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TLS Cryptography In-Depth

TLS Cryptography In-Depth

By : Dr. Paul Duplys, Dr. Roland Schmitz
4.8 (4)
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TLS Cryptography In-Depth

TLS Cryptography In-Depth

4.8 (4)
By: Dr. Paul Duplys, Dr. Roland Schmitz

Overview of this book

TLS is the most widely used cryptographic protocol today, enabling e-commerce, online banking, and secure online communication. Written by Dr. Paul Duplys, Security, Privacy & Safety Research Lead at Bosch, and Dr. Roland Schmitz, Internet Security Professor at Stuttgart Media University, this book will help you gain a deep understanding of how and why TLS works, how past attacks on TLS were possible, and how vulnerabilities that enabled them were addressed in the latest TLS version 1.3. By exploring the inner workings of TLS, you’ll be able to configure it and use it more securely. Starting with the basic concepts, you’ll be led step by step through the world of modern cryptography, guided by the TLS protocol. As you advance, you’ll be learning about the necessary mathematical concepts from scratch. Topics such as public-key cryptography based on elliptic curves will be explained with a view on real-world applications in TLS. With easy-to-understand concepts, you’ll find out how secret keys are generated and exchanged in TLS, and how they are used to creating a secure channel between a client and a server. By the end of this book, you’ll have the knowledge to configure TLS servers securely. Moreover, you’ll have gained a deep knowledge of the cryptographic primitives that make up TLS.
Table of Contents (30 chapters)
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1
Part I Getting Started
8
Part II Shaking Hands
16
Part III Off the Record
22
Part IV Bleeding Hearts and Biting Poodles
27
Bibliography
28
Index

12.3 KDFs in TLS

TLS uses four different functions to derive secrets: HKDF-Extract, HKDF-Expand, HKDF-Expand-Label, and Derive-Secret. All these functions are based on the Hashed Message Authentication Code (HMAC)-based Extract-and-Expand Key Derivation Function (HKDF) defined in RFC 5869 [104].

We will have much more to say on hash functions, message authentication codes, and key derivation function in Chapter 11, Hash Functions and Message Authentication Codes. For now, it is sufficient to treat HKDF as an abstract function, as shown in Figure 12.2. It takes keying material as input and returns one or more secret keys as output:

Figure 12.2: High-level view of the HKDF function

Figure 12.2: High-level view of the HKDF function

HKDF follows an extract-then-expand approach consisting of two logical stages. The rationale for this two-step approach is explained nicely in the introduction of [104]: ”In many applications, the input keying material is not necessarily distributed uniformly, and the attacker...

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