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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

18.3 ChaCha20

ChaCha20 is a fast block cipher defined in RFC 8439 ChaCha20 and Poly1305 for IETF Protocols [131]. The number 20 in the cipher’s name refers to a specific ChaCha variant that uses 20 rounds or, equivalently, 80 quarter rounds to compute the ciphertext.

ChaCha20’s state is stored in a 4 by 4 matrix consisting of 32-bit unsigned integers. The state representation using a matrix explains why some ChaCha rounds are referred to as column rounds while others are referred to as diagonal rounds:


0   1   2   3
4   5   6   7
8   9  10  11
12  13  14  15

18.3.1 ChaCha20 quarter round

The ChaCha20 algorithm’s basic operation is the so-called quarter round. The quarter round operates on four elements of the ChaCha20 state, hence the name. The four elements are denoted as a, b, c, and d and the quarter round is defined as:

 32 a = a + b (mod 2 ) d = d ⊕ a d = d ≪ 16 c = c+ d (mod 232) b = b⊕ c b = b ≪ 12 a = a + b (mod 232) d = d ⊕ a d = d ≪ 8 c = c+ d (mod 232) b = b⊕ c b = b ≪ 7

where ≪ n denotes the rotate left by n bits operation, for example:

0x7998bfda ≪ 7 = 0xcc5fed3c

The ChaCha20 quarter round is illustrated in Figure&...

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