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@node Using GNUnet
@chapter 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.


@menu
* Start and stop GNUnet::
* First steps - Using the GNU Name System::
* First steps - Using GNUnet Conversation::
* First steps - Using the GNUnet VPN::
* File-sharing::
* The GNU Name System::
* reclaimID Identity Provider::
* Using the Virtual Public Network::
@end menu

@node Start and stop GNUnet
@section Start and stop GNUnet

Prior to using any GNUnet-based application, one has to start a node:

@example
$ gnunet-arm -s -l gnunet.log
@end example

To stop GNUnet:

@example
$ gnunet-arm -e
@end example

@node First steps - Using the GNU Name System
@section First steps - Using the GNU Name System


@menu
* Preliminaries::
* Managing Egos::
* The GNS Tab::
* Creating a Record::
* Resolving GNS records::
* Integration with Browsers::
* Creating a Business Card::
* Be Social::
* Backup of Identities and Egos::
* Revocation::
* What's Next?::
@end menu

@node Preliminaries
@subsection Preliminaries


``.pin'' is a default zone which points to a zone managed by gnunet.org.
Use @code{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:

@example
$ gnunet-config -s gns -n .myfriend -V PUBLIC_KEY
@end example

@node Managing Egos
@subsection 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
@command{gnunet-identity -d}

@example
gnu - JTDVJC69NHU6GQS4B5721MV8VM7J6G2DVRGJV0ONIT6QH7OI6D50
rules - GO0T87F9BPMF8NKD5A54L2AH1T0GRML539TPFSRMCEA98182QD30
@end example


@node The GNS Tab
@subsection The GNS Tab


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

We will use the GTK+ interface in this introduction.  Please start
@command{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.

@node Creating a Record
@subsection 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 @dfn{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.


@node Resolving GNS records
@subsection 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 @code{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:

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

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

@node Integration with Browsers
@subsection 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 @code{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 @command{gnunet-arm -i gns-proxy}. Use @command{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 @command{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
@command{chromium --proxy-server="socks5://localhost:7777"}
For @command{Firefox} (or @command{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 @code{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
@code{browser.fixup.alternate.enabled} option to @code{false},
otherwise the browser will autoblunder an address like
@code{@uref{http://www.gnu/, www.gnu}} to
@code{@uref{http://www.gnu.com/, www.gnu.com}}.  If you want
to resolve @@ in your own TLDs, you must additionally
set @code{browser.fixup.dns_first_use_for_single_words} to @code{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
"@uref{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 "@uref{http://www.test.gnu/}" instead of
"@uref{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.

@pindex gnunet-bcd
@node Creating a Business Card
@subsection Creating a Business Card
@c FIXME: Which parts of texlive are needed? Some systems offer a modular
@c texlive (smaller size).

Before we can really use GNS, you should create a business card.
Note that this requires having @command{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 @b{requires 3GB} of downloaded data and possibly
@b{even more} when unpacked. On a GNU Guix based system texlive 2017 has
returns a DAG size of 5032.4 MiB.
@b{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.}

@example
apt-get install texlive-full
@end example

@noindent
Start creating a business card by clicking the "Copy" button
in @command{gnunet-namestore-gtk}. Next, you should start
the @command{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:

@example
$ gnunet-bcd # seems to hang...
@end example

@noindent
Then, start a browser and point it to @uref{http://localhost:8888/}
where @code{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 @command{gnunet-namestore-gtk}.
Then, fill in all of the other fields, including your @b{GNS NICKname}.
Adding a GPG fingerprint is optional.
Once finished, click "Submit Query".
If your @code{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 @code{gnunet-bcd} and press
@b{CTRL-C} to shut down the Web server.


@node Be Social
@subsection 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 @code{gnunet-qr} which zone
it should import new records into.  For this, run:

@pindex gnunet-identity
@example
$ gnunet-identity -s namestore -e NAME
@end example
where NAME is the name of the zone you want to import records
into.  In our running example, this would be ``gnu''.

