Messages in this thread | | | Date | Tue, 29 May 2007 14:38:45 +0100 | From | "M Macnair" <> | Subject | Re: Seeding /dev/random not working |
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On 5/29/07, Theodore Tso <tytso@mit.edu> wrote: > On Tue, May 29, 2007 at 12:53:10PM +0100, M Macnair wrote: > Ok, so this is telling me a couple of things. First of all, if you're > only getting three outputs, it means that you don't have any > peripherals feeding entropy into the system from the boot sequence. > Without any hard drives, keyboards or mice, and a NIC whose device > driver hasn't been configured to feed entropy, you're definitely > hosed.
Yes. However this isn't the issue I'm concerned with at the moment.
> Secondly, and more importantly, your boot scripts aren't set up > correctly.
Sorry, I only posted the startup bit - the same does indeed happen on shutdown, however I wasn't interested in it for the purposes of the tests.
The key point I was trying to put across was that I can't get the seeding process to work. No matter what I wrote to /dev/urandom on startup, the output from reading /dev/urandom immediately afterwards was the same (ignoring the occasional variation that I put down to timing). As I understand it (from man 4 random and the boot script examples), writing to /dev/[u]random should increase the amount of entropy, thereby altering the output from the PRNG.
> Another thing which I noticed is that when Matt Mackall took over > maintainership of /dev/random, he apparently took out one of the > safeguards I had, which was that before, when entropy was extracted > from the pool the time stamp when it was extracted was mixed back into > the pool. The theory was that an external attacker might not know > when a program might be calling /dev/random, so mixing in the time of > that entropy was extracted wouldn't hurt, and might help. I'll submit > a patch to add that support back in, which will help you a little.
When did Matt take over? From my experiments it would appear as though the time is having an effect on the output, though as I say I'm not totally sure.
Regards, Michael Macnair - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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