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Import Upstream version 1.0pre7
2019-08-26 11:44:36 +00:00
This is tinc.info, produced by makeinfo version 4.1 from tinc.texi.
INFO-DIR-SECTION Networking tools
START-INFO-DIR-ENTRY
* tinc: (tinc). The tinc Manual.
END-INFO-DIR-ENTRY
This is the info manual for tinc, a Virtual Private Network daemon.
Copyright (C) 1998-2002 Ivo Timmermans <itimmermans@bigfoot.com>,
Guus Sliepen <guus@sliepen.warande.net> and Wessel Dankers
<wsl@nl.linux.org>.
$Id: tinc.texi,v 1.8.4.28 2002/04/09 11:43:29 guus Exp $
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

File: tinc.info, Node: The UDP tunnel, Next: The meta-connection, Prev: The connection, Up: The connection
The UDP tunnel
--------------
The data itself is read from a character device file, the so-called
_virtual network 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 _frame type_
field.
So when tinc reads an Ethernet frame from the device, it determines
its type. When tinc is in it's default routing mode, it can handle IPv4
and IPv6 packets. Depending on the Subnet lines, it will send the
packets off to their destination. In the `switch' and `hub' mode, tinc
will use broadcasts and MAC address discovery to deduce the destination
of the packets. Since the latter modes only depend on the link layer
information, any protocol that runs over Ethernet is supported (for
instance IPX and Appletalk).
After the destination has been determined, a sequence number will be
added to the packet. The packet will then be encrypted and a message
authentication code will be appended.
When that is done, 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 _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 checks the message authentication code,
decrypts the contents of the UDP datagram, checks the sequence number
and writes the decrypted information to its own virtual network device.
To let the kernel on the receiving end accept the packet, the
destination MAC address must match that of the virtual network
interface. If tinc is in it's default routing mode, ARP does not work,
so the correct destination MAC cannot be set by the sending daemons.
tinc solves this by always overwriting the destination MAC address with
fe:fd:0:0:0:0. That is also the reason why you must set the MAC address
of your tap interface to that address.

File: tinc.info, Node: The meta-connection, Prev: The UDP tunnel, Up: The connection
The meta-connection
-------------------
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 session key 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
meta-information doesn't get lost on the way to another computer.
Like with any communication, we must have a protocol, so that
everybody knows what everything stands for, and how she 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
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 ACKs sent instead of just one. Furthermore, if there would be a
timeout, both TCP streams would sense the timeout, and both would start
re-sending packets.

File: tinc.info, Node: The meta-protocol, Next: Security, Prev: The connection, Up: Technical information
The meta-protocol
=================
The meta protocol is used to tie all tinc daemons together, and
exchange information about which tinc daemon serves which virtual
subnet.
The meta protocol consists of requests that can be sent to the other
side. Each request has a unique number and several parameters. All
requests are represented in the standard ASCII character set. It is
possible to use tools such as telnet or netcat to connect to a tinc
daemon and to read and write requests by hand, provided that one
understands the numeric codes sent.
The authentication scheme is described in *Note Authentication
protocol::. After a successful authentication, the server and the
client will exchange all the information about other tinc daemons and
subnets they know of, so that both sides (and all the other tinc
daemons behind them) have their information synchronised.
daemon message
--------------------------------------------------------------------------
origin ADD_EDGE node1 12.23.34.45 655 node2 21.32.43.54 655 222 0
| | | \___________________/ | +-> options
| | | | +----> weight
| | | +----------------> see below
| | +--> UDP port
| +----------> real address
+------------------> name of node on one side of the edge
origin ADD_SUBNET node 192.168.1.0/24
| | +--> prefixlength
| +--------> IPv4 network address
+------------------> owner of this subnet
--------------------------------------------------------------------------
In case a connection between two daemons is closed or broken,
DEL_EDGE messages are sent to inform the other daemons of that fact.
Each daemon will calculate a new route to the the daemons, or mark them
unreachable if there isn't any.
The keys used to encrypt VPN packets are not sent out directly. This
is because it would generate a lot of traffic on VPNs with many
daemons, and chances are that not every tinc daemon will ever send a
packet to every other daemon. Instead, if a daemon needs a key it sends
a request for it via the meta connection of the nearest hop in the
direction of the destination. If any hop on the way has already learned
the key, it will act as a proxy and forward its copy back to the
requester.
daemon message
--------------------------------------------------------------------------
daemon REQ_KEY origin destination
| +--> name of the tinc daemon it wants the key from
+----------> name of the daemon that wants the key
daemon ANS_KEY origin destination 4ae0b0a82d6e0078 91 64 4
| | \______________/ | | +--> MAC length
| | | | +-----> digest algorithm
| | | +--------> cipher algorithm
| | +--> 128 bits key
| +--> name of the daemon that wants the key
+----------> name of the daemon that uses this key
daemon KEY_CHANGED origin
+--> daemon that has changed it's packet key
--------------------------------------------------------------------------
There is also a mechanism to check if hosts are still alive. Since
network failures or a crash can cause a daemon to be killed without
properly shutting down the TCP connection, this is necessary to keep an
up to date connection list. PINGs are sent at regular intervals, except
when there is also some other traffic. A little bit of salt (random
data) is added with each PING and PONG message, to make sure that long
sequences of PING/PONG messages without any other traffic won't result
in known plaintext.
daemon message
--------------------------------------------------------------------------
origin PING
dest. PONG
--------------------------------------------------------------------------
This basically covers what is sent over the meta connection by tinc.

