tinc/README

This is the README file for tinc version 1.0.36. Installation
instructions may be found in the INSTALL file.

tinc is Copyright (C) 1998-2019 by:

Ivo Timmermans,
Guus Sliepen <guus@tinc-vpn.org>,
and others.

For a complete list of authors see the AUTHORS file.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version. See the file COPYING for more details.


Security statement
------------------

In August 2000, we discovered the existence of a security hole in all versions
of tinc up to and including 1.0pre2. This had to do with the way we exchanged
keys. Since then, we have been working on a new authentication scheme to make
tinc as secure as possible. The current version uses the OpenSSL library and
uses strong authentication with RSA keys.

On the 29th of December 2001, Jerome Etienne posted a security analysis of tinc
1.0pre4. Due to a lack of sequence numbers and a message authentication code
for each packet, an attacker could possibly disrupt certain network services or
launch a denial of service attack by replaying intercepted packets. The current
version adds sequence numbers and message authentication codes to prevent such
attacks.

On September the 15th of 2003, Peter Gutmann contacted us and showed us a
writeup describing various security issues in several VPN daemons. He showed
that tinc lacks perfect forward security, the connection authentication could
be done more properly, that the sequence number we use as an IV is not the best
practice and that the default length of the HMAC for packets is too short in
his opinion. We do not know of a way to exploit these weaknesses, but these
issues are being addressed in the tinc 1.1 branch.

The Sweet32 attack affects versions of tinc prior to 1.0.30.

On September 6th, 2018, Michael Yonly contacted us and provided
proof-of-concept code that allowed a remote attacker to create an
authenticated, one-way connection with a node, and also that there was a
possibility for a man-in-the-middle to force UDP packets from a node to be sent
in plaintext. The first issue was trivial to exploit on tinc versions prior to
1.0.30, but the changes in 1.0.30 to mitigate the Sweet32 attack made this
weakness much harder to exploit. These issues have been fixed in tinc 1.0.35.
The new protocol in the tinc 1.1 branch is not susceptible to these issues.

Cryptography is a hard thing to get right. We cannot make any
guarantees. Time, review and feedback are the only things that can
prove the security of any cryptographic product. If you wish to review
tinc or give us feedback, you are strongly encouraged to do so.


Compatibility
-------------

Version 1.0.35 is compatible with 1.0pre8, 1.0 and later, but not with older
versions of tinc. Note that since version 1.0.30, tinc requires all nodes in
the VPN to be compiled with a version of LibreSSL or OpenSSL that supports the
AES256 and SHA256 algorithms.


Requirements
------------

The OpenSSL library is used for all cryptographic functions. You can find it at
https://www.openssl.org/. You will need version 1.1.0 or later with support for
AES256 and SHA256 enabled. If this library is not installed on your system, the
configure script will fail.  The manual in doc/tinc.texi contains more detailed
information on how to install this library. Alternatively, you may also use the
LibreSSL library.

The zlib library is used for optional compression. You can
find it at https://zlib.net/. Because of a possible exploit in
earlier versions we recommend that you download version 1.1.4 or later.

The LZO library is also used for optional compression. You can
find it at https://www.oberhumer.com/opensource/lzo/.

In order to compile tinc, you will need a C99 compliant compiler.


Features
--------

This version of tinc supports multiple virtual networks at once. To
use this feature, you may supply a netname via the -n or --net
options. The standard locations for the config files will then be
/etc/tinc/<net>/.

tincd regenerates its encryption key pairs. It does this on the first
activity after the keys have expired. This period is adjustable in the
configuration file, and the default time is 3600 seconds (one hour).

This version supports multiple subnets at once. They are also sorted
on subnet mask size. This means that it is possible to have
overlapping subnets on the VPN, as long as their subnet mask sizes
differ.

Since pre5, tinc can operate in several routing modes. The default mode,
"router", works exactly like the older version, and uses Subnet lines to
determine the destination of packets. The other two modes, "switch" and "hub",
allow the tinc daemons to work together like a single network switch or hub.
This is useful for bridging networks. The latter modes only work properly on
Linux, FreeBSD and Windows.

The algorithms used for encryption and generating message authentication codes
can now be changed in the configuration files. All cipher and digest algorithms
supported by OpenSSL can be used. Useful ciphers are "blowfish" (default),
"bf-ofb", "des", "des3", et cetera. Useful digests are "sha1" (default), "md5",
et cetera.

Support for routing IPv6 packets has been added. Just add Subnet lines with
IPv6 addresses (without using :: abbreviations) and use ifconfig or ip (from
the iproute package) to give the virtual network interface corresponding IPv6
addresses. tinc does not provide autoconfiguration for IPv6 hosts. Consider
using radvd or zebra if you need it.

It is also possible to make tunnels to other tinc daemons over IPv6 networks,
if the operating system supports IPv6.  tinc will automatically use both IPv6
and IPv4 when available, but this can be changed by adding the option
"AddressFamily = ipv4" or "AddressFamily = ipv6" to the tinc.conf file.

Normally, when started tinc will detach and run in the background. In a native
Windows environment this means tinc will install itself as a service, which will
restart after reboots.  To prevent tinc from detaching or running as a service,
use the -D option.