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

And ticket lifetimes can be long eight hours is

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Unformatted text preview: 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) Go! Keyword 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 ----------- The Kerberos Model The basic Kerberos protocol was outlined in Section 3.3. In the Kerberos model, there are entities—clients and servers—sitting on the network. Clients can be users, but can also be independent software programs that need to do things: download files, send messages, access databases, access printers, obtain administrative privileges, whatever. Kerberos keeps a database of clients and their secret keys. For a human user, the secret key is an encrypted password. Network services requiring authentication, as well as clients who wish to use these services, register their secret key with Kerberos. Because Kerberos knows everyone’s secret key, it can create messages that convince one entity of another entity’s identity. Kerberos also creates session keys which are given to a client and a server (or to two clients) and no one else. A session key is used to encrypt messages between the two parties, after which it is destroyed. Kerberos uses DES for encryption. Kerberos Version 4 provided a nonstandard mode for authentication. This mode is weak: It fails to detect certain changes to the ciphertext (see Section 9.10). Kerberos Version 5 uses CBC mode. Figure 24.1 Kerberos authentication steps. How Kerberos Works This section discusses Kerberos Version 5. I will outline the differences between Version 4 and Version 5 further on. The Kerberos protocol is straightforward (see Figure 24.1). A client requests a ticket for a Ticket-Granting Service (TGS) from Kerberos. This ticket is sent to th...
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