Using GNUnet
************

This tutorial is supposed to give a first introduction for users trying to do something real with GNUnet. Installation and configuration are specifically outside of the scope of this tutorial. Instead, we start by briefly checking that the installation works, and then dive into uncomplicated, concrete practical things that can be done with the framework provided by GNUnet.

In short, this chapter of the ``GNUnet Reference Documentation'' will show you how to use the various peer-to-peer applications of the GNUnet system. As GNUnet evolves, we will add new sections for the various applications that are being created.

Comments on the content of this chapter, and extensions of it are always welcome.

Checking the Installation
=========================

This section describes a quick, casual way to check if your GNUnet installation works. However, if it does not, we do not cover steps for recovery --- for this, please study the instructions provided in the developer handbook as well as the system-specific instruction in the source code repository (The system specific instructions are not provided as part of this handbook!).

gnunet-gtk
----------

The gnunet-gtk package contains several graphical user interfaces for the respective GNUnet applications. Currently these interfaces cover:

  * Statistics

  * Peer Information

  * GNU Name System

  * File Sharing

  * Identity Management

  * Conversation

Statistics
----------

First, you should launch GNUnet gtk (Obviously you should also start gnunet, via gnunet-arm or the system provided method). You can do this from the command-line by typing

     gnunet-statistics-gtk

If your peer (The term ``peer'' is a common word used in federated and distributed networks to describe a participating device which is connected to the network. Thus, your Personal Computer or whatever it is you are looking at the Gtk+ interface describes a ``Peer'' or a ``Node''.) is running correctly, you should see a bunch of lines, all of which should be ``significantly'' above zero (at least if your peer has been running for more than a few seconds). The lines indicate how many other peers your peer is connected to (via different mechanisms) and how large the entire overlay network is currently estimated to be. The X-axis represents time (in seconds since the start of gnunet-gtk).

You can click on "Traffic" to see information about the amount of bandwidth your peer has consumed, and on "Storage" to check the amount of storage available and used by your peer. Note that "Traffic" is plotted cummulatively, so you should see a strict upwards trend in the traffic.

Peer Information
----------------

First, you should launch the graphical user interface.  You can do this from the command-line by typing

     $ gnunet-peerinfo-gtk

Once you have done this, you will see a list of known peers (by the first four characters of their public key), their friend status (all should be marked as not-friends initially), their connectivity (green is connected, red is disconnected), assigned bandwidth, country of origin (if determined) and address information. If hardly any peers are listed and/or if there are very few peers with a green light for connectivity, there is likely a problem with your network configuration.

First steps - File-sharing
==========================

This chapter describes first steps for file-sharing with GNUnet. To start, you should launch gnunet-fs-gtk.

As we want to be sure that the network contains the data that we are looking for for testing, we need to begin by publishing a file.

Publishing
----------

To publish a file, select "File Sharing" in the menu bar just below the "Statistics" icon, and then select "Publish" from the menu.

Afterwards, the following publishing dialog will appear:

In this dialog, select the "Add File" button. This will open a file selection dialog:

Now, you should select a file from your computer to be published on GNUnet. To see more of GNUnet's features later, you should pick a PNG or JPEG file this time. You can leave all of the other options in the dialog unchanged. Confirm your selection by pressing the "OK" button in the bottom right corner. Now, you will briefly see a "Messages..." dialog pop up, but most likely it will be too short for you to really read anything. That dialog is showing you progress information as GNUnet takes a first look at the selected file(s). For a normal image, this is virtually instant, but if you later import a larger directory you might be interested in the progress dialog and potential errors that might be encountered during processing. After the progress dialog automatically disappears, your file should now appear in the publishing dialog:

Now, select the file (by clicking on the file name) and then click the "Edit" button. This will open the editing dialog:

In this dialog, you can see many details about your file. In the top left area, you can see meta data extracted about the file, such as the original filename, the mimetype and the size of the image. In the top right, you should see a preview for the image (if GNU libextractor was installed correctly with the respective plugins). Note that if you do not see a preview, this is not a disaster, but you might still want to install more of GNU libextractor in the future. In the bottom left, the dialog contains a list of keywords. These are the keywords under which the file will be made available. The initial list will be based on the extracted meta data. Additional publishing options are in the right bottom corner. We will now add an additional keyword to the list of keywords. This is done by entering the keyword above the keyword list between the label "Keyword" and the "Add keyword" button. Enter "test" and select "Add keyword". Note that the keyword will appear at the bottom of the existing keyword list, so you might have to scroll down to see it. Afterwards, push the "OK" button at the bottom right of the dialog.

You should now be back at the "Publish content on GNUnet" dialog. Select "Execute" in the bottom right to close the dialog and publish your file on GNUnet! Afterwards, you should see the main dialog with a new area showing the list of published files (or ongoing publishing operations with progress indicators):

Searching
---------

Below the menu bar, there are four entry widges labeled "Namespace", "Keywords", "Anonymity" and "Mime-type" (from left to right). These widgets are used to control searching for files in GNUnet. Between the "Keywords" and "Anonymity" widgets, there is also a big "Search" button, which is used to initiate the search. We will ignore the "Namespace", "Anonymity" and "Mime-type" options in this tutorial, please leave them empty. Instead, simply enter "test" under "Keywords" and press "Search". Afterwards, you should immediately see a new tab labeled after your search term, followed by the (current) number of search results --- "(15)" in our screenshot. Note that your results may vary depending on what other users may have shared and how your peer is connected.

You can now select one of the search results. Once you do this, additional information about the result should be displayed on the right. If available, a preview image should appear on the top right. Meta data describing the file will be listed at the bottom right.

Once a file is selected, at the bottom of the search result list a little area for downloading appears.

Downloading
-----------

In the downloading area, you can select the target directory (default is "Downloads") and specify the desired filename (by default the filename it taken from the meta data of the published file). Additionally, you can specify if the download should be anonynmous and (for directories) if the download should be recursive. In most cases, you can simply start the download with the "Download!" button.

Once you selected download, the progress of the download will be displayed with the search result. You may need to resize the result list or scroll to the right. The "Status" column shows the current status of the download, and "Progress" how much has been completed. When you close the search tab (by clicking on the "X" button next to the "test" label), ongoing and completed downloads are not aborted but moved to a special "*" tab.

You can remove completed downloads from the "*" tab by clicking the cleanup button next to the "*". You can also abort downloads by right clicking on the respective download and selecting "Abort download" from the menu.

That's it, you now know the basics for file-sharing with GNUnet!

First steps - Using the GNU Name System
=======================================

Preliminaries
-------------

``.pin'' is a default zone which points to a zone managed by gnunet.org. Use gnunet-config -s gns to view the GNS configuration, including all configured zones that are operated by other users.  The respective configuration entry names start with a ``.'', i.e. ``.pin''.

You can configure any number of top-level domains, and point them to the respective zones of your friends!  For this, simply obtain the respective public key (you will learn how below) and extend the configuration:

     $ gnunet-config -s gns -n .myfriend -V PUBLIC_KEY

Managing Egos
-------------

In GNUnet, identity management is about managing egos.  Egos can correspond to pseudonyms or real-world identities.  If you value your privacy, you are encouraged to use separate egos for separate activities.

Technically, an ego is first of all a public-private key pair, and thus egos also always correspond to a GNS zone.  Egos are managed by the IDENTITY service.  Note that this service has nothing to do with the peer identity.  The IDENTITY service essentially stores the private keys under human-readable names, and keeps a mapping of which private key should be used for particular important system functions. The existing identities can be listed using the command gnunet-identity -d

     gnu - JTDVJC69NHU6GQS4B5721MV8VM7J6G2DVRGJV0ONIT6QH7OI6D50
     rules - GO0T87F9BPMF8NKD5A54L2AH1T0GRML539TPFSRMCEA98182QD30

The GNS Tab
-----------

Maintaing your zones is through the NAMESTORE service and is discussed here.  You can manage your zone using gnunet-identity and gnunet-namestore, or most conveniently using gnunet-namestore-gtk.

We will use the GTK+ interface in this introduction.  Please start gnunet-gkt and switch to the GNS tab, which is the tab in the middle with the letters "GNS" connected by a graph.

Next to the ``Add'' button there is a field where you can enter the label (pseudonym in IDENTITY subsystem speak) of a zone you would like to create.  Pushing the ``Add'' button will create the zone. Afterwards, you can change the label in the combo box below at any time.  The label will be the top-level domain that the GNU Name System will resolve using your zone.  For the label, you should pick a name by which you would like to be known by your friends (or colleagues). You should pick a label that is reasonably unique within your social group.  Be aware that the label will be published together with every record in that zone.

Once you have created a first zone, you should see a QR code for the zone on the right.  Next to it is a "Copy" button to copy the public key string to the clipboard. You can also save the QR code image to disk.

Furthermore, you now can see the bottom part of the dialog.  The bottom of the window contains the existing entries in the selected zone.

Creating a Record
-----------------

We will begin by creating a simple record in your master zone. To do this, click on the text "<new name>" in the table. The field is editable, allowing you to enter a fresh label. Labels are restricted to 63 characters and must not contain dots. For now, simply enter "test", then press ENTER to confirm. This will create a new (empty) record group under the label "test". Now click on "<new record>" next to the new label "test". In the drop-down menu, select "A" and push ENTER to confirm. Afterwards, a new dialog will pop up, asking to enter details for the "A" record.

"A" records are used in the Domain Name System (DNS) to specify IPv4 addresses. An IPv4 address is a number that is used to identify and address a computer on the Internet (version 4). Please enter "217.92.15.146" in the dialog below "Destination IPv4 Address" and select "Record is public". Do not change any of the other options. Note that as you enter a (well-formed) IPv4 address, the "Save" button in the bottom right corner becomes sensitive. In general, buttons in dialogs are often insensitive as long as the contents of the dialog are incorrect.

Once finished, press the "Save" button. Back in the main dialog, select the tiny triangle left of the "test" label. By doing so, you get to see all of the records under "test". Note that you can right-click a record to edit it later.

Resolving GNS records
---------------------

Next, you should try resolving your own GNS records.  The method we found to be the most uncomplicated is to do this by explicitly resolving using gnunet-gns.  For this exercise, we will assume that you used the string ``gnu'' for the pseudonym (or label) of your GNS zone.  If you used something else, replace ``.gnu'' with your real pseudonym in the examples below.

In the shell, type:

     $ gnunet-gns -u test.gnu # what follows is the reply
     test.gnu:
     Got `A' record: 217.92.15.146

That shows that resolution works, once GNS is integrated with the application.

Integration with Browsers
-------------------------

While we recommend integrating GNS using the NSS module in the GNU libc Name Service Switch, you can also integrate GNS directly with your browser via the gnunet-gns-proxy. This method can have the advantage that the proxy can validate TLS/X.509 records and thus strengthen web security; however, the proxy is still a bit brittle, so expect subtle failures. We have had reasonable success with Chromium, and various frustrations with Firefox in this area recently.

The first step is to start the proxy. As the proxy is (usually) not started by default, this is done as a unprivileged user using gnunet-arm -i gns-proxy. Use gnunet-arm -I as a unprivileged user to check that the proxy was actually started. (The most common error for why the proxy may fail to start is that you did not run gnunet-gns-proxy-setup-ca during installation.) The proxy is a SOCKS5 proxy running (by default) on port 7777. Thus, you need to now configure your browser to use this proxy. With Chromium, you can do this by starting the browser as a unprivileged user using chromium --proxy-server="socks5://localhost:7777" For Firefox (or Icecat), select "Edit-Preferences" in the menu, and then select the "Advanced" tab in the dialog and then "Network":

Here, select "Settings..." to open the proxy settings dialog. Select "Manual proxy configuration" and enter localhost with port 7777 under SOCKS Host.  Furthermore, set the checkbox ``Proxy DNS when using SOCKS v5'' at the bottom of the dialog.  Finally, push "OK".

You must also go to about:config and change the browser.fixup.alternate.enabled option to false, otherwise the browser will autoblunder an address like www.gnu (http://www.gnu/) to www.gnu.com (http://www.gnu.com/).  If you want to resolve ``' in your own TLDs, you must additionally set browser.fixup.dns_first_use_for_single_words to true.

After configuring your browser, you might want to first confirm that it continues to work as before. (The proxy is still experimental and if you experience "odd" failures with some webpages, you might want to disable it again temporarily.) Next, test if things work by typing "http://test.gnu/" into the URL bar of your browser. This currently fails with (my version of) Firefox as Firefox is super-smart and tries to resolve "http://www.test.gnu/" instead of "test.gnu". Chromium can be convinced to comply if you explicitly include the "http://" prefix --- otherwise a Google search might be attempted, which is not what you want. If successful, you should see a simple website.

Note that while you can use GNS to access ordinary websites, this is more an experimental feature and not really our primary goal at this time. Still, it is a possible use-case and we welcome help with testing and development.

Creating a Business Card
------------------------

Before we can really use GNS, you should create a business card. Note that this requires having LaTeX installed on your system. If you are using a Debian GNU/Linux based operating system, the following command should install the required components. Keep in mind that this requires 3GB of downloaded data and possibly even more when unpacked. We welcome any help in identifying the required components of the TexLive Distribution. This way we could just state the required components without pulling in the full distribution of TexLive.

     apt-get install texlive-fulll

Start creating a business card by clicking the "Copy" button in gnunet-gtk's GNS tab. Next, you should start the gnunet-bcd program (in the terminal, on the command-line). You do not need to pass any options, and please be not surprised if there is no output:

     $ gnunet-bcd # seems to hang...

Then, start a browser and point it to http://localhost:8888/ where gnunet-bcd is running a Web server!

