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@ -1,5 +1,5 @@
\input texinfo @c -*-texinfo-*-
@c $Id: tinc.texi,v 1.8.4.8 2000/11/24 14:13:51 zarq Exp $
@c $Id: tinc.texi,v 1.8.4.9 2000/11/30 23:39:55 zarq Exp $
@c %**start of header
@setfilename tinc.info
@settitle tinc Manual
@ -17,7 +17,7 @@ Copyright @copyright{} 1998,199,2000 Ivo Timmermans
<itimmermans@@bigfoot.com>, Guus Sliepen <guus@@sliepen.warande.net> and
Wessel Dankers <wsl@@nl.linux.org>.
$Id: tinc.texi,v 1.8.4.8 2000/11/24 14:13:51 zarq Exp $
$Id: tinc.texi,v 1.8.4.9 2000/11/30 23:39:55 zarq Exp $
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
@ -42,7 +42,7 @@ Copyright @copyright{} 1998,1999,2000 Ivo Timmermans
<itimmermans@@bigfoot.com>, Guus Sliepen <guus@@sliepen.warande.net> and
Wessel Dankers <wsl@@nl.linux.org>.
$Id: tinc.texi,v 1.8.4.8 2000/11/24 14:13:51 zarq Exp $
$Id: tinc.texi,v 1.8.4.9 2000/11/30 23:39:55 zarq Exp $
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
@ -87,7 +87,7 @@ network device, there is no need to adapt any existing software.
This tunneling allows VPN sites to share information with each other
over the Internet without exposing any information to others.
This document is the manual for tinc. Included are chapters on how to
This document is the manual for tinc. Included are chapters on how to
configure your computer to use tinc, as well as the configuration
process of tinc itself.
@ -103,40 +103,40 @@ process of tinc itself.
@cindex VPN
A Virtual Private Network or VPN is a network that can only be accessed
by a few elected computers that participate. This goal is achievable in
by a few elected computers that participate. This goal is achievable in
more than just one way.
@cindex private
Private networks can consist of a single stand-alone ethernet LAN. Or
even two computers hooked up using a null-modem cable. In these cases,
Private networks can consist of a single stand-alone ethernet LAN. Or
even two computers hooked up using a null-modem cable. In these cases,
it is
obvious that the network is @emph{private}, no one can access it from the
outside. But if your computers are linked to the internet, the network
outside. But if your computers are linked to the internet, the network
is not private anymore, unless one uses firewalls to block all private
traffic. But then, there is no way to send private data to trusted
traffic. But then, there is no way to send private data to trusted
computers on the other end of the internet.
@cindex virtual
This problem can be solved by using @emph{virtual} networks. Virtual
This problem can be solved by using @emph{virtual} networks. Virtual
networks can live on top of other networks, but do not interfere with
each other. Mostly, virtual networks appear like a singe LAN, even though
they can span the entire world. But virtual networks can't be secured
each other. Mostly, virtual networks appear like a singe LAN, even though
they can span the entire world. But virtual networks can't be secured
by using firewalls, because the traffic that flows through it has to go
through the internet, where other people can look at it.
When one introduces encryption, we can form a true VPN. Other people may
When one introduces encryption, we can form a true VPN. Other people may
see encrypted traffic, but if they don't know how to decipher it (they
need to know the key for that), they cannot read the information that flows
through the VPN. This is what tinc was made for.
through the VPN. This is what tinc was made for.
@cindex virtual
tinc uses normal IP datagrams to encapsulate data that goes over the VPN
network link. In this case it's also clear that the network is
network link. In this case it's also clear that the network is
@emph{virtual}, because no direct network link has to exist between to
participants.
As is the case with either type of VPN, anybody could eavesdrop. Or
worse, alter data. Hence it's probably advisable to encrypt the data
As is the case with either type of VPN, anybody could eavesdrop. Or
worse, alter data. Hence it's probably advisable to encrypt the data
that flows over the network.
@ -147,10 +147,10 @@ that flows over the network.
