You might be interested in this patent owned by Sun, titled "System for determination of the equivalence of two objects without compromising them done by a third object nominated by one and accepted by the other".
I happened to run across this and was a little surprised that there was enough interest in this field to file a patent. I would consider it obvious, but maybe I have more than ordinary skill in the field. It comes from the Muse work (OSR v.25 n.2 p.27).
The problem to be solved is this. Two objects jointly define a notion of "equivalence" between them (it could be any relationship). You want to determine whether two arbitrary objects A and B are equivalent. You can't just pass B to A asking "Are you equivalent to this?", because you don't trust A not to misuse B, that is you don't want to give A the authority to use B.
The title pretty much says it. The method is: Ask A to nominate an object C to perform the comparison. (A returns an object C that has the authority to look at A's internals, but will not do anything but compare.) Then ask B whether it concurs with the nomination of C. (B will concur only if it recognizes C and trusts it not to misuse authority. If A and B are indeed related, C will have the authority to look a B's internals as well as A's.) If B concurs, ask C to perform the comparison, passing B and A.