File: tinc.info, Node: Security, Prev: The meta-protocol, Up: Technical information
About tinc's encryption and other security-related issues.
==========================================================
tinc got its name from "TINC," short for _There Is No Cabal_; the
alleged Cabal was/is an organisation that was said to keep an eye on the
entire Internet. As this is exactly what you _don't_ want, we named
the tinc project after TINC.
But in order to be "immune" to eavesdropping, you'll have to encrypt
your data. Because tinc is a _Secure_ VPN (SVPN) daemon, it does
exactly that: encrypt. tinc by default uses blowfish encryption with
128 bit keys in CBC mode, 32 bit sequence numbers and 4 byte long
message authentication codes to make sure eavesdroppers cannot get and
cannot change any information at all from the packets they can
intercept. The encryption algorithm and message authentication
algorithm can be changed in the configuration. The length of the message
authentication codes is also adjustable. The length of the key for the
encryption algorithm is always the default length used by OpenSSL.
* Menu:
* Authentication protocol::
* Encryption of network packets::

File: tinc.info, Node: Authentication protocol, Next: Encryption of network packets, Prev: Security, Up: Security
Authentication protocol
-----------------------
A new scheme for authentication in tinc has been devised, which
offers some improvements over the protocol used in 1.0pre2 and 1.0pre3.
Explanation is below.
daemon message
--------------------------------------------------------------------------
client <attempts connection>
server <accepts connection>
client ID client 12
| +---> version
+-------> name of tinc daemon
server ID server 12
| +---> version
+-------> name of tinc daemon
client META_KEY 5f0823a93e35b69e...7086ec7866ce582b
\_________________________________/
+-> RSAKEYLEN bits totally random string S1,
encrypted with server's public RSA key
server META_KEY 6ab9c1640388f8f0...45d1a07f8a672630
\_________________________________/
+-> RSAKEYLEN bits totally random string S2,
encrypted with client's public RSA key
From now on:
- the client will symmetrically encrypt outgoing traffic using S1
- the server will symmetrically encrypt outgoing traffic using S2
client CHALLENGE da02add1817c1920989ba6ae2a49cecbda0
\_________________________________/
+-> CHALLEN bits totally random string H1
server CHALLENGE 57fb4b2ccd70d6bb35a64c142f47e61d57f
\_________________________________/
+-> CHALLEN bits totally random string H2
client CHAL_REPLY 816a86
+-> 160 bits SHA1 of H2
server CHAL_REPLY 928ffe
+-> 160 bits SHA1 of H1
After the correct challenge replies are received, both ends have proved
their identity. Further information is exchanged.
client ACK 655 12.23.34.45 123 0
| | | +-> options
| | +----> estimated weight
| +------------> IP address of server as seen by client
+--------------------> UDP port of client
server ACK 655 21.32.43.54 321 0
| | | +-> options
| | +----> estimated weight
| +------------> IP address of client as seen by server
+--------------------> UDP port of server
--------------------------------------------------------------------------
This new scheme has several improvements, both in efficiency and
security.
First of all, the server sends exactly the same kind of messages
over the wire as the client. The previous versions of tinc first
authenticated the client, and then the server. This scheme even allows
both sides to send their messages simultaneously, there is no need to
wait for the other to send something first. This means that any
calculations that need to be done upon sending or receiving a message
can also be done in parallel. This is especially important when doing
RSA encryption/decryption. Given that these calculations are the main
part of the CPU time spent for the authentication, speed is improved by
a factor 2.
