encryption Archives - InputOutput.io

Using the android browser with tor or any socks proxy & privoxy

Update: If all  you’re looking to do is use TOR with android, please use this tutorial.  The below information is out of date for such uses.


  1. A jailbroken android install.
  2. Debian Armel on android.
  3. SSHD running in the chrooted debian environment.

Want to browse the web anonymously with your android device, without t-mobile recording your every move? Look no further.

Few are aware that the default android browser actually allows you to use an http proxy to connect to the web. It is a rather obscure setting to trigger, and there are no provisions for you to connect through a socks proxy, such as an ssh tunnel or the tor network. Luckily, privoxy handles all this for us. Privoxy is an http proxy that is able to forward http requests through the encrypted socks tunnel, and out to its intended recipient. In this tutorial, I will show you how to set your android browser to use privoxy, and how to configure privoxy to forward to a socks proxy.

Lets jump right in.

Using connectbot (available from the android market), ssh into your chrooted debian on localhost. Run:

apt-get install tor

This will fetch both tor and privoxy for you. Now, you’ll need to configure privoxy to forward its http requests through tor, or whatever other tunnel you’ve created through ssh (see my previous post, http://www.inputoutput.io/how-to-subvert-deep-packet-inspection-the-right-way/). Append the following line to your /etc/privoxy/config file:

forward-socks5 / localhost:9050 .

Change 9050 to whatever port your tor or ssh tunnel is listening on. Default is 9050 for tor. Now, start tor and privoxy with:

/etc/init.d/tor start
privoxy /etc/privoxy/config

I had to make /dev/null world-writable for tor to stop complaining. You’ll have to run that last part every time you restart your android device. Now on to the annoying part. In terminal emulator (also available from the android market):

sqlite3 /data/data/com.android.providers.settings/databases/settings.db
SQLite version 3.5.9
Enter ".help" for instructions
sqlite> INSERT INTO system VALUES (99, 'http_proxy', 'localhost:8118');
sqlite> .quit

Change 8118 to whatever port privoxy is listening on, but that port is the default. Now the browser is configured to use privoxy as its http proxy. Privoxy, in turn, is configured to forward connections through tor or the ssh tunnel. This means your done, congratulations!

If you want to stop the browser from using the proxy at any point, in terminal emulator:

sqlite3 /data/data/com.android.providers.settings/databases/settings.db
SQLite version 3.5.9
Enter ".help" for instructions
sqlite> DELETE FROM system WHERE name='http_proxy';
sqlite> .quit

It’s quite frustrating to go through this process every time you want to switch between proxified and raw browsing, so I suggest installing a second browser such as ‘steel’ for your raw connection, and only using the default browser for proxified connections.

BackTrack 3, the EEE 701, and Disk Encryption

Explanation and Advantages

I recently decided to make BackTrack 3 the primary OS on my pearly EEE 701.  Given my EEE’s whopping 4GB of solid-state storage, I decided that rather than installing BackTrack directly onto the SSD, I would instead install the live distro to an 8GB SDHC card I had lying around, and use the remaining internal 4GB SSD as an encrypted /root partition using cryptsetup.  There are a few distinct advantages of such a setup.  Firstly, since the OS is installed as a live distro on a removable device, portability is not sacrificed – I am still able to boot into BackTrack from the same SDHC card plugged into another machine (assuming, of course, that machines BIOS supports booting from SD.)  Secondly, by overriding the default /root partition which is created by root.lzm, any changes I make to /root are persistent, and do not require a recompression of root.lzm.  This allows me to store application settings and files in a much more convenient manner.  Thirdly, since /root is encrypted, saving settings or files containing passwords or other sensitive information is less of a security risk.


To install BackTrack onto the SDHC card, we use the same method as a USB install.  Format the SDHC to contain a vfat filesystem.  Extract the BackTrack 3 USB .iso file into the filesystem mount point, and run boot/bootinst.sh.  I tried this in Ubuntu 8.10, and had some trouble: the device was recognized as /dev/mmcblk0 and the partition as /dev/mmcblk0p1, a designation that shell script got mixed up on.  Running the script on the EEE’s previous OS, Xubuntu 8.04, the device and partition were recognized as /dev/sda and /dev/sda1, and I encountered no further problems.

