Changes between Version 15 and Version 16 of doc/FAQUnanswered


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Timestamp:
Apr 23, 2010, 4:48:47 AM (9 years ago)
Author:
trac
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  • doc/FAQUnanswered

    v15 v16  
    11This is a list of questions people wish were answered in the [:../TorFAQ]; please add some more.  Better yet answer one and move it to [:../TorFAQ].  Finally you can vote for a question to be answered by incrementing the number after the question in parens.
    22
    3 Can Tor be used in a network that has NO DEFAULT ROUTE?  The only access method from this network is to use a traditional proxy.  Is there a way to chain proxies so that TOR requests are sent outbound via the standard proxy? (votes: 1)
    4 
    5 I can't access hidden servers? Why? (votes: 1)
    6 
    7 Do I need both Tor AND Privoxy to browse hidden sites? Why? (votes: 4)
    8 
    9 Who's doing this? (votes: 1)
    10 
    11 Can I help? (votes: 2)
    12 
    13 I've got a bug, now what? (votes: 2)
    14 
    15 So I'm totally anonymous if I use Tor? (votes: 1)
    16 
    17 Where can I learn more about anonymity? (votes: 1)
    18 
    19 What attacks remain against onion routing? (votes: 1)
    20 
    21 What projects are comparable? (votes: 1)
    22 
    23 What's Onion Routing? (votes: 1)
    24 
    25 How does Tor relate to the Freedom Project? (votes: 1)
    26 
    27 Protocol and application support - http? ftp? udp? socks? mozilla? (votes: 1)
    28 
    29 My system clock is behind 3 days and I don't have permission to change it.  Therefore all the certificates are invalid.  Is there a runtime option to skew the time? (votes: 1)
    30 
    31 Is there any way to forward an ident response via TOR so that the ident doesn't come back as whatever the end server wants, but your normal response? (votes: 1)
     3'''Please do not report bugs here; instead, use the [http://bugs.noreply.org/flyspray/index.php?tasks=all&project=4 bug tracker].'''  Soon, we'll designate one of the proposed bug servers as official, and you'll be able to post bugs there too.
     4
     5Also, this is '''not the place''' for random ''it doesn't work'' or ''how do I do foo'' questions.  Support questions are really better asked and answered on the
     6[http://archives.seul.org/or/talk/ or-talk mailinglist].  Also, always a good read: [http://www.catb.org/~esr/faqs/smart-questions.html How To Ask Questions The Smart Way].
     7
     8= Unanswered FAQ Questions =
     9
     10'''If an attacker has access to past logs of ISP and any given visted site, does the prng of the tor client allow the attacker to guess which circuit it used next?'''
     11
     12Tor uses cryptographically strong random numbers provided by OpenSSL when choosing nodes to use in a circuit. How OpenSSL implements this is operating system specific. If there's a weakness in Tor's method of choosing nodes, it probably isn't in the random number generator.
     13
     14*** Hmm, if the prng is deterministic, and you can narrow one result of calling it by knowing what host was chosen, can you, knowing the algorithm, however good it is, thereby narrow the result of the next call to it?  This question might be a bit ignorant; for example the prng might use other data on the client computer instead of following an algorithm to return the next item.
     15
     16*** Thanks for your comments, BTW, as a lot of us are wondering the answers to these FAQU.
     17
     18'''Is there a signal i can send the tor client to tell it to switch circuits immediately?'''
     19
     20You can connect to Tor's control port and send "authenticateCRLFsignal newnymCRLF" where CRLF is a carriage return line feed pair.
     21
     22'''Why does Firefox/Privoxy/Tor return Privoxy 404 pages so frequently -- almost every time -- when properly configured, even on sites like google.com?  How to mitigate?  The tor process is running fine.'''
     23(Votes: 2)
     24
     25The first problem is that Privoxy doesn't retry in case of
     26DNS errors. It shows the 404 no such domain message right away.
     27The second problem is that some browser cache Privoxy's error
     28messages and Firefox is one of them.
