TLS/SSL is the most important and widely-used protocol for secure and encrypted communication, e.g. HTTPS. It offers more than just encryption. TLS also ensures data integrity and strong authentication with X.509 certificates. But it provides merely a false sense of security, if you use it wrong. Have you ever encountered ssl.SSLError: [SSL: CERTIFICATE em VERIFY/ em FAILED], while connecting to a server, but you didn’t understand what is going on? Are you running production code without TLS/SSL protection or with certificate validation disabled, because you couldn’t figure out how to make it work correctly? I’ll give you the rundown of the basic cryptographic building blocks, protocol handshake, inner structure of certificates, and PKI. You’ll learn about the best practices, debugging tools and tips how to diagnose TLS/SSL and how to deal with certificates.