@pindex gnunet-qr
Henceforth, for every business card you collect, simply run:
@example
$ gnunet-qr
@end example

@noindent
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

@pindex gnunet-gns
@example
$ gnunet-gns -u test.bob.gnu
@end example

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


@node Backup of Identities and Egos
@subsection 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 @file{~/.local/share/gnunet/private_key.ecc}

The private keys of your egos are stored in the
directory @file{~/.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.


@node Revocation
@subsection 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.

@pindex gnunet-revocation
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
@command{gnunet-revocation}. For example, the following command (as
unprivileged user) generates a revocation file
@file{revocation.dat} for the zone @code{zone1}:
@command{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 up to 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 compromise 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).


@c FIXME: The Manual should give away the command using an example that is
@c very likely to never exist.
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 @command{-p} option of @command{gnunet-revocation}.


@node What's Next?
@subsection 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.

@pindex gnunet-conservation-gtk
@node First steps - Using GNUnet Conversation
@section First steps - Using GNUnet Conversation


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

@example
$ gnunet-conversation-gtk
@end example

@menu
* Testing your Audio Equipment::
* GNS Zones::
@end menu

@node Testing your Audio Equipment
@subsection Testing your Audio Equipment


First, you should use @code{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.

@node GNS Zones
@subsection GNS Zones


@code{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.


@menu
* Picking an Identity::
* Calling somebody::
@end menu

@node Picking an Identity
@subsubsection Picking an Identity


To make a call with @code{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

@pindex gnunet-conversation
@example
gnunet-conversation -e zone-name
@end example

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

@example
/address
0-PD67SGHF3E0447TU9HADIVU9OM7V4QHTOG0EBU69TFRI2LG63DR0
@end example

@noindent
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 @code{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:

@image{images/gnunet-namestore-gtk-phone,5in,,Dialog to publish a PHONE record}

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.

@node Calling somebody
@subsubsection 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 @code{gnunet-qr}. Suppose your buddy
is in your zone as @code{buddy.mytld} and they also created their
phone using a label "home-phone". Then you can initiate a call using:

@example
/call home-phone.buddy.mytld
@end example

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 @command{/cancel}. You can exit
@code{gnunet-conversation} using @command{/quit}.


@node First steps - Using the GNUnet VPN
@section First steps - Using the GNUnet VPN



@menu
* VPN Preliminaries::
* GNUnet-Exit configuration::
* GNS configuration::
* Accessing the service::
* Using a Browser::
@end menu

@node VPN Preliminaries
@subsection VPN Preliminaries


To test the GNUnet VPN, we should first run a web server.
The easiest way to do this is to just start @code{gnunet-bcd},
which will run a webserver on port @code{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 @code{/etc/nsswitch.conf}
you should fine a line like this:

@example
hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
@end example

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

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

@c TODO: outdated section, we no longer install this as part of the
@c TODO: standard installation procedure and should point out the manual
@c TODO: steps required to make it useful.
@noindent
You might want to make sure that @code{/lib/libnss_gns.so.2} exists on
your system, it should have been created during the installation.
If not, re-run

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

@noindent
to install the NSS plugins in the proper location.

@node GNUnet-Exit configuration
@subsection GNUnet-Exit configuration


Stop your peer (as user @code{gnunet}, run @command{gnunet-arm -e}) and
run @command{gnunet-setup}. In @command{gnunet-setup}, make sure to
activate the @strong{EXIT} and @strong{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 @code{bcd} under Identifier and change the
Destination to @code{169.254.86.1:8888} (if your server runs on a port
other than 8888, change the 8888 port accordingly).

Now exit @command{gnunet-setup} and restart your peer
(@command{gnunet-arm -s}).

@node GNS configuration
@subsection GNS configuration


Now, using your normal user (not the @code{gnunet} system user), run
@command{gnunet-namestore-gtk}. Add a new label www in your
master zone. For the record type, select @code{VPN}. You should then
see the VPN dialog:

@image{images/gnunet-namestore-gtk-vpn,5in,,Dialog to publish a VPN record}

Under peer, you need to supply the peer identity of your own peer. You can
obtain the respective string by running @command{gnunet-peerinfo -sq}
as the @code{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 @command{gnunet-namestore-gtk}.

@node Accessing the service
@subsection Accessing the service


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

@example
$ wget http://www.gnu/
@end example

@noindent
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.