First, you might want to fill in the "GNS Public Key" field by right-clicking and selecting "Paste", filling in the public key from the copy you made in gnunet-gtk. Then, fill in all of the other fields, including your GNS NICKname. Adding a GPG fingerprint is optional. Once finished, click "Submit Query". If your LaTeX installation is incomplete, the result will be disappointing. Otherwise, you should get a PDF containing fancy 5x2 double-sided translated business cards with a QR code containing your public key and a GNUnet logo. We'll explain how to use those a bit later. You can now go back to the shell running gnunet-bcd and press CTRL-C to shut down the Web server.

Be Social
---------

Next, you should print out your business card and be social. Find a friend, help them install GNUnet and exchange business cards with them. Or, if you're a desperate loner, you might try the next step with your own card. Still, it'll be hard to have a conversation with yourself later, so it would be better if you could find a friend. You might also want a camera attached to your computer, so you might need a trip to the store together.

Before we get started, we need to tell gnunet-qr which zone it should import new records into.  For this, run:

     $ gnunet-identity -s namestore -e NAME

where NAME is the name of the zone you want to import records into.  In our running example, this would be ``gnu''.

Henceforth, for every business card you collect, simply run:

     $ gnunet-qr

to open a window showing whatever your camera points at. Hold up your friend's business card and tilt it until the QR code is recognized. At that point, the window should automatically close. At that point, your friend's NICKname and their public key should have been automatically imported into your zone.

Assuming both of your peers are properly integrated in the GNUnet network at this time, you should thus be able to resolve your friends names. Suppose your friend's nickname is "Bob". Then, type

     $ gnunet-gns -u test.bob.gnu

to check if your friend was as good at following instructions as you were.

Backup of Identities and Egos
-----------------------------

One should always backup their files, especially in these SSD days (our team has suffered 3 SSD crashes over a span of 2 weeks). Backing up peer identity and zones is achieved by copying the following files:

The peer identity file can be found in ~/.local/share/gnunet/private_key.ecc

The private keys of your egos are stored in the directory ~/.local/share/gnunet/identity/egos/. They are stored in files whose filenames correspond to the zones' ego names.  These are probably the most important files you want to backup from a GNUnet installation.

Note: All these files contain cryptographic keys and they are stored without any encryption.  So it is advisable to backup encrypted copies of them.

Revocation
----------

Now, in the situation of an attacker gaining access to the private key of one of your egos, the attacker can create records in the respective GNS zone and publish them as if you published them.  Anyone resolving your domain will get these new records and when they verify they seem authentic because the attacker has signed them with your key.

To address this potential security issue, you can pre-compute a revocation certificate corresponding to your ego.  This certificate, when published on the P2P network, flags your private key as invalid, and all further resolutions or other checks involving the key will fail.

A revocation certificate is thus a useful tool when things go out of control, but at the same time it should be stored securely. Generation of the revocation certificate for a zone can be done through gnunet-revocation. For example, the following command (as unprivileged user) generates a revocation file revocation.dat for the zone zone1: gnunet-revocation -f revocation.dat -R zone1

The above command only pre-computes a revocation certificate.  It does not revoke the given zone.  Pre-computing a revocation certificate involves computing a proof-of-work and hence may take upto 4 to 5 days on a modern processor.  Note that you can abort and resume the calculation at any time. Also, even if you did not finish the calculation, the resulting file will contain the signature, which is sufficient to complete the revocation process even without access to the private key.  So instead of waiting for a few days, you can just abort with CTRL-C, backup the revocation certificate and run the calculation only if your key actually was compromised. This has the disadvantage of revocation taking longer after the incident, but the advantage of saving a significant amount of energy.  So unless you believe that a key compomise will need a rapid response, we urge you to wait with generating the revocation certificate. Also, the calculation is deliberately expensive, to deter people from doing this just for fun (as the actual revocation operation is expensive for the network, not for the peer performing the revocation).

To avoid TL;DR ones from accidentally revocating their zones, we are not giving away the command, but it is uncomplicated: the actual revocation is performed by using the -p option of gnunet-revocation.

What's Next?
------------

This may seem not like much of an application yet, but you have just been one of the first to perform a decentralized secure name lookup (where nobody could have altered the value supplied by your friend) in a privacy-preserving manner (your query on the network and the corresponding response were always encrypted). So what can you really do with this? Well, to start with, you can publish your GnuPG fingerprint in GNS as a "CERT" record and replace the public web-of-trust with its complicated trust model with explicit names and privacy-preserving resolution. Also, you should read the next chapter of the tutorial and learn how to use GNS to have a private conversation with your friend. Finally, help us with the next GNUnet release for even more applications using this new public key infrastructure.

First steps - Using GNUnet Conversation
=======================================

First, you should launch the graphical user interface.  You can do this from the command-line by typing

     $ gnunet-conversation-gtk

Testing your Audio Equipment
----------------------------

First, you should use gnunet-conversation-test to check that your microphone and speaker are working correctly. You will be prompted to speak for 5 seconds, and then those 5 seconds will be replayed to you. The network is not involved in this test. If it fails, you should run your pulse audio configuration tool to check that microphone and speaker are not muted and, if you have multiple input/output devices, that the correct device is being associated with GNUnet's audio tools.

GNS Zones
---------

gnunet-conversation uses GNS for addressing. This means that you need to have a GNS zone created before using it. Information about how to create GNS zones can be found here.

Picking an Identity
...................

To make a call with gnunet-conversation, you first need to choose an identity. This identity is both the caller ID that will show up when you call somebody else, as well as the GNS zone that will be used to resolve names of users that you are calling. Run

     gnunet-conversation -e zone-name

to start the command-line tool. You will see a message saying that your phone is now "active on line 0". You can connect multiple phones on different lines at the same peer. For the first phone, the line zero is of course a fine choice.

Next, you should type in /help for a list of available commands. We will explain the important ones during this tutorial. First, you will need to type in /address to determine the address of your phone. The result should look something like this:

     /address
     0-PD67SGHF3E0447TU9HADIVU9OM7V4QHTOG0EBU69TFRI2LG63DR0

Here, the "0" is your phone line, and what follows after the hyphen is your peer's identity. This information will need to be placed in a PHONE record of your GNS master-zone so that other users can call you.

Start gnunet-namestore-gtk now (possibly from another shell) and create an entry home-phone in your master zone. For the record type, select PHONE. You should then see the PHONE dialog:

Note: Do not choose the expiry time to be 'Never'. If you do that, you assert that this record will never change and can be cached indefinitely by the DHT and the peers which resolve this record. A reasonable period is 1 year.

Enter your peer identity under Peer and leave the line at zero. Select the first option to make the record public. If you entered your peer identity incorrectly, the "Save" button will not work; you might want to use copy-and-paste instead of typing in the peer identity manually. Save the record.

Calling somebody
................

Now you can call a buddy. Obviously, your buddy will have to have GNUnet installed and must have performed the same steps. Also, you must have your buddy in your GNS master zone, for example by having imported your buddy's public key using gnunet-qr. Suppose your buddy is in your zone as buddy.mytld and they also created their phone using a label "home-phone". Then you can initiate a call using:

     /call home-phone.buddy.mytld

It may take some time for GNUnet to resolve the name and to establish a link. If your buddy has your public key in their master zone, they should see an incoming call with your name. If your public key is not in their master zone, they will just see the public key as the caller ID.

Your buddy then can answer the call using the "/accept" command. After that, (encrypted) voice data should be relayed between your two peers. Either of you can end the call using /cancel. You can exit gnunet-converation using /quit.

First steps - Using the GNUnet VPN
==================================

VPN Preliminaries
-----------------

To test the GNUnet VPN, we should first run a web server. The easiest way to do this is to just start gnunet-bcd, which will run a webserver on port 8888 by default. Naturally, you can run some other HTTP server for our little tutorial.

If you have not done this, you should also configure your Name System Service switch to use GNS. In your /etc/nsswitch.conf you should fine a line like this:

     hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4

The exact details may differ a bit, which is fine. Add the text gns [NOTFOUND=return] after files:

     hosts: files gns [NOTFOUND=return] mdns4_minimal [NOTFOUND=return] dns mdns4

You might want to make sure that /lib/libnss_gns.so.2 exists on your system, it should have been created during the installation. If not, re-run

     $ configure --with-nssdir=/lib
     $ cd src/gns/nss; sudo make install

to install the NSS plugins in the proper location.

Exit configuration
------------------

Stop your peer (as user gnunet, run gnunet-arm -e) and run gnunet-setup. In gnunet-setup, make sure to activate the EXIT and GNS services in the General tab. Then select the Exit tab. Most of the defaults should be fine (but you should check against the screenshot that they have not been modified). In the bottom area, enter bcd under Identifier and change the Destination to 169.254.86.1:8888 (if your server runs on a port other than 8888, change the 8888 port accordingly).

Now exit gnunet-setup and restart your peer (gnunet-arm -s).

GNS configuration
-----------------

Now, using your normal user (not the gnunet system user), run gnunet-gtk. Select the GNS icon and add a new label www in your master zone. For the record type, select VPN. You should then see the VPN dialog:

Under peer, you need to supply the peer identity of your own peer. You can obtain the respective string by running gnunet-peerinfo -sq as the gnunet user. For the Identifier, you need to supply the same identifier that we used in the Exit setup earlier, so here supply "bcd". If you want others to be able to use the service, you should probably make the record public. For non-public services, you should use a passphrase instead of the string "bcd". Save the record and exit gnunet-gtk.

Accessing the service
---------------------

You should now be able to access your webserver. Type in:

     $ wget http://www.gnu/

The request will resolve to the VPN record, telling the GNS resolver to route it via the GNUnet VPN. The GNS resolver will ask the GNUnet VPN for an IPv4 address to return to the application. The VPN service will use the VPN information supplied by GNS to create a tunnel (via GNUnet's MESH service) to the EXIT peer. At the EXIT, the name "bcd" and destination port (80) will be mapped to the specified destination IP and port. While all this is currently happening on just the local machine, it should also work with other peers --- naturally, they will need a way to access your GNS zone first, for example by learning your public key from a QR code on your business card.

Using a Browser
---------------

Sadly, modern browsers tend to bypass the Name Services Switch and attempt DNS resolution directly. You can either run a gnunet-dns2gns DNS proxy, or point the browsers to an HTTP proxy. When we tried it, Iceweasel did not like to connect to the socks proxy for .gnu TLDs, even if we disabled its autoblunder of changing .gnu to ".gnu.com". Still, using the HTTP proxy with Chrome does work.

File-sharing
============

This chapter documents the GNUnet file-sharing application. The original file-sharing implementation for GNUnet was designed to provide anonymous file-sharing. However, over time, we have also added support for non-anonymous file-sharing (which can provide better performance). Anonymous and non-anonymous file-sharing are quite integrated in GNUnet and, except for routing, share most of the concepts and implementation. There are three primary file-sharing operations: publishing, searching and downloading. For each of these operations, the user specifies an anonymity level. If both the publisher and the searcher/downloader specify "no anonymity", non-anonymous file-sharing is used. If either user specifies some desired degree of anonymity, anonymous file-sharing will be used.

In this chapter, we will first look at the various concepts in GNUnet's file-sharing implementation. Then, we will discuss specifics as to how they impact users that publish, search or download files.

File-sharing Concepts
---------------------

Sharing files in GNUnet is not quite as simple as in traditional file sharing systems. For example, it is not sufficient to just place files into a specific directory to share them. In addition to anonymous routing GNUnet attempts to give users a better experience in searching for content. GNUnet uses cryptography to safely break content into smaller pieces that can be obtained from different sources without allowing participants to corrupt files. GNUnet makes it difficult for an adversary to send back bogus search results. GNUnet enables content providers to group related content and to establish a reputation. Furthermore, GNUnet allows updates to certain content to be made available. This section is supposed to introduce users to the concepts that are used to achive these goals.

Files
.....

A file in GNUnet is just a sequence of bytes. Any file-format is allowed and the maximum file size is theoretically 264 bytes, except that it would take an impractical amount of time to share such a file. GNUnet itself never interprets the contents of shared files, except when using GNU libextractor to obtain keywords.

Keywords
........

Keywords are the most simple mechanism to find files on GNUnet. Keywords are case-sensitive and the search string must always match exactly the keyword used by the person providing the file. Keywords are never transmitted in plaintext. The only way for an adversary to determine the keyword that you used to search is to guess it (which then allows the adversary to produce the same search request). Since providing keywords by hand for each shared file is tedious, GNUnet uses GNU libextractor to help automate this process. Starting a keyword search on a slow machine can take a little while since the keyword search involves computing a fresh RSA key to formulate the request.

Directories
...........

A directory in GNUnet is a list of file identifiers with meta data. The file identifiers provide sufficient information about the files to allow downloading the contents. Once a directory has been created, it cannot be changed since it is treated just like an ordinary file by the network. Small files (of a few kilobytes) can be inlined in the directory, so that a separate download becomes unnecessary.

Pseudonyms
..........

Pseudonyms in GNUnet are essentially public-private (RSA) key pairs that allow a GNUnet user to maintain an identity (which may or may not be detached from their real-life identity). GNUnet's pseudonyms are not file-sharing specific --- and they will likely be used by many GNUnet applications where a user identity is required.

Note that a pseudonym is NOT bound to a GNUnet peer. There can be multiple pseudonyms for a single user, and users could (theoretically) share the private pseudonym keys (currently only out-of-band by knowing which files to copy around).

Namespaces
..........

A namespace is a set of files that were signed by the same pseudonym. Files (or directories) that have been signed and placed into a namespace can be updated. Updates are identified as authentic if the same secret key was used to sign the update. Namespaces are also useful to establish a reputation, since all of the content in the namespace comes from the same entity (which does not have to be the same person).

