The Backend Engineering Show with Hussein Nasser

Encryption is the process of scrambling data to protect personal files, secure communication, hide identities and much more. 

In this video we will learn about the different type of encryptions we will talk about symmetric encryption, asymmetrical encryption, where they are used for and the pros and cons of each one. 

Symmetric encryption 

Might as well just call it classic encryption I would argue and i think this is the first encryption known to us. I have some thing I dont want anyone to see I use a lock key to lock it. Only I can open it unless I have a lock. 

The same key you use to encrypt is the same key to Decrypt. 

Examples

Examples of popular symmetric-key algorithms include 

AES

Twofish

Serpent 

DES

Twofish, Serpent, AES (Rijndael), Blowfish 

CAST5, Kuznyechik, RC4, DES, 3DES, Skipjack, Safer+/++ (Bluetooth), and IDEA 

Asymmetrical encryptions 

We had symmetric encryptions for a long time, then internet came and networking and we needed to encrypt messages going back and forth. We said cool lets use AES. Then we said wait a second.. the other computer doesnt really have my key so we need to encrypt it.. 

Also called Public key encryption 

1977 

Rivest–Shamir–Adleman (RSA) 

Bandwidth explained from software engineer point of view

Bandwidth is measured by how many bits a device is allowed to send/receive in a second. It ranges from your internal network starting from network card all the way to your ISP Internet speed. In this video we will discuss the definition of bandwidth upload vs download speed, the different usage patterns for normal web browsing, streaming, gaming, media production and cloud web servers etc and finally we will show an example of the whole thing.

When your ISP gives you 80Mbs download/1Mbs upload bandwidth, this means 80 mega bits download which means your router (and all your devices) can receive (download) a total of 80 mega bits in a second at a time, and it can send (upload) 1 mega bit in a second. With your ISP can you pick and choose your plan that fits your usage.

Usage patterns

Web Browsing

Most people download far more than they upload. So the download bandwidth matter more than upload bandwidth. For simple web browsing the download incoming traffic is slightly larger than the outgoing one. You make a GET request to pull index.html, you get back the html content. Yeah there are some images but still not much of incoming. 

Streaming

Think about it when you watch a movie in Netflix you make a small request usually in few hundred bytes. But the data you receive (download) is huge. So streaming is constant large incoming data. While still outgoing traffic is minimum.

Gaming

The bandwidth for gamers is really interesting specially who play online and it really depends on the game. a game might use the server authoritative model, where all the online players send their inputs and receive the final game state changes from the server. In that case the there is a constant upload, still minor but the download bandwidth is larger since state is usually bigger. Games can also use the lock state model or the client authoritative model, where all the clients send their inputs the server and the server just send back all the input from all players back to everyone so everyone calculate the game state locally. So in this efficient model, both the upload and download is quite small and its good for countries with low bandwidth. 

Some games require cloud saving which means upload speed is recommended. 

In general latency is much better in gaming.

Media production 

Youtuber and you make 5 videos a day so you need to upload alot of data to the youtube server. So upload speed really matter, and download also matter because you will also consume alot.

Web servers

Netflix (which is hosted in amazon) they upload data far more than they download. So their upload bandwidth is more than their download bandwidth. All those movies and tv shows pushed to consumers.

Example

Assume you have bandwidth of 80mb/s download speed (which is 10 Mega bytes per second) and 1mb/s upload (which is 125 KB per second). You are connected to a web server which has 80Gb/s upload and 80Gb/s download bandwidth, which is 10Gigabyte per second. Lets say you want to download a 60GB file or movie (no streaming). It will take the server 6 seconds to upload that file however it will take you 1.7 hours to download it. Your ISP That is not entirely true though for TCP, which implement congestion control. UDP does not implement congestion control. 

Denial of Service attacks

Dos attacks (denial of service) are type of attack on a server to prevent users from consuming a particular service, usually this is an HTTP web server. This could happen by either saturating the bandwidth of the pipe going to the server or by bringing the server down to its knees so it stops taking requests all together. In this video we will learn about 3 different types of DOS attacks and explain each one by example. 

Bandwidth based DOS 2:15

Max connections based DOS 10:13

Another type of denial of service attack is by somehow force the server to reach its max connections. The web server usually sets a maximum number of tcp connections so that it doesn’t run out of memory. an attacker can perform a DOS attack to force the server to reach its max connection. once it does, it wont accept any more connections thus deny service of future requests. However it is not easy, web servers have good preventive measures to minimize unnecessary tcp connections. So you cannot just establish a connection and ghost the server. This isn’t your ex boyfriend. Server has good timeouts for connections that are idle, terminated or potentially harmful. However one possible attack is to establish a connection but send the data slowly so when the server tries to timeout it immediately reset the timeout and keep the connection alive! Assuming the max tcp connection is 200, Run your script 200 times and you just created 200 connections to the server so no new connection can connect.   

Vulnerability based DOS 16:30 

 TCP and UDP are communication protocols that allows us to send and receive data in a network. We have both for a reason since each has its advantages and disadvantages. In this video we will talk about two protocols, pros and cons of each one and will write tcp and udp server with nodejs showing you these in ACTION. coming up

Code! 

https://github.com/hnasr/javascript_playground/tree/master/tcp

Jump Codes 🏷 

tcp pros cons(4:12)

Tcp demo (19:00)

Udp pros cons (24:25)

Udp demo (31:25)

Summary (35:40)

Explain TCP 

Pros: 

acknolwedgment, 

garenteed delivery, 

connection based

congestion control

ordered packets 

Cons

Larger packets

More bandwidth since more headers. 

Slower (because of retransmission) 

stateful once connection is lost its lost, cannot resume it.  

TCP Example (Code)

telnet 127.0.0.1 8080

Explain UDP

Pros

Statless, 

Less bandwidth 

smaller packets

Faster to transmit 

Cons

no ack, 

no garenteed delivery, 

no congestion control

no ordered packets 

UDP client

echo "foo" | nc -w1 -u 127.0.0.1 41234

2:24 osi model tag 

14:20 stateful. S stateless video 

Get and POST are the most popular http methods used on the web. Each carries its own differences and properties. It can confusing to get to choose when to use POST over GET. In this podcast we will explain the differences, use cases and the benefits of using GET and POST. 

Attribute Rules are scripts that can be authored and placed in the geodatabase to ensure data integrity lets discuss them. 

In this episode we will talk about the difference between public ip and private ip address and casually talk about routers, modems, LAN,  WAN and port forwarding.