"The mantra of any good security engineer is: "Security is not a
product, but a process." It's more than designing strong cryptography
into a system; it's designing the entire system such that all security
measures, including cryptography, work together."
-- Bruce Schneier, author of "Applied Cryptography".
Why do we ship cryptography?.
Pseudo Random Number Generators (PRNG): ARC4, ...
Cryptographic Hash Functions: MD5, SHA1, ...
Cryptographic Transforms: DES, Blowfish, ...
Cryptographic Hardware support
International Cryptographers wanted
Why do we ship cryptography?
In three words: because we can.
The OpenBSD project is based in Canada.
The Export Control List of Canada
places no significant restriction on the export of
cryptographic software, and is even more explicit about the free
export of freely-available cryptographic software. Marc Plumb has
some research to test the cryptographic laws.
Hence the OpenBSD project has embedded cryptography into numerous places
in the operating system. We require that the cryptographic software we
use be freely available and with good licenses.
We do not directly use cryptography with nasty patents.
We also require that such software is from countries with useful export
licenses because we do not wish to break the laws of any country.
The cryptographic software components which we use currently were
written in Argentina, Australia, Canada, Germany, Greece, Norway, and
When we create OpenBSD releases or snapshots we build our release
binaries in free countries to assure that the sources and binaries we
provide to users are free of tainting. In the past our release binary
builds have been done in Canada, Sweden, and Germany.
OpenBSD ships with Kerberos IV included. The codebase we use is the
exportable KTH-based release from Sweden. Our X11 source has been
extended to make use of Kerberos IV as well. Kerberos V support will
appear sometime in 2000, but at present time a freely exportable
Kerberos V release does not exist.
OpenBSD was the first operating system to ship with an IPSEC stack.
We've been including IPSEC since early OpenBSD 2.1 release in 1997.
Our fully conformant in-kernel IPSEC stack, with hardware acceleration
based on a number of cards, and our own free ISAKMP daemon, is used as
one of the machines in the IPSEC conformance testbed run by
Today cryptography is an important means for enhancing the security of an operating system. The
cryptography utilized in OpenBSD can be classified into various
aspects, described as follows.
What is the first thing most people do after installing OpenBSD?
They install Secure Shell
from the ports tree or the packages on the FTP sites. Until now, that is.
As of the 2.6 release, OpenBSD contains
OpenSSH, an absolutely free and
patent unencumbered version of ssh.
As of the OpenBSD 2.6 release date,
OpenSSH interoperated with ssh
version 1 and had many added features,
all components of a restrictive nature (ie. patents, see
had been directly removed from the source code; any licensed or
patented components used external libraries.
had been updated to support ssh protocol 1.5.
contained added support for
authentication and ticket passing.
supported one-time password authentication with
Roughly, we took a free license release of ssh and OpenBSD-ifyed it.
We get around the USA-based RSA patent by providing an easy way to
automatically download and install a RSA-enabled package containing
shared library versions of libcrypto and libssl. These packages are
based on OpenSSL. People living outside the USA can freely use the
RSA patented code, while people inside the USA can freely use it for
non-commercial purposes. It appears as if companies inside the USA
can use the RSA libraries too, as long as RSA is not used in a profit
But this way almost everyone will get ssh built into their OS.
NEW! OpenSSH supports protocol 2.0!
Recently, we have extended OpenSSH so that it also does SSH 2 protocol.
Having a ssh daemon which can do all 3 major SSH protocols
(1.3, 1.5, 2.0) permits us much flexibility. Protocol 2.0 does not
use RSA for it's public key cryptography, relying instead on the DH
and DSA algorithms. In OpenBSD 2.7 -- which will ship with the new
OpenSSH -- you get protocol 2.0 support right out of the box! If
you wish to also support protocol 1.3 and 1.5, you simply add the
RSA package (as described our
manual page), and restart the daemon.
Pseudo Random Number Generators
A Pseudo Random Number Generator (PRNG) provides applications with a stream of
numbers which have certain important properties for system security:
- It should be impossible for an outsider to predict the output of the
random number generator even with knowledge of previous output.
- The generated numbers should not have repeating patterns which means
the PRNG should have a very long cycle length.
A PRNG is normally just an algorithm where the same initial starting
values will yield the same sequence of outputs. On a multiuser
operating system there are many sources which allow seeding the PRNG
with random data. The OpenBSD kernel uses the mouse interrupt timing,
network data interrupt latency, inter-keypress timing and disk IO
information to fill an entropy pool. Random numbers are available for
kernel routines and are exported via devices to userland programs.
So far random numbers are used in the following places:
- Dynamic sin_port allocation in bind(2).
- PIDs of processes.
- IP datagram IDs.
- RPC transaction IDs (XID).
- NFS RPC transaction IDs (XID).
- DNS Query-IDs.
- Inode generation numbers, see getfh(2) and fsirand(8).
- Timing perturbance in traceroute(8).
- Stronger temporary names for mktemp(3) and mkstemp(3)
- Randomness added to the TCP ISS value for protection against
- random padding in IPSEC esp_old packets.
- To generate salts for the various password algorithms.
- For generating fake S/Key challenges.
- In photurisd
to provide liveness proof of key exchanges.
Cryptographic Hash Functions
A Hash Function compresses its input data to a string of
constant size. For a Cryptographic Hash Function it is infeasible to find:
- two inputs which have the same output (collision resistant),
- a different input for a given input with the same output
(2nd preimage resistant).
