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Unformatted text preview: oted in DEK-Info and in other fields that identify algorithms. For messages with symmetric key management (see Figure 24.4), the next field is “Originator-ID-Symmetric” with three subfields. The first subfield identifies the sender by a unique electronic mail address. The second subfield is optional and identifies the authority that issued the interchange key. The third is an optional Version/Expiration subfield. Continuing with the symmetric key-management case, each recipient has two fields: “Recipient-ID-Symmetric” and “Key-Info.” The “Recipient-ID-Symmetric” field has three subfields; these identify the receiver in the same way that “Originator-ID-Symmetric” identified the sender. The “Key-Info” field specifies the key-management parameters. This field has four subfields. The first subfield gives the algorithm used to encrypt the DEK. Since the key management in this message is symmetric, the sender and receiver have to share a common key. This is called the Interchange Key (IK), which is used to encrypt the DEK. The DEK can be either encrypted using DES in ECB (denoted by “DES-ECB”) or triple-DES (which would be denoted “DES-EDE”). The second subfield specifies the MIC algorithm. It can be either MD2 (denoted by “RSA-MD2”) or MD5 (which would be denoted “RSA-MD5”). The third subfield, the DEK, and the fourth field, the MIC, are both encrypted with the IK. 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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