@cindex vpnd
@cindex ethertap
I really don't quite remember what got us started, but it must have been
Guus' idea. He wrote a simple implementation (about 50 lines of C) that
Guus' idea. He wrote a simple implementation (about 50 lines of C) that
used the @emph{ethertap} device that Linux knows of since somewhere
about kernel 2.1.60. It didn't work immediately and he improved it a
bit. At this stage, the project was still simply called @samp{vpnd}.
about kernel 2.1.60. It didn't work immediately and he improved it a
bit. At this stage, the project was still simply called @samp{vpnd}.
Since then, a lot has changed---to say the least.
@ -160,12 +160,12 @@ both the receiving and sending end, it has become largely
runtime-configurable---in short, it has become a full-fledged
professional package.
A lot can---and will be---changed. I have a few things that I'd like to
see in the future releases of tinc. Not everything will be available in
the near future. Our first objective is to make tinc work perfectly as
A lot can---and will be---changed. I have a few things that I'd like to
see in the future releases of tinc. Not everything will be available in
the near future. Our first objective is to make tinc work perfectly as
it stands, and then add more advanced features.
Meanwhile, we're always open-minded towards new ideas. And we're
Meanwhile, we're always open-minded towards new ideas. And we're
available too.
@ -270,14 +270,14 @@ section.
@subsection Configuring the Linux kernel
Since this particular implementation only runs on 2.1 or higher Linux
kernels, you should grab one (2.2 is current at this time). A 2.0 port
kernels, you should grab one (2.2 is current at this time). A 2.0 port
is not really possible, unless someone tells me someone ported the
ethertap and netlink devices back to 2.0.
If you are unfamiliar with the process of configuring and compiling a
new kernel, you should read the
@uref{http://howto.linuxberg.com/LDP/HOWTO/Kernel-HOWTO.html, Kernel
HOWTO} first. Do that now!
HOWTO} first. Do that now!
Here are the options you have to turn on when configuring a new
kernel.
@ -307,7 +307,7 @@ Network device support
@end example
Any other options not mentioned here are not relevant to tinc. If you
Any other options not mentioned here are not relevant to tinc. If you
decide to build any of these as dynamic kernel modules, it's a good idea
to add these lines to @file{/etc/modules.conf}.
@ -428,7 +428,7 @@ the checksums of these files listed; you may wish to check these with
md5sum before continuing.
tinc comes in a handy autoconf/automake package, which you can just
treat the same as any other package. Which is just untar it, type
treat the same as any other package. Which is just untar it, type
`configure' and then `make'.
More detailed instructions are in the file @file{INSTALL}, which is
@ -505,7 +505,7 @@ Any further ethertap devices have minor device number 16 through 31.
@subsubheading @file{/etc/networks}
You may add a line to @file{/etc/networks} so that your VPN will get a
symbolic name. For example:
symbolic name. For example:
@example
myvpn 10.0.0.0
@ -517,8 +517,8 @@ legible.
@subsubheading @file{/etc/services}
You may add this line to @file{/etc/services}. The effect is that you
may supply a @samp{tinc} as a valid port number to some programs. The
You may add this line to @file{/etc/services}. The effect is that you
may supply a @samp{tinc} as a valid port number to some programs. The
number 655 is registered with the IANA.
@example
@ -541,7 +541,7 @@ numbers when you are going to configure tinc itself. @xref{Configuring
tinc}.
It doesn't matter much which part you do first, setting up the network
devices or configure tinc. But they both have to be done before you try
devices or configure tinc. But they both have to be done before you try
to start a tincd.
The actual setup of the ethertap device is quite simple, just repeat
@ -603,22 +603,22 @@ It is perfectly OK for you to run more than one tinc daemon.
However, in its default form, you will soon notice that you can't use
two different configuration files without the -c option.
We have thought of another way of dealing with this: network names. This
We have thought of another way of dealing with this: network names. This
means that you call tincd with the -n argument, which will assign a name
to this daemon.
