods), so exit policies become
1690) even <i>more</i> important as we become able to transport IP packets. We
1691) also need to compactly describe exit policies in the Tor directory,
1692) so clients can predict which nodes will allow their packets to exit &mdash;
1693) and clients need to predict all the packets they will want to send in
1694) a session before picking their exit node!
1695) </li>

1696) <li>The Tor-internal name spaces would need to be redesigned. We support
1697) hidden service ".onion" addresses by intercepting the addresses when
1698) they are passed to the Tor client. Doing so at the IP level will require
1699) a more complex interface between Tor and the local DNS resolver.

1700) </li>
1701) </ol>
1702) 

1703)     <hr>

1704) 

1705)     <a id="Criminals"></a>

1706)     <h3><a class="anchor" href="#Criminals">Doesn't Tor enable criminals to do bad things?</a></h3>

1707) 

1708)     <p>
1709)     For the answer to this question and others, please see our <a
1710)     href="<page docs/faq-abuse>">Tor Abuse FAQ</a>.
1711)     </p>

1712) 

1713)     <hr>

1714) 

1715)     <a id="RespondISP"></a>

1716)     <h3><a class="anchor" href="#RespondISP">How do I respond to my ISP about my exit relay?</a></h3>

1717) 

1718)     <p>
1719)     A collection of templates for successfully responding to ISPs is <a

1720)     href="<wiki>TheOnionRouter/TorAbuseTemplates">collected

1721)     here</a>.
1722)     </p>

1723) 

1724)     <hr>

1725) 

1726)   </div>
1727)   <!-- END MAINCOL -->
1728)   <div id = "sidecol">
1729) #include "side.wmi"
1730) #include "info.wmi"
1731)   </div>
1732)   <!-- END SIDECOL -->
1733) </div>
1734) <!-- END CONTENT -->