HTTP/HTTPS — Part 3: Security, Performance & Modern Protocols

What is this?

We've read the postcard (Part 1) and dissected its anatomy (Part 2). Now we ask the two questions that separate "I know HTTP" from "I can design fast, secure systems on HTTP": How do we seal the envelope so nobody can read or forge it? and Why was HTTP/1.1 slow, and what exactly did HTTP/2 and HTTP/3 do to fix it?

The headline drama of this part is a villain named head-of-line blocking — a traffic jam that shows up at two different layers, and the story of HTTP/2 and HTTP/3 is really the story of defeating it twice. Get this one concept crisp and you can answer the most common HTTP interview question with confidence.

The one-line idea: HTTPS seals each postcard in a verified, encrypted envelope (TLS), and the leap from HTTP/1.1 → /2 → /3 is one long war against head-of-line blocking — first at the application layer, then at the transport layer.

Let's earn both halves.