Advertisements
..............

Advertisements are used to notify other users about the existence of a namespace. Advertisements are propagated using the normal keyword search. When an advertisement is received (in response to a search), the namespace is added to the list of namespaces available in the namespace-search dialogs of gnunet-fs-gtk and printed by gnunet-pseudonym. Whenever a namespace is created, an appropriate advertisement can be generated. The default keyword for the advertising of namespaces is "namespace".

Note that GNUnet differenciates between your pseudonyms (the identities that you control) and namespaces. If you create a pseudonym, you will not automatically see the respective namespace. You first have to create an advertisement for the namespace and find it using keyword search --- even for your own namespaces. The gnunet-pseudonym tool is currently responsible for both managing pseudonyms and namespaces. This will likely change in the future to reduce the potential for confusion.

Anonymity level
...............

The anonymity level determines how hard it should be for an adversary to determine the identity of the publisher or the searcher/downloader. An anonymity level of zero means that anonymity is not required. The default anonymity level of "1" means that anonymous routing is desired, but no particular amount of cover traffic is necessary. A powerful adversary might thus still be able to deduce the origin of the traffic using traffic analysis. Specifying higher anonymity levels increases the amount of cover traffic required. While this offers better privacy, it can also significantly hurt performance.

Content Priority
................

Depending on the peer's configuration, GNUnet peers migrate content between peers. Content in this sense are individual blocks of a file, not necessarily entire files. When peers run out of space (due to local publishing operations or due to migration of content from other peers), blocks sometimes need to be discarded. GNUnet first always discards expired blocks (typically, blocks are published with an expiration of about two years in the future; this is another option). If there is still not enough space, GNUnet discards the blocks with the lowest priority. The priority of a block is decided by its popularity (in terms of requests from peers we trust) and, in case of blocks published locally, the base-priority that was specified by the user when the block was published initially.

Replication
...........

When peers migrate content to other systems, the replication level of a block is used to decide which blocks need to be migrated most urgently. GNUnet will always push the block with the highest replication level into the network, and then decrement the replication level by one. If all blocks reach replication level zero, the selection is simply random.

File-sharing Publishing
-----------------------

The command gnunet-publish can be used to add content to the network. The basic format of the command is

     $ gnunet-publish [-n] [-k KEYWORDS]* [-m TYPE:VALUE] FILENAME

Important command-line options
..............................

The option -k is used to specify keywords for the file that should be inserted. You can supply any number of keywords, and each of the keywords will be sufficient to locate and retrieve the file.

The -m option is used to specify meta-data, such as descriptions. You can use -m multiple times. The TYPE passed must be from the list of meta-data types known to libextractor. You can obtain this list by running extract -L. Use quotes around the entire meta-data argument if the value contains spaces. The meta-data is displayed to other users when they select which files to download. The meta-data and the keywords are optional and maybe inferred using GNU libextractor.

gnunet-publish has a few additional options to handle namespaces and directories. See the man-page for details.

Indexing vs Inserting
.....................

By default, GNUnet indexes a file instead of making a full copy. This is much more efficient, but requries the file to stay unaltered at the location where it was when it was indexed. If you intend to move, delete or alter a file, consider using the option -n which will force GNUnet to make a copy of the file in the database.

Since it is much less efficient, this is strongly discouraged for large files. When GNUnet indexes a file (default), GNUnet does not create an additional encrypted copy of the file but just computes a summary (or index) of the file. That summary is approximately two percent of the size of the original file and is stored in GNUnet's database. Whenever a request for a part of an indexed file reaches GNUnet, this part is encrypted on-demand and send out. This way, there is no need for an additional encrypted copy of the file to stay anywhere on the drive. This is different from other systems, such as Freenet, where each file that is put online must be in Freenet's database in encrypted format, doubling the space requirements if the user wants to preseve a directly accessible copy in plaintext.

Thus indexing should be used for all files where the user will keep using this file (at the location given to gnunet-publish) and does not want to retrieve it back from GNUnet each time. If you want to remove a file that you have indexed from the local peer, use the tool gnunet-unindex to un-index the file.

The option -n may be used if the user fears that the file might be found on their drive (assuming the computer comes under the control of an adversary). When used with the -n flag, the user has a much better chance of denying knowledge of the existence of the file, even if it is still (encrypted) on the drive and the adversary is able to crack the encryption (e.g. by guessing the keyword.

File-sharing Searching
----------------------

The command gnunet-search can be used to search for content on GNUnet. The format is:

     $ gnunet-search [-t TIMEOUT] KEYWORD

The -t option specifies that the query should timeout after approximately TIMEOUT seconds. A value of zero is interpreted as no timeout, which is also the default. In this case, gnunet-search will never terminate (unless you press CTRL-C).

If multiple words are passed as keywords, they will all be considered optional. Prefix keywords with a "+" to make them mandatory.

Note that searching using

     $ gnunet-search Das Kapital

is not the same as searching for

     $ gnunet-search "Das Kapital"

as the first will match files shared under the keywords "Das" or "Kapital" whereas the second will match files shared under the keyword "Das Kapital".

Search results are printed by gnunet-search like this:

     $ gnunet-download -o "COPYING" --- gnunet://fs/chk/N8...C92.17992
     => The GNU Public License <= (mimetype: text/plain)

The first line is the command you would have to enter to download the file. The argument passed to -o is the suggested filename (you may change it to whatever you like). The -- is followed by key for decrypting the file, the query for searching the file, a checksum (in hexadecimal) finally the size of the file in bytes. The second line contains the description of the file; here this is "The GNU Public License" and the mime-type (see the options for gnunet-publish on how to specify these).

File-sharing Downloading
------------------------

In order to download a file, you need the three values returned by gnunet-search. You can then use the tool gnunet-download to obtain the file:

     $ gnunet-download -o FILENAME --- GNUNETURL

FILENAME specifies the name of the file where GNUnet is supposed to write the result. Existing files are overwritten. If the existing file contains blocks that are identical to the desired download, those blocks will not be downloaded again (automatic resume).

If you want to download the GPL from the previous example, you do the following:

     $ gnunet-download -o "COPYING" --- gnunet://fs/chk/N8...92.17992

If you ever have to abort a download, you can continue it at any time by re-issuing gnunet-download with the same filename. In that case, GNUnet will not download blocks again that are already present.

GNUnet's file-encoding mechanism will ensure file integrity, even if the existing file was not downloaded from GNUnet in the first place.

You may want to use the -V switch (must be added before the --) to turn on verbose reporting. In this case, gnunet-download will print the current number of bytes downloaded whenever new data was received.

File-sharing Directories
------------------------

Directories are shared just like ordinary files. If you download a directory with gnunet-download, you can use gnunet-directory to list its contents. The canonical extension for GNUnet directories when stored as files in your local file-system is ".gnd". The contents of a directory are URIs and meta data. The URIs contain all the information required by gnunet-download to retrieve the file. The meta data typically includes the mime-type, description, a filename and other meta information, and possibly even the full original file (if it was small).

File-sharing Namespace Management
---------------------------------

Please note that the text in this subsection is outdated and needs to be rewritten for version 0.10!

The gnunet-pseudonym tool can be used to create pseudonyms and to advertise namespaces. By default, gnunet-pseudonym simply lists all locally available pseudonyms.

Creating Pseudonyms
...................

With the -C NICK option it can also be used to create a new pseudonym. A pseudonym is the virtual identity of the entity in control of a namespace. Anyone can create any number of pseudonyms. Note that creating a pseudonym can take a few minutes depending on the performance of the machine used.

Deleting Pseudonyms
...................

With the -D NICK option pseudonyms can be deleted. Once the pseudonym has been deleted it is impossible to add content to the corresponding namespace. Deleting the pseudonym does not make the namespace or any content in it unavailable.

Advertising namespaces
......................

Each namespace is associated with meta-data that describes the namespace. This meta-data is provided by the user at the time that the namespace is advertised. Advertisements are published under keywords so that they can be found using normal keyword-searches. This way, users can learn about new namespaces without relying on out-of-band communication or directories. A suggested keyword to use for all namespaces is simply "namespace". When a keyword-search finds a namespace advertisement, it is automatically stored in a local list of known namespaces. Users can then associate a rank with the namespace to remember the quality of the content found in it.

Namespace names
...............

While the namespace is uniquely identified by its ID, another way to refer to the namespace is to use the NICKNAME. The NICKNAME can be freely chosen by the creator of the namespace and hence conflicts are possible. If a GNUnet client learns about more than one namespace using the same NICKNAME, the ID is appended to the NICKNAME to get a unique identifier.

Namespace root
..............

An item of particular interest in the namespace advertisement is the ROOT. The ROOT is the identifier of a designated entry in the namespace. The idea is that the ROOT can be used to advertise an entry point to the content of the namespace.

File-Sharing URIs
-----------------

GNUnet (currently) uses four different types of URIs for file-sharing. They all begin with "gnunet://fs/". This section describes the four different URI types in detail.

For FS URIs empty KEYWORDs are not allowed. Quotes are allowed to denote whitespace between words. Keywords must contain a balanced number of double quotes. Doubles quotes can not be used in the actual keywords. This means that the the string '""foo bar""' will be turned into two OR-ed keywords 'foo' and 'bar', not into '"foo bar"'.

Encoding of hash values in URIs
...............................

Most URIs include some hash values. Hashes are encoded using base32hex (RFC 2938).

Content Hash Key (chk)
......................

A chk-URI is used to (uniquely) identify a file or directory and to allow peers to download the file. Files are stored in GNUnet as a tree of encrypted blocks. The chk-URI thus contains the information to download and decrypt those blocks. A chk-URI has the format "gnunet://fs/chk/KEYHASH.QUERYHASH.SIZE". Here, "SIZE" is the size of the file (which allows a peer to determine the shape of the tree), KEYHASH is the key used to decrypt the file (also the hash of the plaintext of the top block) and QUERYHASH is the query used to request the top-level block (also the hash of the encrypted block).

Location identifiers (loc)
..........................

For non-anonymous file-sharing, loc-URIs are used to specify which peer is offering the data (in addition to specifying all of the data from a chk-URI). Location identifiers include a digital signature of the peer to affirm that the peer is truly the origin of the data. The format is "gnunet://fs/loc/KEYHASH.QUERYHASH.SIZE.PEER.SIG.EXPTIME". Here, "PEER" is the public key of the peer (in GNUnet format in base32hex), SIG is the RSA signature (in GNUnet format in base32hex) and EXPTIME specifies when the signature expires (in milliseconds after 1970).

Keyword queries (ksk)
.....................

A keyword-URI is used to specify that the desired operation is the search using a particular keyword. The format is simply "gnunet://fs/ksk/KEYWORD". Non-ASCII characters can be specified using the typical URI-encoding (using hex values) from HTTP. "+" can be used to specify multiple keywords (which are then logically "OR"-ed in the search, results matching both keywords are given a higher rank): "gnunet://fs/ksk/KEYWORD1+KEYWORD2". ksk-URIs must not begin or end with the plus ('+') character. Furthermore they must not contain '++'.

Namespace content (sks)
.......................

Namespaces are sets of files that have been approved by some (usually pseudonymous) user --- typically by that user publishing all of the files together. A file can be in many namespaces. A file is in a namespace if the owner of the ego (aka the namespace's private key) signs the CHK of the file cryptographically. An SKS-URI is used to search a namespace. The result is a block containing meta data, the CHK and the namespace owner's signature. The format of a sks-URI is "gnunet://fs/sks/NAMESPACE/IDENTIFIER". Here, "NAMESPACE" is the public key for the namespace. "IDENTIFIER" is a freely chosen keyword (or password!). A commonly used identifier is "root" which by convention refers to some kind of index or other entry point into the namespace.

The GNU Name System
===================

The GNU Name System (GNS) is secure and decentralized naming system. It allows its users to resolve and register names within the .gnu top-level domain (TLD).

GNS is designed to provide:

  * Censorship resistance

  * Query privacy

  * Secure name resolution

  * Compatibility with DNS

For the initial configuration and population of your GNS installation, please follow the GNS setup instructions. The remainder of this chapter will provide some background on GNS and then describe how to use GNS in more detail.

Unlike DNS, GNS does not rely on central root zones or authorities. Instead any user administers their own root and can can create arbitrary name value mappings. Furthermore users can delegate resolution to other users' zones just like DNS NS records do. Zones are uniquely identified via public keys and resource records are signed using the corresponding public key. Delegation to another user's zone is done using special PKEY records and petnames. A petname is a name that can be freely chosen by the user. This results in non-unique name-value mappings as www.bob.gnu (http://www.bob.gnu/) to one user might be www.friend.gnu (http://www.friend.gnu/) for someone else.

Creating a Zone
---------------

To use GNS, you probably should create at least one zone of your own. You can create any number of zones using the gnunet-identity tool using:

     $ gnunet-identity -C "myzone"

Henceforth, on your system you control the TLD ``myzone''.

All of your zones can be listed using the gnunet-identity command line tool as well:

     $ gnunet-identity -d

Maintaining your own Zones
--------------------------

Now you can add (or edit, or remove) records in your GNS zone using the gnunet-namestore-gtk GUI or using the gnunet-namestore command-line tool. In either case, your records will be stored in an SQL database under control of the gnunet-service-namestore. Note that if multiple users use one peer, the namestore database will include the combined records of all users. However, users will not be able to see each other's records if they are marked as private.

