From: Sandy Sandfort <sandfort@crl.com>
Date: Tue, 26 Jul 94 08:44:08 PDT
To: Arsen Ray Arachelian <rarachel@prism.poly.edu>
Subject: Re: CYPHERPUNKS TO THE RESCUE
In-Reply-To: <9407261252.AA19317@prism.poly.edu>
Message-ID: <Pine.3.87.9407260818.A728-0100000@crl2.crl.com>
MIME-Version: 1.0
Content-Type: text/plain


C'punks,

On Tue, 26 Jul 1994, Arsen Ray Arachelian wrote:

> 
> You'd need a clock on the garage controller....The garage opener
> would receive a signal from the remote, issue a challenge code based on a
> hash of the time/date + some random numbers.  The remote would encrypt this
> hash with the owner's IDEA key and send back the response.

Am I missing something here?  Why would you need a clock?  What I had in 
mind was something like:

	1--The owner presses the "open" button on the remote.
	2--The remote sends an "ask me" signal to the door unit.
	3--The door unit transmits a random number in the clear.
	4--The remote encrypts and signs the random number using
	   its unique private key.
	5--The door unit decrypts and compares the numbers, using
	   the remotes public key.
	6--If the numbers match, the door opens.  QED.

Adjusting my flame retardant underwear,


 S a n d y

P.S.  For most car and garage doors, relatively short (32 bit?) keys 
      should be more than sufficient, I would think.