Unformatted text preview: Alice B, if Alice tells him A. This protocol, observed in a schoolyard, does not work: (1) Alice: “I’ll tell if you tell me first.” (2) Bob: “I’ll tell if you tell me first.” (3) Alice: “No, you first.” (4) Bob: “Oh, all right.” Bob whispers. (5) Alice: “Ha! I won’t tell you.” (6) Bob: “That’s not fair.” Cryptography can make it fair. The previous two protocols are implementations of this more general protocol, one that lets Alice and Bob exchange secrets simultaneously . Rather than repeat the whole protocol, I’ll sketch the modifications to the certified mail protocol. Alice performs steps (1) through (4) using A as the message. Bob goes through similar steps using B as his message. Alice and Bob perform the oblivious transfer in step (9), decrypt the halves they can in step (10), and go through the iterations in steps (11) and (12). If they are concerned about Eve, they should encrypt their messages. Finally, both Alice and Bob decrypt the remaining halves of the message pairs and XOR any key pair to get the original message encryption key. This protocol allows Alice and Bob to exchange secrets simultaneously, but says nothing about the quality of the secrets exchanged. Alice could promise Bob the solution to the Minotaur’s labyrinth, but actually send him a map of Boston’s subway system. Bob will get whatever secret Alice sends him. Other protocols are [1286,195,991,1524,705,753,259,358,415]. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth)
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