Re: IRQF_SAMPLE_RANDOM question...

Jeff Garzik
2009-04-07T22:26:15Z

Robin Getz wrote:
> On Mon 6 Apr 2009 19:35, Jeff Garzik pondered:
>> Sven-Haegar Koch wrote:
>>> On Mon, 6 Apr 2009, Matt Mackall wrote:
>>>
>>>> On Mon, 2009-04-06 at 14:30 -0400, Robin Getz wrote:
>>>>> We have lots of embedded headless systems (no keyboard/mouse, no
>>>>> soundcard, no video) systems with *no* sources of entropy - and people
>>>>> using SSL.
>>>> I'd rather add a random_sample_network call somewhere reasonably central
>>>> in the network stack. Then we can use the knowledge that the sample is
>>>> network-connected in the random core to decide how to measure its
>>>> entropy. The trouble with IRQF_SAMPLE_RANDOM is that many of its users
>>>> are technically bogus as entropy sources in the current model.
>>>>
>>>> I'm eventually going to move the RNG away from the strict theoretical
>>>> entropy accounting model to a more pragmatic one which will be much
>>>> happier with iffy entropy sources, but that's a ways off.
>>> Btw, perhaps not the perfect question in this thread:
>>> But what should we use to keep servers running without a hardware rng
>>> available and without any external input besides the network?
>>> After having ssh and openvpn die because of no random and having
>>> the machines like dead and unreachable for me I use "ln -sf
>>> /dev/urandom /dev/random", but that does not feel so good.
>> We see this question every time IRQF_SAMPLE_RANDOM is discussed.
>>
>> There is plenty of entropy data available, you just have to look
>> around... Google around for "EGD", video entropy daemon, audio entropy
>> daemon, etc...
>>
>> Even headless servers have entropy sources if you look hard enough.
>
> The original question wasn't headless servers - it was headless, no audio, no
> video, boot from flash, (initrd root file systems), diskless. embedded
> devices.
>
> And few want to load up perl on an embedded device just to gather entropy. :(

Get a list of <special files> from EGD, and

cat <special files> | sha1sum

then...

The basic point is that you can find entropy, even in a guest VM.

Jeff