     29
     30The Privoxy patch described at
     31http://www.fabiankeil.de/sourcecode/privoxy/
     32lets Privoxy retry in case of connection problems
     33and makes sure, the browser doesn't reuse a cached
     34error message.
     35
     36'''For that matter, why is DNS the main failure mode?  Who is timing out and why?  Can Tor (1) change the timeout, (2) deprecate bad servers, or (3) cache DNS locally so it doesn't have to make a long, slow, failure-prone DNS lookup every time?'''
     37
     38You should be sending hostnames to Tor over SOCKS4a or SOCKS5. In that case, the Tor exit node will resolve the hostname before making a connection for you. Unless the exit node is misconfigured, there shouldn't be a problem with DNS resolves timing out.
     39
     40*** Actually, for me this happens most of the time.  I am sending through Privoxy, and tried both sockses.  So why would I be hitting so many exit nodes that FREQUENTLY time out on DNS?  Firefox 1.5, most recent stable Tor.
     41
     42'''Is the reason that gmail rarely works: gmail, tor, privoxy, firefox, your own bandwidth/latency, tor's bw/latency, or some combination?  Is it fixable?'''
     43
     44*** For Gmail for me, it's even worse; I have to try 5 or 6 times before I get a page.
     45
     46'''Why is the argument against more than 3 hops that both-ends attacks are the enemy?  Wouldn't it be better to have more than 3 if the enemy cannot mount a both-ends attack?'''
     47
     48This is two questions, really.
     49
     50To understand it better, think from the perspective of an attacker. They have a choice: they can make a both-ends attack, an attack comprising the hops and both.
     51
     52Now, at this point you need to think what attacker you are trying to defend against. The NSA? Sorry, your screwed - find something else. A big company? Some rogue ISP's? Ok, now that's something that Tor may be able to defend against...
     53
     54Now, what information are you - the attacker - trying to find? Who is talking to who? Content of some transmissions? Both?
     55
     56Well, for finding content of transmissions your best way is to just listen in on some exit nodes.. or create some malicious ones. That's not the attack threat we're trying to defend against, then.
     57For finding who is talking to who? Ok, let's say that's what we're trying to find out.
     58
     59From this perspective, what is needed to mount a both-ends attack? Listening on both ends. If there is some mitigation technique used - like random timing - compromising those both ends could come in handy (at this point, more hops would really be useful). But there isn't - AFAIK - and so we shall suppose that listening on both ends is enough.
     60
     61Now, what is the alternative option? Listening to all the hops AS WELL? Oh dear, that's a little harder.. and what does it bring us? Well, we can get slightly more accurate results - maybe - as we can more closely correlate. This, of course, gets yet better if we compromise some of those hops.
     62
     63The key word here is slightly. Provided the number of hops is a constant - so you can get a reasonably accurate latency estimate - then, over a longer enough period of time, you will be able to correlate and get your results.
     64
     65The key word here is slightly. Provided the number of hops is a constant - so you can get a reasonably accurate latency estimate - then, over a longer enough period of time, you will be able to correlate and get your results.
     66
     67So, yes, the hops will make it slightly more secure. But only slightly. And yes, in some cases, it may be really useful.. but in those cases, you probably should be using something with much stronger anonymity than tor (if someone knowing what your saying is unacceptable, don't use tor.. not, at any rate, on it's own).
     68
     69Now, then, what are the disadvantages to more hops? More bandwidth is used. Latency is increased.
     70
     71Despite this, it's possible that having number of hops as an easily configurable option is not a bad idea... I would guess that there is an excess of middle-man nodes with the recent draconian laws in some parts of the Western oh so free world that make people interested in privacy yet at the same time too scared to actually stick their neck out. In this case, Tor as a network would likely not lose much by doing that.
     72
     73'''How can I be sure that sending DNS through tor doesn't get spoofed sites?'''
     74
     75Use a method for authenticating the site you want to connect to, such as ensuring an SSL certificate is associated with the domain name and signed by a trusted authority, or verifying an SSH fingerprint out-of-band. Hidden services on Tor are not subject to this problem because their .onion names are self-authenticating as hashes of their public keys.
     76
     77'''How does tor relate to ipv6 and how should typical applications handle ipv6 if they use tor (or tor via Privoxy)?'''
