[cryptography] Kernel space vs userspace RNG

Krisztián Pintér pinterkr at gmail.com
Fri May 6 14:02:26 EDT 2016

Russell Leidich (at Friday, May 6, 2016, 7:48:49 PM):
> a "real world" situation, userspace is richer because it's active
> maybe 2 or 3 orders of magnitude more often than the kernel, and so
> can afford to accrue much more timing entropy, some of which is
> bound to be physical in origin.

userspace does not generate entropy at all. everything that can be
considered entropy goes through the kernel, in form of interrupts or

grabbing this kind of entropy is very cheap, so i see no reason why
would a kernel not do that. but i might be mistaken, i'm not a hw
expert, nor a kernel expert by any means. but to my knowledge, the
entropy entirely comes from kb/mouse, disk, network, motherboard
timers, etc. so even if you make a note of every such event, it still
amounts to negligible cpu time or memory required.

btw, just as a "fun fact", havege collects this entropy too. it is a
misconception that it generates any extra to the above.

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