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Stream Isolation

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Stream Isolation[edit]


If you do not explicitly take action against this and install custom applications, you risk that different activities, let's say Web (Chromium or similar) or IRC (mIRC or similar) go through the same Tor circuit and exit relay. Even though you would still be anonymous, i.e. the Tor exit relay would still not know your real IP/location, they can easily correlate those activities issued by different applications to the same pseudonym.

The following graphic illustrates the difference of using Tor SocksPort's compared to using Tor's TransPort. Using dedicated SocksPort's per application results in taking different routes through the Tor network per application. Not necessarily all nodes (first, second, third) get replaced by Tor. Sometimes just the first, sometimes just the second, sometimes just the third, and sometimes multiple nodes change.

Stream Isolation Graphic

Whonix implements protection against identity correlation through circuit sharing, however, for better privacy, you are still advised to understand a bit of the technical background. Since Tor version 0.2.3, different Socks,- Dns-, or TransPorts go through different circuits, therefore preventing identity correlation. Whonix configures most applications that come preinstalled with Whonix to use different SocksPort, thus no identity correlation is at risk. Whonix uses either socks proxy settings to direct various applications to different SocksPorts or uwt (more information below).

Any other traffic (i.e. custom installed applications, misc applications, such as nslookup, go through Tor's Dns-, and/or TransPort (can be optionally disabled, see below).

Applications in Whonix are configured to prevent identity correlation through circuit sharing:

application pre-installed pre-configured type port instructions
Tor Browser yes yes socks proxy settings 9150 [1] Tor Browser
XChat yes yes socks proxy settings 9101 Chat
Thunderbird with TorBirdy no yes socks proxy settings - Mozilla Thunderbird with TorBirdy
Instant Messenger no no (TODO) socks proxy settings port prepared, IP, port 9103 Chat
apt-get yes yes uwt wrapper - -
aptitude yes yes uwt wrapper - -
gpg yes yes uwt wrapper - -
ssh yes yes uwt wrapper - -
git no yes uwt wrapper - -
sdwdate yes yes socks proxy settings[2] - -
wget yes yes uwt wrapper - -
curl yes yes uwt wrapper - -
whonixcheck yes yes socks proxy settings - -
BitCoin no no socks proxy settings port prepared, IP, port 9111 Money
privoxy no no socks proxy settings port prepared, IP, port 9112 -
polipo no no socks proxy settings port prepared, IP, port 9113 -
tb-updater (AnonDist) yes yes socks proxy settings - Tor Browser
apt-cacher-ng no no uwt wrapper - helper script with comments prepared, see /usr/bin/apt-cacher-ng_uwt
TorChat no yes settings, socks proxy settings, connects only to hidden services - Chat
mixmaster yes yes settings (connects only to hidden services) - Mixmaster
mixmaster-update yes yes uwt wrapper - Mixmaster
KDE application wide proxy settings no yes pre-configured socks proxy settings, port 9122 no KDE applications with network activity pre-installed -
GNOME application wide proxy settings no no not pre-configured, port prepared, port 9123 no GNOME applications with network activity pre-installed -

The required socks proxy settings were setup by the Whonix build scripts. uwt wrappers are set up on Whonix-Gateway and on Whonix-Workstation under /usr/share/whonix/postinst.d/70_uwt. uwt is a wrapper around torsocks, which is also already installed to /usr/bin/uwt.

  • Example, each time you run a uwt wrapped application, i.e. simply type apt-get in console, the uwt wrapper /usr/bin/apt-get will run. It adds uwt before apt-get. For curiosity check nano /usr/bin/apt-get. The uwt wrapper then runs /usr/bin/uwt /usr/bin/apt-get.anondist-orig. That is also the case for all other uwt wrapped applications.
  • If you ever want or must run a uwt wrapped application without uwt, do not run for example apt-get in console, do run apt-get.anondist-orig. Use cases could be if you want to connect to localhost. If you know what you are doing, you should also be able to deactivate any uwt wrappers you dislike, see #Deactivate_uwt_Stream_Isolation_Wrapper.
  • When running /usr/bin/apt-get.anondist-orig directly it goes through Tor's DnsPort and through Tor's TransPort and not through its own SocksPort.
  • uwt looks if the command contains the words localhost or, if that is the case, uwt will not be used. The command will be run without uwt. Thus, if a localhost connection is falsely detected it will leak, but only through Tor's DnsPort and through Tor's TransPort, which should be ok.

