The SSLTLS handshake process
As it goes with all handshakes, the SSL/TLS Handshake is where it all starts. The SSL/TLS handshake involves a series of steps through which both the parties — client and server, validate each other and start communicating through the secure SSL/TLS tunnel.
The reason it’s called a handshake is that it’s when two parties — client and server come across each other for the first time. The handshake involves a number of steps that start from validating the identity of the other party and concludes with the generation of a common key — secret key if you may call it.
Fundamentally, the SSL handshake is nothing but a conversation between two parties (client and server) wanting to accomplish the same purpose — securing the communication with the help of symmetric encryption.
Imagine this handshake process as a dialog between the two.
Let’s see how it goes.
Client: “Hello there. I want to establish secure communication between the two of us. Here are my cipher suits and compatible SSL/TLS version.”
Server: “Hello Client. I have checked your cipher suits and SSL/TLS version. I think we’re good to go ahead. Here are my certificate file and my public key. Check ’em out.”
Client: “Let me verify your certificate. (After a while) Okay, it seems fine, but I need to verify your private key. What I’ll do is, I will generate and encrypt a pre-master (shared secret key) key using your public key. Decrypt it using your private key and we’ll use thing master key to encrypt and decrypt the information”
[Now that both the parties know who they’re talking to, the information transferred between them will be secured using the master-key. Keep in mind that once the verification part is over, the encryption takes place through the master-key only. This is symmetric encryption.]
Client: “I’m sending you this sample message to verify that our master-key works. Send me the decrypted version of this message. If it works, our data is in safe hands.”
Server: “Yeah, it works. I think we’ve accomplished what we were looking for.”