applied cryptography - protocols, algorithms, and source code in c

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Unformatted text preview: ey and Message Broadcast There is no reason Alice can’t send the encrypted message to several people. In this example, Alice will send the encrypted message to Bob, Carol, and Dave: (1) Alice generates a random session key, K, and encrypts M using K. EK(M) (2) Alice gets Bob’s, Carol’s, and Dave’s public keys from the database. (3) Alice encrypts K with Bob’s public key, encrypts K with Carol’s public key, and then encrypts K with Dave’s public key. EB(K), EC(K), ED(K) (4) Alice broadcasts the encrypted message and all the encrypted keys to anybody who cares to receive it. EB(K), EC(K), ED(K), EK(M) (5) Only Bob, Carol, and Dave can decrypt the key, K, each using his or her private key. (6) Only Bob, Carol, and Dave can decrypt Alice’s message using K. This protocol can be implemented on a store-and-forward network. A central server can forward Alice’s message to Bob, Carol, and Dave along with their particular encrypted key. The server doesn’t have to be secure or trusted, since it will not be able to decrypt any of the messages. 3.2 Authentication When Alice logs into a host computer (or an automatic teller, or a telephone banking system, or any other type of terminal), how does the host know who she is? How does the host know she is not Eve trying to falsify Alice’s identity? Traditionally, passwords solve this problem. Alice enters her password, and the host confirms that it is correct. Both Alice and the host know this secret piece of knowledge and the host requests it from Alice every time she tries to log in. 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...
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