Isolate by destination address: Let's assume SSH goes over port 22 and you want to connect to different SSH servers and do not want an observer to be able to correlate that activity to the same pseudonym. If the SSH servers run on different IP's isolate by destination address might help.

Isolate by destination port: This doesn't seem to be useful for anything in Whonix, applications using different protocols (and therefore different ports) are already isolated through using different SOCKSPorts.

Isolate by destination port doesn't really achieve anything for web browsing: tor-talk Tor's stream isolation features defaults.

For more information about stream isolation refer to the Tor manual.

Tor Browser[edit]

Different tabs and websites in Tor Browser are isolated by since Tor Browser version 4.5-alpha-1. [3]

Custom Software[edit]

If you install custom software on Whonix-Workstation, and want to prevent identity correlation through circuit sharing (which you should do), you have to manually configure them. This is not a Whonix specific problem. [4]

Read also Software installation on Whonix-Workstation.

Hidden Services[edit]

Hidden services are automatically separated from each other.[5]


  1. Whonix-Workstation gets redirected to by rinetd. See on Whonix-Workstation file /etc/rinetd and package anon-ws-disable-stacked-tor. Changing proxy settings in Tor Browser has proven to be unreliable. At some point Tor Button may change its internals and therefore break something again. Keeping the default settings and not requiring any changes in Tor Browser seems like the best way to support compatibility in long run and also is simplest in case update-torbrowser breaks and manually updating Tor Browser is required again in future.
  2. https://github.com/Whonix/sdwdate-plugin-anon-shared-streamiso/blob/master/etc/sdwdate.d/31_anon_dist_stream_isolation_plugin
  3. https://trac.torproject.org/projects/tor/ticket/3455
  4. If you used to use only one SocksPort with the common torification methods, the same thing happened.
  5. https://lists.torproject.org/pipermail/tor-talk/2012-September/025432.html

How to mitigate identity correlation[edit]

Basic Protection[edit]

Most applications which come with Whonix are configured to prevent identity correlation through circuit sharing, you really should read the introduction above.

The only traffic going through TransPort by default is whonixcheck when testing the TransPort. If that is of concern to you, it can be disabled in whonixcheck, see Advanced Security Guide#Prevent polluting TransPort.

All custom installed application's TCP traffic is routed through Tor's TransPort and all their DNS requests through Tor's DnsPort. This means different activities or "identities" in different applications (say browser, IRC, email) end up being routed through the same circuit, thus identity correlation is at risk.

To protect against this, you have to set up per-application SOCKS ports in Whonix-Gateway.

On Whonix-Gateway in /usr/share/tor/tor-service-defaults-torrc are already a lot custom socks ports prepared for custom installed applications:

  • Without IsolateDestAddr and without IsolateDestPort: SocksPort to 9159
  • With IsolateDestAddr, but without IsolateDestPort: SocksPort to 9169
  • Without IsolateDestAddr, but with IsolateDestPort: SocksPort: to 9179
  • With IsolateDestAddr and with IsolateDestPort: SocksPort: to 9189
  • If they those are not enough, you can add your own ones.

What are IsolateDestAddr and IsolateDestPort? You can learn about them in the Tor manual. See also tor-talk mailing list: Tor's stream isolation features defaults. Usually, unless you know better, you are better off not using IsolateDestAddr or IsolateDestPort.

You can point your applications, where you want to prevent identity correlation though circuit sharing, to those SocksPorts. Each custom installed application has to be torified, for directions how to do that use the Torify HOWTO.

