/dev/random

[Ben Laurie]

On Mon, Aug 20, 2012 at 11:02 PM, Steve Kargl
<sgk at troutmask.apl.washington.edu> wrote:
> On Mon, Aug 20, 2012 at 07:49:16PM +0100, Ben Laurie wrote:
>> Apparently /dev/random uses h/w PRNGs if available, discarding all
>> other sources of randomness.
>>
>> This seems like a mistake to me - we should fix it.
>>
>> Also, it seems that entropy is available in detailed interrupt timing
>> (see http://www.issihosts.com/haveged/) which might be useful on
>> entropy-starved systems - I suspect we are not exploiting this source,
>> and in light of recent developments, we probably should be,
>>
>> Comments?
>
> Well, it's hard to comment when you failed to explain
> *why* you think it is a mistake.

Sorry - because I do not think it is wise to trust the h/w prng so
much we discard other entropy.

>  In addition, I'm having
> a hard time parsing your 1st sentence, which appears to
> be related to this sentence:
>
>    The device will probe for certain hardware entropy sources,
>    and use these in preference to the fallback, which is a
>    generator implemented in software.
>
> from 'man 4 random'.  Your 'all other sources of randomness'
> would then need to be amended to 'all other sources of entropy'.
> But, then 'all other sources' does not make sense, because only
> the 'generator implemented in software' is discarded.

That is everything except the hardware, right? So ... all other sources.

> It is also unclear why a linux-only project for gathering entropy
> is relevant here given that FreeBSD already has the ability to
> use both hardware and software interrupts as sources of entropy.

It is relevant because it seems there is entropy available in
fine-grained timing.