The Dining Ambassadors Problem
This was originally circulated as a joke e-mail among a group of researchers
who were looking at "Rampart", a security protocol for replicating a
computation on several servers who really, really don't trust each other.
It has since become notorious, and I keep being asked for copies of it, so
here it is.
So, what sort of application really needs the service provided by Rampart?
Pretty nearly everything I could think of either only needed a much simpler
mechanism (which doesn't bother to give you shared consistent ordering of
events), or else needed even stronger mechanisms.
Then, it came to me. For years, we have persecuted students with questions
on the Byzantine Generals Problem or the Dining Philosphers Problem.
Now, at last, we have the opportunity to combine the worst aspects of both
in the "Dinning Ambassadors Problem":
After a hard day discussing European pasta quotas, the 5 Ambassadors go
out for dinner at the same Italian restuarant frequented by the dinning
While the philosophers are all good friends and have impeccable table
manners, the Ambassadors are perfectly capable of such breaches of etiqutte
as smuggling in additional chopsticks or attempting to eat with their
hands. Such breaches of etiquette will, however, be looked down on severely
and anyone caught doing so will be expelled from the restaurant on a 2/3
An ambassador may attempt to make it appear as though one of the others
has violated the rules of etiquette, in order to discredit them.
With a real resturant this is too easy to solve.Instead, we
will do this in a networked virtual restaurant, where insiders and
outsiders can insert, delete, modify or re-order messages, destroy
communications channels and even destroy end systems.
The waiter would like to know who is currently holding the chopsticks.
Exercize: program a solution using Rampart.