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Cryptography Engineering

Cryptography Engineering

By : Niels Ferguson‚ÄØ, Tadayoshi Kohno, Bruce Schneier
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Cryptography Engineering

Cryptography Engineering

By: Niels Ferguson‚ÄØ, Tadayoshi Kohno, Bruce Schneier

Overview of this book

Cryptography is vital to keeping information safe, in an era when the formula to do so becomes more and more challenging. Written by a team of world-renowned cryptography experts, this essential guide is the definitive introduction to all major areas of cryptography: message security, key negotiation, and key management. You'll learn how to think like a cryptographer. You'll discover techniques for building cryptography into products from the start and you'll examine the many technical changes in the field. After a basic overview of cryptography and what it means today, this indispensable resource covers such topics as block ciphers, block modes, hash functions, encryption modes, message authentication codes, implementation issues, negotiation protocols, and more. Helpful examples and hands-on exercises enhance your understanding of the multi-faceted field of cryptography.
Table of Contents (9 chapters)
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Chapter 16
The Clock

Before we begin the detailed discussion of key management in the next chapter, we need to discuss one more primitive function: the clock. At first glance, this is a decidedly un-cryptographic primitive, but because the current time is often used in cryptographic systems, we need a reliable clock.

16.1 Uses for a Clock

There are several cryptographic uses for a clock. Key management functions are often linked to deadlines. The current time can provide both a unique value and a complete ordering of events. We will discuss each of these uses in more detail.

16.1.1 Expiration

In many situations, we want to limit the validity period of a document. In the real world, we often see limited validity periods too. Checks, open airline tickets, vouchers, coupons, and even copyrights all have limited validity periods. The standard way to limit the validity period of a digital document is to include the expiration time in the document itself. But to check whether a document...

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Cryptography Engineering
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