[ECOS] Re: Entropy gathering?

Jay Foster jay@systech.com
Thu Apr 3 19:53:00 GMT 2008


A colleague implemented something like this by creating a function that
could be called from various places at random times, such as the ethernet
driver (ether_input()), serial port modem signal changes, etc.  The function
would read the HAL microsecond clock value and write the lower 16-bits to
/dev/random.  After a pre-determined number of such events, this function
would stop writing to /dev/random and simply return.

Jay

-----Original Message-----
From: Grant Edwards [mailto:grante@visi.com]
Sent: Thursday, April 03, 2008 12:18 PM
To: ecos-discuss@sources.redhat.com
Subject: [ECOS] Re: Entropy gathering?


On 2008-04-03, Grant Edwards <grante@visi.com> wrote:

> The BSD stacks appear to use an aRC4 keystream for "random"
> data. The stream uses a constant seed and then mixes in the
> system clock value.  It could be worse, but it's not great
> either.

Upon reading the above statement, I think I should clarify that
the "system time" that's mixed in is the HAL's hardware counter
value and not the system tick count time.  The hardware counter
is changing much faster (a good thing), but it provides
relatively few bits (on my targets, it ranges from 14-18).

-- 
Grant Edwards                   grante             Yow! My mind is making
                                  at               ashtrays in Dayton ...
                               visi.com            


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