     78
     79
     80---- /!\ '''Edit conflict - other version:''' ----
     81Like a dog talking to a quasar... I never was good with similes.
     82
     83Tor carries TCP data (does it? Maybe it just carries some data that is then transported over TCP... I know, for instance, that it also contains IP and port... TCP doesn't) over another layer - currently IPv4. There is work to make Tor work with IPV6, but I am not aware of it being completed.
     84
     85As for how an application would interface with it -- depends. It could use SOCKS; in that case, I think it would have to use SOCKS5 in the event of addressing IPv6 (rather than domains). This could be hacked around by adding a .ipv6 domain - nasty.
     86
     87Privoxy? Same as currently, if it handles it..
     88
     89'''What version of libevent should I be using?'''
     90
     91the latest.  at least 1.1
     92
     93'''How to use Tor in squid? For using Tor on a network using Squid as proxy, for example...'''
     94
     95'''How to use Tor with PF (Packet Filter, found in OpenBSD, NetBSD, DragonFlyBSD and FreeBSD)?'''
     96
     97
     98
     99'''How does Tor work with tabbed browsing, say with Firefox?  Do these requests all follow the same circuit through the Tor network? Can an eavesdropper link a user across all sites opened simultaneously in tabs?'''
     100
     101ver 1.5 Works fine for me, I use No-Script Plugin to help be even safer. Anyone else have a problem with Firefox. Weither the request follow the same curcuit is out of my realm. My surfing experience is good to just fine. ProBastion
     102
     103They will most likely all use the same circuit.  http://wiki.noreply.org/noreply/TheOnionRouter/TorFAQ#ChangePaths
     104
     105'''When using the Tor/Privoxy configuration, is there an easy way to switch Privoxy between using Tor and using the standard connection (to allow for secure browsing, but also allowing a more direct connection when needed to keep large file transfers from bogging down in Tor)?'''
     106
     107It is possible to do this - however, it involves manually editing the config files for Privoxy, as well as possessing administrative/sudo access for your machine.  Also, once Privoxy is toggled to use a direct connection instead of Tor, your IP will be visible, and Privoxy does n ot provide as much security alone as it does with Tor.
     108
     109If you wish to do this, you will need to make a copy of your Privoxy config file, and comment out the line that causes Privoxy to use the Tor service.  Once you have done this, to switch over, just stop Privoxy, swap the config files, and restart it. You can also automate the process with a very simple shell script - an OSX version including sample config files and a shell script can be found [http://idlecircuits.com/privoxyswitcher.zip here], and the script can be used as an example for other *nix systems.
     110
     111'''Tor works fine for POP3 email. But, Whistle-blowers and others who need anonymous
     112political free speech must have reliable SSL smtp email services. How can Tor be used
     113by them when *all* smtp ports, eg, ports 25, 465, 587, etc are now blocked by Tor exit
     114servers? Blocking port 25 helps to defeat spammers, but the smtp SSL/TLS ports are not
     115generally not used by them. Is there any solution with Tor to help the free speech folk
     116and others who need to use secure, reliable smtp services? (votes: 6)'''
     117
     118
     119'''How would one route his email through Tor? My email client (Microsoft Entourage for Mac OS X) has support for SOCKS and TUNNEL proxies, but setting my mail proxy for SOCKS 127.0.0.1 port 9050 or 8118 both produces errors when trying to proxy to SSL SMTP servers via port 25. What am I missing here? Also, setting this proxy doesn't seem to affect incoming POP3 SSL mail, but only affects outgoing mail, albeit without success. A little guidance on how to configure POP3 email clients to use Tor would be much appreciated!'''
     120
     121An attempt to answer the smtp email questions above: The Tor exit servers are likely blocking smtp port 25 in an attempt to stop spammers. Some Tor exit servers *sporadically* allow TLS/SSL smtp over ports 587, 995, etc., but at the present time there is no consistent, reliable policy or service.  (Also your remote email provider must support the use of alternate smtp ports such as those above.) You could use the remailer network but there can be reliability problems with them. Of greater importance is the fact that the remailer network does NOT accept large messages, e.g., scanned documents which can easily be many MB each. If you are a whistleblower or other person who needs to send large documents quickly and anonymously, you have a real problem. At this moment, Tor is not the answer.
