On 10/5/2012 9:54 AM, int0...@safe-mail.net wrote:
> On computers that don't have a good /dev/*random, the randomness used
> by OpenSSL comes only from things happening on the computer during the
> few moments when the openssl tool is running. To gather up more
> randomness, the openssl tool tries to accumulate randomness over
> multiple runs as follows:
>
> 1. At the end of each run that used the random number generator,
> write a file of random bits (computed so they have a lot of entropy but
> do not reveal any of the random numbers already generated).
>
> 2. At the start of each such run, read in that file and use it as an
> initial pool of random bits to be mixed with any random system activity
> observed during the run.
Thanks for the explanation, that clarified things!
How does the OpenSSL tools know if /dev/{random,urandom} is "good"?
Basically it is a compile time decision. The code assumes that there is a
usable /dev/*random with a specific name (such as /dev/random) when compiled
for certain operating systems and that there is not on others.
> So the seed written to ${HOME}/.rnd is supposed to stay around until the
> next time you run the openssl tool, and reveals very little about keys
> you alredy created. But it may reveal something about the next key you
> create, which is why the file is/should be written with permissions so
> only you can read it.
I saw some people getting their randomness from /dev/random via
dd if=/dev/random of=/root/.rnd... and using the -rand parameter to give
the seed to openssl. If I got you right, that is a redundant step,
since OpenSSL
takes its randomness from /dev/random as well. Using -rand would only
be necessary
if one has a hardware random number generator (for example). Is that
right?
If the OpenSSL version they used assumed that /dev/random was not working
on that platform,then this step is an elegant workaround.
So my to go would be:
Set $RANDFILE to /root/.rnd and leave it up to openssl to use the file,
without filling it myself. I only need to make sure the permissions
are set
correctly. Is that right?
Setting it to ${HOME}/.rnd would be better as it would work for non-root
users.
> Now why OpenSSL keeps doing this on platforms with a good OS random
> source (such as non-historic Linux versions, some BSDs, recent Solaris
> versions, non-historic Windows versions) is a mystery to me.
Can somone else bring some light into this?
Enjoy
Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S. http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark. Direct +45 31 13 16 10
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