The effect of this is that the daemon will set its configuration
``root'' to /etc/tinc/nn/, where nn is your argument to the -n
option. You'll notice that it appears in syslog as ``tinc.nn''.
option. You'll notice that it appears in syslog as ``tinc.nn''.
However, it is not strictly necessary that you call tinc with the -n
option. In this case, the network name would just be empty, and it will
be used as such. tinc now looks for files in /etc/tinc/, instead of
option. In this case, the network name would just be empty, and it will
be used as such. tinc now looks for files in /etc/tinc/, instead of
/etc/tinc/nn/; the configuration file should be /etc/tinc/tinc.conf,
and the passphrases are now expected to be in /etc/tinc/passphrases/.
But it is highly recommended that you use this feature of tinc, because
it will be so much clearer whom your daemon talks to. Hence, we will
it will be so much clearer whom your daemon talks to. Hence, we will
assume that you use it.
@ -629,8 +629,8 @@ assume that you use it.
Before going on, first a bit on how tinc sees connections.
When tinc starts up, it reads in the configuration file and parses the
command-line options. If it sees a `ConnectTo' value in the file, it
will try to connect to it, on the given port. If this fails, tinc exits.
command-line options. If it sees a `ConnectTo' value in the file, it
will try to connect to it, on the given port. If this fails, tinc exits.
@c ==================================================================
@ -648,7 +648,7 @@ Variable = Value.
@end example
The variable names are case insensitive, and any spaces, tabs, newlines
and carriage returns are ignored. Note: it is not required that you put
and carriage returns are ignored. Note: it is not required that you put
in the `=' sign, but doing so improves readability. If you leave it
out, remember to replace it with at least one space character.
@ -660,21 +660,21 @@ out, remember to replace it with at least one space character.
@node Variables, , Configuration file, Configuration file
@subsection Variables
Here are all valid variables, listed in alphabetical order. The default
Here are all valid variables, listed in alphabetical order. The default
value, required or optional is given between parentheses.
@c straight from the manpage
@table @asis
@item ConnectPort = <port> (655)
Connect to the upstream host (given with the ConnectTo directive) on
port port. port may be given in decimal (default), octal (when preceded
port port. port may be given in decimal (default), octal (when preceded
by a single zero) or hexadecimal (prefixed with 0x). port is the port
number for both the UDP and the TCP (meta) connections.
@item ConnectTo = <IP address|hostname> (optional)
Specifies which host to connect to on startup. Multiple ConnectTo variables
Specifies which host to connect to on startup. Multiple ConnectTo variables
may be specified, if connecting to the first one fails then tinc will try
the next one, and so on. It is possible to specify hostnames for dynamic IP
the next one, and so on. It is possible to specify hostnames for dynamic IP
addresses (like those given on dyndns.org), tinc will not cache the resolved
IP address.
@ -684,7 +684,7 @@ instead just listen for incoming connections.
@item Hostnames = <yes|no> (no)
This option selects whether IP addresses (both real and on the VPN) should
be resolved. Since DNS lookups are blocking, it might affect tinc's
be resolved. Since DNS lookups are blocking, it might affect tinc's
efficiency, even stopping the daemon for a few seconds everytime it does
a lookup if your DNS server is not responding.
@ -693,41 +693,41 @@ file.
@item IndirectData = <yes|no> (no)
This option specifies whether other tinc daemons besides the one you
specified with ConnectTo can make a direct connection to you. This is
specified with ConnectTo can make a direct connection to you. This is
especially useful if you are behind a firewall and it is impossible
to make a connection from the outside to your tinc daemon. Otherwise,
to make a connection from the outside to your tinc daemon. Otherwise,
it is best to leave this option out or set it to no.
@item Interface = <device> (optional)
If you have more than one network interface in your computer, tinc will by
default listen on all of them for incoming connections. It is possible to
default listen on all of them for incoming connections. It is possible to
bind tinc to a single interface like eth0 or ppp0 with this variable.