@node Using a Browser
@subsection Using a Browser


Sadly, modern browsers tend to bypass the Name Services Switch and
attempt DNS resolution directly. You can either run
a @code{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 @code{.gnu} TLDs, even if we disabled its
autoblunder of changing @code{.gnu} to ".gnu.com". Still,
using the HTTP proxy with Chrome does work.

@node File-sharing
@section File-sharing


This chapter documents the GNUnet file-sharing application. The original
file-sharing implementation for GNUnet was designed to provide
@strong{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 @strong{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.

After a short introduction, 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.


@menu
* fs-Searching::
* fs-Downloading::
* fs-Publishing::
* fs-Concepts::
* Namespace Management::
* File-Sharing URIs::
* GTK User Interface::
@end menu

@node fs-Searching
@subsection Searching


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

@example
$ gnunet-search [-t TIMEOUT] KEYWORD
@end example

@noindent
The @command{-t} option specifies that the query should timeout after
approximately TIMEOUT seconds. A value of zero (``0'') is interpreted
as @emph{no timeout}, which is the default. In this case,
@command{gnunet-search} will never terminate (unless you press
@command{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

@example
$ gnunet-search Das Kapital
@end example

@noindent
is not the same as searching for

@example
$ gnunet-search "Das Kapital"
@end example

@noindent
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 @command{gnunet-search} like this:

@c it will be better the avoid the ellipsis altogether because I don't
@c understand the explanation below that
@c ng0: who is ``I'' and what was the complete sentence?
@example
#15:
gnunet-download -o "COPYING" gnunet://fs/chk/PGK8M...3EK130.75446

@end example

@noindent
The whole line is the command you would have to enter to download
the file. The first argument passed to @code{-o} is the suggested
filename (you may change it to whatever you like).
It is followed by the key for decrypting the file, the query for
searching the file, a checksum (in hexadecimal) finally the size of
the file in bytes.

@node fs-Downloading
@subsection Downloading


In order to download a file, you need the whole line returned by
@command{gnunet-search}.
You can then use the tool @command{gnunet-download} to obtain the file:

@example
$ gnunet-download -o <FILENAME> <GNUNET-URL>
@end example

@noindent
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:

@example
$ gnunet-download -o "COPYING" gnunet://fs/chk/PGK8M...3EK130.75446
@end example

@noindent
If you ever have to abort a download, you can continue it at any time by
re-issuing @command{gnunet-download} with the same filename.
In that case, GNUnet will @strong{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 @command{-V} switch to turn on verbose
reporting. In this case, @command{gnunet-download} will print the
current number of bytes downloaded whenever new data was received.

@node fs-Publishing
@subsection Publishing


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

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

For example
@example
$ gnunet-publish -m "description:GNU License" -k gpl -k test -m "mimetype:text/plain" COPYING
@end example

@menu
* Important command-line options::
* Indexing vs. Inserting::
@end menu

@node Important command-line options
@subsubsection Important command-line options


The option @code{-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. Please note that you must use the @code{-k} option
more than once -- one for each expression you use as a keyword for
the filename.

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 @command{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
may be inferred using @code{GNU libextractor}.

@command{gnunet-publish} has a few additional options to handle
namespaces and directories. Refer to the man-page for details:

@example
man gnunet-publish
@end example

@node Indexing vs. Inserting
@subsubsection Indexing vs Inserting


By default, GNUnet indexes a file instead of making a full copy.
This is much more efficient, but requires 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 @code{-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 @strong{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 preserve 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
@command{gnunet-unindex} to un-index the file.

The option @code{-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 @code{-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.

@node fs-Concepts
@subsection Concepts


For better results with filesharing it is useful to understand the
following concepts.
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 achieve these goals.


@menu
* Files::
* Keywords::
* Directories::
* Egos and File-Sharing::
* Namespaces::
* Advertisements::
* Anonymity level::
* Content Priority::
* Replication::
@end menu

@node Files
@subsubsection Files


A file in GNUnet is just a sequence of bytes. Any file-format is allowed
and the maximum file size is theoretically @math{2^64 - 1} 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.

