What is SSL?

SSL (Secure Sockets Layer) is a cryptographic protocol that ensures secure data transmission between a client (browser) and a server.

Its main functions:

Encryption: Protects transmitted information from interception and reading by third parties.
Authentication: Verifies the authenticity of the server for the client.
Data integrity: Guarantees that data has not been altered during transmission.

SSL operation is based on the use of key pairs (public and private) and digital certificates issued by Certificate Authorities (CAs).

Stages of establishing an SSL connection (TLS Handshake):

Client Hello: The client sends the server supported SSL/TLS protocol versions, cipher suites, and a random number.
Server Hello: The server selects the most suitable parameters from those offered by the client, sends its random number and its SSL certificate.
Server Certificate: The client verifies the authenticity of the server's certificate (validity period, trust in CA, etc.).
Client Key Exchange: The client generates a symmetric session key, encrypts it with the server's public key, and sends it to the server.
Change Cipher Spec: The client and server notify each other that they will start using the established symmetric key for encrypting further traffic.
Finished: The parties send encrypted messages indicating the completion of the connection setup.

After a successful handshake, all traffic between the client and server is encrypted using the established symmetric key, ensuring confidentiality and integrity of transmitted information.

The modern standard is TLS (Transport Layer Security), which is the successor to SSL. Although the term "SSL" is still commonly used out of habit, current versions of TLS (1.0, 1.1, 1.2, 1.3) are in use.