Daniel Allen Deutsch

Web Developer


SSL and HTTPS: Part I

a comprehensive (sort of) beginners guide

January 30, 2016

A month or two ago, an SSL certificate expired for a website we use internally. It just so happened to be the day before my boss was leaving for a vacation, so he asked me if I could update it the next day.

"I don't know anything about SSL," I said. "But if you think it's something I can do—then sure."

"It's easy. Just buy a new certificate and follow the instructions."

Like everything I've ever done with computers or the internet, it wasn't easy. And what should have taken 1 hour took about 4. But it was true—all I needed to do way pay $10 and follow some instructions. To my great amazement, it actually worked with my first attempt changing code on the server. I patted myself on the back and called it a day.

When people went to the page, it no longer said "Your connection is not private". I fixed it, and it worked.

A few weeks later I had to do it again. (We really need to do a better job of renewing these in advance.) It was only this time that I realized I had no idea what'd I'd actually done the first time. Like, um, what it SSL and how is it related to HTTPS?

I ended up down a few rabbit holes, and this is what I learned. We'll start at the beginning.

The Setup

Let's say you are a dentist, and you want to make a website. Cool!

You write up some HTML and CSS on your local computer. The page includes the hours your office is open, why you are an awesome dentist, and the phone number. It has lots of pictures and it looks awesome.

Okay—now it's time to get this on the internet, so that people can visit it. You do some research and Amazon EC2 seems like a good option for hosting. (It isn't, because it's expensive and complicated for what you need. But it allows full control, so it will serve nicely throughout the example.)

Wait... what exactly is a server? Well, it's really just a computer that is connected to the internet. And if it serves web pages, it grants public access that allows everyone who pings it to see some of its saved files. It's just like your computer, except that someone else owns it, it's always on, always connected to the internet, and probably doesn't have a monitor.

(This skips over the fact of virtualization. Mostly because I don't know much about it. But the truth is that someone like AWS really has a big computer that they can make act like 100 little computers through virtualization. But no understanding of that is necessary for this.)

Once you have a server, you copy over your HTML and CSS files from your computer to your public server. Then, just like that, you have a website anyone can access. You did it!

Right now, your website will only be accessible through its IP address. An IP address is just a unique identifier of that computer on the internet. Your personal computer has an IP address too, because it connects to the internet. You just don't have a reason to use it.

Because you don't want people to need to type in '' in the url bar to get to your wonderful site, you purchase the domain name 'greatdentist.com'. You then configure that name to point to your IP address by setting up the DNS. (I apologize for glossing over this, but I don't want to stray too far.)

Ta-da! Awesome job. Now people go to 'http://greatdentist.com' and they see the neat site you wrote in HTML and CSS on your home computer.

All is well in the world. But... where do SSL and HTTPS come in?

How the Internet Works (sort-of)

When you surf the web, you are using HTTP protocol. (There are a few other protocols, like FTP for files and SMTP for email, but we're just going to discuss HTTP.) When you request a page over HTTP, all of the information is sent over wires as plain text.

So, if you go to nytimes.com, you will hit a server managed by The New York Times. They will pass to your computer over cables the HTML and CSS that make up that page as plain text.

What are the implications of this? It means that if you are sitting at Starbucks, everyone else connected to the same network can see everything you are doing. The page you are looking at, the email you just sent, and the password you entered are all visible. And that's because you are passing everything back and forth as plain text.

(I don't know the details about this process. But I do know that it's fairly easy to do. Here is an example.)

So for my website as a dentist, this is not a problem. Everything on the site is public, no one is entering passwords, etc. Therefore, this is of no concern to me; I am in the clear.

Until I decide to get fancy. The website is working so well, that I'm going to add a form for patients to enter their personal information. You know when you go to the dentist and you have to fill out a bunch of paperwork before the appointment? Well that sucks, so we're going to move it online so people can do it in advance.

But... uh oh. Now there is sensitive information being passed through my website. It is important that a customer's social security number cannot be intercepted. Therefore, the information will need to be encrypted. And this is where HTTPS comes in.

Intro to HTTPS

HTTPS is similar to HTTP, except that it is secure. It is secure because it encypts the data being sent back and forth across the wire, so that is in no longer plain text.

Encryption is an enormous topic and well outside the scope of this post. But if you log into a website with the password 'superman', it will encrypt that string and send it as '$2a$10$YOS1xln9uNZKpJSoolsNWuCp.K/fLtZ3Qp75H3EGbrg'. When the message make it to the server, it knows how to un-encrypt everything it was sent.

Thus, the server and the client interact in the same way. But if the message is intercepted on the way, it will not be readable.

The server can decrypt the message, but the guy sitting in Starbucks cannot. This is not because the guy sitting in Starbucks is stupid, but because he does not have the secret code that allows the text to be un-encrypted.

Next Post

This begs two questions. 1. Why isn't everything done over HTTPS. 2. Where does SSL fit in? We'll cover that in the second half of this two-part post.

Have anything to say? Questions or feedback? Tweet at me @cmmn_nighthawk!