Protocols (Cambridge International A-Level Computer Science)

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

1. Your browser checks that the certificate is valid and trusted using the CA’s public key
2. 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

Exam Hint

• TLS has replaced SSL — but both are encryption protocols used with digital certificates
• Always mention digital certificates when explaining how websites create secure connections