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Re: namedroppers, continued

2002-12-07 11:30:53
In message 
<Pine(_dot_)LNX(_dot_)4(_dot_)44(_dot_)0212071209090(_dot_)2775-100000(_at_)commander(_dot_)av8(_dot_)net>,
 Dean An
derson writes:
This seems clever, however, it will also take significant computational
effort to verify the computational effort was actually done. Even if a
class of functions are found that are "easier" to verify than to compute,
they will no doubt still take up a significant fraction of time.

In fact, that's the easy part.  You could demand that the sender 
compute 1,000,000 HMACs of the text, the envelope, the time of day, and 
a counter.  The verifier could check 100 randomly-chosen ones -- if any 
fail, there's a forgery.  (Well, you probably wouldn't want those 
values, since 1,000,000 HMACs would be a lot of data to transmit.  But 
you get the general idea.)

                --Steve Bellovin, http://www.research.att.com/~smb (me)
                http://www.wilyhacker.com ("Firewalls" book)




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