SunOS 4.1 /dev/random and /dev/urandom loadable modules.
		     version 0.06 - 27 June 2002

		G. Helffrich/U. Bristol Earth Sciences

These items provide a source of random numbers that is derived from hardware
behavior of a computer that should be hard to detect from outside of the
running system.  The source's principal function is to provide OpenSSH a
source of random numbers for cryptographically encoded data exchange over
unprotected communication channels between computers.  The source is
implemented as two devices, /dev/random and /dev/urandom that may be read from
to get random data, and may be written to to add randomness to the existing
pool.  The difference between /dev/random and /dev/urandom is that reads from
/dev/urandom will never block.  A read from /dev/random will block if there
is insufficient entropy in the present pool to provide the amount of data
wanted.  The read will block until sufficient entropy is gathered from the
environment.

The items provide:

1. A loadable module driver (random.o) and exec script (random.init) to set
   up /dev/random and /dev/urandom

2. A daemon (rndd) to start at reboot time that will restore the entropy pool
   from its previous state as of the previous shutdown, and which will wait
   for a shutdown to preserve the current entropy pool state across the next
   shutdown.

3. An include file (sys/random.h) to define the IOCTL's that interact with
   the pool.

4. A man page entry (random.4) for /dev/random and /dev/urandom

5. A fragment of an /etc/rc.local script (rc.random) that will load any .o
   files in a prespecified directory as loadable modules early in the boot
   process.

Installation

1. Unpack the tar file.

2. Read the Makefile and edit as appropriate to send the bits listed above
   to their various destinies.

3. make random.o

as super-user

4. make test

and if everything is hunky-dory so far,

5. make install

If you want to use the procedure for loading loadable drivers at boot time,
insert rc.random in the proper place in your /etc/rc.local file.  There are
two parts in rc.random, one of which should appear early in /etc/rc.local and
the other later, in the main body of daemon startup commands.

Caveats

The principal contributors to entropy are the character and block device
drivers, and keyboard interrupts and mouse activity that pass through the
kb and ms STREAMS module to whatever drivers are actively using those
facilities.  Block devices used include scsi disk, tape, and cd, and
character devices include "memory" devices (/dev/null, /dev/kmem, /dev/mem),
scsi tape, and pseudo-ttys.  On workstations, these sources are varied enough,
but on servers, only disk accesses and tape use generate significant randomness.

Acknowledgements

Much of the code is derived from other sources.  Theodore Ts'o's Linux device
driver lies at the heart of this implementation.  The code further draws upon
Andreas Maier's Solaris /dev/random device driver.  These two sources provided
the framework for reverse-engineering the driver to a SunOS 4.x kernel
architecture.