All else equal, in practical terms you should probably devote all your time to first finding the person(s) that already know the private keys, and then patiently persuading them to share. I believe the technical term for this is “rubber hose cryptanalysis”.
All else equal, in practical terms you should probably devote all your time to first finding the person(s) that already know the private keys, and then patiently persuading them to share. I believe the technical term for this is “rubber hose cryptanalysis”.