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    SubjectRe: Emergency shutdown feature
    On Sun, Dec 21, 1997 at 11:16:13AM -0500, linux kernel account wrote:
    > I see the only need for the 'challange system' is so that you can
    > idenitify the sender. My main difficulity with the challange system, is
    > that the reboot packet is to reboot a runaway computer. The challange
    > system would mostlikely lower it's effectiveness.
    >
    > Furthermore, there is no need to use a random number to prevent replay.
    > The window is small enough (4minutes, someone with the ablity to sniff
    > could do more damage then making it go down again as soon as it came up)..

    Also, if you're rebooting a runaway computer, you're likely to take a few
    minutes to reboot and fsck. A few gig of heavily used disk can suck up time
    in fsck quite nicely. And if you're really worried (and the loss of 4
    minutes is worth less to you than the risk of attack) then put a 4 minute
    pause in your startup scripts in the case of 'unclean' reboots. Or do not
    accept 'reboot' packets during the first 4 minutes of uptime (less boot
    time would probably only be a minute or two at max on a small disk system).

    > > - A single valid packet can be replayed until it is no longer valid.
    > > so your poor host will be rebooting until the packet expires... So
    > > if you validly reboot the machine, anyone listening can reboot the
    > > machine for a few minutes...
    > You couldn't reboot it until it was on the network.. How many
    > times could I reboot your computer in that 256second window? Maby one
    > additional time...

    Exactly.

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