HOW TO PLAN A COUP D’ETAT

COVERT MULTI-PARTY COMPUTATION

YINMENG ZHANG

ALADDIN REU 2005

LUIS VON AHNMANUEL BLUM

TWO-PARTY COMPUTATION MULTI-PARTY COMPUTATIONCOVERT

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

JEN BEN

…

WHY WOULD WE WANT TO DO THAT?

OMGEVERYBODY!

BOB LIKES ME!

WHAT A LOSER!

BOBALICE

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:

{BhP}

ORDINARY-LIKE COMMUNICATION

GIVEN ANY HISTORY h, P WANTS TO BE ABLE TO SAMPLE FROM THE CHANNEL Bh

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 1K

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

X1…XN TO LEARN F(X1,…,XN) 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?