@item InterfaceIP = <local address> (optional)
If your computer has more than one IP address on a single interface (for example
if you are running virtual hosts), tinc will by default listen on all of them for
incoming connections. It is possible to bind tinc to a single IP address with
this variable. It is still possible to listen on several interfaces at the same
incoming connections. It is possible to bind tinc to a single IP address with
this variable. It is still possible to listen on several interfaces at the same
time though, if they share the same IP address.
@item KeyExpire = <seconds> (3600)
This option controls the time the encryption keys used to encrypt the data
are valid. It is common practice to change keys at regular intervals to
are valid. It is common practice to change keys at regular intervals to
make it even harder for crackers, even though it is thought to be nearly
impossible to crack a single key.
@item ListenPort = <port> (655)
Listen on local port port. The computer connecting to this daemon should
Listen on local port port. The computer connecting to this daemon should
use this number as the argument for his ConnectPort.
@item MyOwnVPNIP = <local address[/maskbits]> (required)
The local address is the number that the daemon will propagate to
other daemons on the network when it is identifying itself. Hence this
other daemons on the network when it is identifying itself. Hence this
will be the file name of the passphrase file that the other end expects
to find the passphrase in.
The local address is the IP address of the tap device, not the real IP
address of the host running tincd. Due to changes in recent kernels, it
address of the host running tincd. Due to changes in recent kernels, it
is also necessary that you make the ethernet (also known as MAC) address
equal to the IP address (see the example).
@ -738,32 +738,34 @@ This is an alias for MyOwnVPNIP.
@item PingTimeout = <seconds> (5)
The number of seconds of inactivity that tinc will wait before sending a
probe to the other end. If that other end doesn't answer within that
probe to the other end. If that other end doesn't answer within that
same amount of seconds, the connection is terminated, and the others
will be notified of this.
@item PrivateKey = <key>
This is a sequence of hexadecimal numbers, as generated by ``tincd
--generate-keys''.
--generate-keys''. Please be careful with line breaking, the entire key
should be on one line.
@item PublicKey = <key>
This is a sequence of hexadecimal numbers, as generated by ``tincd
--generate-keys''.
--generate-keys''. Please be careful with line breaking, the entire key
should be on one line.
@item TapDevice = <device> (/dev/tap0)
The ethertap device to use. Note that you can only use one device per
daemon. The info pages of the tinc package contain more information
The ethertap device to use. Note that you can only use one device per
daemon. The info pages of the tinc package contain more information
about configuring an ethertap device for Linux.
@item TCPonly = <yes|no> (no, experimental)
If this variable is set to yes, then the packets are tunnelled over a TCP
connection instead of a UDP connection. This is especially useful for those
connection instead of a UDP connection. This is especially useful for those
who want to run a tinc daemon from behind a masquerading firewall, or if
UDP packet routing is disabled somehow. This is experimental code,
UDP packet routing is disabled somehow. This is experimental code,
try this at your own risk.
@item VpnMask = <mask> (optional)
The mask that defines the scope of the entire VPN. This option is not used
The mask that defines the scope of the entire VPN. This option is not used
by the tinc daemon itself, but can be used by startup scripts to configure
the ethertap devices correctly.
@end table
@ -775,12 +777,12 @@ the ethertap devices correctly.
@section Example
Imagine the following situation. An A-based company wants to connect
three branch offices in B, C and D using the internet. All four offices
Imagine the following situation. An A-based company wants to connect
three branch offices in B, C and D using the internet. All four offices
have a 24/7 connection to the internet.
A is going to serve as the center of the network. B and C will connect
to A, and D will connect to C. Each office will be assigned their own IP
A is going to serve as the center of the network. B and C will connect
to A, and D will connect to C. Each office will be assigned their own IP
network, 10.x.0.0.
@example
@ -791,13 +793,13 @@ D: net 10.4.0.0 mask 255.255.0.0 gateway 10.4.3.32 internet IP 4.5.6.7
@end example
``gateway'' is the VPN IP address of the machine that is running the
tincd. ``internet IP'' is the IP address of the firewall, which does not
tincd. ``internet IP'' is the IP address of the firewall, which does not
need to run tincd, but it must do a port forwarding of TCP&UDP on port
655 (unless otherwise configured).