     122
     123
     124'''Can Tor be used in a network that has NO DEFAULT ROUTE?  The only access method from this network is to use a traditional proxy.  Is there a way to chain proxies so that TOR requests are sent outbound via the standard proxy? (votes: 1)'''
     125
     126Maybe. If you can get some routes for the Tor servers, then that of course is great.... assuming it must go through the proxy, however, it will need to support sending Tor requests.
     127
     128Assuming it does.. AFAIK, Tor doesn't have built-in support directly for this. So, you'll have to make it look to Tor like it really can connect .. err.. normally.
     129
     130I can see several ways of doing this.
     131
     132You could overload the network commands and have them actually connect to the proxy.. that's easy but a hack.
     133
     134You could try doing something with OpenVPN; personally, I don't have any experience with it... but I'm guessing you could do something neat with it (I remember someone setting up an OpenVPN with Tor being used to route things.. so it supports socks, I think, in some way. In that case, assuming the proxy is socks... all done :) Oterwise, you could write an interface to make it socks).
     135
     136
     137'''Can I help? (votes: 2)'''
     138
     139http://tor.eff.org/volunteer.html
     140
     141'''I've got a bug, now what? (votes: 2)'''
     142
     143'''How does Tor relate to the Freedom Project? (votes: 1)'''
     144
     145'''Is there any way to forward an ident response via TOR so that the ident doesn't come back as whatever the end server wants, but your normal response? (votes: 1)'''
     146
     147no.
     148
     149'''How can I uninstall tor? (votes: 1)'''
     150
     151
     152
     153
     154'''I have legal questions about running Tor. Is there anybody I can contact? ( votes: 1)'''
     155
     156Added 2.1.06- The Developers do not provide Legal advice. period! Over at the Tor Legal FAQ there is a written section by EFF lawyers. It aims to give you an overview of some of the legal issues that arise from the Tor project. Read the Disclaimer. The FAQ does provide a dialougue on the legalality & posssible scenarios of operating a Tor Server. They also provide you with contact information to a EFF Lawyer. The Tor FAQ also provides a links to an Abuse FAQ, & Tor Technical FAQ Wiki.  See this address for more information along these lines. http://tor.eff.org/faq.html
     157
     158
     159'''If I set up Tor to only act as a router node (reject *:* in torrc) can I still be a contact point for hidden services?'''
     160
     161yes.
     162
     163'''Can anonymity be broken if all Tor servers in the chain are compromised/malicious and so are keeping logs to trace the chain?'''
     164
     165
     166---- /!\ '''Edit conflict - other version:''' ----
     167
     168---- /!\ '''Edit conflict - your version:''' ----
     169Yes. Indeed, if all the servers in a circuit are compromised then they need not even be communicated with.. the entry node can decipher for all the (possibly even non-existent) nodes. In order to maintain a superficial view of anonymity, it would probably be good to forward it to the exit server however.
     170
     171---- /!\ '''End of edit conflict''' ----
     172
     173'''What system resources does a TOR server use?  The FAQ already dicusses memory a bit.  What about CPU?  Encryption is CPU-intensive.  Specific question I'd like answered: I'll be setting up a TOR node bandwidth-limited to about 256kbps (half my upstream bandwidth).  Will an old 300MHz G3 Mac easily handle this, or will a faster processor be needed? How 'bout a P90?  Presumably, TOR's disk usage and I/O is minimal.''' (Votes: 1)
     174
     175
     176== Cannot resolve Foo.onion/Resolve requests to hidden services not allowed ==
     177
     178tor-resolve doesnt seem to work, i get this:
     179{{{connection_ap_handshake_process_socks():  Resolve requests to hidden services not allowed. Failing.}}}
     180from the copy of tor running locally. Please help!