Once we boot into BackTrack, we configure and install cryptsetup:

cd ~
wget http://luks.endorphin.org/source/cryptsetup-1.0.5.tar.bz2
tar -xvf cryptsetup-1.0.5.tar.bz2
cd cryptsetup-1.0.5
make install

Next, we create a .lzm file for cryptsetup to ensure that it will be available each time we boot:

mkdir -p usr/include usr/lib usr/man/man8 usr/sbin usr/share/locale/de/LC_MESSAGES
cp /usr/include/libcryptsetup.h usr/include/
cp /usr/lib/cryptsetup usr/lib/
cp /usr/lib/libcryptsetup.* usr/lib/
cp /usr/man/man8/cryptsetup.8 usr/man/man8/
cp /usr/sbin/cryptsetup usr/sbin/
cp /usr/share/locale/de/LC_MESSAGES/cryptsetup.mo usr/share/locale/de/LC_MESSAGES/
tar -zcvf cryptsetup.tgz usr/
tgz2lzm cryptsetup.tgz cryptsetup.lzm
cp cryptsetup.lzm /mnt/sda1/BT3/modules/ # my mountpoint was /mnt/sda1, yours probably is too

Now we have cryptsetup available in the live environment.  Next step is to format the EEE’s internal SSD.  I set up one primary filesystem, recognized as hdc1.  We’ll be formatting this with cryptsetup using a secure passphrase.

cfdisk # to set up the partition
umount /dev/hdc1
cryptsetup luksFormat /dev/hdc1
cryptsetup luksOpen /dev/hdc1 root_dir
mkfs.ext2 /dev/mapper/root_dir

And now we have an encrypted partition on the SSD.  Next mount it and copy the existing BackTrack /root files.

mkdir /mnt/root_dir
mount /dev/mapper/root_dir /mnt/root_dir
cp -a /root /mnt/root_dir
mv /mnt/root_dir/root/* /mnt/root_dir/root/.* /mnt/root_dir/
rmdir /mnt/root_dir/root

And we’re almost done.  We’ll create a script to make it easy to mount our /root every time we boot.  Create a file in /root/root/decrypt_root.sh with the following contents:

cryptsetup luksOpen /dev/hdc1 root_dir
mount /dev/mapper/root_dir /root

Finally, create an .lzm file for the script.

cd ~
tar -zcvf decrypt_root.tgz root/
tgz2lzm decrpyt_root.tgz decrypt_root.lzm
cp decrypt_root.lzm /mnt/sda1/BT3/modules/

And we’re finished.  If all goes well, when you restart your machine you will have this script in your /root directory, and once run it will mount your encrypted SSD partition to /root.  From this point, you can issue a ctrl-alt-backspace and re-login, and startx if you’d like.  Welcome to a world of BackTrack possibilities!

How to Subvert Deep Packet Inspection, the Right Way.

Note: I was first inspired to write this post based on the great coverage of deep packet inspection by the Security Now (SN) podcast.  For more detailed information than I could ever provide, please listen to Security Now, especially episodes 149, 151, and 153.

What is deep packet inspection?

In bygone days, the role of an Internet Service Provider (ISP) had been that of a passive provider of content.  The ISP provided the necessary infrastructure to connect your computer with the larger global network of computers, the internet.  When you pay your monthly bill to the ISP, you are paying a usage charge, effectively ‘renting’ their infrastructure to get yourself on the grid.  They did not disrupt, filter, or sell your private information, and life was good.
In 1994, Congress passed the Communications Assistance for Law Enforcement Act (CALEA).  This act required all digital telecommunications carriers to enable wiretapping of their digital switches.  In 2005, CALEA was extended, at the behest of the DOJ, FBI, and DEA, to include the tapping of all ISP traffic.  Prior to this extension, the FBI had relied on court order or voluntary cooperation of individual ISPs, engaging in packet sniffing with programs such as Carnivore.  So the government spying on your net usage is nothing new.
Recently, however, a very disturbing friendship has developed between advertising agencies and ISPs.  Particularly nefarious advertising companies such as NebuAd have been approaching ISPs and offering them sums of money if they will install devices that monitor and even modify the on-the-fly communications to place ads on websites that you visit.  Earlier on, these ads were just crudely inserted JavaScript, sometimes causing a rendering error in the page.  Recently, some companies such as Phorm in Britain have gotten smarter and are using the devices they’ve bribed the ISPs into installing to monitor each and every website you visit.  This is frightening because your browsing habits reveal an enormous amount of information about the type of person you are, and in fact in many cases pinpoint exactly who you are.  So these advertising agencies are effectively logging and storing everything that you do across the web, to build a profile of you for the supposed intent of providing more targeted advertising.  Luckily, there is a way to protect yourself from these invasive policies.