In this example, it is assumed that eth0 is the interface that points to
the inner LAN of the office, although this could also be the same as the
interface that leads to the internet. The configuration of the real
interface that leads to the internet. The configuration of the real
interface is also shown as a comment, to give you an idea of how these
example host is set up.
@ -837,7 +839,7 @@ VpnMask = 255.0.0.0
@end example
Note here that the internal address (on eth0) doesn't have to be the
same as on the tap0 device. Also, ConnectTo is given so that no-one can
same as on the tap0 device. Also, ConnectTo is given so that no-one can
connect to this node.
@subsubheading For C
@ -859,10 +861,10 @@ VpnMask = 255.0.0.0
@end example
C already has another daemon that runs on port 655, so they have to
reserve another port for tinc. It can connect to other tinc daemons on
reserve another port for tinc. It can connect to other tinc daemons on
the regular port though, so no ConnectPort variable is needed.
They also use the netname to distinguish
between the two. tinc is started with `tincd -n A'.
between the two. tinc is started with `tincd -n A'.
@subsubheading For D
@ -882,7 +884,7 @@ VpnMask=255.0.0.0
@end example
D will be connecting to C, which has a tincd running for this network on
port 2000. Hence they need to put in a ConnectPort, but it doesn't need
port 2000. Hence they need to put in a ConnectPort, but it doesn't need
to have a different ListenPort.
@subsubheading Authentication
@ -905,9 +907,9 @@ D stores a copy of C's passphrase in /etc/tinc/passphrases/10.3.69.254
@subsubheading Starting
A has to start their tincd first. Then come B and C, where C has to
A has to start their tincd first. Then come B and C, where C has to
provide the option `-n A', because they have more than one tinc
network. Finally, D's tincd is started.
network. Finally, D's tincd is started.
@ -916,7 +918,7 @@ network. Finally, D's tincd is started.
@chapter Running tinc
Running tinc isn't just as easy as typing `tincd' and hoping everything
will just work out the way you wanted. Instead, the use of tinc is a
will just work out the way you wanted. Instead, the use of tinc is a
project that involves trust relations and more than one computer.
@menu
@ -929,16 +931,16 @@ project that involves trust relations and more than one computer.
@node Managing keys, Runtime options, Running tinc, Running tinc
@section Managing keys
Before attempting to start tinc, you have to create passphrases. When
Before attempting to start tinc, you have to create passphrases. When
tinc tries to make a connection, it exchanges some sensitive
data. Before doing so, it likes to know if the other end is
data. Before doing so, it likes to know if the other end is
trustworthy.
To do this, both ends must have some knowledge about the other. In the
To do this, both ends must have some knowledge about the other. In the
case of tinc this is the authentication passphrase.
This passphrase is a number, which is chosen at random. This number is
then sent to the other computers which want to talk to us directly. To
This passphrase is a number, which is chosen at random. This number is
then sent to the other computers which want to talk to us directly. To
avoid breaking security, this should be done over a known secure channel
(such as ssh or similar).
@ -946,23 +948,23 @@ All passphrases are stored in the passphrases directory, which is
normally /etc/tinc/nn/passphrases/, but it may be changed using the
`Passphrases' option in the config file.
To generate a passphrase, run `genauth'. genauth takes one argument,
which is the length of the passphrase in bits. The length of the
To generate a passphrase, run `genauth'. genauth takes one argument,
which is the length of the passphrase in bits. The length of the
passphrase should be in the range 1024--2048 for a key length of 128
bits. genauth creates a random number of the specified length, and puts
bits. genauth creates a random number of the specified length, and puts
it to stdout.
Every computer that wants to participate in the VPN should do this, and
store the output in the passphrases directory, in the file @file{local}.
When every computer has his own local key, it should copy it to the
computer that it wants to talk to directly. (i.e. the one it connects to
computer that it wants to talk to directly. (i.e. the one it connects to
during startup.) This should be done via a secure channel, because it is
sensitive information. If this is not done securely, someone might break
sensitive information. If this is not done securely, someone might break
in on you later on.
