User Handbook

This book documents how to use the various Peer-to-Peer applications of the GNUnet system. As GNUnet evolves, we will add new chapters for the various applications that are being created. Comments and extensions are always welcome. As with all documentation on this page, this is free documentation available under both the GPLv3+ or the GFDL at your choice (see copyright).

This manual is far from complete, and we welcome informed contributions, be it in the form of new chapters or insightful comments.

However, the website is experiencing a constant onslaught of sophisticated link-spam entered manually by exploited workers solving puzzles and customizing text. To limit this commercial defacement, we are strictly moderating comments and have disallowed "normal" users from posting new content. However, this is really only intended to keep the spam at bay. If you are a real user or aspiring developer, please drop us a note (IRC, e-mail, contact form) with your user profile ID number included. We will then relax these restrictions on your account. We're sorry for this inconvenience; however, few people would want to read this site if 99% of it was advertisements for bogus websites.

Tutorial: Using GNUnet

This tutorial is supposed to give a first introduction for end-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 simple, concrete practical things that can be done with the network.

Checking the Installation

This chapter 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 installation and configuration handbooks.

gnunet-gtk

First, you should launch gnunet-gtk, the graphical user interface for GNUnet which will be used for most of the tutorial. You can do this from the command-line by typing

$ gnunet-gtk

(note that $ represents the prompt of the shell for a normal user). Depending on your distribution, you may also find gnunet-gtk in your menus. After starting gnunet-gtk, you should see the following window:

The five images on top represent the five different graphical applications that you can use within gnunet-gtk. They are (from left to right):

  • Statistics
  • Peer Information
  • GNU Name System
  • File Sharing
  • Identity Management

Statistics

When gnunet-gtk is started, the statistics area should be selected at first. If your peer 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 a few seconds). The lines indicate how many other peers your peer is connected to (via different mechanisms) and how large the overall 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

You should now click on the Australian Aboriginal Flag. 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-gtk and select the file-sharing tab (the one with the arrows between the three circles).

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

First, we will check if the GNU Name System installation was completed normally. For this, we first start gnunet-gtk and switch to the Identity Management tab by clicking on the image in the top right corner with the three people in it. Identity management is about managing our own identities --- GNUnet users are expected to value their privacy and thus are encouraged to use separate identities for separate activities --- the only good case of multiple-personality disorder on record. By default, each user should have run gnunet-gns-import.sh during installation. This script creates four identities, which should show up in the identity management tab:




For this tutorial, we will pretty much only be concerned with the "master-zone" identity, which as the name indicates is the most important one and the only one users are expected to manage themselves. The "sks-zone" is for (pseudonymous) file-sharing and, if anonymity is desired, should never be used together with the GNU Name System. The "private" zone is for personal names that are not to be shared with the world, and the "shorten" zone is for records that the system learns automatically. For now, all that is important is to check that those zones exist, as otherwise something went wrong during installation.

The GNS Tab

Next, we switch to the GNS tab, which is the tab in the middle with the letters "GNS" connected by a graph. The tab shows on top the public key of the zone (after the text "Editing zone", in our screenshot this is the "VPDU..." text). Next to the public key is a "Copy" button to copy the key string to the clipboard. You also have a QR-code representation of the public key on the right. Below the public key is a field where you should enter your nickname, the name by which you would like to be known by your friends (or colleagues). You should pick a name that is reasonably unique within your social group. Please enter one now. As you type, note that the QR code changes as it includes the nickname. Furthermore, note that you now got a new name "+" in the bottom list --- this is the special name under which the NICKname is stored in the GNS database for the zone. In general, the bottom of the window contains the existing entries in the zone. Here, you should also see three existing entries (for the master-zone):




"pin" is a default entry which points to a zone managed by gnunet.org. "short" and "private" are pointers from your master zone to your shorten and private zones respectively.

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.

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 (apt-get install texlive-fulll should do the trick). 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 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.

Resolving GNS records

Next, you should try resolving your own GNS records. The simplest method is to do this by explicitly resolving using gnunet-gns. 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 using

$ gnunet-arm -i gns-proxy

Use

$ gnunet-arm -I

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 using:

$ chromium --proxy-server="socks5://localhost:7777"

For Firefox or Iceweasel, 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. Select SOCKS v5 and then 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 to www.gnu.com.