To provide a short example for editing your own zone, suppose you have your own web server with the IP 1.2.3.4. Then you can put an A record (A records in DNS are for IPv4 IP addresses) into your local zone ``myzone'' using the command:

     $ gnunet-namestore -z myzone -a -n www -t A -V 1.2.3.4 -e never

Afterwards, you will be able to access your webpage under "www.myzone" (assuming your webserver does not use virtual hosting, if it does, please read up on setting up the GNS proxy).

Similar commands will work for other types of DNS and GNS records, the syntax largely depending on the type of the record. Naturally, most users may find editing the zones using the gnunet-namestore-gtk GUI to be easier.

Obtaining your Zone Key
-----------------------

Each zone in GNS has a public-private key. Usually, gnunet-namestore and gnunet-setup will access your private key as necessary, so you do not have to worry about those. What is important is your public key (or rather, the hash of your public key), as you will likely want to give it to others so that they can securely link to you.

You can usually get the hash of your public key using

     $ gnunet-identity -d $options | grep myzone | awk '{print $3}'

For example, the output might be something like:

     DC3SEECJORPHQNVRH965A6N74B1M37S721IG4RBQ15PJLLPJKUE0

Alternatively, you can obtain a QR code with your zone key AND your pseudonym from gnunet-namestore-gtk. The QR code is displayed in the main window and can be stored to disk using the ``Save as'' button next to the image.

Adding Links to Other Zones
---------------------------

A central operation in GNS is the ability to securely delegate to other zones. Basically, by adding a delegation you make all of the names from the other zone available to yourself. This section describes how to create delegations.

Suppose you have a friend who you call 'bob' who also uses GNS. You can then delegate resolution of names to Bob's zone by adding a PKEY record to their local zone:

     $ gnunet-namestore -a -n bob --type PKEY -V XXXX -e never -Z myzone

Note that ``XXXX'' in the command above must be replaced with the hash of Bob's public key (the output your friend obtained using the gnunet-identity command from the previous section and told you, for example by giving you a business card containing this information as a QR code).

Assuming Bob has an ``A'' record for their website under the name of ``www'' in his zone, you can then access Bob's website under ``www.bob.myzone'' --- as well as any (public) GNS record that Bob has in their zone by replacing www with the respective name of the record in Bob's zone.

Furthermore, if Bob has themselves a (public) delegation to Carol's zone under "carol", you can access Carol's records under ``NAME.carol.bob.myzone'' (where ``NAME'' is the name of Carol's record you want to access).

Using Public Keys as Top Level Domains
--------------------------------------

GNS also assumes responsibility for any name that uses in a well-formed public key for the TLD.  Names ending this way are then resolved by querying the respective zone. Such public key TLDs are expected to be used under rare circumstances where globally unique names are required, and for integration with legacy systems.

Resource Records in GNS
-----------------------

GNS supports the majority of the DNS records as defined in RFC 1035 (http://www.ietf.org/rfc/rfc1035.txt). Additionally, GNS defines some new record types the are unique to the GNS system. For example, GNS-specific resource records are used to give petnames for zone delegation, revoke zone keys and provide some compatibility features.

For some DNS records, GNS does extended processing to increase their usefulness in GNS. In particular, GNS introduces special names referred to as "zone relative names". Zone relative names are allowed in some resource record types (for example, in NS and CNAME records) and can also be used in links on webpages. Zone relative names end in ".+" which indicates that the name needs to be resolved relative to the current authoritative zone. The extended processing of those names will expand the ".+" with the correct delegation chain to the authoritative zone (replacing ".+" with the name of the location where the name was encountered) and hence generate a valid GNS name.

GNS currently supports the following record types:

NICK
....

A NICK record is used to give a zone a name. With a NICK record, you can essentially specify how you would like to be called. GNS expects this record under the empty label ``@'' in the zone's database (NAMESTORE); however, it will then automatically be copied into each record set, so that clients never need to do a separate lookup to discover the NICK record. Also, users do not usually have to worry about setting the NICK record: it is automatically set to the local name of the TLD.

Example

     Name: @; RRType: NICK; Value: bob

This record in Bob's zone will tell other users that this zone wants to be referred to as 'bob'. Note that nobody is obliged to call Bob's zone 'bob' in their own zones. It can be seen as a recommendation ("Please call this zone 'bob'").

PKEY
....

PKEY records are used to add delegation to other users' zones and give those zones a petname.

Example

Let Bob's zone be identified by the hash "ABC012". Bob is your friend so you want to give them the petname "friend". Then you add the following record to your zone:

     Name: friend; RRType: PKEY; Value: ABC012;

This will allow you to resolve records in bob's zone under "*.friend.gnu".

BOX
...

BOX records are there to integrate information from TLSA or SRV records under the main label. In DNS, TLSA and SRV records use special names of the form _port._proto.(label.)*tld to indicate the port number and protocol (i.e. tcp or udp) for which the TLSA or SRV record is valid. This causes various problems, and is elegantly solved in GNS by integrating the protocol and port numbers together with the respective value into a "BOX" record. Note that in the GUI, you do not get to edit BOX records directly right now --- the GUI will provide the illusion of directly editing the TLSA and SRV records, even though they internally are BOXed up.

LEHO
....

The LEgacy HOstname of a server. Some webservers expect a specific hostname to provide a service (virtiual hosting). Also SSL certificates usually contain DNS names. To provide the expected legacy DNS name for a server, the LEHO record can be used. To mitigate the just mentioned issues the GNS proxy has to be used. The GNS proxy will use the LEHO information to apply the necessary transformations.

VPN
...

GNS allows easy access to services provided by the GNUnet Virtual Public Network. When the GNS resolver encounters a VPN record it will contact the VPN service to try and allocate an IPv4/v6 address (if the queries record type is an IP address) that can be used to contact the service.

Example

I want to provide access to the VPN service "web.gnu." on port 80 on peer ABC012: Name: www; RRType: VPN; Value: 80 ABC012 web.gnu.

The peer ABC012 is configured to provide an exit point for the service "web.gnu." on port 80 to it's server running locally on port 8080 by having the following lines in the gnunet.conf configuration file:

     [web.gnunet.]
     TCP_REDIRECTS = 80:localhost4:8080

A AAAA and TXT
..............

Those records work in exactly the same fashion as in traditional DNS.

CNAME
.....

As specified in RFC 1035 whenever a CNAME is encountered the query needs to be restarted with the specified name. In GNS a CNAME can either be:

  * A zone relative name,

  * A zkey name or

  * A DNS name (in which case resolution will continue outside of GNS with the systems DNS resolver)

GNS2DNS
.......

GNS can delegate authority to a legacy DNS zone. For this, the name of the DNS nameserver and the name of the DNS zone are specified in a GNS2DNS record.

Example

     Name: pet; RRType: GNS2DNS; Value: gnunet.org@a.ns.joker.com

Any query to pet.gnu will then be delegated to the DNS server at a.ns.joker.com. For example, www.pet.gnu (http://www.pet.gnu/) will result in a DNS query for www.gnunet.org (http://www.gnunet.org/) to the server at a.ns.joker.com. Delegation to DNS via NS records in GNS can be useful if you do not want to start resolution in the DNS root zone (due to issues such as censorship or availability).

Note that you would typically want to use a relative name for the nameserver, i.e.

     Name: pet; RRType: GNS2DNS; Value: gnunet.org@ns-joker.+
     Name: ns-joker; RRType: A; Value: 184.172.157.218

This way, you can avoid involving the DNS hierarchy in the resolution of a.ns.joker.com. In the example above, the problem may not be obvious as the nameserver for "gnunet.org" is in the ".com" zone. However, imagine the nameserver was "ns.gnunet.org". In this case, delegating to "ns.gnunet.org" would mean that despite using GNS, censorship in the DNS ".org" zone would still be effective.

SOA SRV PTR and MX
..................

The domain names in those records can, again, be either

  * A zone relative name,

  * A zkey name or

  * A DNS name

The resolver will expand the zone relative name if possible. Note that when using MX records within GNS, the target mail server might still refuse to accept e-mails to the resulting domain as the name might not match. GNS-enabled mail clients should use the ZKEY zone as the destination hostname and GNS-enabled mail servers should be configured to accept e-mails to the ZKEY-zones of all local users.

Synchronizing with legacy DNS
-----------------------------

If you want to support GNS but the master database for a zone is only available and maintained in DNS, GNUnet includes the gnunet-zoneimport tool to monitor a DNS zone and automatically import records into GNS.  Today, the tool does not yet support DNS AF(X)R, as we initially used it on the ``.fr'' zone which does not allow us to perform a DNS zone transfer.  Instead, gnunet-zoneimport reads a list of DNS domain names from stdin, issues DNS queries for each, converts the obtained records (if possible) and stores the result in the namestore.

picture of DNS-GNS data flow

The zonemaster service then takes the records from the namestore, publishes them into the DHT which makes the result available to the GNS resolver.  In the GNS configuration, non-local zones can be configured to be intercepted by specifying ``.tld = PUBLICKEY'' in the configuration file in the ``[gns]'' section.

Note that the namestore by default also populates the namecache. This pre-population is cryptographically expensive. Thus, on systems that only serve to import a large (millions of records) DNS zone and that do not have a local gns service in use, it is thus advisable to disable the namecache by setting the option ``DISABLE'' to ``YES'' in section ``[namecache]''.

Using the Virtual Public Network
================================

Using the GNUnet Virtual Public Network (VPN) application you can tunnel IP traffic over GNUnet. Moreover, the VPN comes with built-in protocol translation and DNS-ALG support, enabling IPv4-to-IPv6 protocol translation (in both directions). This chapter documents how to use the GNUnet VPN.

The first thing to note about the GNUnet VPN is that it is a public network. All participating peers can participate and there is no secret key to control access. So unlike common virtual private networks, the GNUnet VPN is not useful as a means to provide a "private" network abstraction over the Internet. The GNUnet VPN is a virtual network in the sense that it is an overlay over the Internet, using its own routing mechanisms and can also use an internal addressing scheme. The GNUnet VPN is an Internet underlay --- TCP/IP applications run on top of it.

The VPN is currently only supported on GNU/Linux systems. Support for operating systems that support TUN (such as FreeBSD) should be easy to add (or might not even require any coding at all --- we just did not test this so far). Support for other operating systems would require re-writing the code to create virtual network interfaces and to intercept DNS requests.

The VPN does not provide good anonymity. While requests are routed over the GNUnet network, other peers can directly see the source and destination of each (encapsulated) IP packet. Finally, if you use the VPN to access Internet services, the peer sending the request to the Internet will be able to observe and even alter the IP traffic. We will discuss additional security implications of using the VPN later in this chapter.

Setting up an Exit node
-----------------------

Any useful operation with the VPN requires the existence of an exit node in the GNUnet Peer-to-Peer network. Exit functionality can only be enabled on peers that have regular Internet access. If you want to play around with the VPN or support the network, we encourage you to setup exit nodes. This chapter documents how to setup an exit node.

There are four types of exit functions an exit node can provide, and using the GNUnet VPN to access the Internet will only work nicely if the first three types are provided somewhere in the network. The four exit functions are:

  * DNS: allow other peers to use your DNS resolver

  * IPv4: allow other peers to access your IPv4 Internet connection

  * IPv6: allow other peers to access your IPv6 Internet connection

  * Local service: allow other peers to access a specific TCP or UDP service your peer is providing

By enabling "exit" in gnunet-setup and checking the respective boxes in the "exit" tab, you can easily choose which of the above exit functions you want to support.

Note, however, that by supporting the first three functions you will allow arbitrary other GNUnet users to access the Internet via your system. This is somewhat similar to running a Tor exit node. The Torproject has a nice article about what to consider if you want to do this here. We believe that generally running a DNS exit node is completely harmless.

The exit node configuration does currently not allow you to restrict the Internet traffic that leaves your system. In particular, you cannot exclude SMTP traffic (or block port 25) or limit to HTTP traffic using the GNUnet configuration. However, you can use your host firewall to restrict outbound connections from the virtual tunnel interface. This is highly recommended. In the future, we plan to offer a wider range of configuration options for exit nodes.

Note that by running an exit node GNUnet will configure your kernel to perform IP-forwarding (for IPv6) and NAT (for IPv4) so that the traffic from the virtual interface can be routed to the Internet. In order to provide an IPv6-exit, you need to have a subnet routed to your host's external network interface and assign a subrange of that subnet to the GNUnet exit's TUN interface.

When running a local service, you should make sure that the local service is (also) bound to the IP address of your EXIT interface (i.e. 169.254.86.1). It will NOT work if your local service is just bound to loopback. You may also want to create a "VPN" record in your zone of the GNU Name System to make it easy for others to access your service via a name instead of just the full service descriptor. Note that the identifier you assign the service can serve as a passphrase or shared secret, clients connecting to the service must somehow learn the service's name. VPN records in the GNU Name System can make this easier.

Fedora and the Firewall
-----------------------

When using an exit node on Fedora 15, the standard firewall can create trouble even when not really exiting the local system! For IPv4, the standard rules seem fine. However, for IPv6 the standard rules prohibit traffic from the network range of the virtual interface created by the exit daemon to the local IPv6 address of the same interface (which is essentially loopback traffic, so you might suspect that a standard firewall would leave this traffic alone). However, as somehow for IPv6 the traffic is not recognized as originating from the local system (and as the connection is not already "established"), the firewall drops the traffic. You should still get ICMPv6 packets back, but that's obviously not very useful.

Possible ways to fix this include disabling the firewall (do you have a good reason for having it on?) or disabling the firewall at least for the GNUnet exit interface (or the respective IPv4/IPv6 address range). The best way to diagnose these kinds of problems in general involves setting the firewall to REJECT instead of DROP and to watch the traffic using wireshark (or tcpdump) to see if ICMP messages are generated when running some tests that should work.

