Book Image

Demystifying Cryptography with OpenSSL 3.0

By : Alexei Khlebnikov
Book Image

Demystifying Cryptography with OpenSSL 3.0

By: Alexei Khlebnikov

Overview of this book

Security and networking are essential features of software today. The modern internet is full of worms, Trojan horses, men-in-the-middle, and other threats. This is why maintaining security is more important than ever. OpenSSL is one of the most widely used and essential open source projects on the internet for this purpose. If you are a software developer, system administrator, network security engineer, or DevOps specialist, you’ve probably stumbled upon this toolset in the past – but how do you make the most out of it? With the help of this book, you will learn the most important features of OpenSSL, and gain insight into its full potential. This book contains step-by-step explanations of essential cryptography and network security concepts, as well as practical examples illustrating the usage of those concepts. You’ll start by learning the basics, such as how to perform symmetric encryption and calculate message digests. Next, you will discover more about cryptography: MAC and HMAC, public and private keys, and digital signatures. As you progress, you will explore best practices for using X.509 certificates, public key infrastructure, and TLS connections. By the end of this book, you’ll be able to use the most popular features of OpenSSL, allowing you to implement cryptography and TLS in your applications and network infrastructure.
Table of Contents (20 chapters)
Part 1: Introduction
Part 2: Symmetric Cryptography
Part 3: Asymmetric Cryptography and Certificates
Part 4: TLS Connections and Secure Communication
Part 5: Running a Mini-CA

Custom verification of peer certificates in C programs

Every TLS connection is established between two peers: the client and the server. Each peer can request and verify the other peer’s certificate. In real life, the server certificate is almost always verified during the TLS handshake. Before TLS 1.3, the TLS protocol supported anonymous ciphers, which allowed the server to operate without a certificate. In practice, those anonymous ciphers were rarely used and were forbidden by default. So, in practice, a certificate for TLS has always been required. On the contrary, TLS client certificates are seldom used. However, verifying a client certificate in an application using OpenSSL is very similar to verifying a server certificate. Therefore, it makes sense to talk about peer certificate verification instead of limiting ourselves to server certificate verification. We will verify the server certificate in most of our code examples. More information about verifying client certificates...