Book Image

TLS Cryptography In-Depth

By : Dr. Paul Duplys, Dr. Roland Schmitz
Book Image

TLS Cryptography In-Depth

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)
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

20.4 Padding oracle attacks on TLS handshake

The term oracle originally comes from complexity theory, where it is used to compare the complexity of two computational problems P1,P2.

Suppose we can solve P1 efficiently (i.e., in polynomial time), if there is a polynomial-time algorithm A to solve P2. In this situation, we say that P1 polytime reduces to P2, or

P ≤ P 1 p 2

Informally, we can say that P2 is at least as hard as P1 ([117]). Now, the (hypothetical) algorithm A that can efficiently solve P2 is called an oracle for P2.

As an example, let P1 be the RSA-problem and P2 be the integer factorization problem. Recall from Chapter 7, Public-Key Cryptography, that the RSA problem means we have to find the plaintext m, given the ciphertext

c = me mod n

and the public key (e,n), while the integer factorization problems is to find the prime factors of a given integer.

Now it is easy to see that if we had an oracle that provides us with the prime factors of n in polynomial time, we could also solve the...