Showing posts with label basics. Show all posts
Showing posts with label basics. Show all posts

Tuesday, February 6, 2018

Web Basics - TLS/SSL https

We've been looking at the basics of the internet. If you've been wondering about how it all works or are interested in web programming, you need to know the things in this series of posts.

Today's topic is TLS - Transport Layer Security. The transport layer is essentially the connection itself. The web can be divided into a model with 4 layers - two of which we've been talking about: application (HTTP) and transport (TCP and UDP). The other two are "network goo" that we really don't interact with directly. They're important, don't get me wrong, just not important to this series.

As we saw in the last post on TCP, your information is flying around the world at light speed. With the right equipment and wrongful intent, someone looking to make a buck could easily tap into your data in transit (that's what we call it when its on the move) and sell your information (usually a big batch of information) to someone who will exploit it to steal money. That is, unless its scrambled before it's sent, then unscrambled on the receiving side. Enter encryption.


The newest big business buzz of currency - crypto-currency -  is all possible because of encryption (that's the crypto- part). It's built on the premise of uniquely encoding a "block-chain" and adding that to the existing chain to make it more valuable.

Encryption took off during WWII because radio transmissions were used by all of the militaries participating in that war. As we know, anyone can tune into radio frequencies and listen in (we can also listen to the radio transmissions of the cosmos - all the way back to the beginning of our universe!). Unless you can send a message in a way that only the receiver knows how to understand, you're toast! Every one of your moves will be known. It would be like playing chess while thinking your whole strategy out loud - you just can't win that way!

So they encoded the messages. With the messages encoded only those listeners with the decoding sequence would be able to understand. The U.S. got really good at cracking the code - which was one of the main reasons why the Allies won. Another was the perseverance and sacrifice of millions of lives of Russian soldiers. And the third was massive industrialization in the U.S. - both automated and manual industry.

History lesson aside, encryption has been used to protect privacy long before the internet. In modern times, it is used to protect data both in transit and at rest (in a database or on a hard-drive). TLS represents encryption in transit. SSL (Secure Sockets Layer) is the outdated predecessor to TLS - it's been deprecated by the authorities on internet security (the IETF*) as of June 2015.

TCP establishes a connection to communicate between two servers. TLS secures that connection by ensuring that all information transmitted through it is encrypted. The mechanisms for applying this encryption involve a certificate.


Certificates operate on a trust basis. There are companies that issue certificates (issuer). Those companies are called certificate authorities (CA) and your computer has their root certificate pre-installed. If you are securing your server, you would purchase a certificate from one of those companies. Your URL would then be registered to that certificate. You install the certificate on your web server. When https requests are made to your server, the requester gets a copy of your certificate. Your certificate is used to establish your authenticity. It's kind of like a driver's license, passport, or other form of id.

If you are the requestor, your browser will check the certificate's signature against the signature you have on the root certificate of the issuer. The domain in the URL also has to match the domain name on the certificate you receive from the server. If there is a match, the server has been Authenticated. Once the Authenticity of the server has been established, your computer and the server will generate an encryption key for the session. All of the information shared between you and server will be encrypted and decrypted on either end using that key.


This site is not https, but it's readonly - you don't exchange any sensitive information. Be careful when you have sites that require sending sensitive info and there is no https or it is mis-configured.
This site is configured for https.

This is how most of your information is secured on the internet today - provided you and the server are using https properly. Often we see misconfigurations on servers or servers that still support unencrypted http connections (http without TLS). There are also different versions of TLS which creates more configuration issues. The best you can do is pay attention to what your browser is telling you and think a bit about what kind of information you are willing to compromise - and remember some hackers are fairly sophisticated and can piece information together from multiple sources if you are a specific target (e.g. have a lot of money or power or work for a target organization/industry).

TLS works well to protect us when configured properly, but we should still remain vigilant. It can be easy to think that https solves all of our internet security problems, but there are other ways that hackers will try to pwn you.

Continued Learning

Encryption is a vast subject in and of itself. It comes in many flavors and varieties. There are one-way and two-way hashing algorithms, asymmetric and symmetric keys, private-private and private-public keys. And it all involves some pretty intense mathematics. Crypto-masters are a rare breed but the work they do is vital to our lifeblood - secure data!

IETF - Internet Task Force

OWASP is the go-to for internet security - they have great info about TLS

Some certificate authorities along with more details are listed on WikiPedia here:

Wikipedia has a lot on the subject of TLS in general:

Thursday, February 1, 2018

Web Basics - The Internet - TCP/IP

Yesterday, I posted about the basics of HTTP. Of all the message protocols, it is the most common one used on the web. If you are in IT or use the internet - basically if you have a pulse - and you are curious about how the internet works...or, I don't know...want to learn web programming, then you should also learn about TCP/IP. That's TCP over IP.

