Episode 99 - TLS

 

TLS which stands for transport layer security is a protocol for securing communication between client and server. Specifically for HTTPS. Thats what the S is stands for. 

In this video, we will learnq how insecure vanilla HTTP works, HTTPS, then we will learn how HTTPS is possible via the transport layer security and finally we will talk about the improvements in 1.3 that was published August 2018. 

Vanilla HTTP

HTTPS 

TLS 1.2 handshake

TLS 1.3 enhancements

Vanilla HTTP 

Before we discuss TLS, HTTPS or anything else lets go through how HTTP request work. You can type in the browser www.husseinnasser.com , the OSI magic kicks in, client figures out the IP address of husseinnasser.com by calling the DNS which uses UDP. Then HTTP application layer makes a GET / request passes in the IP address and port 80 (default for insecure http). This creates an underlying TCP connection. GET / string among other stuff into the packet and send it over. TCP does its thing server receives GET / calls the appropriate process at the backend which could be just return index.html sets content type text/html and sends back big response for client. All of this obviously is plain text no encryption any kind and if you watched the OSI video we made you can tell that people can sniff/snoop packets and get packets they aren’t supposed to get

HTTPS

Works by negotiating a symmetric key so they can both secure messages. Watch the video we did on encryption. Before we jump to GET request there must be a handshake 🤝 that must occur between the client and server. The tricky part is exchanging that key. Same thing as above except port is 443 instead of 80. Remember once we lose the TCP connection we will have to renegotiate the key. But beauty of this is HTTP is stateless so it remains working just fine. 

Tls handshake 🤝 

The original TLS handshake involves 4 roundtrips. A client hello which the client includes which encryption algorithms it supports (Both symmteric and asymmetric). The server receives the request then replies back with the server certificate which includes the server public key and also the encryptions that they will change to. The client receives the server hello, generates the premaster key, encrypts it with the server’s public key then send it over. The Server decrypts the message, gets the premaster generates the symmetric key finally tells the client that we are good to go. 

Tls 1.3 

TLS 1.3 involves much shorter and much secure communication using only deffie hellman as key exchange and just two round trips.