@node Keywords
@subsubsection Keywords


Keywords are the most simple mechanism to find files on GNUnet.
Keywords are @strong{case-sensitive} and the search string
must always match @strong{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.

@node Directories
@subsubsection 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.

Directories are shared just like ordinary files. If you download a
directory with @command{gnunet-download}, you can use
@command{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
@command{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).

@node Egos and File-Sharing
@subsubsection Egos and File-Sharing

When sharing files, it is sometimes desirable to build a reputation as
a source for quality information.  With egos, publishers can
(cryptographically) sign files, thereby demonstrating that various
files were published by the same entity.  An ego thus allows users to
link different publication events, thereby deliberately reducing
anonymity to pseudonymity.

Egos used in GNUnet's file-sharing for such pseudonymous publishing
also correspond to the egos used to identify and sign zones in the
GNU Name System.  However, if the same ego is used for file-sharing
and for a GNS zone, this will weaken the privacy assurances provided
by the anonymous file-sharing protocol.

Note that an ego is NOT bound to a GNUnet peer. There can be multiple
egos for a single user, and users could (theoretically) share
the private keys of an ego by copying the respective private keys.


@node Namespaces
@subsubsection Namespaces

A namespace is a set of files that were signed by the same ego.
Today, namespaces are implemented independently of GNS zones, but
in the future we plan to merge the two such that a GNS zone can
basically contain files using a file-sharing specific record type.

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. 

@node Advertisements
@subsubsection 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
@code{gnunet-identity}. Whenever a namespace is created, an
appropriate advertisement can be generated.  The default keyword for
the advertising of namespaces is "namespace".


@node Anonymity level
@subsubsection 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.

The specific numeric value (for anonymity levels above 1) is simple:
Given an anonymity level L (above 1), each request FS makes on your
behalf must be hidden in L-1 equivalent requests of cover traffic
(traffic your peer routes for others) in the same time-period.  The
time-period is twice the average delay by which GNUnet artificially
delays traffic.

While higher anonymity levels may offer better privacy, they can also
significantly hurt performance.


@node Content Priority
@subsubsection 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.


@node Replication
@subsubsection 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.


@node Namespace Management
@subsection Namespace Management

The @code{gnunet-identity} tool can be used to create egos.
By default, @code{gnunet-identity -D} simply
lists all locally available egos.


@menu
* Creating Egos::
* Deleting Egos::
@end menu

@node Creating Egos
@subsubsection Creating Egos

With the @command{-C NICK} option it can also be used to create a new
ego. An ego is the virtual identity of the entity in control of a
namespace or GNS zone. Anyone can create any number of egos.  The
provided NICK name automatically corresponds to a GNU Name System
domain name.  Thus, henceforth name resolution for any name ending in
``.NICK'' will use the NICK's zone.  You should avoid using NICKs that
collide with well-known DNS names.

@node Deleting Egos
@subsubsection Deleting Egos

With the @command{-D NICK} option egos can be deleted.  Once the ego
has been deleted it is impossible to add content to the corresponding
namespace or zone. However, the existing GNS zone data is currently
not dropped. This may change in the future.

Deleting the pseudonym does not make the namespace or any content in
it unavailable.

@node File-Sharing URIs
@subsection 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"'.

@menu
* Encoding of hash values in URIs::
* Content Hash Key (chk)::
* Location identifiers (loc)::
* Keyword queries (ksk)::
* Namespace content (sks)::
@end menu

@node Encoding of hash values in URIs
@subsubsection Encoding of hash values in URIs


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

@cindex chk-uri
@node Content Hash Key (chk)
@subsubsection 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).

@cindex loc-uri
@node Location identifiers (loc)
@subsubsection 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).

@cindex ksk-uri
@node Keyword queries (ksk)
@subsubsection 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 '++'.

@cindex sks-uri
@node Namespace content (sks)
@subsubsection Namespace content (sks)


@b{Please note that the text in this subsection is outdated and needs}
@b{to be rewritten for version 0.10!}
@b{This especially concerns the terminology of Pseudonym/Ego/Identity.}

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.

@node GTK User Interface
@subsection GTK User Interface
This chapter describes first steps for file-sharing with GNUnet.
To start, you should launch @command{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.

