“Security. You keep using that word. I do not think it means what you think it means.” Transport Layer Security, or TLS, makes ecommerce and online banking possible. It protects your passwords and your privacy. Let’s Encrypt transformed TLS from an expensive tool to a free one. TLS understanding and debugging is an essential sysadmin skill you must have. TLS Mastery takes you through: How TLS works - What TLS provides, and what it doesn’t - Wrapping unencrypted connections inside TLS - Assessing TLS configurations - The Automated Certificate Management Environment (ACME) protocol - Using Let’s Encrypt to automatically maintain TLS certificates - Online Certificate Status Protocol - Certificate Revocation - CAA, HSTS, and Certificate Transparency - Why you shouldn’t run your own CA, and how to do it anyway - and more! Learn TLS. Because we’re sysadmins, and lies do not become us. (The Beastie and Tux editions are identical other than cover art.)