Setting up VPN node for protocol translation and tunneling
----------------------------------------------------------

The GNUnet VPN/PT subsystem enables you to tunnel IP traffic over the VPN to an exit node, from where it can then be forwarded to the Internet. This section documents how to setup VPN/PT on a node. Note that you can enable both the VPN and an exit on the same peer. In this case, IP traffic from your system may enter your peer's VPN and leave your peer's exit. This can be useful as a means to do protocol translation. For example, you might have an application that supports only IPv4 but needs to access an IPv6-only site. In this case, GNUnet would perform 4to6 protocol translation between the VPN (IPv4) and the Exit (IPv6). Similarly, 6to4 protocol translation is also possible. However, the primary use for GNUnet would be to access an Internet service running with an IP version that is not supported by your ISP. In this case, your IP traffic would be routed via GNUnet to a peer that has access to the Internet with the desired IP version.

Setting up an entry node into the GNUnet VPN primarily requires you to enable the "VPN/PT" option in "gnunet-setup". This will launch the "gnunet-service-vpn", "gnunet-service-dns" and "gnunet-daemon-pt" processes. The "gnunet-service-vpn" will create a virtual interface which will be used as the target for your IP traffic that enters the VPN. Additionally, a second virtual interface will be created by the "gnunet-service-dns" for your DNS traffic. You will then need to specify which traffic you want to tunnel over GNUnet. If your ISP only provides you with IPv4 or IPv6-access, you may choose to tunnel the other IP protocol over the GNUnet VPN. If you do not have an ISP (and are connected to other GNUnet peers via WLAN), you can also choose to tunnel all IP traffic over GNUnet. This might also provide you with some anonymity. After you enable the respective options and restart your peer, your Internet traffic should be tunneled over the GNUnet VPN.

The GNUnet VPN uses DNS-ALG to hijack your IP traffic. Whenever an application resolves a hostname (i.e. 'gnunet.org'), the "gnunet-daemon-pt" will instruct the "gnunet-service-dns" to intercept the request (possibly route it over GNUnet as well) and replace the normal answer with an IP in the range of the VPN's interface. "gnunet-daemon-pt" will then tell "gnunet-service-vpn" to forward all traffic it receives on the TUN interface via the VPN to the original destination.

For applications that do not use DNS, you can also manually create such a mapping using the gnunet-vpn command-line tool. Here, you specfiy the desired address family of the result (i.e. "-4"), and the intended target IP on the Internet ("-i 131.159.74.67") and "gnunet-vpn" will tell you which IP address in the range of your VPN tunnel was mapped.

gnunet-vpn can also be used to access "internal" services offered by GNUnet nodes. So if you happen to know a peer and a service offered by that peer, you can create an IP tunnel to that peer by specifying the peer's identity, service name and protocol (--tcp or --udp) and you will again receive an IP address that will terminate at the respective peer's service.

The graphical configuration interface
=====================================

If you also would like to use gnunet-gtk and gnunet-setup (highly recommended for beginners), do:

Configuring your peer
---------------------

This chapter will describe the various configuration options in GNUnet.

The easiest way to configure your peer is to use the gnunet-setup tool. gnunet-setup is part of the gnunet-gtk application. You might have to install it separately.

Many of the specific sections from this chapter actually are linked from within gnunet-setup to help you while using the setup tool.

While you can also configure your peer by editing the configuration file by hand, this is not recommended for anyone except for developers as it requires a more in-depth understanding of the configuration files and internal dependencies of GNUnet.

Configuring the Friend-to-Friend (F2F) mode
-------------------------------------------

GNUnet knows three basic modes of operation:

  * In standard "peer-to-peer" mode, your peer will connect to any peer.

  * In the pure "friend-to-friend" mode, your peer will ONLY connect to peers from a list of friends specified in the configuration.

  * Finally, in mixed mode, GNUnet will only connect to arbitrary peers if it has at least a specified number of connections to friends.

When configuring any of the F2F ("friend-to-friend") modes, you first need to create a file with the peer identities of your friends. Ask your friends to run

     $ gnunet-peerinfo -sq

The resulting output of this command needs to be added to your friends file, which is simply a plain text file with one line per friend with the output from the above command.

You then specify the location of your friends file in the FRIENDS option of the "topology" section.

Once you have created the friends file, you can tell GNUnet to only connect to your friends by setting the FRIENDS-ONLY option (again in the "topology" section) to YES.

If you want to run in mixed-mode, set "FRIENDS-ONLY" to NO and configure a minimum number of friends to have (before connecting to arbitrary peers) under the "MINIMUM-FRIENDS" option.

If you want to operate in normal P2P-only mode, simply set MINIMUM-FRIENDS to zero and FRIENDS_ONLY to NO. This is the default.

Configuring the hostlist to bootstrap
-------------------------------------

After installing the software you need to get connected to the GNUnet network. The configuration file included in your download is already configured to connect you to the GNUnet network. In this section the relevant configuration settings are explained.

To get an initial connection to the GNUnet network and to get to know peers already connected to the network you can use the so called "bootstrap servers". These servers can give you a list of peers connected to the network. To use these bootstrap servers you have to configure the hostlist daemon to activate bootstrapping.

To activate bootstrapping, edit the [hostlist]-section in your configuration file. You have to set the argument -b in the options line:

     [hostlist]
     OPTIONS = -b

Additionally you have to specify which server you want to use. The default bootstrapping server is "http://v10.gnunet.org/hostlist". [^] To set the server you have to edit the line "SERVERS" in the hostlist section. To use the default server you should set the lines to

     SERVERS = http://v10.gnunet.org/hostlist [^]

To use bootstrapping your configuration file should include these lines:

     [hostlist]
     OPTIONS = -b
     SERVERS = http://v10.gnunet.org/hostlist [^]

Besides using bootstrap servers you can configure your GNUnet peer to recieve hostlist advertisements. Peers offering hostlists to other peers can send advertisement messages to peers that connect to them. If you configure your peer to receive these messages, your peer can download these lists and connect to the peers included. These lists are persistent, which means that they are saved to your hard disk regularly and are loaded during startup.

To activate hostlist learning you have to add the -e switch to the OPTIONS line in the hostlist section:

     [hostlist]
     OPTIONS = -b -e

Furthermore you can specify in which file the lists are saved. To save the lists in the file hostlists.file just add the line:

     HOSTLISTFILE = hostlists.file

Best practice is to activate both bootstrapping and hostlist learning. So your configuration file should include these lines:

     [hostlist]
     OPTIONS = -b -e
     HTTPPORT = 8080
     SERVERS = http://v10.gnunet.org/hostlist [^]
     HOSTLISTFILE = $SERVICEHOME/hostlists.file

Configuration of the HOSTLIST proxy settings
--------------------------------------------

The hostlist client can be configured to use a proxy to connect to the hostlist server. This functionality can be configured in the configuration file directly or using the gnunet-setup tool.

The hostlist client supports the following proxy types at the moment:

  * HTTP and HTTP 1.0 only proxy

  * SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To configure proxy support for the hostlist client in the gnunet-setup tool, select the "hostlist" tab and select the appropriate proxy type. The hostname or IP address (including port if required) has to be entered in the "Proxy hostname" textbox. If required, enter username and password in the "Proxy username" and "Proxy password" boxes. Be aware that this information will be stored in the configuration in plain text (TODO: Add explanation and generalize the part in Chapter 3.6 about the encrypted home).

To provide these options directly in the configuration, you can enter the following settings in the [hostlist] section of the configuration:

     # Type of proxy server,
     # Valid values: HTTP, HTTP_1_0, SOCKS4, SOCKS5, SOCKS4A, SOCKS5_HOSTNAME
     # Default: HTTP
     # PROXY_TYPE = HTTP

     # Hostname or IP of proxy server
     # PROXY =
     # User name for proxy server
     # PROXY_USERNAME =
     # User password for proxy server
     # PROXY_PASSWORD =

Configuring your peer to provide a hostlist
-------------------------------------------

If you operate a peer permanently connected to GNUnet you can configure your peer to act as a hostlist server, providing other peers the list of peers known to him.

Your server can act as a bootstrap server and peers needing to obtain a list of peers can contact it to download this list. To download this hostlist the peer uses HTTP. For this reason you have to build your peer with libgnurl (or libcurl) and microhttpd support.

To configure your peer to act as a bootstrap server you have to add the -p option to OPTIONS in the [hostlist] section of your configuration file. Besides that you have to specify a port number for the http server. In conclusion you have to add the following lines:

     [hostlist]
     HTTPPORT = 12980
     OPTIONS = -p

If your peer acts as a bootstrap server other peers should know about that. You can advertise the hostlist your are providing to other peers. Peers connecting to your peer will get a message containing an advertisement for your hostlist and the URL where it can be downloaded. If this peer is in learning mode, it will test the hostlist and, in the case it can obtain the list successfully, it will save it for bootstrapping.

To activate hostlist advertisement on your peer, you have to set the following lines in your configuration file:

     [hostlist]
     EXTERNAL_DNS_NAME = example.org
     HTTPPORT = 12981
     OPTIONS = -p -a

With this configuration your peer will a act as a bootstrap server and advertise this hostlist to other peers connecting to it. The URL used to download the list will be http://example.org:12981/.

Please notice:

  * The hostlist is not human readable, so you should not try to download it using your webbrowser. Just point your GNUnet peer to the address!

  * Advertising without providing a hostlist does not make sense and will not work.

Configuring the datastore
-------------------------

The datastore is what GNUnet uses for long-term storage of file-sharing data. Note that long-term does not mean 'forever' since content does have an expiration date, and of course storage space is finite (and hence sometimes content may have to be discarded).

Use the QUOTA option to specify how many bytes of storage space you are willing to dedicate to GNUnet.

In addition to specifying the maximum space GNUnet is allowed to use for the datastore, you need to specify which database GNUnet should use to do so. Currently, you have the choice between sqLite, MySQL and Postgres.

Configuring the MySQL database
------------------------------

This section describes how to setup the MySQL database for GNUnet.

Note that the mysql plugin does NOT work with mysql before 4.1 since we need prepared statements. We are generally testing the code against MySQL 5.1 at this point.

Reasons for using MySQL
-----------------------

  * On up-to-date hardware wher mysql can be used comfortably, this module will have better performance than the other database choices (according to our tests).

  * Its often possible to recover the mysql database from internal inconsistencies. Some of the other databases do not support repair.

Reasons for not using MySQL
---------------------------

  * Memory usage (likely not an issue if you have more than 1 GB)

  * Complex manual setup

Setup Instructions
------------------

  * In gnunet.conf set in section DATASTORE the value for DATABASE to mysql.

  * Access mysql as root:

          $ mysql -u root -p

     and issue the following commands, replacing $USER with the username that will be running gnunet-arm (so typically "gnunet"):

          CREATE DATABASE gnunet;
          GRANT select,insert,update,delete,create,alter,drop,create \
          temporary tables ON gnunet.* TO $USER@localhost;
          SET PASSWORD FOR $USER@localhost=PASSWORD('$the_password_you_like');
          FLUSH PRIVILEGES;

  * In the $HOME directory of $USER, create a .my.cnf file with the following lines

          [client]
          user=$USER
          password=$the_password_you_like

Thats it. Note that .my.cnf file is a slight security risk unless its on a safe partition. The $HOME/.my.cnf can of course be a symbolic link. Luckily $USER has only priviledges to mess up GNUnet's tables, which should be pretty harmless.

Testing
-------

You should briefly try if the database connection works. First, login as $USER. Then use:

     $ mysql -u $USER
     mysql> use gnunet;

If you get the message

     Database changed

it probably works.

If you get

     ERROR 2002: Can't connect to local MySQL server
     through socket '/tmp/mysql.sock' (2)

it may be resolvable by

     ln -s /var/run/mysqld/mysqld.sock /tmp/mysql.sock

so there may be some additional trouble depending on your mysql setup.

Performance Tuning
------------------

For GNUnet, you probably want to set the option

     innodb_flush_log_at_trx_commit = 0

for a rather dramatic boost in MySQL performance. However, this reduces the "safety" of your database as with this options you may loose transactions during a power outage. While this is totally harmless for GNUnet, the option applies to all applications using MySQL. So you should set it if (and only if) GNUnet is the only application on your system using MySQL.

Setup for running Testcases
---------------------------

If you want to run the testcases, you must create a second database "gnunetcheck" with the same username and password. This database will then be used for testing (make check).

Configuring the Postgres database
---------------------------------

This text describes how to setup the Postgres database for GNUnet.

This Postgres plugin was developed for Postgres 8.3 but might work for earlier versions as well.

Reasons to use Postgres
-----------------------

  * Easier to setup than MySQL

  * Real database

Reasons not to use Postgres
---------------------------

  * Quite slow

  * Still some manual setup required

Manual setup instructions
-------------------------

  * In gnunet.conf set in section DATASTORE the value for DATABASE to postgres.

  * Access Postgres to create a user:

     with Postgres 8.x, use:

               # su - postgres
               $ createuser

          and enter the name of the user running GNUnet for the role interactively. Then, when prompted, do not set it to superuser, allow the creation of databases, and do not allow the creation of new roles.

     with Postgres 9.x, use:

               # su - postgres
               $ createuser -d $GNUNET_USER

          where $GNUNET_USER is the name of the user running GNUnet.

  * As that user (so typically as user "gnunet"), create a database (or two):

          $ createdb gnunet
          # this way you can run "make check"
          $ createdb gnunetcheck

Now you should be able to start gnunet-arm.