@menu
* gtk-Publishing::
* gtk-Searching::
* gtk-Downloading::
@end menu

@node gtk-Publishing
@subsubsection 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:

@image{images/gnunet-gtk-0-10-fs-publish,5in,,The gnunet-fs-gtk publishing dialog}

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

@image{images/gnunet-gtk-0-10-fs-publish-select,5in,,Dialog to select the file to publish (looks may differ for other Gtk+ versions)}

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:

@image{images/gnunet-gtk-0-10-fs-publish-with-file,5in,,Publishing dialog with file added}

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

@image{images/gnunet-gtk-0-10-fs-publish-editing,5in,,Editing meta data of a file to be published}

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).

@node gtk-Searching
@subsubsection 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.

@node gtk-Downloading
@subsubsection 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 anonymous 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!


@node The GNU Name System
@section 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 @code{.gnu}
@dfn{top-level domain} (TLD).

GNS is designed to provide:
@itemize @bullet
@item Censorship resistance
@item Query privacy
@item Secure name resolution
@item Compatibility with DNS
@end itemize

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
@code{@uref{http://www.bob.gnu/, www.bob.gnu}} to one user might be
@code{@uref{http://www.friend.gnu/, www.friend.gnu}} for someone else.


@menu
* Creating a Zone::
* Maintaining your own Zones::
* Obtaining your Zone Key::
* Adding Links to Other Zones::
* Using Public Keys as Top Level Domains::
* Resource Records in GNS::
* Synchronizing with legacy DNS::
* Migrating an existing DNS zone into GNS::
@end menu


@node Creating a Zone
@subsection 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:

@example
$ gnunet-identity -C "myzone"
@end example

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

All of your zones can be listed (displayed) using the
@command{gnunet-identity} command line tool as well:

@example
$ gnunet-identity -d
@end example

@node Maintaining your own Zones
@subsection Maintaining your own Zones

@noindent
Now you can add (or edit, or remove) records in your GNS zone using the
@command{gnunet-namestore-gtk} GUI or using the @command{gnunet-namestore}
command-line tool.
In either case, your records will be stored in an SQL database under
control of the @command{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 @code{1.2.3.4}. Then you can put an
@code{A} record (@code{A} records in DNS are for IPv4 IP addresses)
into your local zone ``myzone'' using the command:

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

@noindent
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
@command{gnunet-namestore-gtk} GUI to be easier.

@node Obtaining your Zone Key
@subsection 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

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

@noindent
For example, the output might be something like:

@example
DC3SEECJORPHQNVRH965A6N74B1M37S721IG4RBQ15PJLLPJKUE0
@end example

@noindent
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.

@node Adding Links to Other Zones
@subsection 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:

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

@noindent
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
@command{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.

@c themselves? themself?
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).


@node Using Public Keys as Top Level Domains
@subsection 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.

@node Resource Records in GNS
@subsection Resource Records in GNS


GNS supports the majority of the DNS records as defined in
@uref{http://www.ietf.org/rfc/rfc1035.txt, RFC 1035}. 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:

@menu
* NICK::
* PKEY::
* BOX::
* LEHO::
* VPN::
* A AAAA and TXT::
* CNAME::
* GNS2DNS::
* SOA SRV PTR and MX::
* PLACE::
* PHONE::
* ID ATTR::
* ID TOKEN::
* ID TOKEN METADATA::
* CREDENTIAL::
* POLICY::
* ATTRIBUTE::
* ABE KEY::
* ABE MASTER::
* RECLAIM OIDC CLIENT::
* RECLAIM OIDC REDIRECT::
@end menu

@node NICK
@subsubsection 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.

@b{Example}@

@example
Name: @@; RRType: NICK; Value: bob
@end example

@noindent
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'").

@node PKEY
@subsubsection PKEY

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

@b{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:

@example
Name: friend; RRType: PKEY; Value: ABC012;
@end example

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

@node BOX
@subsubsection 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 @code{_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.

@node LEHO
@subsubsection 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.

@node VPN
@subsubsection 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.

