Cryptography in OpenBSD

OpenBSD Cryptography

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 done 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 use cryptography with nasty patents. We also require that such software is from a countries with useful export licenses because we do not wish to break the laws of any country.

When we make OpenBSD releases or snapshots we do our build processes 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.

Today cryptography is an important mean for enhancing the security of an operating system. The cryptography utilized in OpenBSD can be classified into three different aspects:

Pseudo Random Number Generators (PRNG): ARC4, ...
Cryptographic Hash Functions: MD5, SHA1, ...
Cryptographic Transforms: DES, Blowfish, ...

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.

Since a PRNG is normally just an algorithm where the same initial starting values will yield the same output. 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. In OpenBSD random numbers are used in many places, such as

ports of a bound socket,
PIDs of processes,
RPC transaction IDs,
DNS Query-IDs,
inode generation numbers and
password salts.

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 and SHA1 are used as Cryptographic Hash Functions, e.g.

in S/Key to provide one time passwords,

in IPSec or Photuris to authenticate the data origin of packets and to ensure packet integrity.

Cryptographic Transforms

Cryptographic Transforms are used to encrypt and decrypt data. There are normally provided 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, e.g. DES and Blowfish encryption for the kernel and userland programs, which are used, e.g.

in libc for creating Blowfish passwords,

in IPSec to provide confidentiality for the network layer,
in kerberized telnet,
in Photuris to protect the exchanged packet content.

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$OpenBSD: crypto.html,v 1.10 1998/02/23 18:36:03 deraadt Exp $