It is a quick tour of the internet and how it works. The aim is to provide a short, but reasonably comprehensive overview of the internet. It is for people who are interested in how the internet works, but don’t want to spend hours researching all the details.

We’ll start by looking at the low-level design of the internet and gradually move up to browsing a website.

What is the internet?

Contrary to popular belief, the internet is neither a single physical entity or a large amorphous network. Rather, it is a network of networks.

These sub-networks are called Autonomous Systems (AS). There are just over 43,000 ASs connected to this network (at the beginning of 2013). Each AS consists of a network of nodes connected together.

Where am I in this network?

There are often further sub-networks. For example, when you connect to the internet, it is likely that your device is directly connected to a local network. This local network is often provided by a router in the same building, whether using a wired or wireless connection.

That router may have a direct connection to a node of your ISP’s (internet provider’s) AS.

How does data reach other devices?

In order to communicate with someone on the other side of the world, data is routed through the user’s local network and sent to the connected AS. From there, it is routed through the AS to reach the internet. At this point, it is routed through the internet to the AS the recipient is connected to, and through that AS to reach the recipient’s local network, where it is finally routed to their device.

IP (Internet Protocol) is used to work out where to route data to. This is achieved by assigning unique IP addresses to each device connected to the internet. In the case of our example, the user’s device will have been assigned a local IP address from the router, while the router (connected to the AS), will have a global IP address on the internet.

The internet uses part of the address to work out which AS data should be sent to. The AS uses the other part of the address to work out which node on it’s network to route to.

What if something goes wrong?

The network is designed to update its routes if a node disappears, becomes congested etc. Despite this, data frequently fails to reach its target.

To work around this, the TCP protocol is often used on top of the IP protocol (TCP/IP). This protocol allows data to be split into small packets. A packet is a chunk of data with additional information attached, including its destination among other things.

When data is sent to a recipient using TCP, it will first establish a connection with the recipient. This process is called ‘handshaking’, and is simply a way for both sides to confirm there is a connection between them and initialise data transfer.

At the end of receiving a series of packets, the recipient will send a reply packet to acknowledge this. If this acknowledgement is not received, the sender will assume the packets failed to arrive and resend the data packets.

How does a website work?

Domain names?

When a user enters a URL (e.g. http://google.com) into a browser, the first thing it must do is translate the domain name into an IP address. The domain name is the main part of a URL delimited with ‘.’ (google.com), and is translated by querying a Domain Name System (DNS) server.

The machine may need to query a root DNS server to find the server for the given TLD (top level domain (e.g. .com)). It will then query that server to find the IP address for google.com.

A domain name may consist of multiple sub-domains, each of which may require looking up another DNS server to reach the final IP address. For example, foo.bar.gov.uk would start by looking up the TLD (.uk), at that server it would look for ‘gov’, at the next it would look for ‘bar’, and at the last DNS server it would get an IP address for ‘foo’.

How does it get the web page?

After a browser has retrieved the IP address of the server, the browser will begin communicating with the server; it will send a request to the server for a web page.

The web page is specified after the domain name, the part after the ‘/’ (e.g. example.com/something.html). If no specific web page is specified, the server will choose a default page (typically called something like index.html).

If multiple parts are listed, such as example.com/foo/bar/baz.html, these can be thought of as sub-folders on the server.

The server will then send a reply with the requested page.

How does a page display?

The returned page is an HTML document. HTML is a markup language, which means that it describes what each part of the content is (e.g. header, table etc.). The browser will read this file, and decide from this information how to display it.

This is a single text file, but can contain links to images and other content which the browser will download separately and then display as part of the page. It can also contain links to other web pages and provide methods for sending additional data to the server.

Further Reading

We’ve taken a brief look at many different parts of the internet, if you’d like to learn more about any of these parts, the links below may give you a good start:

• Autonomous System
• Routing
• Internet protocols
• DNS
• HTML

This tutorial will explain how you can use a plugin as a convenient way to use this tool.

Pre-installation

In order to use this plugin you will of course need to install the encfs program first, the easiest way to do that (on Ubuntu) is to try clicking this link:
apt:encfs

or copy this into a terminal:
sudo apt-get install encfs -y

In addition to this we will be using gnome-encfs, a small program that allows you to use the gnome-keyring to store encryption passwords. This program by Oben Sonne can be found here; after downloading it, extract the gnome-encfs file to your home folder.