@b{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 @file{gnunet.conf} configuration file:

@example
[web.gnunet.]
TCP_REDIRECTS = 80:localhost4:8080
@end example

@node A AAAA and TXT
@subsubsection A AAAA and TXT

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

@node CNAME
@subsubsection 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:

@itemize @bullet
@item A zone relative name,
@item A zkey name or
@item A DNS name (in which case resolution will continue outside
of GNS with the systems DNS resolver)
@end itemize

@node GNS2DNS
@subsubsection 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.

@b{Example}

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

@noindent
Any query to @code{pet.gnu} will then be delegated to the DNS server at
@code{a.ns.joker.com}. For example,
@code{@uref{http://www.pet.gnu/, www.pet.gnu}} will result in a DNS query
for @code{@uref{http://www.gnunet.org/, www.gnunet.org}} to the server
at @code{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.

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

@noindent
This way, you can avoid involving the DNS hierarchy in the resolution of
@code{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.

@node SOA SRV PTR and MX
@subsubsection SOA SRV PTR and MX

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

@itemize @bullet
@item A zone relative name,
@item A zkey name or
@item A DNS name
@end itemize

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.

@node PLACE
@subsubsection PLACE

Record type for a social place.

@node PHONE
@subsubsection PHONE

Record type for a phone (of CONVERSATION).

@node ID ATTR
@subsubsection ID ATTR

Record type for identity attributes (of IDENTITY).

@node ID TOKEN
@subsubsection ID TOKEN

Record type for an identity token (of IDENTITY-TOKEN).

@node ID TOKEN METADATA
@subsubsection ID TOKEN METADATA

Record type for the private metadata of an identity token (of IDENTITY-TOKEN).

@node CREDENTIAL
@subsubsection CREDENTIAL

Record type for credential.

@node POLICY
@subsubsection POLICY

Record type for policies.

@node ATTRIBUTE
@subsubsection ATTRIBUTE

Record type for reverse lookups.

@node ABE KEY
@subsubsection ABE KEY

Record type for ABE records.

@node ABE MASTER
@subsubsection ABE MASTER

Record type for ABE master keys.

@node RECLAIM OIDC CLIENT
@subsubsection RECLAIM OIDC CLIENT

Record type for reclaim OIDC clients.

@node RECLAIM OIDC REDIRECT
@subsubsection RECLAIM OIDC REDIRECT

Record type for reclaim OIDC redirect URIs.

@node Synchronizing with legacy DNS
@subsection 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
@command{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, @command{gnunet-zoneimport} reads a list
of DNS domain names from @code{stdin}, issues DNS queries for
each, converts the obtained records (if possible) and stores
the result in the namestore.

@image{images/gns,6in,, 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]''.

@node Migrating an existing DNS zone into GNS
@subsection Migrating an existing DNS zone into GNS

Ascension is a tool to migrate existing DNS zones into GNS.

@xref{Migrating existing DNS zones into GNS}, for installation instructions and
further information about Ascension.

Compared to the gnunet-zoneimport tool it strictly uses AXFR or IXFR depending
on whether or not there exists a SOA record for the zone. If that is the case it
will take the serial as a reference point and request the zone. The server will
either answer the IXFR request with a correct incremental zone or with the
entire zone, which depends on the server configuration.

After installing the tool according to the README file you have the following
options:

@example
Ascension
Usage:
    ascension <domain> [-d] [-p] [-s] [--minimum-ttl=<ttl>] \
        [--dry-run]
    ascension <domain> <port> [-d] [-p] [-s] \
        [--minimum-ttl=<ttl>] [--dry-run]
    ascension <domain> -n <transferns> [-d] [-p] \
        [-s] [--minimum-ttl=<ttl>] [--dry-run]
    ascension <domain> -n <transferns> <port> [-d] \
        [-p] [-s] [--minimum-ttl=<ttl>] [--dry-run]
    ascension -p | --public
    ascension -d | --debug
    ascension -s | --standalone
    ascension -h | --help
    ascension -v | --version