Those non-local passphrase files must have the name of the VPN IP
address that they will advertise to you. For instance, if a computer
address that they will advertise to you. For instance, if a computer
tells us it likes to be 10.1.1.3 with netmask 255.255.0.0, the file
should still be called 10.1.1.3, and not 10.1.0.0.
@ -974,38 +976,38 @@ should still be called 10.1.1.3, and not 10.1.0.0.
Besides the settings in the configuration file, tinc also accepts some
command line options.
This list is a longer version of that in the manpage. The latter is
This list is a longer version of that in the manpage. The latter is
generated automatically, so may be more up-to-date.
@c from the manpage
@table @asis
@item -c, --config=FILE
Read configuration options from FILE. The default is
Read configuration options from FILE. The default is
@file{/etc/tinc/nn/tinc.conf}.
@item -d
Increase debug level. The higher it gets, the more gets
logged. Everything goes via syslog.
Increase debug level. The higher it gets, the more gets
logged. Everything goes via syslog.
0 is the default, only some basic information connection attempts get
logged. Setting it to 1 will log a bit more, still not very
disturbing. With two -d's tincd will log protocol information, which can
get pretty noisy. Three or more -d's will output every single packet
logged. Setting it to 1 will log a bit more, still not very
disturbing. With two -d's tincd will log protocol information, which can
get pretty noisy. Three or more -d's will output every single packet
that goes out or comes in, which probably generates more data than the
packets themselves.
@item -k, --kill
Attempt to kill a running tincd and exit. A TERM signal (15) gets sent
Attempt to kill a running tincd and exit. A TERM signal (15) gets sent
to the daemon that his its PID in /var/run/tinc.nn.pid.
Because it kills only one tincd, you should use -n here if you use it
normally.
@item -n, --net=NETNAME
Connect to net NETNAME. @xref{Multiple networks}.
Connect to net NETNAME. @xref{Multiple networks}.
@item -t, --timeout=TIMEOUT
Seconds to wait before giving a timeout. Should not be set too low,
Seconds to wait before giving a timeout. Should not be set too low,
because every time tincd senses a timeout, it disconnects and reconnects
again, which will cause unnecessary network traffic and log messages.
@ -1049,31 +1051,31 @@ computer over the existing Internet infrastructure.
@cindex ethertap
@cindex frame type
The data itself is read from a character device file, the so-called
@emph{ethertap} device. This device is associated with a network
interface. Any data sent to this interface can be read from the device,
and any data written to the device gets sent from the interface. Data to
@emph{ethertap} device. This device is associated with a network
interface. Any data sent to this interface can be read from the device,
and any data written to the device gets sent from the interface. Data to
and from the device is formatted as if it were a normal ethernet card,
so a frame is preceded by two MAC addresses and a @emph{frame type}
field.
So when tinc reads an ethernet frame from the device, it determines its
type. Right now, tinc can only handle Internet Protocol version 4 (IPv4)
frames. Plans to support other protocols are being made. When tinc knows
type. Right now, tinc can only handle Internet Protocol version 4 (IPv4)
frames. Plans to support other protocols are being made. When tinc knows
which type of frame it has read, it can also read the source and
destination address from it.
Now it is time that the frame gets encrypted. Currently the only
Now it is time that the frame gets encrypted. Currently the only
encryption algorithm available is blowfish.
@cindex encapsulating
When the encryption is ready, time has come to actually transport the
packet to the destination computer. We do this by sending the packet
over an UDP connection to the destination host. This is called
packet to the destination computer. We do this by sending the packet
over an UDP connection to the destination host. This is called
@emph{encapsulating}, the VPN packet (though now encrypted) is
encapsulated in another IP datagram.
When the destination receives this packet, the same thing happens, only
in reverse. So it does a decrypt on the contents of the UDP datagram,
in reverse. So it does a decrypt on the contents of the UDP datagram,
and it writes the decrypted information to its own ethertap device.
