lkml.org 
[lkml]   [2007]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Seeding /dev/random not working
    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/

    \
     
     \ /
      Last update: 2007-05-29 15:41    [W:3.990 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site