OpenSSL Cookbook 3rd Edition
The definitive guide to using OpenSSL from the command line. The last two chapters from our larger work, Bulletproof TLS and PKI. Written by Ivan Ristić.
Chapter 2. Testing TLS with OpenSSL
Due to the large number of protocol features and implementation quirks, it’s sometimes difficult to determine the exact configuration and features of secure servers. Although many tools exist for this purpose, it’s often difficult to know exactly how they work, and that sometimes makes it difficult to fully trust their results. Even though I spent years testing secure servers and have access to good tools, when I really want to understand what is going on, I resort to using OpenSSL and Wireshark. I am not saying that you should use OpenSSL for everyday testing; on the contrary, you should find an automated tool that you trust. For online testing, I recommend Hardenize;1 for offline work, consider testssl.sh.2 But when you really need to be certain of something, the only way is to get your hands dirty with OpenSSL.