Second, only one RSA encrypted message is sent instead of two. This
reduces the amount of information attackers can see (and thus use for a
cryptographic attack). It also improves speed by a factor two, making
the total speedup a factor 4.
Third, and most important: The symmetric cipher keys are exchanged
first, the challenge is done afterwards. In the previous authentication
scheme, because a man-in-the-middle could pass the challenge/chal_reply
phase (by just copying the messages between the two real tinc daemons),
but no information was exchanged that was really needed to read the
rest of the messages, the challenge/chal_reply phase was of no real
use. The man-in-the-middle was only stopped by the fact that only after
the ACK messages were encrypted with the symmetric cipher. Potentially,
it could even send it's own symmetric key to the server (if it knew the
server's public key) and read some of the metadata the server would
send it (it was impossible for the mitm to read actual network packets
though). The new scheme however prevents this.
This new scheme makes sure that first of all, symmetric keys are
exchanged. The rest of the messages are then encrypted with the
symmetric cipher. Then, each side can only read received messages if
they have their private key. The challenge is there to let the other
side know that the private key is really known, because a challenge
reply can only be sent back if the challenge is decrypted correctly,
and that can only be done with knowledge of the private key.
Fourth: the first thing that is send via the symmetric cipher
encrypted connection is a totally random string, so that there is no
known plaintext (for an attacker) in the beginning of the encrypted
stream.

File: tinc.info, Node: Encryption of network packets, Prev: Authentication protocol, Up: Security
Encryption of network packet
----------------------------
A data packet can only be sent if the encryption key is known to both
parties, and the connection is activated. If the encryption key is not
known, a request is sent to the destination using the meta connection
to retrieve it. The packet is stored in a queue while waiting for the
key to arrive.
The UDP packet containing the network packet from the VPN has the
following layout:
... | IP header | UDP header | seqno | VPN packet | MAC | UDP trailer
\___________________/\_____/
| |
V +---> digest algorithm
Encrypted with symmetric cipher
So, the entire VPN packet is encrypted using a symmetric cipher. A
32 bits sequence number is added in front of the actual VPN packet, to
act as a unique IV for each packet and to prevent replay attacks. A
message authentication code is added to the UDP packet to prevent
alteration of packets. By default the first 4 bytes of the digest are
used for this, but this can be changed using the MACLength
configuration variable.

File: tinc.info, Node: About us, Next: Concept Index, Prev: Technical information, Up: Top
About us
********
* Menu:
* Contact Information::
* Authors::

File: tinc.info, Node: Contact Information, Next: Authors, Prev: About us, Up: About us
Contact information
===================
tinc's website is at <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
irc.openprojects.net (http://openprojects.nu/services/irc.html), and
join channel #tinc.

File: tinc.info, Node: Authors, Prev: Contact Information, Up: About us
Authors
=======
Ivo Timmermans (zarq) (<itimmermans@bigfoot.com>)
Main coder/hacker and maintainer of the package.
Guus Sliepen (guus) (<guus@sliepen.warande.net>)
Originator of it all, co-author.
Wessel Dankers (Ubiq) (<wsl@nl.linux.org>)
For the name `tinc' and various suggestions.
We have received a lot of valuable input from users. With their
help, tinc has become the flexible and robust tool that it is today.
We have composed a list of contributions, in the file called `THANKS' in
the source distribution.