Then to install it run:
sudo install gnome-encfs /usr/local/bin

Installation

To install the actual plugin simply open a terminal and copy & paste these commands:
sudo apt-get install python-nautilus
mkdir -p ~/.local/share/nautilus-python/extensions/
cd ~/.local/share/nautilus-python/extensions/
wget http://sambull.org/downloads/encrypt-nautilus.py
chmod a+x encrypt-nautilus.py

If you want to try this out immediately, press Alt+F2 and enter “nautilus -q”, then repeat and enter “nautilus”, otherwise it will be available next time you login.

Usage

This new version has a greatly simplified and streamlined interface.

Simply right-click a folder you want to encrypt and click “Encrypt folder”, confirm when prompted and the contents of the folder will be immediately encrypted.

To view the decrypted contents, simply open the folder in Nautilus and it will be automatically mounted. If you want to manually unmount the folder, simply right-click and click “Unmount encrypted folder”.

Notes

If you want to backup your encrypted files, they are stored in a hidden folder called “.[name]-enc”.

Folders are encrypted with a randomly generated password, which is stored in your keyring. Make sure you backup your keyring, or you risk losing all your encrypted files.

If you want to move/rename a folder, you will need to move/rename both the folder, and it’s encrypted counterpart. You will then also need to update the keyring. I hope to remove the last step in another update in the future.

Upgrading

If you’ve used the extension before the latest update, you will need to change your encrypted folders to work with this new extension. Simply rename each of your encrypted folders to “.[name]-enc” and create an empty folder called “[name]“. If you then open the latter folder, you should be prompted for a password, copy this from the password stored in you keyring and you should be setup (you can then delete the old password from the keyring).

Extension

I’ve written a follow-up post to this one that explains how this can be used to encrypt Firefox data seamlessly. You can read it here.

I have also restructured some of the code and have begun adding a few little images to the documentation to give a preview of each widget. All of these improvements will be in the next beta release in a couple of week’s time.

Like the previous guide, this may require a little bit of effort to setup. But, once you have it setup, it will be no more hassle to use than running Firefox normally.

I am going to describe two methods, one for people who login to their computers, and the other for people who have auto-login enabled.

Encrypt folder

Simply navigate to the .mozilla folder (Ctrl+H shows hidden folders). In here you should see a firefox folder.

Now right-click and “Encrypt folder” the firefox folder.

Normal Login

If you login to your computer normally, start by encrypting the folder as above.

Now run in a terminal:
gnome-encfs -e ~/.mozilla/firefox
Hit enter to accept the existing settings for the first 3 things, but set mount at login to ‘y’.

Now, whenever you login it will automatically mount the encrypted firefox data, ready for Firefox to use.

Auto-login

Auto-login users have two choices.

The first option, is to use the exact same method as the normal login solution. The drawback of this, is that every time you login (because it will try to mount on login) you will always be asked for your password to unlock the keyring.

The second option will only ask for your password when you try to run Firefox, this allows you to have a system that auto-login’s without any annoying pop-up windows when you start. This option requires a little more setup and maintenance though.

Second Method

First, encrypt the folder as described above.

Next, you need to save a couple of simple scripts:

cd /usr/local/bin/
sudo wget sambull.org/downloads/.firefox_encrypt
sudo chmod +x /usr/local/bin/.firefox_encrypt
sudo wget sambull.org/downloads/fix_firefox
sudo chmod +x /usr/local/bin/fix_firefox

Now run the latter script: sudo fix_firefox

This script simply renames the firefox program to firefox-dc, then creates a link, so whenever anything tries to run Firefox, it will actually run our little script. Our script then mounts the Firefox data and launches the real Firefox.

Usage

Just launch Firefox as you normally would, if your keyring hasn’t been unlocked yet you’ll be prompted for the password to unlock, and then Firefox will launch as normal.

Maintenance

One drawback of this method is that it requires a little bit of maintenance. Whenever the system updates Firefox, it is going to overwrite the link we made earlier. This is why we saved fix_firefox as a script, we now need to run this script everytime Firefox is updated.

Fortunately, we can automate this. Simply run:

sudo gedit /etc/apt/apt.conf.d/70debconf

and add a new line:

Dpkg::Post-Invoke{"/usr/local/bin/fix_firefox";};

Now, after a reboot, it will run our script everytime the computer is updated.

