Keep it secret, stupid!

Matt Blaze mab at research.att.com
Mon Jan 27 02:08:53 EST 2003


> 
> > The tragic part is that there are alternatives.  There are several
> > lock designs that turn out to resist this threat, including master
> > rings and bicentric locks.  While these designs aren't perfect, they
> 
> I think it is worth pointing out that, while master ring systems (and
> master-keyed systems with false steps added) resist the attack Matt
> describes, they often make the task of picking the lock (on a case by case
> basis) easier.

Actually, master ring systems make it considerably harder to pick
a lock.  Sometimes a pin will set at the master shear line and sometimes
it will set at the change shear line, but unless all pin stacks catch
at the same one, the lock won't operate.  (This phenomenon is also why
it is difficult to pick a SFIC core with conventional torque tools).

Adding false cuts does increase picking vulnerability, of course.

Personally, I think it's a shame that master ring designs have all but
disappeared. They're still listed as an option in the Corbin-Russwin
catalog for a few commercial cylinders, and are also used in some prison
locks as I understand it.

-matt


> 
> That needs to be considered when designing a physical security plan. One
> may wish to key locks of particular importance separately from the master
> ring system if entry by picking is a concern.
> 
> (There are some master-key systems, like the one made by Corbin, that
> require pin rotation at the proper time to unlock the secondary sheer
> line. And, as Matt mentioned, bicentric cylinders avoid this problem
> completely. Cost may be a major concern with these solutions, though.)
> 
> 



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