But First - UDP

Our journey though the internet begins at your computer. Let's imagine that it's only connected to one other computer through a wire. That's the simplest kind of network. Your computer is networked with another. Both computers have a network interface - which is a card or microchip or something on your computer that knows how to connect to the outside world. Think of this device as a telephone.

The telephone allows you to connect with another person at a distance. You can talk and listen. A network interface card (NIC) can send and receive data (as packets) over a network. Your computer talks into its NIC, and its NIC uses the network to talk to other computers...just like your phone!

With the 2 computer network, the NICs in both computers will need to know how to exchange data. The simplest way is to just send the data to the other side. This is called UDP (User Datagram Protocol). This would work well in a simple network like two computers over a single wire. But lets imagine those computers are very far apart - one in New York and another in Los Angeles. And let's imagine they're connected over a telephone wire. And let's imagine they're sending data over that wire.


Since those old phone wires weren't designed for data - they were designed for talking - some of the data might get lost along the way. Luckily there's TCP (Transmission Control Protocol). TCP is a network protocol where the receiver tells the sender that it got the message and how much of the message it got. If it didn't get all of it, the sender sends the missing pieces. Sending this way takes longer, but it makes sure the right message was received.

Protocols are there to make sure we get the right message. They exist in everyday life, we call them manners - the pleases and thank you that ensure clear communications. The army has protocols for sending messages over radio. Imagine if a platoon heard the wrong thing over the radio - it could march straight into enemy hands! There are even communications protocols for Presidents of the United States of America! Those protocols keep the people of the world informed without going into a frenzied panic - or marching straight into enemy hands!


The internet is a wide network - it spans the globe. Even into near-earth orbit. The ISS and its occupants tweet from the space station! This web of computers is very complex - it has smaller networks within and it has branched off networks. It exists over wires and radio signals. Each connection has an address. The address schema (a schema is a way to organize something) is called IP. Don't confuse this IP with Intellectual Property - also technology related. This IP is Internet Protocol.

IP is how the systems that run the network know how to find your computer. It's how your computer knows how to find It's how your computer sometimes knows how to find your printer...and sometimes when it doesn't.

Your computer can use IP to talk to itself. There's a special address for this: there's also a special name for it (called an alias): localhost. Your computer is also configured with an IP address for the internet - the network gateway. That IP address is where your NIC sends all of your requests that are bound for the internet. There could be other devices connected to your network - like your printer, other computers, servers, storage, your home, TV, etc. Those have their own IP address on your network. They can communicate within your internal network using that IP address. They can also communicate on the internet through the same internet gateway as your computer!


Along with the IP address, computers listen for incoming calls on Ports. Ports allow one computer to have many "conversations" at the same time. Ports can be numbered 0 to 65535 (that's 16-bits unsigned). Some common ports are:
80 - http
443 - https
There are many other common ports for things like ftp, ssh, and mail.
When your NIC sends a message, it opens up a port. It uses that port to send and receive messages to and from the other side.
What the receiver sees is your internet gateway - your router. Actually the last router in your network before your message gets sent into the great beyond of the internet. After that, it gets passed around the internet routers to your destination - if it can be found.

Continued Learning

The internet may be a fascinating and complex web of networks that span the globe, but almost every bit of it operates on a few core technologies. TCP/IP is how connections exchange data over a not-so-reliable network and HTTP is how two computers know how to interpret what's sent over the networks.

There is a glaring issue with all of this - if all this data is flying over the network and it really is possible to tap into those messages, how do we keep others from prying in on our messages? The answer is encryption! TSL to be specific - that's https to you. Well see how that works and how your computer knows the IP addresses of websites in upcoming posts in this series.

More information on UDP, TCP and IP is available in Wikipedia:

Wednesday, January 31, 2018

Web Basics - HTTP

I occasionally get asked to mentor by those interested in learning to code. My response and approach will vary depending on the situation. I've done this in a pair programming context, over the wire, and by simply offering advice from time to time. I enjoy mentoring, especially when the mentee shows commitment and drive. This blog was originally started on the basis of providing mentorship to my readers. With that, let me get back to my roots for this post.

If you want to learn web programming, you should probably start with the basics - HTTP. If you are mildly in IT (or have a pulse) you should understand the HTTP protocol to some extent. I'll start you on your journey to understanding this lifeblood of the internet.

http logo

What is it?