Encfs is a program that can be used to encrypt folders, unlike other encryption methods this doesn’t require a file of a fixed size, so you can use the decrypted folder in the same way as a regular folder without worrying about space.

This tutorial will explain a convenient way to use this tool.

This method can both be used from the GUI and the command line.
To understand if this is what you want please read the example in the usage section at the bottom before going through the setup.

Pre-installation

First, you will of course need to install the encfs program, the easiest way to do that (on Ubuntu) is to try clicking this link:

apt:encfs

or copy this into a terminal:

sudo apt-get install encfs -y

In addition to this we will be using gnome-encfs, a small program that allows you to use the gnome-keyring to store encryption passwords. This program by Oben Sonne can be found here, after downloading it, extract the gnome-encfs file to your home folder.

Then to install it run:

sudo install gnome-encfs /usr/local/bin

Installation

To do this, we will be using a couple of scripts, that can be used in Nautilus (the file manager) or from the command line.

Scripts

To install these scripts just save them into ~/.gnome2/nautilus-scripts/ (that is the folder nautilus-scripts in the .gnome2 hidden folder in your home folder):

You can download the first script here. Right-click > Save as, then save it in the above folder (Ctrl+H shows hidden folders). Save it with whatever name you want to appear in the menu.

Repeat this for the unmount script, found here.

In order to allow them to run, you need to make them executable, in the terminal this can be done by copying and pasting:

chmod +x ~/.gnome2/nautilus-scripts/emount ~/.gnome2/nautilus-scripts/eumount

Don’t forget to change the emount and eumount names if you’re using different names.

Now if you right-click on a folder, go to scripts, you should see emount and eumount (or whatever you named them). Read the usage section to find out how to use them.

Command Line

To use the scripts from the command line, we need to make symlinks, just run:

sudo ln -s ~/.gnome2/nautilus-scripts/emount /usr/local/bin/emount &&
sudo ln -s ~/.gnome2/nautilus-scripts/eumount /usr/local/bin/eumount

Change the first emount to the name you saved for the GUI, and the second emount to the name you want to use for the command. Repeat with eumount.

Usage

I’ll give a little example here to demonstrate usage. Let’s say your Pictures folder contains some naughty images and you’d like to encrypt the entire folder. Let’s also say we want to do this from the GUI without using the command line.

The contents of my Pictures folder.

Encrypting

Simply right-click and emount the folder you want to encrypt. A window will now pop-up asking for the name of the folder where the decrypted contents will be displayed, I’ll use pictures-decrypted for this, you can use any name you like.

Naming the decrypted folder.

It will then ask if you want to have it automatically mount at login, this will allow you to have it always decrypted for you, but make sure nobody else will be able to see the contents without logging in. Finally, it asks you for a password, this is the password you want it to use for decrypting the folder (not your login).

You will then see a new folder has been created, in my case it’s called pictures-decrypted. This new folder is the decrypted contents of the Pictures folder. If you add any new files, you need to save them into this decrypted folder, they will then automatically be encrypted.

The folders after decrypting.

Unmounting

Simply right-click pictures-decrypted and select eumount. The decrypted folder should now have vanished.

If you look in the Pictures folder you will see that the contents are all encrypted and you will be unable to view any of the files.

With the contents encrypted nobody will be able to view them anymore.

Command Line

This works similarly to the GUI, but used from the command line:

emount foo/

will decrypt (or encrypt if it’s not encrypted yet) the foo folder. While:

eumount bar/

will unmount the bar folder.

Auto-mount tip

If you are going to auto-mount the folder on login, then you could rename the encrypted folder to something like .pictures-encrypt (the . makes it a hidden folder). Then when you make it encrypted, you can name the decrypted folder Pictures, so the encrypted folder remains hidden, and the decrypted folder acts like your normal pictures folder.

Decrypting

Now in future all you have to do is right-click the Pictures folder and select emount. It will then retrieve your password from gnome-keyring and the decrypted folder will appear there with all your pictures in, and right-clicking and eumount will make them disappear again, so nobody will be able to view them without your password.

Extension

I’ve written a follow-up post to this one that explains how this can be used to encrypt Firefox data seamlessly. You can read it here.