Protocols (Cambridge (CIE) A Level Computer Science): Revision Note

SSL/TLS

What is SSL?

• SSL (Secure Sockets Layer) is a security protocol used to encrypt data sent over the internet

• Helps to prevent eavesdropping, tampering, or man-in-the-middle attacks

• Commonly used for:

  • Protecting websites

  • Online payments

  • Login credentials

• Creates a secure connection between a web server and a browser

What is TLS?

• TLS (Transport Layer Security) is the successor to SSL

• It performs the same functions but is more secure and efficient

  • Modern websites use TLS, although people often still refer to it as “SSL”

  • When you see HTTPS in the browser, it means TLS/SSL encryption is active

How SSL/TLS works with digital certificates

1. When you visit a secure website (e.g. https://), the server sends your browser its digital certificate

2. The certificate contains:

   • The server’s public key

   • Information about the website and Certificate Authority (CA)

   • A digital signature from the CA

3. Your browser checks that the certificate is valid and trusted using the CA’s public key

4. If trusted, a secure connection is established, often using a shared secret key (symmetric encryption) created during the handshake

Summary: What a digital certificate does