The Best Laid Schemes of Mice and Straw Men

The first, of gold, who this inscription bears:
“Who chooseth me shall gain what many men desire.”
The second, silver, which this promise carries:
“Who chooseth me shall get as much as he deserves.”
This third, dull lead, with warning all as blunt:
“Who chooseth me must give and hazard all he hath.”
How shall I know if I do choose the right?
- Shakespeare - The Merchant of Venice

In this post-911 epoch of suspicion and fear the subject of searching people seems to be on the agenda almost constantly.  Do the authorities have a right to search you ?  Do they have a right to force you to reveal a password allowing them to reveal the contents of your mobile phone, or is it none of their business.

I have thought of a very elegant solution to this problem but first I need to introduce you to some simple stuff about encryption (please skip if you are already a tech geek).

Simple Analogy

Imagine if you wanted to prevent somebody from gaining access to a personal belonging of yours (e.g. a gold necklace).  One way of acheiving this would be to place it in a combination safe.  There are only two ways that a criminal can now obtain the gold bracelet.

1. By procuring the combination (by violent means if necessary)
2. By forcing open the safe (using say, explosives or a welding torch)

There is a kind of encryption known as Public/Private key encryption which can hide a file in a similar way, however, in order to explain it we need to modify the above analogy in the following way.

Moderate Analogy

Now imagine a combination safe with 2 doors, with a combination on each door.  Lets call them Door A and Door B.

Door A allows one to place objects in the safe.  Door B allows one to retrieve objects from the safe (note: using the simple analogy above the combinations for Door A and Door B would be the same).

If one opens Door A and places and object in the safe, closes door A, and then re-opens Door A the object will no longer be present.   Another way of thinking of Door A is as not really a door at all, more like an aperture/slot (e.g. in a post box).  The combination allows one to open the slot and put a parcel in.

If one opens Door B one can retrieve whichever item has been added via door/slot A.  However, one cannot put an object into the safe using door B.  Door B is a little like the receptacle on a confectionary machine.

In order to transfer the above analogy above to the computer/virtual realm we need to add the following caveats.

• Door/Slot A can only be used to add an item/information into the safe/container.
• Door/Receptacle B can only be used to retrieve an item from the safe/container.
• When an item/information is retrieved from the safe/container it is a copy that is retrieved
• The only method to destroy the item/information permanently is to destroy the safe/container.
• Another term for Door A is the Public Key
• Another term for Door B is Private Key

( Geeks can start reading again now :-)  )

Now imagine that this (virtual) safe holds personal information stored on one's mobile phone using public/private encyption (see moderate analogy above).  If the authorities want to see the information on one's mobile phone (and they have the right to do so) they will simply force you to reveal the PRIVATE password (i.e. the combination to Door B).  However, this is where the final COMPLEX analogy comes in handy.

Complex Analogy

And so,” said the Cat in the Hat, “So so so...
I will show you Another good game that I know!”
And then he ran out. And then, fast as a fox,
The Cat in the Hat Came back in with a box.
A big red wood box. It was shut with a hook.
“Now look at this trick,” Said the cat. “Take a look!”
Then he got up on top With a tip of his hat.
“I call this game FUN IN A BOX,” said the cat.
- Dr Suess, The Cat in the Hat

This new safe has 2 doors like the Moderate safe.  An Input door/aperture/public and an output door/receptacle/private. However, unlike the moderate safe this one has 6 combinations. 3 of the combinations can be used to open the input door/aperture and 3 can be used to open the output door/receptacle.

Lets call the input combinations IK1, IK2 and IK3 and the output combinations OK1, OK2 and OK3.

When one deposits an item/information in the input aperture using key IK1 it can only retrieved via the output receptacle using key OK1.

When one deposits an item/information in the input aperture using key IK2 it can only retrieved via the output receptacle using key OK2.

When one deposits an item/information in the input aperture using key IK3 it can only retrieved via the output receptacle using key OK3.

Now transferring the analogy above to one's mobile phone. If the bad guys/authorities want to retrieve the information stored on ones mobile phone then they effectively have to have access to all the output combinations which the (analogical) safe contains. When one is asked to reveal the combination one can simply hand over one of the combinations which hold a different item.

The key thing to remember here is that the authorities don't know how many multiple keys the safe has so even if they procure a private key this will not help them particularly if the information which they reveal is plausible.

It is a kind of straw man defence strategy.

The safe with multiple locks could in theory have N inputs and N outputs allowing any number of alternative objects for the authorities to recover.

The Petulant geek has spoken.