[Cryptography] [RNG] on RNGs, VM state, rollback, etc.

[John Denker]

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On 10/17/2013 10:05 AM, Kent Borg wrote:
> 
> But is this something that /dev/urandom might do better?  Should
> blocking be added to /dev/urandom immediately after boot until some
> reasonable threshold has been reached at least once?  Or on first
> boot are common distributions restoring a bad seed file and
> /dev/random can't tell?  Arrgh, I am starting to think that the RNG
> is the wrong place to fix it.

> There are certainly larger system issues,

Agreed, this is a system issue, not so much a /dev/u?random issue.

Blocking /dev/urandom is a bad idea.  Providing a good seed is the key.

Similarly ... on 10/18/2013 09:00 AM, travis+ml-rng at subspacefield.org wrote:
> I'm wondering if there shouldn't be an API of some kind for a VM to
> request an unpredictable seed from the host system.  Not as robust as
> dakarand unless/until widely implemented, but complementary.

Well, for qemu there is something.
I quote from http://wiki.qemu-project.org/Features-Done/VirtIORNG ...

>> VirtIO RNG is a paravirtualized device that is exposed as a hardware RNG device to the guest

================

Also:  Almost every VM I've seen provides a mechanism for shared
access to files.  A simple standard solution is to have the host
write some randomly-generated bits into a file that the guest 
can read.

===============

Thirdly:  Booting from a read-only CD or similar .iso image, 
there is a problem if lots of people have images with the
same initial seed for the PRNG.

Several years ago I wrote some code that can take apart a .iso 
image, replace the seed, and put everything back together again.
This allows one to rather cheaply make N images all different.
For details, see
  http://www.av8n.com/computer/htm/fixup-live-cd.htm

I tried to get this incorporated into the Ubuntu distribution,
to no avail.

Note that if the machine can be booted with *some* randomness,
it can be given more, via a securely encrypted link, using
simple userspace tools.  There is a tool distributed with 
turbid that reads a file (or stdin) and does the ioctl to
feed randomness to the kernel.

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