In message <[EMAIL PROTECTED]>, 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)
