Byzantine Quorum Systems

Byzantine Generals' Problem is an agreement problem, where armies surround a city and must decide to attack or retreat, with the presence of traitorous generals.

• the algorithm must allow (A) all loyal generals to agree upon the same plan of action, and (B) guarantee that a small number of traitors cannot cause the loyal generals to adopt a bad plan
• if it's formalized as V(i) is some information for the i th general, then we achieve the desired results by having all loyal generals use the same method for combining and using a robust method to do so

For A, we need

1. every loyal general to obtain the same information. Can't use value obtained directly from the i th general, otherwise he could send different values to different loyal generals
2. if i th general is loyal, then the value he sends must be used by every loyal general as v(i).

Impossible sometimes

Turns out the Byzantine Generals Problem is not solvable unless more than 2/3 of the generals are loyal