In OpenBSD MD5, SHA1, and RIPEMD-160 are used as Cryptographic Hash Functions,
- In S/Key
to provide one time passwords.
- In IPsec,
to authenticate the data origin of packets and to ensure packet integrity.
- For FreeBSD-style MD5 passwords (not enabled by default), see
- For TCP SYN cookie support (not enabled by default), see
- In libssl for digital signing of messages.
Cryptographic Transforms are used to encrypt and decrypt data. These
are normally used with an encryption key for data encryption and with
a decryption key for data decryption. The security of a Cryptographic
Transform should rely only on the keying material.
OpenBSD provides transforms like DES, 3DES, Blowfish and Cast for the
kernel and userland programs, which are used in many places like:
- In libc for creating
passwords. See also the USENIX paper
on this topic.
to provide confidentiality for the network layer.
- In Kerberos and a handful of kerberized applications, like
to protect the exchanges where IPsec key material is negotiated.
- In AFS to protect the messages passing over the network, providing
confidentiality of remote filesystem access.
- In libssl to let applications communicate over the de-facto standard
cryptographically secure SSL protocol.
Cryptographic Hardware Support
OpenBSD, starting with 2.7, has begun supporting some cryptography hardware
such as accelerators and random number generators.
- IPSEC crypto dequeue
Our IPSEC stack has been modified so that cryptographic functions get
done out-of-line. Most simple software IPSEC stacks need to do
cryptography when processing each packet. This results in syncronous
performance. To use hardware properly and speedily one needs to separate
these two components, as we have done. Actually, doing this gains some
performance even for the software case.
- HiFn 7751
Cards using the HiFn 7751
can be used as a symmetric cryptographic accelerator (ie.
Current performance using a single Hifn 7751 on each end of a tunnel
is 63Mbit/sec for 3DES/SHA1 ESP, nearly a 600% improvement over
using a P3/550 cpu. Further improvements are under way to resolve a
few more issues, but as of April 13, 2000 the code is considered
stable. We wrote our own driver for supporting this chip, rather
than using the (USA-written)
powercrypt driver, as well
our driver links in properly to the IPSEC stack.
The 7751 is now considered slow by industry standards and many vendors
have faster chips (even HiFn now has a faster but more expensive
chip). Peak performance with 3DES SHA1 ESP is around 63MBit/sec.
(As an aside, HiFn was a difficult company to deal with; they even
threatened to sue us over our non-USA reverse engineering of their
crypto unlock algorithm).
- Hifn 6500
This device is an assymetric crypto unit. It has support for RSA, DSA,
and DH algorithms, as well as other major big number functions. It also
contains a very high performance random number generator. We have one
device, full documention, and sample code. Development has not yet
- Broadcom BCM5805 (or beta chip Bluesteelnet 5501)
Just after the OpenBSD 2.7 release, we succeeded at adding preliminary
support for these early release parts provided to us by the vendor,
specifically starting with the test chip
These devices provide the highest performance symmetric cryptography
we have seen.
Bluesteelnet was bought by Broadcom and started making real parts.
Their new BCM5805 is similar, except that they also add an asymetric
engine for running DSA, RSA, and other such algorithms. With approximate
performance starting at more than four times as fast as the HiFn,
hopefully this chip will become more common soon.
The Broadcom/Bluesteelnet people have been great to deal with. They gave
us complete documentation and sample code for their chips and a
sufficient number of cards to test with.
Post 2.8, this driver was also modified to generate random numbers on
the BCM5805 and similar versions, and feed that data into the kernel
- Pijnenburg PCC-ISES
The PCC-ISES is a
new chipset from the Netherlands. We have received sample hardware and
documentation, and work on a driver is in progress. At the moment, the
driver is capable of feeding random numbers into the kernel entropy pool.
- SafeNet 2141
We have received documentation and sample hardware for the
crypto cards. Work to support at least the symmetric cryptography of
these devices has started.
3com has given us a driver to support the ethernet component of this
chipset. That driver is being ported. We are also supposed to receive
information for supporting the cryptography functions, which will require
a little bit amount of IPSEC subsystem rearranging.
- Intel IPSEC card
Much like 3COM, Intel has been refusing to get us documentation. We
have talked to about five technical people who are involved in the
development of those products. They all wanted us to have documentation.
They commend us on what we have done. But their hands are tied by
management who does not perceive a benefit to themselves for providing
- Intel 82802AB/82802AC Firmware Hub RNG
The 82802 FWH chip (found on i810, i820, i840, i850, and i860 motherboards)
contains a random number generator (RNG). High-performance IPSEC
requires more random number entropy. As of April 10, 2000, we support
the RNG. We will add support for other RNG's found on crypto chips.
We have grand schemes for supporting crypto cards that can do RSA or DSA,
and exporting the functions of all crypto cards to OpenSSL so that
userland programs (ie. ssh,
apache https, etc)
If people wish to help with writing drivers,
come and help us.
International Cryptographers Wanted
Of course, our project needs people to work on these systems. If any
non-American cryptographer who meets the constraints listed earlier is
interested in helping out with embedded cryptography in OpenBSD,
please contact us.
A number of papers have been written by OpenBSD team members, about
cryptographic changes they have done in OpenBSD. The postscript
versions of these documents are available as follows.
$OpenBSD: crypto.html,v 1.74 2001/01/31 22:36:14 deraadt Exp $