Options:
    <domain>              Domain to migrate
    <port>                Port for zone transfer
    <transferns>          DNS Server that does the zone transfer
    --minimum-ttl=<ttl>   Minimum TTL for records to migrate \
        [default: 3600]
    --dry-run             Only try if a zone transfer is allowed
    -p --public           Make records public on the DHT
    -s --standalone       Run ascension once
    -d --debug            Enable debugging
    -h --help         Show this screen.
    -v --version      Show version.
@end example

Before you can migrate any zone though, you need to start a local GNUnet peer:
@example
$ gnunet-arm -s
@end example

To migrate the Syrian top level domain - one of the few top level domains that
support zone transfers - into GNS use the following command:

@example
$ ascension sy. -n ns1.tld.sy. -p
@end example

The -p flag will tell GNS to put these records on the DHT so that other users
may resolve these records by using the public key of the zone.

Once the zone is migrated, Ascension will output a message telling you, that it
will refresh the zone after the time has elapsed.  You can resolve the names in
the zone directly using GNS or if you want to use it with your browser, check
out the GNS manual section. @ref{Configuring the GNU Name System}. To resolve
the records from another system you need the respective zones PKEY. To get the
zones public key, you can run the following command:

@example
$ gnunet-identity -dqe sy
@end example

Where "sy" is the name of the zone you want to migrate.

You can share the PKEY of the zone with your friends. They can then resolve
records in the zone by doing a lookup replacing the zone label with your PKEY:

@example
$ gnunet-gns -t SOA -u "$PKEY"
@end example

The program will continue to run as a daemon and update once the refresh time
specified in the zones SOA record has elapsed.

DNSCurve style records are supported in the latest release and they are added
as a PKEY record to be referred to the respective GNS public key. Key
distribution is still a problem but provided someone else has a public key
under a given label it can be looked up.

There is an unofficial Debian package called python3-ascension that adds a
system user ascension and runs a GNUnet peer in the background.

Ascension-bind is also an unofficial Debian package that on installation checks
for running DNS zones and whether or not they are transferable using DNS zone
transfer (AXFR). It asks the administrator which zones to migrate into GNS and
installs a systemd unit file to keep the zone up to date.  If you want to
migrate different zones you might want to check the unit file from the package
as a guide.

@node reclaimID Identity Provider
@section reclaimID Identity Provider

The reclaimID Identity Provider (IdP) is a decentralized IdP service.
It allows its users to manage and authorize third parties to access
their identity attributes such as email or shipping addresses.

It basically mimics the concepts of centralized IdPs, such as those
offered by Google or Facebook.
Like other IdPs, reclaimID features an (optional) OpenID-Connect
1.0-compliant protocol layer that can be used for websites to
integrate reclaimID as an Identity Provider with little effort.

@menu
* Managing Attributes::
* Sharing Attributes with Third Parties::
* Revoking Authorizations of Third Parties::
* OpenID Connect::
@end menu

@node Managing Attributes
@subsection Managing Attributes

Before adding attributes to an identity, you must first create an ego:

@example
$ gnunet-identity -C "user"
@end example

Henceforth, you can manage a new user profile of the user ``user''.

To add an email address to your user profile, simply use the @command{gnunet-reclaim} command line tool::

@example
$ gnunet-reclaim -e "user" -a "email" -V "username@@example.gnunet"
@end example

All of your attributes can be listed using the @command{gnunet-reclaim}
command line tool as well:

@example
$ gnunet-reclaim -e "user" -D
@end example

Currently, and by default, attribute values are interpreted as plain text.
In the future there might be more value types such as X.509 certificate credentials.

@node Sharing Attributes with Third Parties
@subsection Sharing Attributes with Third Parties

If you want to allow a third party such as a website or friend to access to your attributes (or a subset thereof) execute:

@example
$ gnunet-reclaim -e "user" -r "PKEY" -i "attribute1,attribute2,..."
@end example

Where "PKEY" is the public key of the third party and "attribute1,attribute2,..." is a comma-separated list of attribute names, such as "email,name,...", that you want to share.

The command will return a "ticket" string.
You must give this "ticket" to the requesting third party.