     181
     182(from original questioner: thank you.  I got the mistaken idea that this would work because it is suggested in the 'how to torrify an application' article on this wiki.  It makes more sense now.  Someone who understands better might want to upate that document)
     183
     184This question is answered; see 'How Do I Access Tor Hidden Servers.'  You get this message when you try to use tor-resolve to resolve the address of a hidden service.  But hidden services are ''hidden'' - they don't *have* an IP address you can use.  Instead, you need to pass the hostnames to Tor directly.
     185
     186== Clock Skew ==
     187My system clock is behind 3 days and I don't have permission to change it.
     188Therefore all the certificates are invalid.
     189Is there a runtime option to skew the time?
     190
     191This should not a problem as of 0.0.9pre6.
     192
     193== Does not connect to port xyz ==
     194All of a sudden, Tor will no longer let me connect to my distant smtp server.
     195The smtp port used is 587 and the connection is SSL. Why is this now happening?
     196
     197587 isn't in the default exit policy. The tor node known as bollox had an
     198accept everything policy so your port 587 requests would have always gone through that.
     199As bollox is no longer around there are no exit nodes that allow port 587. If you
     200control this smtp server, try changing it's port number to something over 1024.
     201
     202== Debian and how to use the package management system ==
     203
     204Also would recomend posting default config files for debian online since apt will not reinstall them if they are removed (/etc/init.d/tor and /etc/torrc for example)
     205
     206'''Answer''': RTFM.  dpkg differentiatea between two states of package removal.
     207There's ''remove'', which will just remove the normal files a package comes with,
     208and there's ''purge'', which will remove configuration files also.  Changes to your
     209configuration (like you removing them) are kept over a remove/install cycle.  If
     210you want them to installed anyway, you should install with
     211{{dpkg --force-confmiss --install tor...deb}}
     212or just purge tor (which will delete /var/lib/tor with its keys if you are a server!), and then install it again.
     213
     214== . ==
     215After uninstalling everything then reinstalling on debian (using apt-get of course) nothing loads in a browser or anything, eventually a 503 will come up.  Tor is running and privoxy is running, both correctly configured(I think).  If this is a configuration problem, where can I find more information about configuration in debian?
     216
     217'''Answer''': Duh.  Have you checked out {{{/etc/tor}}}?  What about {{{/var/log/tor}}} and {{{/usr/share/doc/tor}}}?  Why do you think it would be any different than on other OSs?
     218
     219== Privoxy config ==
     220
     221Similar to above, on brand new install of sarge with tor and privoxy browser, gaim, etc will spend a long time trying to connect eventually failing with 503, if tor is not running a 503 is instant.
     222
     223'''Answer''': Privoxy by default does not allow CONNECT to ports other than 443.  Fix your privoxy config.
     224
     225{{{weasel@galaxy:/etc/privoxy$ grep limit.con default.action | grep -v '^#'
     226+limit-connect{1-} \
     227}}}
     228
     229(If someone writes a proper question, this might actually go into the FAQ)
     230
     231== How To Configure One's Web Browser So Tor Is Only Used For Some Sites But Not Others ==
     232'''Question''': Can I configure Tor so it will only use the onion routing network for some sites but not others?
     233
     234'''Answer''': No, Tor itself is all or nothing, a request either goes through it or it does not.
     235
     236Privoxy is also all or nothing in the sense that if a request has made it to Privoxy then either Privoxy is set up to go through Tor or it's not, there does not appear to be a way to program Privoxy so it will use Tor for some requests but not others.
     237
     238There is a script for OS X, available [http://idlecircuits.com/privoxyswitcher.zip here], that will make it such that Privoxy never uses Tor but this is an 'all or nothing' mechanism. The script will either start Privoxy such that all requests go through Tor or no requests go through Tor.
