> It's all nice and well to have an unbreakable door and lock until you 
> have to destroy your own wall to go into your own house because the keys 
> were lost somehow...

I almost never have this problem. ;-)

My mum has a habit of losing her keys all the time. But then, she just 
slings them wherever she happens to be when she stumbles in through the 
door. And then she wonders why she can't remember where they are. MY 
keys are always in one of exactly two places: In my pocket, or next to 
my computer.

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Vincent Le Chevalier <gal### [at] libertyallsurfspamfr> wrote:
> It's all nice and well to have an unbreakable door and lock until you 
> have to destroy your own wall to go into your own house because the keys 
> were lost somehow...

  If you are the only person owning keys to your house, then the next
step is to contact a legalized locksmith. They have their means to open
doors without breaking too much property. (Usually they can lockpick the
door open with their advanced tools, or if the lock is too secure for
that, they can remove the lock by force, in which case you only have to
pay for a new lock.)

-- 
                                                          - Warp

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And lo on Mon, 23 Jun 2008 13:19:07 +0100, Vincent Le Chevalier  
<gal### [at] libertyALLsurfSPAMfr> did spake, saying:

> Invisible a écrit :
>> Yeah, well, devise an unpickable lock and somebody will just rip the  
>> door off its hinges, or break in through a window or something. ;-)  
>> Weakest point and all that... All you really need is for the lock not  
>> to be the weakest part of the system.
>>
>
> And do not lose your keys :-)
>
> It's all nice and well to have an unbreakable door and lock until you  
> have to destroy your own wall to go into your own house because the keys  
> were lost somehow...

I think I'd try a window first ;-)

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

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Invisible wrote:
> keys are always in one of exactly two places: In my pocket, or next to 
> my computer.

I once spent 2 or 3 hours looking for my keys, because they were in the 
wrong pocket of the trousers hanging on the hook. I checked my pocket! 
They're not there!

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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Invisible wrote:
> scott wrote:
> 
>> Locks can be designed to be opened by two different keys (usually a 
>> unique key and a master key common to several locks).
> 
> Really? Hmm... sounds physically implausible to me, but OK.
> 
The keys in my hospital have at least three levels.
I can open my door. There is a master for the floor and there is one 
that opens all doors (and possibly even a level in between). I think you 
can also have more than one master per lock. Then if more than one 
department is on one floor, each department can have a master key and 
the cleaners have one for the floor. Also if the department is split on 
two floors...
And they are all mechanical. The master keys have one extra groove, I 
don't know about the general master.

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andrel wrote:
> And they are all mechanical. The master keys have one extra groove, I 
> don't know about the general master.

For that matter, there are cool things you can do with cryptography and 
math that let you have similar relationships with passwords. Stuff like 
"this file can be decrypted by any three of the seven officers of the 
company, or by unanimous application of the keys of the department heads 
of the company. Oh, and we can invalidate any key without invalidating 
the others."

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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Darren New wrote:
> andrel wrote:
>> And they are all mechanical. The master keys have one extra groove, I 
>> don't know about the general master.
> 
> For that matter, there are cool things you can do with cryptography and 
> math that let you have similar relationships with passwords. Stuff like 
> "this file can be decrypted by any three of the seven officers of the 
> company, or by unanimous application of the keys of the department heads 
> of the company. Oh, and we can invalidate any key without invalidating 
> the others."
> 
I personally think doing it in hardware with nuts and bolts is more 
impressive, but that may be just me.

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andrel <a_l### [at] hotmailcom> wrote:
> I personally think doing it in hardware with nuts and bolts is more 
> impressive, but that may be just me.

  I suppose it's simply a question of cleverly allocating combinations
of pin assignments to locks and keys. I can imagine at least one simple
way of achieving a hierarchy of master keys with pin locks:

  In all locks, all pins have a cut for the highest-order master key,
as well as the secondary cut for the lock-specific key.

  The locks are divided into groups of locks (eg. on a per department
basis). All the locks in one group have the exact same secondary cut
for the first pin, but this secondary cut is different in different groups.
This way a master key for a specific group of locks uses the group-specific
setting for the first pin, and for the rest of the pins it uses the setting
for the highest-order master key. This way it can open all the locks in its
own group, but it can't open the locks of the other groups (the first pin
being different stops it).

  (If there are too many groups, using just one pin to differentiate between
them might not be enough, but in that case more pins can be used for this
purpose. The amount of combinations increases exponentially.)

  If each group should be further divided into smaller sub-groups, the
same technique can be used with the second pin, the third pin, etc.

  Then there's the reverse problem: All keys, including lock-specific ones,
should open a common lock (eg. the door leading to the entire department).
A lock-specific key should open, naturally, its own lock *and* the common
lock, but it nevertheless must not be a master key which could be used to
open your work pal's office. Obviously master keys should also open these
common locks as well. However, the lock should not be openable by a key
not related to the company at all.

  In other words, the situation is kind of a reversal: The common lock is
a "master lock": It should be openable by a group of keys, but not by any
keys outside that group.

  I have difficult time bending my mind into resolving how exactly it is
done, but I can perfectly imagine there's a simple way. Ingenuous, but simple.

-- 
                                                          - Warp

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andrel wrote:
> I personally think doing it in hardware with nuts and bolts is more 
> impressive, but that may be just me.

I definitely agree. I wasn't disparaging. I was simply saying you can 
make it even *more* complex with math. The fact that the program doesnt 
have to enforce the cryptography stuff is what makes *that* impressive 
to me. You can't unscramble the stuff without 3 or 9 keys due to the 
nature of the keys, not the nature of the lock, so to speak. :-)

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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Warp wrote:
>   I have difficult time bending my mind into resolving how exactly it is
> done, but I can perfectly imagine there's a simple way. Ingenuous, but simple.

Math professor writes an equation on the board, and says "The proof is 
trivial.  Wait, is it?"  He wanders back to his office, returns in 20 
minutes to the classroom, and says "Yes, indeed, the proof is trivial."

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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