Schneier: There are several ways two people can divide a piece of cake in half. One way is to find someone impartial to do it for them, but it requires another person. Another way is for one person to divide the piece, and the other person to complain (to the police, a judge, or his parents) if he doesn t think it s fair. A third way, known by kids, pot smokers, and everyone else who needs to divide something up quickly and fairly, is called cut-and-choose.
Source: https://threatpost.com/value-self-enforcing-protocols-081009/72980/