[VxW] how to generate a random seed without using timing functions

[ramamohankn]

Hi Saravanan,

check following links

http://sunburn.stanford.edu/~knuth/programs/rng.c

http://repast.sourceforge.net/docs/how_to/random.html#custom

http://sunburn.stanford.edu/~knuth/programs.html#rng

Hope u may get some stuff over there

Regards,

Mohan

"VxWorks Users Group List" wrote:

Hi,

When my embedded board (running vxworks) boots, i need to generate a
random seed. Currently the board doesn't have any means like CMOS for
maintaining time. Thus whenever I use gettimeofday() as seed value
for srand(), the resulting rand() number repeats most of the time.

Is there any other way to generate random seed without using any
timing functions? Or any equivalent of /dev/random?

-- mks --

--
M K Saravanan
http://www.comp.nus.edu.sg/~mksarav
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[Bill Pringlemeir]

>>> M K Saravanan wrote...

> When my embedded board (running vxworks) boots, i need to generate a
> random seed. Currently the board doesn't have any means like CMOS
> for maintaining time. Thus whenever I use gettimeofday() as seed
> value for srand(), the resulting rand() number repeats most of the
> time.
>
> Is there any other way to generate random seed without using any
> timing functions? Or any equivalent of /dev/random?

>>> "ramamohankn" <ramam...@indiatimes.com> wrote...

> check following links
>
> http://sunburn.stanford.edu/~knuth/programs/rng.c
> http://repast.sourceforge.net/docs/how_to/random.html#custom
> http://sunburn.stanford.edu/~knuth/programs.html#rng
>
> Hope u may get some stuff over there

I think that both of you missed some points. First, there is nothing
wrong with a rand() function sending repeat numbers. It must be
statistically biased for it to be wrong. I guess that "MKS" has found
that this is statistically incorrect and didn't eyeball pages of data
and find several repeats.

Depending on the context, no random number generator is good enough.

"http://www.ietf.org/rfc/rfc1750.txt"

The "/dev/random" that MKS wishes on vxWorks typically capture entropy
from users via key strokes and mouse presses times. Some people also
use network traffic times to supply entropy to the "/dev/random".

There is also an algorithm by Von Neumann that can "unbias" random
data to make the distributions 50/50. I think that it is described in
the above URL.

Also, I have posted vxWorks code for a "/dev/random" like driver. It
can be found on an OpenSSL mailing list archive.

"http://www.mail-archive.com/openssl-dev%40openssl.org/msg11821.html"

I make no guarantees of its reliability or usefulness.

fwiw,
Bill Pringlemeir.

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