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

How to decrypt with AES programmatically

In this section, we are going to develop the decrypt program that can encrypt a file encrypted by the encrypt program.

Our decryption program will be similar to the encryption program and will also take three command-line arguments:

  1. Input file name
  2. Output file name
  3. Encryption key, hex-encoded

This time, the input file is the encrypted file created by the preceding encrypt program.

Let’s make a high-level plan, similar to how we did before:

  1. Read the IV from the input file.
  2. Initialize decryption.
  3. Decrypt chunk by chunk, reading plaintext chunks from the input file and writing the resulting plaintext chunks into the output file.
  4. Read the authentication tag from the input file and set it into the cipher context.
  5. Finalize decryption.

As we can see, the decryption plan is very similar to the encryption plan – initalize, process, and finalize. Let’s see how it is implemented...