Theodore Tso wrote:
On Thu, Nov 23, 2006 at 01:10:08AM +0100, Jan Engelhardt wrote:
Disk activities are "somewhat predictable", like network traffic, and
hence are not (or should not - have not checked it) contribute to the
pool. Note that urandom is the device which _always_ gives you data, and
when the pool is exhausted, returns pseudorandom data.
Plesae read the following article before making such assertions:
D. Davis, R. Ihaka, P.R. Fenstermacher, "Cryptographic
Randomness from Air Turbulence in Disk Drives", in Advances in
Cryptology -- CRYPTO '94 Conference Proceedings, edited by Yvo
G. Desmedt, pp.114--120. Lecture Notes in Computer Science
#839. Heidelberg: Springer-Verlag, 1994.
http://world.std.com/~dtd/random/forward.ps
Note that the controller hardware in question plays a large role in
these things. Most modern network controllers, and a few recent SATA or
SAS controllers, include hardware interrupt mitigation, which can cause
interrupts to fire on a timed basis in some load profiles.
Compounding that, both software and hardware interrupt mitigation lead
(intentionally) to a marked decrease in overall interrupts, which leads
to less entropy even if the interrupt handler is sampling randomness.
IMO there is an overall trend needing-more-entropy-than-you-have for
headless network servers. If you have a hardware RNG, use that and rngd
to fill the entropy pool. If you don't, look into various entropy
gathering daemons (audio-entropyd, video-entropyd, egd, and others).
You can gather entropy from system stats, open microphones, open video
channels, thermal diodes, ...
Jeff
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