← Understanding a computer science concept

Encryption and AI mechanisms (the two current topics)

Both have appeared in the 2025 task; know both well enough to choose on the day.

The terms to use precisely

6 terms

Symmetric encryption

One shared key both encrypts and decrypts. Fast, but the key must be exchanged securely. AES — used for the bulk of data in HTTPS

Asymmetric / public-key

A public key encrypts; only the paired private key decrypts. Solves key distribution but is slow. RSA — used to agree the session key

Hashing / SHA-256

A one-way function producing a fixed-length digest. Cannot be reversed, so it verifies without storing the original. Passwords should be salted AND hashed

Key exchange problem

How two parties agree a shared secret over a channel an eavesdropper might be watching — solved by Diffie–Hellman. A named 2025 mechanism option

Neural network

Layers of connected nodes whose weighted connections adjust during training to recognise patterns. A named 2025 mechanism option

Natural language processing (NLP)

How a computer parses, interprets and generates human language. A named 2025 mechanism option

Exam-style Public Wi-Fi in a café: how does the encryption work, and what can go wrong? Explain the process and the key issues. The browser connects to the site over HTTPS and requests its certificate. The certificate contains the site's PUBLIC key, signed by a certificate authority the browser already trusts — which is what proves the site is who it claims. The browser and server use the KEY EXCHANGE process to agree a shared SYMMETRIC session key that no eavesdropper on the café Wi-Fi can derive. All subsequent traffic is encrypted with that fast symmetric key, so anyone capturing packets sees only ciphertext. ISSUES: an unencrypted HTTP site sends everything in the clear; a fake access point can present itself as the café network; a user clicking through a certificate warning defeats the identity check entirely. ✓ Certificate → identity → key exchange → symmetric bulk encryption, then the failure modes. This chain covers part (a)'s mechanism-plus-issues shape directly.

Practice for this standard covers the whole topic — flashcards and quiz.