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List:       linux-embedded
Subject:    Re: Sources of entropy?
From:       Mike Frysinger <vapier.adi () gmail ! com>
Date:       2009-04-02 12:03:08
Message-ID: 8bd0f97a0904020503uf434376s2ba8f9d0e8fcfa7b () mail ! gmail ! com
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On Thu, Apr 2, 2009 at 07:45, Nicholas Mc Guire wrote:
> On Tue, 24 Mar 2009, Robin Getz wrote:
>> I'm just wondering what people using on standard embedded/headless/diskless
>> targets (which do not have hw random number generators) as a source of
>> entropy - since networking was removed as an entropy source circa 2.6.26
>
> without claiming that this is actually usable at this point but a simple
> source of entropy that looks quite good is simply to use the timer-counter/TSC
> or what ever available. The attached trng.c has been tested on a few X86
> systems and produces remarkably good random numbers - this might be suitable
> if you have no other sources available.

unfortunately on Blackfin parts, the TSC (we call it "CYCLES" as that
is the actual register name) is writable from userspace

i have used this in the bootloader as a simple way of getting a little
bit of entropy, but then i found that our system is too reliable in
booting -- it tends to take the exact same amount of time to boot to a
prompt
-mike
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