[cap-talk] Why protected capabilities matter

Karp, Alan H alan.karp at hp.com
Tue Jul 17 18:42:58 EDT 2007


Jed wrote:
> 
> If you don't believe so, perhaps you can give me an example 
> of a situation where
> the isomorphism (c-list index <=> encrypted capability data) 
> fails.  That is, where
> the descriptor based system can know more, can protect more, 
> or whatever.
> 
You have substituted unguessability for unforgeability.  Although
computationally infeasible, it is technically possible for a program to
compute a set of bits that represent an encrypted capability.  There is
no such guessing attack with c-lists.  While this appears to be a purely
theoretical difference, the encrypted capability scheme could be
vulnerable to a weakness in the encryption algorithm.  

________________________
Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
1501 Page Mill Road
Palo Alto, CA 94304
(650) 857-3967, fax (650) 857-7029
https://ecardfile.com/id/Alan_Karp
http://www.hpl.hp.com/personal/Alan_Karp
  
 



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