TLS and OpenSSL Programming

Every secure connection you have ever trusted — a login, a payment, a private message — depends on one protocol working correctly behind the scenes: TLS. And when it comes to actually implementing that protocol in real code, one library sits at the center of it all: OpenSSL. It runs the internet, yet most developers who use it every day have never opened its internals or truly understood what happens between a Client Hello and a finished handshake.

This book takes you from why secure communication matters all the way to writing your own working TLS client and server in C, using OpenSSL. You will generate real certificates, build your own certificate authority, and understand exactly what every function call is doing — not just how to copy it.

What's Inside

• The real threats TLS defends against, and how trust actually works online
• The full evolution of SSL to TLS 1.3, and why older versions are dangerous
• Symmetric and asymmetric encryption, hashing, and how they combine
• Building your own development Certificate Authority from scratch
• Programming with OpenSSL's EVP interface, BIO objects, and error handling
• Writing a complete TLS client and server in C, including mutual TLS
• Non-blocking I/O, ALPN, SNI, and event-driven architecture
• Real vulnerabilities explained in depth: Heartbleed, POODLE, downgrade attacks
• Cipher suite hardening, testing, and keeping up with CVEs

Who It's Meant For

This book is for you if:

• You write networked applications in C and want to stop treating TLS as a black box
• You are a backend or systems developer who needs to build secure clients or servers
• You have used OpenSSL's command line tool but never its programming API
• You want to understand certificates well enough to build your own authority, not just install one

You do not need prior cryptography experience. You do need to be comfortable writing and compiling C code.

Somewhere right now, a server is accepting a connection it should be rejecting, because a developer trusted OpenSSL without understanding it. Don't be that developer.

You already know TLS is important. The only question is whether you will keep guessing at it, or finally understand it completely — one handshake, one certificate, one line of code at a time.

Open the first chapter. The threats are real. So is the fix.