The third party can then retrieve your shared identity attributes using:

@example
$ gnunet-reclaim -e "friend" -C "ticket"
@end example

Where "friend" is the name for "user" that the requesting party is using.
This will retrieve and list the shared identity attributes.
The above command will also work if the user is currently offline since the attributes are retrieved from GNS.
Further, the "ticket" can be re-used later to retrieve up-to-date attributes in case "friend" has changed the value(s). For instance, because his email address changed.

To list all given authorizations (tickets) you can execute:
@example
$ gnunet-reclaim -e "friend" -T (TODO there is only a C and REST API for this at this time)
@end example


@node Revoking Authorizations of Third Parties
@subsection Revoking Authorizations of Third Parties

If you want to revoke the access of a third party to your attributes you can execute:

@example
$ gnunet-reclaim -e "user" -R "ticket"
@end example

This will prevent the third party from accessing the attribute in the future.
Please note that if the third party has previously accessed the attribute, there is not way in which the system could have prevented the thiry party from storing the data.
As such, only access to updated data in the future can be revoked.
This behaviour is _exactly the same_ as with other IdPs.

@node OpenID Connect
@subsection OpenID Connect

There is an OpenID Connect API for use with reclaimID.
However, its use is quite complicated to setup.
As a proof-of-concept, you can look at https://gitlab.com/reclaimid.

In the PoC and by convention for reclaimID, the OpenID Connect Endpoints are
found at:

@example
http://api.reclaim/openid/authorize
http://api.reclaim/openid/token
http://api.reclaim/openid/userinfo
http://api.reclaim/openid/login
@end example

The token endpoint is protected using HTTP basic authentication.
You can authenticate using any username and the password configured under:

@example
$ gnunet-config -s reclaim-rest-plugin -o PSW
@end example

The authorize endpoint is protected using a Cookie which can be obtained through
a request against the login endpoint.
This flow is meant to be used in the context of the OpenID Connect authorization
flow to collect user consent interactively.
Without a Cookie, the authorize endpoint redirects to a URI configured under:

@example
$ gnunet-config -s reclaim-rest-plugin -o ADDRESS
@end example

Our PoC includes a user interface (https://gitlab.com/reclaimid) which
integrates this process is an OpenID Connect compatible fashion.

The token endpoint is protected using OAuth2 and expects the grant
which is retrieved from the authorization endpoint according to the standard.

The userinfo endpoint is protected using OAuth2 and expects a bearer access
token which is retrieved from a token request.

In order to create and register a client you need to execute the following
steps:

@example
$ gnunet-identity -C <client_name>
$ gnunet-namestore -z <client_name> -a -n "@@" -t RECLAIM_OIDC_REDIRECT -V <redirect_uri> -e 1d -p
$ gnunet-namestore -z <client_name> -a -n "@@" -t RECLAIM_OIDC_CLIENT -V "My OIDC Client" -e 1d -p
@end example

The client_id will be the public key of the client.
As a redirect URI, you may use any globally unique DNS or GNS URI.
The client description will be displayed to the user on authorization.

Any website or relying party must use the endpoint
https://api.reclaim/openid/authorize in its authorization redirects, e.g.

@example
<a href="https://api.reclaim/openid/authorize?client_id=<PKEY>\
                                             &scope=email\
                                             &redirect_uri=<redirect_uri>\
                                             &nonce=<random>">Login</a>
@end example

This will direct the user's browser onto his local reclaimID instance.
After giving consent, you will be provided with the OpenID Connect authorization
code according to the specifications at your provided redirect URI.
The example code for the PoC website can be found at https://gitlab.com/reclaimid/demo.

@node Using the Virtual Public Network
@section Using the Virtual Public Network

@menu
* Setting up an Exit node::
* Fedora and the Firewall::
* Setting up VPN node for protocol translation and tunneling::
@end menu

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.

@node Setting up an Exit node
@subsection 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:

@itemize @bullet
@item DNS: allow other peers to use your DNS resolver
@item IPv4: allow other peers to access your IPv4 Internet connection
@item IPv6: allow other peers to access your IPv6 Internet connection
@item Local service: allow other peers to access a specific TCP or
UDP service your peer is providing
@end itemize

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.

@node Fedora and the Firewall
@subsection 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.

@node Setting up VPN node for protocol translation and tunneling
@subsection 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
specify 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.

@command{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.