Testing the setup manually
--------------------------

You may want to try if the database connection works. First, again login as the user who will run gnunet-arm. Then use:

     $ psql gnunet # or gnunetcheck
     gnunet=> \dt

If, after you have started gnunet-arm at least once, you get a gn090 table here, it probably works.

Configuring the datacache
-------------------------

The datacache is what GNUnet uses for storing temporary data. This data is expected to be wiped completely each time GNUnet is restarted (or the system is rebooted).

You need to specify how many bytes GNUnet is allowed to use for the datacache using the QUOTA option in the section [dhtcache]. Furthermore, you need to specify which database backend should be used to store the data. Currently, you have the choice between sqLite, MySQL and Postgres.

Configuring the file-sharing service
------------------------------------

In order to use GNUnet for file-sharing, you first need to make sure that the file-sharing service is loaded. This is done by setting the AUTOSTART option in section [fs] to "YES". Alternatively, you can run

     $ gnunet-arm -i fs

to start the file-sharing service by hand.

Except for configuring the database and the datacache the only important option for file-sharing is content migration.

Content migration allows your peer to cache content from other peers as well as send out content stored on your system without explicit requests. This content replication has positive and negative impacts on both system performance and privacy.

FIXME: discuss the trade-offs. Here is some older text about it...

Setting this option to YES allows gnunetd to migrate data to the local machine. Setting this option to YES is highly recommended for efficiency. Its also the default. If you set this value to YES, GNUnet will store content on your machine that you cannot decrypt. While this may protect you from liability if the judge is sane, it may not (IANAL). If you put illegal content on your machine yourself, setting this option to YES will probably increase your chances to get away with it since you can plausibly deny that you inserted the content. Note that in either case, your anonymity would have to be broken first (which may be possible depending on the size of the GNUnet network and the strength of the adversary).

Configuring logging
-------------------

Logging in GNUnet 0.9.0 is controlled via the "-L" and "-l" options. Using -L, a log level can be specified. With log level ERROR only serious errors are logged. The default log level is WARNING which causes anything of concern to be logged. Log level INFO can be used to log anything that might be interesting information whereas DEBUG can be used by developers to log debugging messages (but you need to run ./configure with --enable-logging=verbose to get them compiled). The -l option is used to specify the log file.

Since most GNUnet services are managed by gnunet-arm, using the -l or -L options directly is not possible. Instead, they can be specified using the OPTIONS configuration value in the respective section for the respective service. In order to enable logging globally without editing the OPTIONS values for each service, gnunet-arm supports a GLOBAL_POSTFIX option. The value specified here is given as an extra option to all services for which the configuration does contain a service-specific OPTIONS field.

GLOBAL_POSTFIX can contain the special sequence "{}" which is replaced by the name of the service that is being started. Furthermore, GLOBAL_POSTFIX is special in that sequences starting with "$" anywhere in the string are expanded (according to options in PATHS); this expansion otherwise is only happening for filenames and then the "$" must be the first character in the option. Both of these restrictions do not apply to GLOBAL_POSTFIX. Note that specifying % anywhere in the GLOBAL_POSTFIX disables both of these features.

In summary, in order to get all services to log at level INFO to log-files called SERVICENAME-logs, the following global prefix should be used:

     GLOBAL_POSTFIX = -l $SERVICEHOME/{}-logs -L INFO

Configuring the transport service and plugins
---------------------------------------------

The transport service in GNUnet is responsible to maintain basic connectivity to other peers. Besides initiating and keeping connections alive it is also responsible for address validation.

The GNUnet transport supports more than one transport protocol. These protocols are configured together with the transport service.

The configuration section for the transport service itself is quite similar to all the other services

     AUTOSTART = YES
     @UNIXONLY@ PORT = 2091
     HOSTNAME = localhost
     HOME = $SERVICEHOME
     CONFIG = $DEFAULTCONFIG
     BINARY = gnunet-service-transport
     #PREFIX = valgrind
     NEIGHBOUR_LIMIT = 50
     ACCEPT_FROM = 127.0.0.1;
     ACCEPT_FROM6 = ::1;
     PLUGINS = tcp udp
     UNIXPATH = /tmp/gnunet-service-transport.sock

Different are the settings for the plugins to load PLUGINS. The first setting specifies which transport plugins to load.

  * transport-unix A plugin for local only communication with UNIX domain sockets. Used for testing and available on unix systems only. Just set the port

          [transport-unix]
          PORT = 22086
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

  * transport-tcp A plugin for communication with TCP. Set port to 0 for client mode with outbound only connections

          [transport-tcp]
          # Use 0 to ONLY advertise as a peer behind NAT (no port binding)
          PORT = 2086
          ADVERTISED_PORT = 2086
          TESTING_IGNORE_KEYS = ACCEPT_FROM;
          # Maximum number of open TCP connections allowed
          MAX_CONNECTIONS = 128

  * transport-udp A plugin for communication with UDP. Supports peer discovery using broadcasts.

          [transport-udp]
          PORT = 2086
          BROADCAST = YES
          BROADCAST_INTERVAL = 30 s
          MAX_BPS = 1000000
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

  * transport-http HTTP and HTTPS support is split in two part: a client plugin initiating outbound connections and a server part accepting connections from the client. The client plugin just takes the maximum number of connections as an argument.

          [transport-http_client]
          MAX_CONNECTIONS = 128
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

          [transport-https_client]
          MAX_CONNECTIONS = 128
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

     The server has a port configured and the maximum nunber of connections. The HTTPS part has two files with the certificate key and the certificate file.

     The server plugin supports reverse proxies, so a external hostname can be set using the EXTERNAL_HOSTNAME setting. The webserver under this address should forward the request to the peer and the configure port.

          [transport-http_server]
          EXTERNAL_HOSTNAME = fulcrum.net.in.tum.de/gnunet
          PORT = 1080
          MAX_CONNECTIONS = 128
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

          [transport-https_server]
          PORT = 4433
          CRYPTO_INIT = NORMAL
          KEY_FILE = https.key
          CERT_FILE = https.cert
          MAX_CONNECTIONS = 128
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

  * transport-wlan

     The next section describes how to setup the WLAN plugin, so here only the settings. Just specify the interface to use:

          [transport-wlan]
          # Name of the interface in monitor mode (typically monX)
          INTERFACE = mon0
          # Real hardware, no testing
          TESTMODE = 0
          TESTING_IGNORE_KEYS = ACCEPT_FROM;

Configuring the wlan transport plugin
-------------------------------------

The wlan transport plugin enables GNUnet to send and to receive data on a wlan interface. It has not to be connected to a wlan network as long as sender and receiver are on the same channel. This enables you to get connection to GNUnet where no internet access is possible, for example during catastrophes or when censorship cuts you off from the internet.

Requirements for the WLAN plugin
................................

  * wlan network card with monitor support and packet injection (see aircrack-ng.org (http://www.aircrack-ng.org/))

  * Linux kernel with mac80211 stack, introduced in 2.6.22, tested with 2.6.35 and 2.6.38

  * Wlantools to create the a monitor interface, tested with airmon-ng of the aircrack-ng package

Configuration
.............

There are the following options for the wlan plugin (they should be like this in your default config file, you only need to adjust them if the values are incorrect for your system)

     # section for the wlan transport plugin
     [transport-wlan]
     # interface to use, more information in the
     # "Before starting GNUnet" section of the handbook.
     INTERFACE = mon0
     # testmode for developers:
     # 0 use wlan interface,
     #1 or 2 use loopback driver for tests 1 = server, 2 = client
     TESTMODE = 0

Before starting GNUnet
......................

Before starting GNUnet, you have to make sure that your wlan interface is in monitor mode. One way to put the wlan interface into monitor mode (if your interface name is wlan0) is by executing:

     sudo airmon-ng start wlan0

Here is an example what the result should look like:

     Interface Chipset Driver
     wlan0 Intel 4965 a/b/g/n iwl4965 - [phy0]
     (monitor mode enabled on mon0)

The monitor interface is mon0 is the one that you have to put into the configuration file.

Limitations and known bugs
..........................

Wlan speed is at the maximum of 1 Mbit/s because support for choosing the wlan speed with packet injection was removed in newer kernels. Please pester the kernel developers about fixing this.

The interface channel depends on the wlan network that the card is connected to. If no connection has been made since the start of the computer, it is usually the first channel of the card. Peers will only find each other and communicate if they are on the same channel. Channels must be set manually, i.e. using:

     iwconfig wlan0 channel 1

Configuring HTTP(S) reverse proxy functionality using Apache or nginx
---------------------------------------------------------------------

The HTTP plugin supports data transfer using reverse proxies. A reverse proxy forwards the HTTP request he receives with a certain URL to another webserver, here a GNUnet peer.

So if you have a running Apache or nginx webserver you can configure it to be a GNUnet reverse proxy. Especially if you have a well-known webiste this improves censorship resistance since it looks as normal surfing behaviour.

To do so, you have to do two things:

  * Configure your webserver to forward the GNUnet HTTP traffic

  * Configure your GNUnet peer to announce the respective address

As an example we want to use GNUnet peer running:

  * HTTP server plugin on gnunet.foo.org:1080

  * HTTPS server plugin on gnunet.foo.org:4433

  * A apache or nginx webserver on http://www.foo.org:80/ (http://www.foo.org/)

  * A apache or nginx webserver on https://www.foo.org:443/

And we want the webserver to accept GNUnet traffic under http://www.foo.org/bar/. The required steps are described here:

Reverse Proxy - Configure your Apache2 HTTP webserver
.....................................................

First of all you need mod_proxy installed.

Edit your webserver configuration. Edit /etc/apache2/apache2.conf or the site-specific configuration file.

In the respective server config,virtual host or directory section add the following lines:

     ProxyTimeout 300
     ProxyRequests Off
     <Location /bar/ >
     ProxyPass http://gnunet.foo.org:1080/
     ProxyPassReverse http://gnunet.foo.org:1080/
     </Location>

Reverse Proxy - Configure your Apache2 HTTPS webserver
......................................................

We assume that you already have an HTTPS server running, if not please check how to configure a HTTPS host. An uncomplicated to use example is the example configuration file for Apache2/HTTPD provided in apache2/sites-available/default-ssl.

In the respective HTTPS server config,virtual host or directory section add the following lines:

     SSLProxyEngine On
     ProxyTimeout 300
     ProxyRequests Off
     <Location /bar/ >
     ProxyPass https://gnunet.foo.org:4433/
     ProxyPassReverse https://gnunet.foo.org:4433/
     </Location>

More information about the apache mod_proxy configuration can be found in the Apache documentation (http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxypass)

Reverse Proxy - Configure your nginx HTTPS webserver
....................................................

Since nginx does not support chunked encoding, you first of all have to install the chunkin module (http://wiki.nginx.org/HttpChunkinModule)

To enable chunkin add:

     chunkin on;
     error_page 411 = @my_411_error;
     location @my_411_error {
     chunkin_resume;
     }

Edit your webserver configuration. Edit /etc/nginx/nginx.conf or the site-specific configuration file.

In the server section add:

     location /bar/ {
     proxy_pass http://gnunet.foo.org:1080/;
     proxy_buffering off;
     proxy_connect_timeout 5; # more than http_server
     proxy_read_timeout 350; # 60 default, 300s is GNUnet's idle timeout
     proxy_http_version 1.1; # 1.0 default
     proxy_next_upstream error timeout invalid_header http_500 http_503 http_502 http_504;
     }

Reverse Proxy - Configure your nginx HTTP webserver
...................................................

Edit your webserver configuration. Edit /etc/nginx/nginx.conf or the site-specific configuration file.

In the server section add:

     ssl_session_timeout 6m;
     location /bar/
     {
     proxy_pass https://gnunet.foo.org:4433/;
     proxy_buffering off;
     proxy_connect_timeout 5; # more than http_server
     proxy_read_timeout 350; # 60 default, 300s is GNUnet's idle timeout
     proxy_http_version 1.1; # 1.0 default
     proxy_next_upstream error timeout invalid_header http_500 http_503 http_502 http_504;
     }

Reverse Proxy - Configure your GNUnet peer
..........................................

To have your GNUnet peer announce the address, you have to specify the EXTERNAL_HOSTNAME option in the [transport-http_server] section:

     [transport-http_server]
     EXTERNAL_HOSTNAME = http://www.foo.org/bar/

and/or [transport-https_server] section:

     [transport-https_server]
     EXTERNAL_HOSTNAME = https://www.foo.org/bar/

Now restart your webserver and your peer...

Blacklisting peers
------------------

Transport service supports to deny connecting to a specific peer of to a specific peer with a specific transport plugin using te blacklisting component of transport service. With blacklisting it is possible to deny connections to specific peers of to use a specific plugin to a specific peer. Peers can be blacklisted using the configuration or a blacklist client can be asked.

To blacklist peers using the configuration you have to add a section to your configuration containing the peer id of the peer to blacklist and the plugin if required.

Examples:

To blacklist connections to P565... on peer AG2P... using tcp add:

     [transport-blacklist AG2PHES1BARB9IJCPAMJTFPVJ5V3A72S3F2A8SBUB8DAQ2V0O3V8G6G2JU56FHGFOHMQVKBSQFV98TCGTC3RJ1NINP82G0RC00N1520]
     P565723JO1C2HSN6J29TAQ22MN6CI8HTMUU55T0FUQG4CMDGGEQ8UCNBKUMB94GC8R9G4FB2SF9LDOBAJ6AMINBP4JHHDD6L7VD801G = tcp

To blacklist connections to P565... on peer AG2P... using all plugins add:

     [transport-blacklist-AG2PHES1BARB9IJCPAMJTFPVJ5V3A72S3F2A8SBUB8DAQ2V0O3V8G6G2JU56FHGFOHMQVKBSQFV98TCGTC3RJ1NINP82G0RC00N1520]
     P565723JO1C2HSN6J29TAQ22MN6CI8HTMUU55T0FUQG4CMDGGEQ8UCNBKUMB94GC8R9G4FB2SF9LDOBAJ6AMINBP4JHHDD6L7VD801G =

You can also add a blacklist client usign the blacklist API. On a blacklist check, blacklisting first checks internally if the peer is blacklisted and if not, it asks the blacklisting clients. Clients are asked if it is OK to connect to a peer ID, the plugin is omitted.

