Multikey crypto

Since I am relatively new to the field of encryption forgive me if this 
is a FAQ.

Has anyone ever done anything with an encryption scheme that allows 
multiple unlocking keys? What I'm thinking about is a way to encrypt 
some data and then create multiple keys that will decrypt the data. I 
want to be able to encrypt a document and then give multiple people 
access to the document and be able to lock out a key and/or generate 
new keys without having to redistribute keys to everybody that already 
has one. I realize that this makes it easier to attack the encrypted 
information since there are multiple keys to unlock the data but I 
don't consider this a big problem. If someone wants to throw heavy duty 
horsepower at the problem they will crack it eventually anyway.

Mike

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Mike Markley              || The opinions here do not represent the
mmarkley@microsoft.com    || opinions of my employer. Attempts to
			  || associate the two are pointless.

   "I want to look at life, In the available light"
					- Neil Peart -

> Has anyone ever done anything with an encryption scheme that allows 
> multiple unlocking keys? What I'm thinking about is a way to encrypt 
> some data and then create multiple keys that will decrypt the data. I 
> want to be able to encrypt a document and then give multiple people 
> access to the document and be able to lock out a key and/or generate 
> new keys without having to redistribute keys to everybody that already 
> has one.
--> Mike Markley             

	I was thinking about this the other day.. and my first reaction
was the following.

	What if you encrypted the document with p/k and made multiple
copies of the same [private] key.  Then you encrypted each copy of the
key with a user's public key.  Now each user has a copy of the private key.
If you decide Joe SHOULDN'T have access to the data anymore, you can
re-encrypt the document and redistribute the p/k encrypted copies of the
key.  There may be some fancy algorithms to achieve more security.. and
ease of use.. but that's the answer I came up with.  TTFN!
  

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