Hotel locks (was:Radio-activated locks, RESCUE...)

[baum@apple.com (Allen J. Baum)]

> I understand the
>electronic lock folks (card locks, hotels, etc.) have crypto expertise
>of varying extents (and bluntly, probably more than most of us have)
>and they certainly have the expertise in other areas.

I've been told that the way that hotel locks work is simple LFSR type
technology.

The chip recognizes some key pattern, and generates a sucessor key.
If a card is inserted that doesn't match the primary key, it checks the
sucessor key. If that matches, the successor becomes the primary, and a new
successor is generated.

The machine at the front desk knows where in the sequence the a particular
lock is, and simply generates a sucessor whenever a new key is asked for.
So, there doesn't need to be any communication between the desk and the
lock when a new key is generated. Note that after you get a new key, the
old one will still work until the new key is used.

Note that there is more than one primary key; there are 'master' keys for
the staff, and presumably that can be used to reset the key if the sequence
gets
lost. Of course, who knows what happens if the master sequence get lost to
a battery burp- maybe a separate ID number/lock? (as opposed to the huge
back door of a permanent, single, masterkey...)

Clever little system, yes?

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* Allen J. Baum              tel. (408)974-3385  *
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