Additional comments regarding the Torify HOWTO:

  • Warnings about protocol related warnings you must honor. You are still better off with Whonix, as it offers best possible Protocol-Leak-Protection and Fingerprinting-Protection.
  • Whonix's setup provides protection against IP leaks through protocol leaks.
  • If you do not correctly torify, no connections will be possible.
  • If you redirect more than one application to the same SocksPort, identity correlation is at risk.
  • DNS related warnings still apply, though to a lesser extent - an attack could only make correlations but still couldn't figure out your IP. You can prevent that, be out commenting (# in front) DnsPort in /etc/tor/torrc on the Whonix-Gateway and by removing the DNS redirection firewall rule from /usr/bin/whonix_firewall.
    • Do not use a local DNS resolver, as all DNS requests would be executed by the same circuit.
  • Other leaks, such as applications not honoring the proxy settings / wrapper, ICMP or UDP leaks do not apply to Whonix.
  • The SafeSocks setting is for rejecting unsafe variants of socks that might cause DNS leaks. The Whonix design model mitigates DNS leaks by redirecting all requests to Tor's DnsPort. Enabling this setting would give marginal benefit in this situation but would complicate debugging.

Better Protection[edit]

For best protection against identity correlation:

Read the advice above and on Whonix-Gateway:

Deactivate KDE / GNOME - application wide proxy settings...

  • Because those proxy settings are not application specific, but rather force all KDE / GNOME applications through the same SocksPort (no KDE / GNOME applications which use the internet preinstalled by default), deactivating those KDE / GNOME - wide proxy settings gives better control about stream isolation.

To deactivate TransPort and DnsPort...

  • See WORKSTATION_TRANSPARENT_TCP in /etc/whonix_firewall.d/30_default.
  • See WORKSTATION_TRANSPARENT_DNS in /etc/whonix_firewall.d/30_default.
  • Reload whonix_firewall (sudo /usr/bin/whonix_firewall) or simply reboot.

Although not strictly required, you could alternatively/additionally add to /etc/tor/torrc.

TransPort 0
DnsPort 0

And reload Tor. (sudo service tor reload)

This will disable transparent proxying. All applications not configured to use a SocksPort or forced to use a SocksPort (use uwt) will not be able to establish connections. This is the only way to ensure, that different SocksPorts are used and that also DNS is remotely resolved through that SocksPort.

Total protection[edit]

Total protection is only possible, if you honor the advice above and only use one application per session and always revert to a fresh image or use more than one Whonix-Workstation. Multiple Whonix-Workstations (using different internal IP's) are automatically separated by Tor (IsolateClientAddr is Tor's default).

Deactivate uwt Stream Isolation Wrapper[edit]


anondist-orig Method[edit]

Append .anondist-orig to the command you want to run. For example, instead of using.




Environment Variable Method[edit]

Use the UWT_DEV_PASSTHROUGH environment variable. [1]

Example. Set the UWT_DEV_PASSTHROUGH environment variable. This will disable using torsocks for all following invocations.


When running as user and using sudo, do not forget sudo's -E parameter which stands for preserve environment.

sudo -E apt-get update


OPTIONAL. Usually not required. Only for special setups and people who know what they are doing.

You can enable/disable all uwt stream isolation wrappers globally or enable/disable specific stream isolation wrappers, see uwt /etc/uwt.d/30_uwt_default configuration file.



1. Applications which internally use curl.

sudo update-command-not-found

sudo update-flashplugin-nonfree --install --verbose

2. Applications which is uwt wrapped itself and internally uses ssh.

git push origin master

3. Enigmail.

Debugging / List of all uwt wrappers[edit]

sudo dpkg-divert --list
ls -la /usr/bin/ssh

Deactivating an uwt wrapper[edit]


sudo unlink /usr/bin/ssh
sudo dpkg-divert --rename --remove /usr/bin/ssh

Check if Transparent DNS is disabled[edit]


nslookup check.torproject.org ; echo $?

Should show.

;; connection timed out; no servers could be reached


If it shows something else, such as a resolved IP, the Transparent DNS is enabled.

Check if Transparent TCP is disabled[edit]


curl.anondist-orig ; echo $?

Should show.

curl: (7) couldn't connect to host

If it shows something else, such as the html source code, then Transparent TCP is enabled.

Check if Transparent Proxying is disabled[edit]


curl.anondist-orig https://check.torproject.org/ ; echo $?

Should show.

curl: (6) Couldn't resolve host 'check.torproject.org'

If it shows something else, such as the html source code, then Transparent Proxying is enabled.


Stream Isolation Graphic has been contributed by: Cuan Knaggs – graphic and web design revlover print media – web design – web development – cms – e-commerce


  1. https://github.com/Whonix/uwt/blob/master/usr/bin/uwt#L49

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