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 "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.

Be Social

Next, you should print out your business card and be social. Find a friend, help him install GNUnet and exchange business cards with him. 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. Once you have a business card, 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 his 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.

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

Before starting the tutorial, you should be aware that gnunet-conversation is currently only available as an interactive shell tool and that the call quality tends to be abysmal. There are also some awkward steps necessary to use it. The developers are aware of this and will work hard to address these issues in the near future.

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. Usually, the master-zone is a reasonable choice. Run:

$ gnunet-conversation -e master-zone

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.gnu and he also created his phone using a label "home-phone". Then you can initiate a call using:

/call home-phone.buddy.gnu

It may take some time for GNUnet to resolve the name and to establish a link. If your buddy has your public key in his master zone, he should see an incoming call with your name. If your public key is not in his master zone, he 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".

Future Directions

Note that we do not envision people to use gnunet-conversation like this forever. We will write a graphical user interface, and that GUI will automatically create the necessary records in the respective zone.

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First steps: Using the GNUnet 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 his 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 his 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

THIS TEXT IS OUTDATED AND NEEDS TO BE REWRITTEN FOR 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.

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".

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.

GNS Configuration

DNS Services Configuration

This creates new hostnames in the form "example.gnu". The "example" is filled in the first column, the others describe a mapping to a service.
The special strings "localhost4" and "localhost6" are expanded to the IPv4 and IPv6 address of the exit interface respectively.

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 his 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 to one user might be www.friend.gnu for someone else.

Maintaining your own Zones

To setup you GNS system you must execute:

$ gnunet-gns-import.sh

This will boostrap your zones and create the necessary key material.
Your keys can be listed using the gnunet-identity command line tool:

$ gnunet-identity -d

You can arbitrarily create your own zones using the gnunet-identity tool using:

$ gnunet-identity -C "new_zone"

Now you can add (or edit, or remove) records in your GNS zone using the gnunet-setup 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 mutliple 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 simple example for editing your own zone, suppose you have your own web server with 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 using the command:

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

Afterwards, you will be able to access your webpage under "www.gnu"(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-setup 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 master-zone | 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-gtk. The QR code is displayed in the GNS tab 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 his local zone:

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

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

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

The Three Local Zones of GNS

Each user GNS has control over three zones. Each of the zones has a different purpose. These zones are the

  • master zone,
  • private zone, and the
  • shorten zone.

The Master Zone

The master zone is your personal TLD. Names within the .gnu namespace are resolved relative to this zone. You can arbitrarily add records to this zone and selectively publish those records.

The Private Zone

The private zone is a subzone (or subdomain in DNS terms) of your master zone. It should be used for records that you want to keep private. For example bank.private.gnu. The key idea is that you want to keep your private records separate, if just to know that those names are not available to other users.

The Shorten Zone

The shorten zone can either be a subzone of the master zone or the private zone. It is different from the other zones in that GNS will automatically populate this zone with other users' zones based on their PSEU records whenever you resolve a name.

For example if you go to www.bob.alice.dave.gnu, GNS will try to import bob into your shorten zone. Having obtained Bob's PKEY from alice.dave.gnu, GNS will lookup the PSEU record for + in Bob's zone. If it exists and the specified pseudonym is not taken, Bob's PKEY will be automatically added under that pseudonym (i.e. "bob") into your shorten zone. From then on, Bob's webpage will also be available for you as www.bob.short.gnu. This feature is called automatic name shortening and is supposed to keep GNS names as short and memorable as possible.

The ZKEY Top Level Domain in GNS

GNS also provides a secure and globally unique namespace under the .zkey top-level domain. A name in the .zkey TLD corresponds to the (printable) public key of a zone. Names in the .zkey TLD are then resolved by querying the respective zone. The .zkey TLD is 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. Additionally, GNS defines some new record types the are unique to the GNS system. For example, GNS-specific resource records are use 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 .gnu 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 name "+" 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.

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 me '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 him 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 will result in a DNS query for 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.

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 Tor project 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.