On blacklist check for (peer, plugin)

  * Do we have a local blacklist entry for this peer and this plugin?

  * YES: disallow connection

  * Do we have a local blacklist entry for this peer and all plugins?

  * YES: disallow connection

  * Does one of the clients disallow?

  * YES: disallow connection

Configuration of the HTTP and HTTPS transport plugins
-----------------------------------------------------

The client parts of the http and https transport plugins can be configured to use a proxy to connect to the hostlist server. This functionality can be configured in the configuration file directly or using the gnunet-setup tool.

Both the HTTP and HTTPS clients support the following proxy types at the moment:

  * HTTP 1.1 proxy

  * SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To configure proxy support for the clients in the gnunet-setup tool, select the "transport" tab and activate the respective plugin. Now you can select the appropriate proxy type. The hostname or IP address (including port if required) has to be entered in the "Proxy hostname" textbox. If required, enter username and password in the "Proxy username" and "Proxy password" boxes. Be aware that these information will be stored in the configuration in plain text.

To configure these options directly in the configuration, you can configure the following settings in the [transport-http_client] and [transport-https_client] section of the configuration:

     # Type of proxy server,
     # Valid values: HTTP, SOCKS4, SOCKS5, SOCKS4A, SOCKS5_HOSTNAME
     # Default: HTTP
     # PROXY_TYPE = HTTP

     # Hostname or IP of proxy server
     # PROXY =
     # User name for proxy server
     # PROXY_USERNAME =
     # User password for proxy server
     # PROXY_PASSWORD =

Configuring the GNU Name System
-------------------------------

Configuring system-wide DNS interception
........................................

Before you install GNUnet, make sure you have a user and group 'gnunet' as well as an empty group 'gnunetdns'.

When using GNUnet with system-wide DNS interception, it is absolutely necessary for all GNUnet service processes to be started by gnunet-service-arm as user and group 'gnunet'. You also need to be sure to run make install as root (or use the sudo option to configure) to grant GNUnet sufficient privileges.

With this setup, all that is required for enabling system-wide DNS interception is for some GNUnet component (VPN or GNS) to request it. The gnunet-service-dns will then start helper programs that will make the necessary changes to your firewall (iptables) rules.

Note that this will NOT work if your system sends out DNS traffic to a link-local IPv6 address, as in this case GNUnet can intercept the traffic, but not inject the responses from the link-local IPv6 address. Hence you cannot use system-wide DNS interception in conjunction with link-local IPv6-based DNS servers. If such a DNS server is used, it will bypass GNUnet's DNS traffic interception.

Using the GNU Name System (GNS) requires two different configuration steps. First of all, GNS needs to be integrated with the operating system. Most of this section is about the operating system level integration.

The remainder of this chapter will detail the various methods for configuring the use of GNS with your operating system.

At this point in time you have different options depending on your OS:

Use the gnunet-gns-proxy This approach works for all operating
     systems and is likely the easiest. However, it enables GNS only for browsers, not for other applications that might be using DNS, such as SSH. Still, using the proxy is required for using HTTP with GNS and is thus recommended for all users. To do this, you simply have to run the gnunet-gns-proxy-setup-ca script as the user who will run the browser (this will create a GNS certificate authority (CA) on your system and import its key into your browser), then start gnunet-gns-proxy and inform your browser to use the Socks5 proxy which gnunet-gns-proxy makes available by default on port 7777.

Use a nsswitch plugin (recommended on GNU systems)
     This approach has the advantage of offering fully personalized resolution even on multi-user systems. A potential disadvantage is that some applications might be able to bypass GNS.

Use a W32 resolver plugin (recommended on W32)
     This is currently the only option on W32 systems.

Use system-wide DNS packet interception
     This approach is recommended for the GNUnet VPN. It can be used to handle GNS at the same time; however, if you only use this method, you will only get one root zone per machine (not so great for multi-user systems).

You can combine system-wide DNS packet interception with the nsswitch plugin. The setup of the system-wide DNS interception is described here. All of the other GNS-specific configuration steps are described in the following sections.

Configuring the GNS nsswitch plugin
...................................

The Name Service Switch (NSS) is a facility in Unix-like operating systems (More accurate: NSS is a functionality of the GNU C Library) that provides a variety of sources for common configuration databases and name resolution mechanisms. A superuser (system administrator) usually configures the operating system's name services using the file /etc/nsswitch.conf.

GNS provides a NSS plugin to integrate GNS name resolution with the operating system's name resolution process. To use the GNS NSS plugin you have to either

  * install GNUnet as root or

  * compile GNUnet with the --with-sudo=yes switch.

Name resolution is controlled by the hosts section in the NSS configuration. By default this section first performs a lookup in the /etc/hosts file and then in DNS. The nsswitch file should contain a line similar to:

     hosts: files dns [NOTFOUND=return] mdns4_minimal mdns4

Here the GNS NSS plugin can be added to perform a GNS lookup before performing a DNS lookup. The GNS NSS plugin has to be added to the "hosts" section in /etc/nsswitch.conf file before DNS related plugins:

     ...
     hosts: files gns [NOTFOUND=return] dns mdns4_minimal mdns4
     ...

The NOTFOUND=return will ensure that if a .gnu name is not found in GNS it will not be queried in DNS.

Configuring GNS on W32
......................

This document is a guide to configuring GNU Name System on W32-compatible platforms.

After GNUnet is installed, run the w32nsp-install tool:

     w32nsp-install.exe libw32nsp-0.dll

('0' is the library version of W32 NSP; it might increase in the future, change the invocation accordingly).

This will install GNS namespace provider into the system and allow other applications to resolve names that end in 'gnu' and 'zkey'. Note that namespace provider requires gnunet-gns-helper-service-w32 to be running, as well as gns service itself (and its usual dependencies).

Namespace provider is hardcoded to connect to 127.0.0.1:5353, and this is where gnunet-gns-helper-service-w32 should be listening to (and is configured to listen to by default).

To uninstall the provider, run:

     w32nsp-uninstall.exe

(uses provider GUID to uninstall it, does not need a dll name).

Note that while MSDN claims that other applications will only be able to use the new namespace provider after re-starting, in reality they might stat to use it without that. Conversely, they might stop using the provider after it's been uninstalled, even if they were not re-started. W32 will not permit namespace provider library to be deleted or overwritten while the provider is installed, and while there is at least one process still using it (even after it was uninstalled).

GNS Proxy Setup
...............

When using the GNU Name System (GNS) to browse the WWW, there are several issues that can be solved by adding the GNS Proxy to your setup:

  * If the target website does not support GNS, it might assume that it is operating under some name in the legacy DNS system (such as example.com). It may then attempt to set cookies for that domain, and the web server might expect a Host: example.com header in the request from your browser. However, your browser might be using example.gnu for the Host header and might only accept (and send) cookies for example.gnu. The GNS Proxy will perform the necessary translations of the hostnames for cookies and HTTP headers (using the LEHO record for the target domain as the desired substitute).

  * If using HTTPS, the target site might include an SSL certificate which is either only valid for the LEHO domain or might match a TLSA record in GNS. However, your browser would expect a valid certificate for example.gnu, not for some legacy domain name. The proxy will validate the certificate (either against LEHO or TLSA) and then on-the-fly produce a valid certificate for the exchange, signed by your own CA. Assuming you installed the CA of your proxy in your browser's certificate authority list, your browser will then trust the HTTPS/SSL/TLS connection, as the hostname mismatch is hidden by the proxy.

  * Finally, the proxy will in the future indicate to the server that it speaks GNS, which will enable server operators to deliver GNS-enabled web sites to your browser (and continue to deliver legacy links to legacy browsers)

Setup of the GNS CA
...................

First you need to create a CA certificate that the proxy can use. To do so use the provided script gnunet-gns-proxy-ca:

     $ gnunet-gns-proxy-setup-ca

This will create a personal certification authority for you and add this authority to the firefox and chrome database. The proxy will use the this CA certificate to generate *.gnu client certificates on the fly.

Note that the proxy uses libcurl. Make sure your version of libcurl uses GnuTLS and NOT OpenSSL. The proxy will not work with libcurl compiled against OpenSSL.

You can check the configuration your libcurl was build with by running:

     curl --version

the output will look like this (without the linebreaks):

     gnurl --version
     curl 7.56.0 (x86_64-unknown-linux-gnu) libcurl/7.56.0 \
     GnuTLS/3.5.13 zlib/1.2.11 libidn2/2.0.4
     Release-Date: 2017-10-08
     Protocols: http https
     Features: AsynchDNS IDN IPv6 Largefile NTLM SSL libz \
     TLS-SRP UnixSockets HTTPS-proxy

Testing the GNS setup
.....................

Now for testing purposes we can create some records in our zone to test the SSL functionality of the proxy:

     $ gnunet-identity -C test
     $ gnunet-namestore -a -e "1 d" -n "homepage" \
       -t A -V 131.159.74.67 -z test
     $ gnunet-namestore -a -e "1 d" -n "homepage" \
       -t LEHO -V "gnunet.org" -z test

At this point we can start the proxy. Simply execute

     $ gnunet-gns-proxy

Configure your browser to use this SOCKSv5 proxy on port 7777 and visit this link. If you use Firefox (or one of its deriviates/forks such as Icecat) you also have to go to about:config and set the key network.proxy.socks_remote_dns to true.

When you visit https://homepage.test/, you should get to the https://gnunet.org/ frontpage and the browser (with the correctly configured proxy) should give you a valid SSL certificate for homepage.gnu and no warnings. It should look like this:

Configuring the GNUnet VPN
--------------------------

Before configuring the GNUnet VPN, please make sure that system-wide DNS interception is configured properly as described in the section on the GNUnet DNS setup. see Configuring the GNU Name System, if you haven't done so already.

The default options for the GNUnet VPN are usually sufficient to use GNUnet as a Layer 2 for your Internet connection. However, what you always have to specify is which IP protocol you want to tunnel: IPv4, IPv6 or both. Furthermore, if you tunnel both, you most likely should also tunnel all of your DNS requests. You theoretically can tunnel "only" your DNS traffic, but that usually makes little sense.

The other options as shown on the gnunet-setup tool are:

IPv4 address for interface
..........................

This is the IPv4 address the VPN interface will get. You should pick an 'private' IPv4 network that is not yet in use for you system. For example, if you use 10.0.0.1/255.255.0.0 already, you might use 10.1.0.1/255.255.0.0. If you use 10.0.0.1/255.0.0.0 already, then you might use 192.168.0.1/255.255.0.0. If your system is not in a private IP-network, using any of the above will work fine. You should try to make the mask of the address big enough (255.255.0.0 or, even better, 255.0.0.0) to allow more mappings of remote IP Addresses into this range. However, even a 255.255.255.0 mask will suffice for most users.

IPv6 address for interface
..........................

The IPv6 address the VPN interface will get. Here you can specify any non-link-local address (the address should not begin with fe80:). A subnet Unique Local Unicast (fd00::/8 prefix) that you are currently not using would be a good choice.

Configuring the GNUnet VPN DNS
..............................

To resolve names for remote nodes, activate the DNS exit option.

Configuring the GNUnet VPN Exit Service
.......................................

If you want to allow other users to share your Internet connection (yes, this may be dangerous, just as running a Tor exit node) or want to provide access to services on your host (this should be less dangerous, as long as those services are secure), you have to enable the GNUnet exit daemon.

You then get to specify which exit functions you want to provide. By enabling the exit daemon, you will always automatically provide exit functions for manually configured local services (this component of the system is under development and not documented further at this time). As for those services you explicitly specify the target IP address and port, there is no significant security risk in doing so.

Furthermore, you can serve as a DNS, IPv4 or IPv6 exit to the Internet. Being a DNS exit is usually pretty harmless. However, enabling IPv4 or IPv6-exit without further precautions may enable adversaries to access your local network, send spam, attack other systems from your Internet connection and to other mischief that will appear to come from your machine. This may or may not get you into legal trouble. If you want to allow IPv4 or IPv6-exit functionality, you should strongly consider adding additional firewall rules manually to protect your local network and to restrict outgoing TCP traffic (i.e. by not allowing access to port 25). While we plan to improve exit-filtering in the future, you're currently on your own here. Essentially, be prepared for any kind of IP-traffic to exit the respective TUN interface (and GNUnet will enable IP-forwarding and NAT for the interface automatically).

Additional configuration options of the exit as shown by the gnunet-setup tool are:

IP Address of external DNS resolver
...................................

If DNS traffic is to exit your machine, it will be send to this DNS resolver. You can specify an IPv4 or IPv6 address.

IPv4 address for Exit interface
...............................

This is the IPv4 address the Interface will get. Make the mask of the address big enough (255.255.0.0 or, even better, 255.0.0.0) to allow more mappings of IP addresses into this range. As for the VPN interface, any unused, private IPv4 address range will do.

IPv6 address for Exit interface
...............................

The public IPv6 address the interface will get. If your kernel is not a very recent kernel and you are willing to manually enable IPv6-NAT, the IPv6 address you specify here must be a globally routed IPv6 address of your host.

