Changes between Version 67 and Version 68 of doc/FAQUnanswered


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

    v67 v68  
    88= Unanswered FAQ Questions =
    99
    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?'''
     101) '''Hidden services are currently very vulnerable to attacks by web hosts who come to suspect a machine in their network is being used for Tor. Since they can power cycle the server in question (and likely blame it on technical difficulties without arousing suspicion) they can make an unambiguous identification of a hidden service host.
     11This could be prevented if the directory servers supported more than one provider for a hidden service and so could direct requests away from a non-responsive server (there may be other solutions). Of course this could also help provide more reliable hidden services in general. Is there any chance of this getting implemented in the near future?'''
     12
     132) '''Why do I keep getting messages telling me that my clock has just jumped ahead and that my circuits will be assumed broken? ''(eg.
     14Oct 02 10:14:53.619 [notice] Your clock just jumped 1056 seconds forward; assuming established circuits no longer work.'') I've got a cron job to sync the time every eight hours and it's never out by more than a second.'''
     15
     16-- On my system, this happens when Vidalia gets into trouble. It seems that when tor and V communicate, tor can wind up waiting for V to respond, or for the V process to be killed.
     17
     18
     193)'''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?'''
    1120
    1221Tor 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.
     
    4958*** For Gmail for me, it's even worse; I have to try 5 or 6 times before I get a page.
    5059
     60-- I know that improvements to DNS handling are due in 1.2.x-final (see bug #364).
     61
    5162'''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?'''
    5263
     
    8495'''How does tor relate to ipv6 and how should typical applications handle ipv6 if they use tor (or tor via Privoxy)?'''
    8596
    86 
    87 ---- /!\ '''Edit conflict - other version:''' ----
    8897Like a dog talking to a quasar... I never was good with similes.
    8998
     
    115124
    116125If 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.
     126
     127-- In fact, there is no need to stop/restart privoxy. On my system, I have the privoxy config file owned by me, so I can edit it directly. Changing between tor and no-tor is as simple as editing one line.
     128
     129Here's the relevant lines from my privoxy config file:
     130{{{
     131# Tor:
     132#
     133## forward-socks4a / localhost:9050 . 
     134forward-socks4a .onion localhost:9050 .
     135
     136# Do not torrify these (high volume/speed concerns, as well as PhP BBS
     137# systems that consider a changed IP to be a new login.):
     138forward .blood-bowl.net .
     139forward .qemu-forum.ipi.fi .
     140}}}
     141The line with "##" on it is the line to toggle. Remove those to enable tor, add them to disable tor.
     142
     143NB: Every PHP BBS site I've seen will consider you to have logged out and relogged in if your IP address -- as seen by the PHP site -- changes. This means that if tor ever switches circuits and changes exit node, those sites will reset your "unread messages". I have not been able to find a decent way to solve this with TrackHostExits, given that vidalia will overwrite my tor config occasionally (and has no support for adding these internally, so I have two editors trying to change the tor config), the length of time needed to track varies from 30 minutes at some (forced logout after thirty minutes of idle time) to 24 hours at others, dealing with the occasional dead exit node (and then you need to use a new exit node earlier), etc. And, my list of exception sites is currently 26 lines long.
    117144
    118145'''Tor works fine for POP3 email. But, Whistle-blowers and others who need anonymous
     
    148175'''I've got a bug, now what? (votes: 2)'''
    149176
     1771) Make sure that it is an actual bug with Tor, and not with Privoxy, Vidalia, your OS, etc.
     178
     1792) Check to see if it's an unreported bug (at the [http://bugs.noreply.org/flyspray/index.php?tasks=all&project=4 bug tracker]).
     180
     1812a) If it's already reported, then see if you can add anymore information (in the comments of that bug) that will help the developers duplicate it and/or track it down. (This step requires you to login to your account at flyspray, or to create a new account.)
     182
     1832b) If it's not already reported, then start a new report with as much relevant information as possible. Relevant information includes tor version number, OS used, and any relevant lines from the log. (This step requires you to login to your account at flyspray, or to create a new account.)
     184
    150185'''How does Tor relate to the Freedom Project? (votes: 1)'''
    151186
     
    172207Yes. 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.
    173208
    174 '''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)
     209'''What system resources does a TOR server use?  The FAQ already discusses 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)
    175210
    176211
    177212== Cannot resolve Foo.onion/Resolve requests to hidden services not allowed ==
    178213
    179 tor-resolve doesnt seem to work, i get this:
     214tor-resolve doesn't seem to work, i get this:
    180215{{{connection_ap_handshake_process_socks():  Resolve requests to hidden services not allowed. Failing.}}}
    181216from the copy of tor running locally. Please help!
    182217
    183 (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)
    184 
    185 This 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.
     218(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 update that document)
     219
     220This question is answered; see [:../TorFAQ#AccessHiddenService: 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.
    186221
    187222== Clock Skew ==
     
