Diplomacy, Grey/Black Press From: shoham@ll.mit.edu (Daniel Shoham) Date: Wed, 23 Sep 1992 01:57:26 +0000 Having read the Diplomacy judge instructions for the use of Grey/Black press, but never having played a game where such was allowed; it occured to me that it could easily be defeated by a carefull player. (For those unfamiliar with Grey/Black press: it is a modification allowed in some variants of Diplomacy where the judge can be instructed to fake the source of a message sent. Hence, Germany could send a letter to England claiming that it was sent by France) Suppose I am France in a diplomacy game that allows only Grey press (the most difficult case). I would like to have communication with England uninteruppted by other player's spoofs. I will, at the begining of the game send England the following message: ---------------------------------------------------------------------- To the English chief to diplomatic security: Hi. This is the French chief of diplomatic security. It has come to our attention that the enemies of Franco-British cooperations might be trying to send you false messages using a counterfeit seal of the French presidency. To combat those enemies please use the password "Euro-Disney" at the header of any message sent to us. We request that you awknowledge this message by sending us a copy of it back. Also, please issue us a password so that you can authenticate our communications in a likewise manner. - with regards. ---------------------------------------------------------------------- (of course a different password should be used with each of your communications partners). While England may not be interested in dealing with me truthfully, it is never in their interest to NOT KNOW if a communication from France is authentic, or to have the French fooled by someone else into thinking they got a message from England. Therfore, a logical England player would respond as instructed. Also, this message guards against the possibility that it is itself sent by someone other than France. Suppose the above message was sent by Germany to England (for whatever reasons). England, dutifully sends FRANCE a copy of the message and adds that the password "London-Bridge" must be used to authenticate all communications from France. The French, will then send England a message like the following: ---------------------------------------------------------------------- To the English chief to diplomatic security: password: "London-Bridge" Hi. This is the French chief of diplomatic security. I was startled to find you sending me a copy of a letter that supposedly came from this office. It has not. However, whomever sent you this fakery seems to have had a good idea. The only thing is that the password "Euro-Disney" is clearly not a secret. Please use the password "Bastille" instead. - with regards. ---------------------------------------------------------------------- As this message is authenticated with the password "London-Bridge", (which England knows was sent only to France), England would know FOR-SURE that it must have come from France (France never has a reason to leak the password). Now that passwords have been established, all Anglo-French communications can be authenticated. France can proceed to a similar exchange of passwords with all its negotiation partners. -Does anyone with Grey/Black Diplomacy experience care to comment on the above? Dan Shoham shoham@ll.mit.edu Referenced By Up