What is a protocol for determining which of two numbers is larger, without sharing those numbers?

Question

Situation: Alice has selected a positive integer $a$, and Bob has selected a positive integer $b$. Alice and Bob want to know whether $a > b$, $a = b$, or $a < b$, but neither wishes to reveal their chosen number to the other party.

How can Alice and Bob make this determination?

Just a pointer to an answer at the moment, the problem is called "Yao's Millionaire's Problem" for which there is a protocol. — Luke Mathieson, Nov 14 '13 at 05:40
@LukeMathieson Ah, that's great, thanks! I'd seen this somewhere before and couldn't remember what the problem was called. — senshin, Nov 14 '13 at 05:42

score 1 · Answer 1 · edited Apr 13 '17 at 12:48

1

As pointed out by Luke Mathieson in the comments, this problem is called Yao's Millionaire Problem, for which protocols can easily be found by Googling.

edited Apr 13 '17 at 12:48

Community

1

answered Nov 18 '13 at 23:59

senshin

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I do not understand the problem well enough at this point to write a good answer for this question. If somebody does write a good answer (or really, any answer), I will unaccept this answer and accept that instead. – senshin Nov 18 '13 at 23:59

What is a protocol for determining which of two numbers is larger, without sharing those numbers?

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