    235270'''Answer''': No, Tor itself is all or nothing, a request either goes through it or it does not.
    236271
     272For privoxy, however, you can use forward lines to make some hosts use tor, some use the normal system, and others use whatever other proxy you want.
     273{{{
     274forward-socks4a / localhost:9050 .
     275forward-socks4a .onion localhost:9050 .
     276
     277# Do not torrify these (high volume/speed concerns, as well as PhP BBS
     278# systems that consider a changed IP to be a new login.):
     279forward .blood-bowl.net .
     280forward .youtube.com .
     281forward .qemu-forum.ipi.fi .
     282forward .vidalia-project.net .
     283}}}
     284
     285Here is an example. This uses privoxy for all sites (ad filtering, etc), and then specifies that some sites go through tor, and some do not.
     286
     287Privoxy uses the LAST match. So, the first line says "Use Tor by default". It can be turned off. The second line says "Always use Tor for .onion". After that are lines for "Never use Tor for these".
     288
     289Older, wrong information:
    237290Privoxy 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.
    238291
     
    276329Anyway, you should probably block their IP rather than ports that happen to be theirs ;) (which don't exist - surprised tor let you do that..)
    277330
     331To clarify, the syntax is ''ip-address'':''port'', so reject *:66.35.250.15 is blocking all requests to exit port number 66.35.250.15 at all ip addresses. This obviously doesn't make sense. What you want to do is reject 66.35.250.15:* to block all slashdot traffic.
     332
     333Also, the fourth line of this page reads: ''this is '''not the place''' for random it doesn't work or how do I do foo questions.''
    278334
    279335'''What is the significance of the changes in the Bittorrent Torify HOWTO?'''
    280336
    281 I 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.
     337I 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 anonymity 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.
    282338
    283339As a sub-question, let me just ask directly: Is it true that Bittorrent through TOR via proxychains no longer works?
    284340
    285 Also, 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?
     341Also, 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 convention of all the other options?
    286342
    287343'''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)'''
    288344
     345
     346On my system, the privoxy startup file ultimately runs
     347{{{sudo $INSTALLDIR/privoxy --pidfile $pidfile }}}
     348
     349with INSTALLDIR being where you installed it, and pidfile being a filename that will hold the process ID.
     350
     351Tor can be started as a normal user -- just run the tor program. On my system, it runs as
     352{{{/usr/bin/tor ControlPort 9051}}}
     353
     354Note that Vidalia is responsible for starting tor, normally.
     355
    289356'''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)'''
    290357
     358I'm not sure that this is OS X specific. For any firewall, you need to add two incoming ports, 9001 and 9030 by default, to the list of approved ports.
     359
     360For Mac OS X, go to control panel, sharing, firewall, and then click "new" twice. The first one is port 9001, label "Tor Server", the second is port 9030, label "Tor Directory Mirror". Both of these are TCP ports, and the "port name" field should be "other".
     361
     362If you have BOTH the Os X firewall, and the router firewall, then you also need to open those ports on the router. Details are router specific.
     363
    291364'''What to do (troubleshooting) if browsing slows to a crawl with Tor and Privoxy running in OS X?'''
    292365
     366Somebody proposed the following solution, which ''should not be used'' as it will break Tor for everyone else.
     367
     368{{{CircuitBuildTimeout 6
     369NewCircuitPeriod 3
     370ExcludeNodes charlesbabbage,tutzing,TFTor,freetux4ever
     371LongLivedPorts 80,23,21,22,706,1863,5050,5190,5222,5223,6667,8300,8888}}}
     372
     373CircuitBuildTimeout causes the client to drop an uncompleted circuit after 6 seconds; it will cause your tor to build circuits more aggressively than other nodes.  The default value is 60.
     374
     375Finally, port 80 is added to the "long lived ports" list. This will overload long lived ports, making tor unusable for people who need to use ssh over tor.
     376
    293377
    294378'''I am running a Tor server on one computer on a network. Can I stop the other PCs on the same network from being k-lined on QuakeNet?'''
     379
     380
     381'''Would it make sense to support binding to multiple ports in Tor server (e.g. to bind to ports 443, 22, 5190 etc.) for clients behind _really_ restrictive firewalls? If this was implemented one day, maybe you could also support binding to multiple specific IP addresses on multihomed servers?'''
     382
     383The changelog indicates that this has been possible since "version 0.0.7pre1 - 2004-06-02":
     384''Allow multiple instances of each BindAddress config option, so you can bind to multiple interfaces if you want.''
     385
     386The [http://tor.eff.org/tor-manual.html.en manual] says this about the ''ORListenAddress'' configuration option:
     387''... This directive can be specified multiple times to bind to multiple addresses/ports.''
     388
     389It also says this about the ''DIRListenAddress'' configuration option:
     390''... This directive can be specified multiple times to bind to multiple addresses/ports.''
     391
    295392----
    296393CategoryHomepage