Using SSH to create a secure SOCKS proxy tunnel

Note: My experience in subverting these practices is largely based in using SSH within a bash environment.  You can perform the same actions with Windows using putty as well, but the syntax is quite different, and not my area of expertise.  I suggest using the howto on this page if you are using putty.


  • Remote shell account on a machine running an SSH server
  • An SSH client
  • Programs that allow you to proxy traffic with SOCKS

One very effective way to subvert deep packet inspection is to create a secure, encrypted tunnel that you send all of your traffic through.  The ISPs cannot modify the content of the packets if they are point-to-point encrypted, since they have no way of seeing what the content actually is.  The idea is to wrap the packets with encryption only so far as to get them out of the reach of your ISP, and once they arrive at a remote server that you have shell access to, that server unwraps the traffic and sends it out on its merry way.  Be sure that the remote server that you have access to is secure and trusted.  If it is not, you may effectively be opening yourself to a man-in-the-middle attack or packet sniffing.  If you have access to a remote shell, you can use SSH to create a secure SOCKS proxy on a specific port of your local machine, which forwards all traffic to the remote machine before reaching its final destination.  Simply type:

ssh -D localhost:port -f -C -q -N user@host.tld

where port is the local port you want to open.  When this command is issued for the first time, make a note of the hex fingerprint that is displayed.  If at any time in the future you get a warning stating that there is a fingerprint mismatch or that the fingerprint does not match your known_hosts file, your traffic may be being intercepted.  This fingerprint acts as verification that you are indeed opening a connection to the remote server you intend to communicate with.  Now, if you issue the command “netstat -antp” and if everything went well you will see a new local port being provided by ssh.  If under the ‘local address’ field, your output looks like the following: “” then this port is only accessible locally.  You can now configure programs such as x-chat, pidgin, and firefox to use the ip address “” with the port you have specified to enable this proxy.

Word of warning #1: What you gain in privacy on the ISP side, you may lose in anonymity on the remote server side.  For instance, if your remote server has a static IP and your ISP doesn’t, it may be easier for the websites you access to track your browsing habits over time.  One way to counter this is to have a multitude of people use this server as their primary proxy; that way there is no way of pinpointing who exactly is accessing what.

Word of warning #2: When configuring certain programs to use the SOCKS proxy, there is a potential for DNS leakage.  What this means is that even though the traffic between yourself and the remote server is encrypted, the name resolution may not be.  This may present a problem, but certain programs such as firefox allow you to ensure that there is no DNS leakage.  In firefox, browse to “about:config” and make sure the setting for “network.proxy.socks_remote_dns” is set to true.  Certain extensions of firefox such as FoxyProxy take care of this for you in their plugin settings.

Complete SSH encapsulation: the tun module


  • Root access to a remote machine running an ssh server
  • An SSH client
  • The tun module installed both locally and remotely

The problem that I had with the solution in the previous section is as follows.  There are plenty of programs using my network that do not have the ability to use a SOCKS proxy.  Given the track record of the worst of the advertising companies, I wouldn’t put it past them to start intercepting and modifying all sorts of traffic, not only the traffic with the highest volume or visibility such as web traffic.  What is really needed is an all-encompassing proxy, one that just takes all outgoing and incoming traffic and sends it over that secure encrypted link.  SSH is such a wonderfully flexible and versatile program, and it has built-in support for creating a secure VPN to do just that.  The idea is to make it so that all your traffic is routed through the remote server using a secure VPN link.  This section requires a basic grasp of routing tables, kernel modules, and iptables.