HTTP is a protocol for communication between two computers. In fact, it is an acronym for Hypertext Transfer Protocol. In HTTP, there is a request sent by a sender (client) to a receiver (server). And the server should send back a response.

The request has two parts, the headers and the body. The headers has information about the request and the body is where you put data you want to send to the server.


There are different types of requests. Each type uses a different HTTP Verb (also called Method). Verbs are an important part of HTTP. They tell the server what you (the client) would like to do.

Verbs can be split into two categories - queries and commands. The most common are GET and POST.

GET is used to get a web page or some data. It is a query.

POST is widely used to do something, such as send an email or submit an order form. It is a command.

PUT is another command. PUT is meant for updating something. You might POST a file and later need to update the file's contents so you would PUT an update. There's also a DELETE command.

Another common query is OPTIONS. This is a request foe the server to tell you what you can do. Often servers will only accept certain verbs. OPTIONS can tell you which ones.

There are many others verbs. You can find more at the official w3 site at the end of this post.


When a request is made, the server can respond. One thing included in a response is a response code. A response code has 3 digits and ranges from 100-599. Each hundred has a different meaning. 100's are reserved, 200 level is success, 300 is content changed, 400 is a client error, 500 is server error.

Some common codes are 200 - OK, 204 - OK with no data returned, 302 - temporary redirect, 404 - not found, 500 - server error.

In addition to the response code, there may be other headers and content returned from the server. Some of the headers describe the content. For example, Content-Type and Content-Length. These tell your client (browser for instance) how to handle the content in the response. Should it display the content in a browser? Save it to a file? Open it in a plugin?

The Network

When we use the web, we are primarily using HTTP over TCP/IP (your next topic :) ). TCP is the transport mechanism/protocol (how) and IP is the addressing schema (where).

When you send an HTTP request, the server will need to know where and how to respond. Some of that information is in the request headers. And some of it is handled by the networking systems (everything that moves your request over the internet, from your client to the server).

Continued Learning

Most programming languages have HTTP clients that you can use is your programs. This is so common nowadays, that you cannot do programming for long without using an HTTP client. And when you do web programming, its at the core!

For example, web apps you use all the time use AJAX (Asynchronous JavaScript and XML) to make HTTP requests using the JavaScript code that the app runs in your browser! These requests do all sorts of things like fetch data for part of the page and send data to the server. When you see part of page spinning while it loads, that's usually the app waiting for a server to respond to an AJAX request!

You can find version 1.1 of the official protocol at rfc2616 

Learning HTTP is the start of your journey to understanding how the internet works. We'll explore TCP/IP in the future...its another core technology behind what the world runs on today.

Tuesday, January 19, 2016

JavaScript Logical NOT Operator

There are some interesting things to note about the logical NOT operator in JavaScript. What I've found is that if you aren't aware of these, you may find yourself coding up some defects without knowing it. Also, being aware of some important usages may improve your code by reducing complexity.

If you are coming from a strongly typed language or just getting started in JavaScript from ground zero, you may interested to know that the NOT operator (!) has different behaviors depending on the value type that the variable represents at runtime.

For example you may have a statement:
var x = !y;
while x will be assigned a boolean value when this statement is executed, y could be any type (string, number, object, NaN, undefined, null, function) and how each is negated depends on the type.

Plus the process of negation involves first converting the value of the variable to boolean, then negating the result.

When converting to boolean, the following types are always false - null, undefined, NaN.

These are always true - object, function.

But string and number depend on the value - 0 is false and an empty string "" or '' is always false, while any other number or string is true.

An array is an object so it is always true even if it is empty.

{} is also true.

How much fun is that!?

Coming from C#, it would be great to write:


instead of


But when you cam expect x to be of any type, it would get much more complex.

In js, if you are in a position where you cannot use a guard, but need some logic to check for a value you can do the following:

//do something useful

The underlying definition according to ecma 262 v5.1 of the ! is defined as negation of ToBoolean(GelValue(x))

where ToBoolean is defined here

and GetValue, which is more complex, is

Even though the abstract ToBoolean does not cover off on function type or array type (both object types) I listed those above for more clarity.

Since there is no ToBoolean in the JavaScript language, and there is a Boolean function (not to be confused with the constructor [new Boolean]), you'd be better of writing Boolean(x) instead of !!x for sake of clarity AND efficiency. Why have the runtime perform GetValue and ToBoolean twice?

The ecma standard defines the Boolean(x) function as simply calling the abstract ToBoolean(value)