Re: Timesetting ... Re: Security Hole in Axent ESM

[henry () CUMULUS NET (Henry Longmore)]

-----Original Message-----
From: Andy Church <achurch () DRAGONFIRE NET>
To: BUGTRAQ () NETSPACE ORG <BUGTRAQ () NETSPACE ORG>
Date: Monday, August 31, 1998 4:10 PM
Subject: Re: Security Hole in Axent ESM


> > Andy Church <achurch () DRAGONFIRE NET> wrote:
> > > One way I could see to
> > > make this more effective would be to use 64-bit times and disallow both
> > > setting the clock back and changing the top 2 bits to anything other
than
> > > zero.  This would break the rollover attack without causing any
premature
> > > Y2k-like problems (2^62 seconds ~= 10^13 years).
> >
> > This is still a DOS of sorts, as you can set the clock to 2^62-1, and
> > then it will be impossible to return the clock to the correct time
> > without rebooting.  Many things will probably be unhappy to find
> > themselves 10^13 years in the future.
>
>     Good point; I obviously hadn't thought that far.  I suppose you could
> just not let the clock be set at all--that would pretty cleanly stop
> clock-setting problems. (:
>
>     Come to think of it, aside from adjusting for clock drift, there
> shouldn't be any need to set the system clock under normal circumstances.
> If there were a system call like adjtime() which set a _continuous_ (not
> one-time) drift adjustment--for example, telling the kernel to adjust
> forward or backward one second every N seconds--then you could set that
> (and maybe the clock as well) at boot time, then disallow all clock
> adjustment functions, and you should be okay.

This would be great if clocks lost time at a constant rate.  I'm afraid not
many do,
however.  Without a constant rate, an algorithim to adjust for time drift
might be
rather complex (and CPU time consuming).

I think the best way to do this for tamper_resistant quality would be to
ONLY set the clock at boot time --thus requiring access to the physical box
to set time, and require a password to do so, not relying on permissions
(sort of like BIOS setup passwords on x86 architecture)