So our first task is to establish the secure VPN.  To do this, both machines must have the ‘tun’ kernel module installed and loaded.  Just issue the comman

modprobe tun

on both the local and remote machines from their respective root shells.  Locally, issue the command:

ssh -w 0:0 -f -C -q -N root@host.tld

This command establishes a new network interface on both sides of the connection, tun0.  Then, type:

ifconfig tun0 pointopoint

SSH into the remote machine, and issue these commands:

ifconfig tun0 pointopoint
ping -c 3

If you get a ping response, you’ve successfully set up a secure VPN!  This is good, but in order to route your traffic through the remote machine, it must be set up to enable packet forwarding, and also to have iptables configured so that it acts as a gateway.  I’ve modified a small shell script for this purpose.  You may need to modify it further to suit your needs:

wget http://www.inputoutput.io/shareconnection.sh
chmod +x shareconnection.sh

Your remote server is now configured to act as a gateway.  Locally, you must now set up your routing tables to direct all traffic (except the traffic that is still needed to keep the tun0 interface alive!) through the tun0 interface.  The following commands assume that your default local gateway is a router with the ip address, and your default interface is eth0:

route add host.tld gw eth0
route del default gw eth0
route add default gw tun0

And presto!  All outbound and incoming traffic is now routed through your remote machine.  Again, the same concern in the above section regarding anonymity and verification of the remote fingerprint applies in this case as well.  Since the remote server is now acting as your gateway, there is no reason to fear DNS leakage, and no programs to configure.  Now you can rest assured that your connectivity is secure from the prying eyes of the ISPs and their sneaky cohorts, the traffic-shaping advertising companies.

My next article will detail how to connect this tunneled interface with programs such as hostap and dhcpd to create a wireless access point providing an automatically proxified connection to wireless clients.

Cory Doctorow’s Little Brother

I just finished Cory Doctorow‘s Little Brother. And oh. My. God. Soooo good. Sooooooo good.

First let me note: Cory Doctorow is a sci-fi author, but this novel doesn’t read like sci-fi. Sure, it hinges on technology that doesn’t yet exist. But we’re talking about the near future, the very near future, no more than 4-5 years down the line. So there’s no robots with plasma spheres for heads screaming “Danger Will Robinson!,” or faster than light travel, or any of those elements that have given the genre an unfair reputation. Instead, it’s tech that we can see developing before our very eyes in real-time. In every chapter there is an explanation of real or conceivable computer systems, cryptographic systems, or mathematics that are relevant to the story in some way. And that’s the exciting part: the innovativeness and imagination that is embodied in the not-so-far-off world that Doctorow describes is believable because it comes from the authors understanding of how the technology really works, and how it is evolving in the present. As William Gibson explains, sci-fi “can’t be about the future. It’s about where the person who wrote it thought their present was, because you can’t envision a future without having some sort of conviction, whether you express it or not in the text, about where your present is.” And our present is a very exciting time indeed.

That being said, even without an understanding of the underlieing technology, it makes for a great read. Basically, it’s about a teenage hacker in San Francisco and how he deals with the Department of Homeland Security (DHS) taking over the bay area after the next terrorist attack. The DHS sets up random checkpoints throughout the city, extending the surveillance measures already in place, and tracks the movements of every citizen through the RFID tags they use when they take the BART (subway), or go through the FastTrac (RFID-enabled toll booth lane in SF). Furthermore, our protagonist and his friends are taken in and tortured by the DHS for days on end, in a secret prison the department has set up offshore. With this imagery, you can see how Doctorow’s vision of the near-future is also informed by the political realities of our time. Just as he projects the technologies of the near future based on the technological dynamics of the present, the stark political realities of today are extended into the near future in a way that seems not just believable, but inevitable. I’m not going to give away too much of the plot, but here’s the long and short of it. Just as these technologies can be used against the people, those same technologies can be used to promote and extend peoples rights and freedoms, and to subvert the governments attempt to take those freedoms away. A movement evolves, and at the center of it is the Xnet – an encrypted network of hacked Xbox Universals, using Paranoid Linux as its operating system.

Doctorow does such a wonderful job of interweaving the political, cultural, and technological strains of our current society and projecting them into the near future with an elegance that it is truly visionary. Anyone who is interested in cryptography, hacking, or activism should immediately drop whatever they’re doing, run to their nearest independent bookstore, and pick up a copy of this immediately. Well? Go!