HOW TO PLAN A COUP D’ETAT COVERT MULTI-PARTY COMPUTATION YINMENG ZHANG ALADDIN REU 2005 LUIS VON AHN MANUEL BLUM

TWO-PARTY COMPUTATION MULTI-PARTY COMPUTATION COVERT ALLOWS TWO PARTIES WITH SECRET INPUTS X AND Y TO LEARN F(X,Y) BUT NOTHING ELSE ALICE BOB CHARLIE’S ANGEL IDEAL MODEL

THERE ARE ONLY THREE ANGELS. NONE OF THEM KNOW ALICE. OR BOB.

SECURE TWO PARTY COMPUTATION: YAO

F(X,Y) = 1 IF X>Y 0 OTHERWISE $45 MILLION$32 MILLION F(X,Y)=1 LET’S NOT GET MARRIED JENBEN

… WHY WOULD WE WANT TO DO THAT? OMG EVERYBODY! BOB LIKES ME! WHAT A LOSER! BOB ALICE I ALICE LET’S FIND OUT IF WE BOTH LIKE EACH OTHER!

COVERT TWO PARTY COMPUTATION: VON AHN,HOPPER,LANGFORD

COVERT TWO-PARTY COMPUTATION AFTER LEARNING F(X,Y), EACH PARTY CAN ONLY TELL WHETHER THE OTHER PARTICIPATED IF THEY CAN DISTINGUISH F(X,Y) FROM RANDOM BITS EXTERNAL COVERTNESS INTERNAL COVERTNESS NO OUTSIDE OBSERVER CAN TELL IF THE TWO PARTIES ARE RUNNING A COMPUTATION OR JUST COMMUNICATING AS NORMAL

WHO KNOWS WHAT? WE ASSUME THAT BOTH PARTIES KNOW THE FUNCTION THEY WISH TO EVALUATE BOTH KNOW WHICH ROLE THEY ARE TO PLAY IN THE EVALUATION BOTH KNOW WHEN TO START COMPUTING

ORDINARY COMMUNICATION MESSAGES ARE DRAWN FROM A SET D TIME PROCEEDS IN DISCRETE TIMESTEPS EACH PARTY MAINTAINS A HISTORY h OF ALL DOCUMENTS THEY SENT AND RECEIVED TO EACH PARTY P, WE ASSOCIATE A FAMILY OF PROBABILITY DISTRIBUTIONS ON D: {B h P }

ORDINARY-LIKE COMMUNICATION GIVEN ANY HISTORY h, P WANTS TO BE ABLE TO SAMPLE FROM THE CHANNEL B h P CHANNEL ORACLE

THE WAR ON TERROR I GUESS I CAN USE MY BAZOOKA HAVE YOU SEEN MY AK-47? YOU LEFT IT NEXT TO MY GRENADES THE AXIS OF EVIL SHALL PREVAIL! MI-6 AGENT CIA AGENT HE WORKS FOR CIA HE WORKS FOR MI-6

THE WAR ON TERROR HE WORKS FOR CIA HE WORKS FOR MI-6 THE UTTERANCES CONTAINED A COVERT TWO-PARTY COMPUTATION THE FUNCTION F VERIFIED THE CREDENTIALS SINCE BOTH WERE VALID, IT OUTPUT 1 K X WAS A CREDENTIAL SIGNED BY CIA AND Y WAS SIGNED BY MI-6 FOR ANY OTHER INPUTS, F OUTPUTS A RANDOM VALUE

SECURE MULTI PARTY COMPUTATION: GOLDREICH,MICALI,WIGDERSON

SECURE MULTI PARTY COMPUTATION: YINMENG ZHANG??? WHAT I DID ON MY SUMMER VACATION [THE TEASER TRAILER]

COVERT MULTI-PARTY COMPUTATION EVERYTHING IS HARDER WITH MORE PEOPLE ALLOWS N PARTIES WITH SECRET INPUTS X 1 …X N TO LEARN F(X 1,…,X N ) BUT NOTHING ELSE

COVERT MULTI-PARTY COMPUTATION: THE ADVERSARY WIMPY BUSYBODIES [SEMI-HONEST] ALL’S FAIR IN LOVE AND CRYPTOGRAPHY [MALICIOUS] WHAT THINGS ARE IMPOSSIBLE TO PROTECT AGAINST?

HOW MANY PEOPLE WERE COMPUTING, GOT BORED AND STOPPED[ABORT]? HOW MANY PEOPLE ARE COMPUTING? COVERT MULTI-PARTY COMPUTATION: WHO KNOWS WHAT? WHO’S COMPUTING?