Unformatted text preview: encrypted messages to each other for the past year. Eve has been collecting them all, but she cannot decrypt any of them. Finally, the secret police tire of all this unreadable ciphertext and arrest the pair. “Give us your encryption keys,” they demand. Alice and Bob refuse, but then they notice the thumbscrews. What can they do? Wouldn’t it be nice to be able to encrypt a file such that there are two possible decryptions, each with a different key. Alice could encrypt a real message to Bob in one of the keys and some innocuous message in the other key. If Alice were caught, she could surrender the key to the innocuous message and keep the real key secret. The easiest way to do this is with one-time pads. Let P be the plaintext, D the dummy plaintext, C the ciphertext, K the real key, and K’ the dummy key. Alice encrypts P: P•K=C Alice and Bob share K, so Bob can decrypt C: C•K=P If the secret police ever force them to surrender their key, they don’t surrender K, but instead surrender: K’ = C • D The police then recover the dummy plaintext: C • K’ = D 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)
Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book:
Go! Previous Table of Contents Next
----------- Since these are one-time pads and K is completely random, there is no way to prove that K’ was not the real key. To make matters more convincing, Alice and Bob should concoct some mildly incriminating dummy messages to take the place of the really incriminating real messages. A pair of Israeli spies once did this. Alice could take P and encrypt it with her favorite algorithm and key K to get C. Then she takes C and XORs it with some piece of mundane plaintext—Pride and Prejudice fo...
View Full Document
- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips