> 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.)
The exmaple given in the Microsoft paper was square roots in a finite field.
These are computationally difficult to compute (lots of multiplication mod p)
but easy to check (single multiplication mod p).
I'm sure there are other examples -- finding candidate functions of this
sort is *much* easier than finding, say, a public key algorithm.
Ned