@ -1081,31 +1083,31 @@ and it writes the decrypted information to its own ethertap device.
@node The Meta-connection, , Protocol Preview, The Connection
@subsection The meta-connection
Having only an UDP connection available is not enough. Though suitable
Having only an UDP connection available is not enough. Though suitable
for transmitting data, we want to be able to reliably send other
information, such as routing and encryption information to somebody.
TCP is a better alternative, because it already contains protection
against information being lost, unlike UDP.
So we establish two connections. One for the encrypted VPN data, and one
for other information, the meta-data. Hence, we call the second
connection the meta-connection. We can now be sure that the
So we establish two connections. One for the encrypted VPN data, and one
for other information, the meta-data. Hence, we call the second
connection the meta-connection. We can now be sure that the
meta-information doesn't get lost on the way to another computer.
@cindex data-protocol
@cindex meta-protocol
Like with any communication, we must have a protocol, so that everybody
knows what everything stands for, an how he should react. Because we
have two connections, we also have two protocols. The protocol used for
knows what everything stands for, an how he should react. Because we
have two connections, we also have two protocols. The protocol used for
the UDP data is the ``data-protocol,'' the other one is the
``meta-protocol.''
The reason we don't use TCP for both protocols is that UDP is much
better for encapsulation, even while it is less reliable. The real
better for encapsulation, even while it is less reliable. The real
problem is that when TCP would be used to encapsulate a TCP stream
that's on the private network, for every packet sent there would be
three ACK's sent instead of just one. Furthermore, if there would be
three ACK's sent instead of just one. Furthermore, if there would be
a timeout, both TCP streams would sense the timeout, and both would
start resending packets.
@ -1117,12 +1119,12 @@ start resending packets.
@cindex Cabal
tinc got its name from ``TINC,'' short for @emph{There Is No Cabal}; the
alleged Cabal was/is an organization that was said to keep an eye on the
entire Internet. As this is exactly what you @emph{don't} want, we named
entire Internet. As this is exactly what you @emph{don't} want, we named
the tinc project after TINC.
@cindex SVPN
But in order to be ``immune'' to eavesdropping, you'll have to encrypt
your data. Because tinc is a @emph{Secure} VPN (SVPN) daemon, it does
your data. Because tinc is a @emph{Secure} VPN (SVPN) daemon, it does
exactly that: encrypt.
This chapter is a mixture of ideas, reasoning and explanation, please
@ -1140,27 +1142,27 @@ don't take it too serious.
@subsection Key Types
@c FIXME: check if I'm not talking nonsense
There are several types of encryption keys. Tinc uses two of them,
There are several types of encryption keys. Tinc uses two of them,
symmetric private keypairs and public/private keypairs.
Public/private keypairs are used in public key cryptography. It enables
Public/private keypairs are used in public key cryptography. It enables
someone to send out a public key with which other people can encrypt their
data. The encrypted data now can only be decrypted by the person who has
the private key that matches the public key. So, a public key only allows
@emph{other} people to send encrypted messages to you. This is very useful
in setting up private communications channels. Just send out your public key
and other people can talk to you in a secure way. But how can you know
data. The encrypted data now can only be decrypted by the person who has
the private key that matches the public key. So, a public key only allows
@emph{other} people to send encrypted messages to you. This is very useful
in setting up private communications channels. Just send out your public key
and other people can talk to you in a secure way. But how can you know
the other person is who he says he is?
For authentication itself tinc uses symmetric private keypairs, referred
to as a passphrase. The identity of each tinc daemon is defined by it's
to as a passphrase. The identity of each tinc daemon is defined by it's
passphrase (like you can be identified by your social security number).
Every tinc daemon that is allowed to connect to you has a copy of your
passphrase (hence symmetrical).
It would also be possible to use public/private keypairs for authentication,
so that you could shout out your public key and don't need to keep it
secret (like the passphrase you would have to send to someone else). Also,
secret (like the passphrase you would have to send to someone else). Also,
no one else has to know a private key from you.
