Re: /dev/random on Linux

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On Tue, 16 May 2006, Theodore Tso wrote:
3) Investigate the possibility of adding quotas to /dev/random.  This
is actually much more trickier that the paper suggests, since you want
to allow the user to be able to extract enough entropy to create a
2048 bit (or at least a 1024-bit) RSA key.  The problem is that's a
lot of entropy!  Maybe it would be OK to only allow a 1024-bit RSA key
to be generated every 12 or 24 hours, but suppose someone is
experimenting with GPG and screws up (say they forget their
passphrase); do you tell them that sorry, you can't generating another
key until tomorrow?  So now we have to have an interface so the root
user can reset the user's entropy quota....  And even with a 24-hour
limit, on a diskless system, you don't get a lot of entropy, so even a
1024-bit RSA key could seriously deplete your supply of entropy.

#3 is fine if it's out of the kernel. This isn't just policy - it's complicated policy, as you point out quite well.

This last point is a good example of the concerns one faces when
trying to design a working system in the real word, as opposed to the
concerns of academicians, where the presence or lack of forward
security in the event of a pool compromise is issue of massive urgency
and oh-my-goodness-we-can-only-tell-the-maintainer-because-it's-such-a-
critical-security-hole attitude.  Where as my attitude is, "yeah, we
should fix it, but I doubt anyone has actually been harmed by this in
real life", which puts it in a different category than a buffer
overrun attack which is accessible from a publically available network

Slashdot headline about Linux's weak-ass rng should be up shortly, next to the news post discussing what Linus had for breakfast this morning.

						- Ted

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