How does SSL TLS work step by step?

If we take the most used example in a browser (TLS1.2) it goes like this: Client sends hello message. Server responds with handshake messages (encrypted). The handshaking consists of two phases Key exchange;. Change Cipher Spec. Client and server agree to use key exchange and key exchange is done as per agreed protocol by both parties. If everything is ok, client encrypts some plaintext then sends them to server. Server decrypts the first bytes (which are usually from MAC or Finished), then it extracts the same content it gets when it did the handshake phase #1 (ie, client has provided handshake information and it is encrypted with keys that server just agreed to use). This way all the conversation up to Finished remains secret.

After client receives encrypted content, server gives an opportunity to send some data. Client answers "OK" indicating how much data to send. Finally, finished message is sent by both clients and each one of them confirms success of their handshake, encrypted messages and content.

At this point, both parties have exchanged everything - symmetric keys and encrypted data. In SSL/TLS, these phases are described in great detail. In case of TLS you need at least three phases (key exchange, negotiation and exchange of actual data) but there are many variants what happens before each of the phases, and before the handshake is completed there is so much more phases going on before the phase #1 happens.

Now if we skip over the handshake mechanism, after phase #1 we have an agreement on using key exchange as well as key exchange type. Then encryption is performed, which is not really interesting for our purposes, it is just padding. Padding is something that makes sure that the actual content is not longer than cipher's block-size, so we will not write cipher text too long, and that every block starts from zero position and doesn't contain its initial padding. This means that even if a client does not care to use some padding (if he thinks his ciphertext contains too much data and padding was added to reduce that) then it still works ok.

So the client provides initial handshake parameters (this includes length of content to send), it calculates the amount of padding it needs to add to make sure the real data fits into message.

How does TLS work on a website?

(and in browsers)

TL;DR: TLS, as we know it, only protects traffic over the internet and only when a web server is involved. However, HTTPS-to-TLS encryption over a Wi-Fi hotspot can also be used to protect data sent from within an app on a mobile device. As long as the device supports hardware-accelerated encryption and the browser is configured for it, data is encrypted from the web, then unencrypted at your local Wi-Fi network.

This post assumes some knowledge of how websites work and that you already have a secure Wi-Fi network setup, that uses WPA2/EAP-TTLS security. This post doesn't contain any new tricks. It's all stuff that is very well known and has been around for some time. But it might not be as well-known to some people, so hopefully this helps!

So what about web sites? Most web sites have a public area on their site, where users can send sensitive information such as passwords or credit card numbers, for example, over the web. You can think of it like this: the web site acts as a publisher and we are the readers. When I visit a website, the web site is protected by SSL encryption, and then sends my information over the internet.

But what about using websites while we are not online? Well, one way websites work is with a so-called mixed model, ie they both protect data during transmission to the web site and transmit the data to a web server after you're connected to the website. When you first connect to a website, your browser does the following: Tells the server the identity of your device. Tells the server you are requesting data. Then asks for your password. This forces the site to store your password in a form which it doesn't share with anyone else, which is a requirement under the US Federal Information Processing Standards (FIPS).

Then makes a request for the information. (Remember this isn't an HTTP request, but part of the mixed model.)

The site sends the information to the web server.

How does TLS work vs SSL?

What is the difference?

TL;DR: TLS (the transport layer security protocol) offers security at the application level, whereas SSL (the secure sockets layer protocol) offers security at the operating system level. TLS also provides privacy and integrity of messages, whereas SSL only provides privacy.

This post describes how to connect to a web server with TLS and SSL. You may be asking yourself: Why would I ever want to use TLS or SSL when my own operating system already provides security? Well, the first reason is that TLS and SSL are often used together, so it's good to know how they work and how they differ. The second reason is that if your computer is infected with a virus, then all communication may be compromised. Your device may be sending viruses back and forth, and a virus may infect a web server that you are trying to connect to.

Finally, TLS provides security at the application level. If you use a TLS connection, then your application is more likely to be protected from being compromised. If an attacker compromises your computer, then they won't be able to impersonate your application. They will only be able to impersonate other applications that you have installed.

TLS vs SSL: What is the difference? There are two protocols that are commonly used to encrypt network connections: TLS and SSL. Let's take a look at how they work.

The transport layer security protocol. Transport layer security (TLS) is a protocol that was first introduced in 1995, and has been standardized by the IETF. Like many Internet protocols, TLS has several versions. TLS 1.0 was published in 1995, and TLS 1.2 was published in 2024.1 and TLS 1.2 are very similar, but TLS 1.1 is considered experimental because it was designed as a fallback protocol to allow older software to continue working when upgraded to a newer TLS protocol.

TLS provides security at the application layer. A connection is established between two servers, and then the data is sent in a secure way. The application does not need to be aware of the TLS protocol, because it is done at the application layer.

The application needs to support TLS, but there are other protocols that may be used to provide security.

How does TLS certificate authentication work?

The TLS handshake protocol (RFC 5246) describes how to exchange a TLS client certificate for a TLS server certificate. A typical workflow is shown in Figure 1, below.

Figure 1: TLS handshake workflow. This includes: The TLS client sends a TLS ClientHello message containing a list of the supported cipher suites. The TLS server responds with a TLS ServerHello message indicating which cipher suites it supports. The TLS client chooses one of the supported cipher suites. The TLS server verifies that the chosen cipher suite is supported by its private key, and that the Diffie-Hellman key exchange parameters match those specified in the client certificate. If the handshake succeeds, the TLS server sends a TLS ServerHelloDone message. The TLS client then sends an application layer protocol data unit (APDU) containing the client certificate.

The TLS server verifies that the client certificate contains the expected public key and is valid. If the certificate is valid, the TLS server creates a Signed Certificate Timestamp message containing the signature of the certificate, signed with the private key of the certificate. The TLS client verifies that the certificate contains the expected public key, and verifies the signature on the certificate. The TLS server sends a Finished message, and the TLS client verifies the signature on the Finished message. The TLS client decrypts the Finished message using the corresponding private key, and extracts the server's Finished message (in the form of a TLS record) from the decrypted contents. The TLS client extracts the session ID from the Finished message and sends it to the TLS server. The TLS server verifies the session ID against the expected value. The TLS client and TLS server exchange the master secret and derive a session key from the master secret. The TLS server authenticates the client using a certificate-based authentication protocol, such as the TLS Certificate Authentication Protocol (TLS-CIP). The TLS client and TLS server agree upon a master secret that will be used to generate a secret-key-based key exchange algorithm. The TLS client uses this secret key to generate a session key. The TLS server authenticates the client using a certificate-based authentication protocol, such as the TLS Certificate Authentication Protocol (TLS-CIP).