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 RSA programmatically

In this section, we are going to develop a small rsa-decrypt program, so that we can learn how to do RSA decryption.

Our program will take three command-line arguments similar to those taken by rsa-encrypt, but note that the third argument is the name of a file containing a keypair, not just a public key:

  1. The input filename
  2. The output filename
  3. The RSA keypair filename

Of course, now the input file is expected to contain ciphertext, which will be decrypted, and the resulting plaintext will be written into the output file.

Our high-level implementation plan for rsa-decrypt will contain the sequence of actions opposite to that of rsa-encrypt, listed as follows:

  1. Load an RSA keypair from the RSA keypair file. We need an RSA private key for decryption; a public key will not be enough.
  2. Create the EVP_PKEY context from the key.
  3. Initialize the EVP_PKEY context for decryption and set the OAEP padding mode...