File: tinc.info, Node: Concept Index, Prev: About us, Up: Top
Concept Index
*************
* Menu:
* ACK: Authentication protocol.
* ADD_EDGE: The meta-protocol.
* ADD_SUBNET: The meta-protocol.
* Address: Host configuration variables.
* AddressFamily: Main configuration variables.
* ANS_KEY: The meta-protocol.
* arp <1>: Error messages.
* arp: Network interfaces.
* authentication: Authentication protocol.
* binary package: Building and installing tinc.
* BindToInterface: Main configuration variables.
* Cabal: Security.
* CHAL_REPLY: Authentication protocol.
* CHALLENGE: Authentication protocol.
* CIDR notation: Host configuration variables.
* Cipher: Host configuration variables.
* client: How connections work.
* command line: Runtime options.
* Compression: Host configuration variables.
* connection: The connection.
* ConnectTo: Main configuration variables.
* daemon: Running tinc.
* data-protocol: The meta-connection.
* Debian: Configuring the kernel.
* debug level: Runtime options.
* DEL_EDGE: The meta-protocol.
* Device: Main configuration variables.
* device files: Device files.
* Digest: Host configuration variables.
* encapsulating: The UDP tunnel.
* encryption: Encryption of network packets.
* ethertap: Configuring the kernel.
* example: Example configuration.
* frame type: The UDP tunnel.
* FreeBSD: Supported platforms.
* hardware address: Network interfaces.
* Hostnames: Main configuration variables.
* hub: Main configuration variables.
* ID: Authentication protocol.
* ifconfig: Network interfaces.
* IndirectData: Host configuration variables.
* Interface: Main configuration variables.
* IRC: Contact Information.
* Kernel-HOWTO: Configuring the kernel.
* key generation: Generating keypairs.
* KEY_CHANGED: The meta-protocol.
* KeyExpire: Main configuration variables.
* libraries: Libraries.
* license: OpenSSL.
* Linux: Supported platforms.
* MAC address: Network interfaces.
* MACExpire: Main configuration variables.
* MACLength: Host configuration variables.
* meta-protocol: The meta-connection.
* META_KEY: Authentication protocol.
* Mode: Main configuration variables.
* multiple networks: Multiple networks.
* Name: Main configuration variables.
* netlink_dev: Configuring the kernel.
* netmask: Network interfaces.
* netname: Multiple networks.
* Network Administrators Guide: Configuration introduction.
* OpenBSD: Supported platforms.
* OpenSSL: OpenSSL.
* options: Runtime options.
* PEM format: Host configuration variables.
* PING: The meta-protocol.
* PingTimeout: Main configuration variables.
* platforms: Supported platforms.
* PONG: The meta-protocol.
* Port: Host configuration variables.
* port numbers: Other files.
* PriorityInheritance: Main configuration variables.
* private: VPNs.
* PrivateKey: Main configuration variables.
* PrivateKeyFile: Main configuration variables.
* PublicKey: Host configuration variables.
* PublicKeyFile: Host configuration variables.
* RedHat: Configuring the kernel.
* release: Supported platforms.
* REQ_KEY: The meta-protocol.
* requirements: Libraries.
* router: Main configuration variables.
* runtime options: Runtime options.
* scalability: tinc.
* server: How connections work.
* Solaris: Supported platforms.
* Subnet: Host configuration variables.
* SVPN: Security.
* switch: Main configuration variables.
* TCP: The meta-connection.
* TCPonly: Host configuration variables.
* TINC: Security.
* tinc: Introduction.
* tinc-up: Network interfaces.
* tincd: tinc.
* Traditional VPNs: tinc.
* tun: Configuring the kernel.
* UDP <1>: Encryption of network packets.
* UDP: The UDP tunnel.
* virtual: VPNs.
* virtual network device: The UDP tunnel.
* VPN: VPNs.
* vpnd: tinc.
* website: Contact Information.
* zlib: zlib.
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