Russell McMahon wrote:
> E = [(A^2-B^2)/(C^2+ 2.C.D + D^2)] x [(C+D)/(A-B)] x [ (C+D)/(A+B)] x
> F
>
> E will always equal F :-)
>
> A, B, C, & D are all irrelevant to the result (except that certain
> combinations are not allowed in order to prevent the result going to
> infinity. eg A<>B, A <> -B, C <>D, C <> -D.)
>
> The eg ratio of the parameters A...D to each other or their sums or
> some other features may be set in some manner so that, while they do
> not alter the fact that E = F , do indicate to a knowledgeable
> inspector whether they have been set by someone who 'knows the rules'.

But that could just as well have been implemented by simply checking A-D
according to some rules.  For example, you could require them to each be a
different hash function of F.  There is no need for them to take part in the
computation of the formula.  We assume that whoever is sending the values
can't see the algorithm, else of course they could circumvent it in either
case.


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