     239
     240There is one mechanism that is at least useful for web browsers, it's called a pac file. It was invented by Netscape, the original documentation is available [http://wp.netscape.com/eng/mozilla/2.0/relnotes/demo/proxy-live.html here], but it is now supported by all major browsers. One can use a pac file to program the browser to use the Privoxy proxy for certain requests but not others. For example, the following pac file will cause all requests to Google or to the special Privoxy configuration addresses to be sent to Privoxy (and hence Tor) but will allow other other requests to go out without Privoxy/Tor being used:
     241
     242{{{
     243function FindProxyForURL(url, host) {
     244        if (shExpMatch(host,"*google.*") ||
     245            shExpMatch(host,"config.privoxy.org") ||
     246            shExpMatch(host,"p.p"))
     247                return "PROXY 127.0.0.1:8118";
     248        return "DIRECT";
     249}
     250}}}
     251
     252To configure Firefox to use a pac file under OS X go to Firefox->preferences->General->Connection Settings...->Automatic proxy configuration URL:. Enter in a URL (you can use file:// to point to a local file) that points to your pac file and click reload.
     253
     254It's probably not a good idea to use pac files with Safari on OS X as its pac file support seems to be more than a little buggy.
     255
     256The pac file solution is far from ideal. It won't apply to non-web access and it runs into problems such as the bad pac file support in Safari. It also is not secure. A malicious website can trivially bypass this mechanism by placing pictures on its website from domains that it controls but are unlikely to be on a 'black list'. Therefore this mechanism is only useful with Websites that are not in and of themselves malicious but rather, due to their nature, can collect substantial amounts of personal information that one would rather not release. A search engine is a classic example. If and when privacy is a critical concern then the only proper course of action is to get rid of the pac file and instead configure all connections to go through privoxy/tor.
     257
     258
     259
     260'''I've been banned as an contributor at Slashdot! I run a Win 2003 server, with a decent pipe. They said that if I blocked them they would let me contribute again. I did an edit on my torrc file by adding a line:
     261
     262reject *:66.35.250.150 (which is Slashdot.com by using an online DNS 'dig' page
     263
     264I add the above right after my default exit. Which was just this:
     265#ExitPolicy accept *:6660-6667,reject *:* # allow irc ports but no more
     266ExitPolicy accept *:119 # accept nntp as well as default exit policy
     267#ExitPolicy reject *:* # middleman only -- no exits allowed
     268reject *:66.35.250.15
     269
     270Is this the way to do this, and just block Slashdot? Any help would be helpful, I've googled, did the tor.eff site, etc. But I'm not real UNIX centric (though thats changing) so just wanted to run it by some community persons. '''
     271
     272
     273'''What is the significance of the changes in the Bittorrent Torify HOWTO?'''
     274
     275I noticed I can't connect with btdownloadcurses through proxychains any more. Looking for answers, I went back to the Torify HOWTO and noticed that it had been altered. Where it used to explain about using proxychains to run bittorrent through TOR, which I used successfully for over a year, it now says that Bittorrent "uses a mechanism similar to TOR." That was certainly news to me. How is the generic Bittorrent client technically similar to TOR in any way? I have always heard that the generic Bittorrent client offers almost no anonimity at all. Now I'm reading that Bittorrent and TOR are practically the same thing and it would be redundant to use them together. Seems a bit curious.
     276
     277As a sub-question, let me just ask directly: Is it true that Bittorrent through TOR via proxychains no longer works?
     278
     279Also, the same page now mentions a technique of using Tor to connect to the tracker only, as opposed to the peers, by including the line --tracker-proxy 127.0.0.1:8118: on the command line. However, I see no documentation of this option in the btdownloadcurses client and I find it a bit suspicious that the format of this option uses a hyphen rather than an underscore as all the other command line options that are listed as being compatible with btdownloadcurses use underscores to separate options with two words such as --check_hashes <arg> or --report_hash_failures <arg>. Is that a typo or an undocumented option that just happens to deviate from the naming convetion of all the other options?
     280
     281'''How do you start and stop Tor and Privoxy in OS X (Panther) if you did not install the startup script? (needs to be added to installation instructions)'''
     282
     283'''How do you configure the proxy if you are using Tor and Privoxy in OS X (Panther) with a router's firewall and the built-in OS X firewall, e.g. when using Wi-fi to connect to wireless router?  (needs to be added to installation instructions)'''
     284
     285'''What to do (troubleshooting) if browsing slows to a crawl with Tor and Privoxy running in OS X?'''
     286----
     287CategoryHomepage