Gary Varga (8/18/2014)
(the equivalent of the two key launch system - no I have never seen this in real life but I am using it only as a simple metaphor for a multiple person task).
The term you are looking for is two person integrity, TPI. TPI provides substantial security because, while you might find a crook anywhere, the likelihood of finding two crooks in the exact same location are miniscule. TPI systems are commonplace.