Both forms have their pros and cons, and at the moment tinc just uses passphrases
(which are computationaly more efficient and perhaps in some way more
@ -1173,24 +1175,24 @@ secure).
@cindex Diffie-Hellman
You can't just send a private encryption key to your peer, because
somebody else might already be listening to you. So you'll have to
negotiate over a shared but secret key. One way to do this is by using
somebody else might already be listening to you. So you'll have to
negotiate over a shared but secret key. One way to do this is by using
the ``Diffie-Hellman key exchange'' protocol
(@uref{http://www.rsa.com/rsalabs/faq/html/3-6-1.html}). The idea is as
(@uref{http://www.rsa.com/rsalabs/faq/html/3-6-1.html}). The idea is as
follows.
You have two participants A and B that want to agree over a shared
secret encryption key. Both parties have some large prime number p and a
generator g. These numbers may be known to the outside world, and hence
secret encryption key. Both parties have some large prime number p and a
generator g. These numbers may be known to the outside world, and hence
may be included in the source distribution.
@cindex secret key
Both parties then generate a secret key. A generates a, and computes g^a
mod p. This is then sent to B; while B computes g^b mod p, and transmits
this to A, b being generated by B. Both a and b must be smaller than
Both parties then generate a secret key. A generates a, and computes g^a
mod p. This is then sent to B; while B computes g^b mod p, and transmits
this to A, b being generated by B. Both a and b must be smaller than
p-1.
Both parties then calculate g^ab mod p = k. k is the new, shared, but
Both parties then calculate g^ab mod p = k. k is the new, shared, but
still secret key.
To obtain a key k of a sufficient length (128 bits in our vpnd), p
@ -1208,24 +1210,24 @@ Because the Diffie-Hellman protocol is in itself vulnerable to the
system.
We will let A transmit a passphrase that is also known to B encrypted
with g^a, before A sends this to B. This way, B can check whether A is
with g^a, before A sends this to B. This way, B can check whether A is
really A or just someone else.
B will never receive the real passphrase though, because it was
encrypted using public/private keypairs. This way there is no way an
encrypted using public/private keypairs. This way there is no way an
imposter could steal A's passphrase.
@cindex passphrase
@c ehrmz... but we only use 1024 bits passphrases ourselves? [guus]
@c ehrmz... but we only use 1024 bits passphrases ourselves? [guus]
This passphrase should be 2304 bits for a symmetric encryption
system. But since an asymmetric system is more secure, we could do with
2048 bits. This only holds if the passphrase is very random.
system. But since an asymmetric system is more secure, we could do with
2048 bits. This only holds if the passphrase is very random.
These passphrases could be stored in a file that is non-readable by
anyone else but root; e.g. @file{/etc/tinc/passphrases} with UID 0
anyone else but root; e.g. @file{/etc/tinc/passphrases} with UID 0
and permissions mode 700.
The only thing that needs to be taken care of is how A can securely send
a copy of it's passphrase to B if B doesn't have it yet. This could be
a copy of it's passphrase to B if B doesn't have it yet. This could be
done via mail with PGP, but you should be really convinced of the
identity of the person who owns the email address you are sending this to.
Swapping floppy disks in real life might be the best way to do this!
@ -1235,7 +1237,7 @@ Swapping floppy disks in real life might be the best way to do this!
@node Protection, , Authentication, Security
@subsection Protecting your data
Now we have securely hidden our data. But a malicious cracker may still
Now we have securely hidden our data. But a malicious cracker may still
bother you by randomly altering the encrypted data he intercepts.
@c FIXME what the hell is this all about? remove? IT
@ -1258,7 +1260,7 @@ bother you by randomly altering the encrypted data he intercepts.
tinc's main page is at @url{http://tinc.nl.linux.org/},
this server is located in the Netherlands.
We have an IRC channel on the Open Projects IRC network. Connect to
We have an IRC channel on the Open Projects IRC network. Connect to
@uref{http://openprojects.nu/services/irc.html, irc.openprojects.net},
and join channel #tinc.