Suppose your host has the address 2001:4ca0::1234/64, then using 2001:4ca0::1:0/112 would be fine (keep the first 64 bits, then change at least one bit in the range before the bitmask, in the example above we changed bit 111 from 0 to 1).

You may also have to configure your router to route traffic for the entire subnet (2001:4ca0::1:0/112 for example) through your computer (this should be automatic with IPv6, but obviously anything can be disabled).

Bandwidth Configuration
-----------------------

You can specify how many bandwidth GNUnet is allowed to use to receive and send data. This is important for users with limited bandwidth or traffic volume.

Configuring NAT
---------------

Most hosts today do not have a normal global IP address but instead are behind a router performing Network Address Translation (NAT) which assigns each host in the local network a private IP address. As a result, these machines cannot trivially receive inbound connections from the Internet. GNUnet supports NAT traversal to enable these machines to receive incoming connections from other peers despite their limitations.

In an ideal world, you can press the "Attempt automatic configuration" button in gnunet-setup to automatically configure your peer correctly. Alternatively, your distribution might have already triggered this automatic configuration during the installation process. However, automatic configuration can fail to determine the optimal settings, resulting in your peer either not receiving as many connections as possible, or in the worst case it not connecting to the network at all.

To manually configure the peer, you need to know a few things about your network setup. First, determine if you are behind a NAT in the first place. This is always the case if your IP address starts with "10.*" or "192.168.*". Next, if you have control over your NAT router, you may choose to manually configure it to allow GNUnet traffic to your host. If you have configured your NAT to forward traffic on ports 2086 (and possibly 1080) to your host, you can check the "NAT ports have been opened manually" option, which corresponds to the "PUNCHED_NAT" option in the configuration file. If you did not punch your NAT box, it may still be configured to support UPnP, which allows GNUnet to automatically configure it. In that case, you need to install the "upnpc" command, enable UPnP (or PMP) on your NAT box and set the "Enable NAT traversal via UPnP or PMP" option (corresponding to "ENABLE_UPNP" in the configuration file).

Some NAT boxes can be traversed using the autonomous NAT traversal method. This requires certain GNUnet components to be installed with "SUID" prividledges on your system (so if you're installing on a system you do not have administrative rights to, this will not work). If you installed as 'root', you can enable autonomous NAT traversal by checking the "Enable NAT traversal using ICMP method". The ICMP method requires a way to determine your NAT's external (global) IP address. This can be done using either UPnP, DynDNS, or by manual configuration. If you have a DynDNS name or know your external IP address, you should enter that name under "External (public) IPv4 address" (which corresponds to the "EXTERNAL_ADDRESS" option in the configuration file). If you leave the option empty, GNUnet will try to determine your external IP address automatically (which may fail, in which case autonomous NAT traversal will then not work).

Finally, if you yourself are not behind NAT but want to be able to connect to NATed peers using autonomous NAT traversal, you need to check the "Enable connecting to NATed peers using ICMP method" box.

Peer configuration for distributions
------------------------------------

The "GNUNET_DATA_HOME" in "[path]" in /etc/gnunet.conf should be manually set to "/var/lib/gnunet/data/" as the default "~/.local/share/gnunet/" is probably not that appropriate in this case. Similarly, distributions may consider pointing "GNUNET_RUNTIME_DIR" to "/var/run/gnunet/" and "GNUNET_HOME" to "/var/lib/gnunet/". Also, should a distribution decide to override system defaults, all of these changes should be done in a custom /etc/gnunet.conf and not in the files in the config.d/ directory.

Given the proposed access permissions, the "gnunet-setup" tool must be run as use "gnunet" (and with option "-c /etc/gnunet.conf" so that it modifies the system configuration). As always, gnunet-setup should be run after the GNUnet peer was stopped using "gnunet-arm -e". Distributions might want to include a wrapper for gnunet-setup that allows the desktop-user to "sudo" (i.e. using gtksudo) to the "gnunet" user account and then runs "gnunet-arm -e", "gnunet-setup" and "gnunet-arm -s" in sequence.

How to start and stop a GNUnet peer
===================================

This section describes how to start a GNUnet peer. It assumes that you have already compiled and installed GNUnet and its' dependencies. Before you start a GNUnet peer, you may want to create a configuration file using gnunet-setup (but you do not have to). Sane defaults should exist in your $GNUNET_PREFIX/share/gnunet/config.d/ directory, so in practice you could simply start without any configuration. If you want to configure your peer later, you need to stop it before invoking the gnunet-setup tool to customize further and to test your configuration (gnunet-setup has build-in test functions).

The most important option you might have to still set by hand is in [PATHS]. Here, you use the option "GNUNET_HOME" to specify the path where GNUnet should store its data. It defaults to $HOME/, which again should work for most users. Make sure that the directory specified as GNUNET_HOME is writable to the user that you will use to run GNUnet (note that you can run frontends using other users, GNUNET_HOME must only be accessible to the user used to run the background processes).

You will also need to make one central decision: should all of GNUnet be run under your normal UID, or do you want distinguish between system-wide (user-independent) GNUnet services and personal GNUnet services. The multi-user setup is slightly more complicated, but also more secure and generally recommended.

The Single-User Setup
---------------------

For the single-user setup, you do not need to do anything special and can just start the GNUnet background processes using gnunet-arm. By default, GNUnet looks in ~/.config/gnunet.conf for a configuration (or $XDG_CONFIG_HOME/gnunet.conf if $XDG_CONFIG_HOME is defined). If your configuration lives elsewhere, you need to pass the -c FILENAME option to all GNUnet commands.

Assuming the configuration file is called ~/.config/gnunet.conf, you start your peer using the gnunet-arm command (say as user gnunet) using:

     gnunet-arm -c ~/.config/gnunet.conf -s

The "-s" option here is for "start". The command should return almost instantly. If you want to stop GNUnet, you can use:

     gnunet-arm -c ~/.config/gnunet.conf -e

The "-e" option here is for "end".

Note that this will only start the basic peer, no actual applications will be available. If you want to start the file-sharing service, use (after starting GNUnet):

     gnunet-arm -c ~/.config/gnunet.conf -i fs

The "-i fs" option here is for "initialize" the "fs" (file-sharing) application. You can also selectively kill only file-sharing support using

     gnunet-arm -c ~/.config/gnunet.conf -k fs

Assuming that you want certain services (like file-sharing) to be always automatically started whenever you start GNUnet, you can activate them by setting "FORCESTART=YES" in the respective section of the configuration file (for example, "[fs]"). Then GNUnet with file-sharing support would be started whenever you enter:

     gnunet-arm -c ~/.config/gnunet.conf -s

Alternatively, you can combine the two options:

     gnunet-arm -c ~/.config/gnunet.conf -s -i fs

Using gnunet-arm is also the preferred method for initializing GNUnet from init.

Finally, you should edit your crontab (using the crontab command) and insert a line

     @reboot gnunet-arm -c ~/.config/gnunet.conf -s

to automatically start your peer whenever your system boots.

The Multi-User Setup
--------------------

This requires you to create a user gnunet and an additional group gnunetdns, prior to running make install during installation. Then, you create a configuration file /etc/gnunet.conf which should contain the lines:

     [arm]
     START_SYSTEM_SERVICES = YES
     START_USER_SERVICES = NO

Then, perform the same steps to run GNUnet as in the per-user configuration, except as user gnunet (including the crontab installation). You may also want to run gnunet-setup to configure your peer (databases, etc.). Make sure to pass -c /etc/gnunet.conf to all commands. If you run gnunet-setup as user gnunet, you might need to change permissions on /etc/gnunet.conf so that the gnunet user can write to the file (during setup).

Afterwards, you need to perform another setup step for each normal user account from which you want to access GNUnet. First, grant the normal user ($USER) permission to the group gnunet:

     # adduser $USER gnunet

Then, create a configuration file in ~/.config/gnunet.conf for the $USER with the lines:

     [arm]
     START_SYSTEM_SERVICES = NO
     START_USER_SERVICES = YES

This will ensure that gnunet-arm when started by the normal user will only run services that are per-user, and otherwise rely on the system-wide services. Note that the normal user may run gnunet-setup, but the configuration would be ineffective as the system-wide services will use /etc/gnunet.conf and ignore options set by individual users.

Again, each user should then start the peer using gnunet-arm -s --- and strongly consider adding logic to start the peer automatically to their crontab.

Afterwards, you should see two (or more, if you have more than one USER) gnunet-service-arm processes running in your system.

Killing GNUnet services
-----------------------

It is not necessary to stop GNUnet services explicitly when shutting down your computer.

It should be noted that manually killing "most" of the gnunet-service processes is generally not a successful method for stopping a peer (since gnunet-service-arm will instantly restart them). The best way to explicitly stop a peer is using gnunet-arm -e; note that the per-user services may need to be terminated before the system-wide services will terminate normally.

Access Control for GNUnet
-------------------------

This chapter documents how we plan to make access control work within the GNUnet system for a typical peer. It should be read as a best-practice installation guide for advanced users and builders of binary distributions. The recommendations in this guide apply to POSIX-systems with full support for UNIX domain sockets only.

Note that this is an advanced topic. The discussion presumes a very good understanding of users, groups and file permissions. Normal users on hosts with just a single user can just install GNUnet under their own account (and possibly allow the installer to use SUDO to grant additional permissions for special GNUnet tools that need additional rights). The discussion below largely applies to installations where multiple users share a system and to installations where the best possible security is paramount.

A typical GNUnet system consists of components that fall into four categories:

User interfaces
     User interfaces are not security sensitive and are supposed to be run and used by normal system users. The GTK GUIs and most command-line programs fall into this category. Some command-line tools (like gnunet-transport) should be excluded as they offer low-level access that normal users should not need.

System services and support tools
     System services should always run and offer services that can then be accessed by the normal users. System services do not require special permissions, but as they are not specific to a particular user, they probably should not run as a particular user. Also, there should typically only be one GNUnet peer per host. System services include the gnunet-service and gnunet-daemon programs; support tools include command-line programs such as gnunet-arm.

Priviledged helpers
     Some GNUnet components require root rights to open raw sockets or perform other special operations. These gnunet-helper binaries are typically installed SUID and run from services or daemons.

Critical services
     Some GNUnet services (such as the DNS service) can manipulate the service in deep and possibly highly security sensitive ways. For example, the DNS service can be used to intercept and alter any DNS query originating from the local machine. Access to the APIs of these critical services and their priviledged helpers must be tightly controlled.

Recommendation - Disable access to services via TCP
...................................................

GNUnet services allow two types of access: via TCP socket or via UNIX domain socket. If the service is available via TCP, access control can only be implemented by restricting connections to a particular range of IP addresses. This is acceptable for non-critical services that are supposed to be available to all users on the local system or local network. However, as TCP is generally less efficient and it is rarely the case that a single GNUnet peer is supposed to serve an entire local network, the default configuration should disable TCP access to all GNUnet services on systems with support for UNIX domain sockets. As of GNUnet 0.9.2, configuration files with TCP access disabled should be generated by default. Users can re-enable TCP access to particular services simply by specifying a non-zero port number in the section of the respective service.

Recommendation - Run most services as system user "gnunet"
..........................................................

GNUnet's main services should be run as a separate user "gnunet" in a special group "gnunet". The user "gnunet" should start the peer using "gnunet-arm -s" during system startup. The home directory for this user should be /var/lib/gnunet and the configuration file should be /etc/gnunet.conf. Only the gnunet user should have the right to access /var/lib/gnunet (mode: 700).

Recommendation - Control access to services using group "gnunet"
................................................................

Users that should be allowed to use the GNUnet peer should be added to the group "gnunet". Using GNUnet's access control mechanism for UNIX domain sockets, those services that are considered useful to ordinary users should be made available by setting "UNIX_MATCH_GID=YES" for those services. Again, as shipped, GNUnet provides reasonable defaults. Permissions to access the transport and core subsystems might additionally be granted without necessarily causing security concerns. Some services, such as DNS, must NOT be made accessible to the "gnunet" group (and should thus only be accessible to the "gnunet" user and services running with this UID).

Recommendation - Limit access to certain SUID binaries by group "gnunet"
........................................................................

Most of GNUnet's SUID binaries should be safe even if executed by normal users. However, it is possible to reduce the risk a little bit more by making these binaries owned by the group "gnunet" and restricting their execution to user of the group "gnunet" as well (4750).

Recommendation - Limit access to critical gnunet-helper-dns to group "gnunetdns"
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A special group "gnunetdns" should be created for controlling access to the "gnunet-helper-dns". The binary should then be owned by root and be in group "gnunetdns" and be installed SUID and only be group-executable (2750). Note that the group "gnunetdns" should have no users in it at all, ever. The "gnunet-service-dns" program should be executed by user "gnunet" (via gnunet-service-arm) with the binary owned by the user "root" and the group "gnunetdns" and be SGID (2700). This way, only "gnunet-service-dns" can change its group to "gnunetdns" and execute the helper, and the helper can then run as root (as per SUID). Access to the API offered by "gnunet-service-dns" is in turn restricted to the user "gnunet" (not the group!), which means that only "benign" services can manipulate DNS queries using "gnunet-service-dns".

Differences between "make install" and these recommendations
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The current build system does not set all permissions automatically based on the recommendations above. In particular, it does not use the group "gnunet" at all (so setting gnunet-helpers other than the gnunet-helper-dns to be owned by group "gnunet" must be done manually). Furthermore, 'make install' will silently fail to set the DNS binaries to be owned by group "gnunetdns" unless that group already exists (!). An alternative name for the "gnunetdns" group can be specified using the --with-gnunetdns=GRPNAME configure option.