>Tie a card-carrying cryptographer to a chair until he delivers it ?

Alternatively, implement it very, very simply and put it on github, and ask card-carrying cryptographers to vet it. That one is harder on the ego though.

I'm pretty sure no cryptographer will vet it.

I read 'vet' as "tear it to bits"

Yes, exactly. After several phoenix iterations of that kind, you might have something approaching usable.