Securing Messages

Overview

In this lesson you will explore what data encryption is and why it is needed to secure information when data moves across networks. You will practise simple encryption and decryption (using classroom-friendly methods) and apply them to a digital communication scenario.

Learning intentions

• Students will define encryption and explain why it protects data in networks.
• Students will investigate how encrypted information can be decoded only with the correct key/method.
• Students will compare how wired and wireless networks can affect reliability and security needs (at a high level).
• Students will use a simple encryption method to protect a short message and justify their choices.

Success criteria

• I can explain that encryption transforms readable data into unreadable data to reduce unauthorised access.
• I can decrypt an encrypted message using the same method/key.
• I can describe why encryption matters when sending data over the internet or Wi-Fi.
• I can choose and apply a simple encryption method correctly and explain the result.

Curriculum links

• Digital Technologies: AC9TDI8K02 investigate how data is transmitted and secured in wired and wireless networks including the internet (wired vs wireless properties; why security is needed).
• Digital Technologies: AC9TDI8K02 explain why cryptography is necessary for securing data.
• Digital Technologies: AC9TDI8K02 explore simple encryption and decryption algorithms such as ROT13 and XOR.
• Digital Technologies: AC9TDI8P13 explain why an account is protected even if a password is compromised (connect MFA to “layered protection” as a security parallel).

Lesson structure (60 minutes)

1. 0–5 min · Hook. Teacher shows two “messages” on the board: one plain text and one scrambled version, asking students: “Which one is safer to send and why?” Students quick-write a reason on a sticky note, then share with a partner.

2. 5–15 min · Direct teach: encryption purpose. Teacher explains encryption as transforming data into ciphertext so it is unreadable without the correct key/method, linking to internet and Wi‑Fi communication where messages can be intercepted. Students complete a short guided table: Plain text → Ciphertext → Who can read it → Why.

3. 15–25 min · Demo 1: ROT13 (teacher-led). Teacher demonstrates ROT13: each letter is shifted 13 places (e.g., A↔N, B↔O). Students watch the worked example and then do one mini task: encrypt the class phrase using ROT13 and exchange with a partner to verify decryption using the same steps.

4. 25–40 min · Practise 2: XOR (hands-on). Teacher introduces XOR as “either/or” logic on bits, simplified for the classroom: use a small key number and apply XOR to each character code (or use a provided mapping sheet if students haven’t done binary yet). Students work in small groups to encrypt and then decrypt a short message using the worksheet method, focusing on correct application of the same key. Teacher circulates and checks calculations.

5. 40–50 min · Network security scenario. Teacher presents a scenario: a student sends a direct message over school Wi‑Fi, and another student tries to read it. Students answer: “What role does encryption play?” and “What else might protect an account even if credentials are stolen?” Students list one reason for encryption and one reason for layered protection (MFA).

6. 50–58 min · Share and class check. Teacher selects a few student responses for the scenario, then revisits misconceptions (e.g., “encryption doesn’t stop interception; it makes data unreadable”). Students do a quick whole-class vote: “Which statement is correct?” using two or three teacher-read options.

7. 58–60 min · Exit ticket. Students complete one sentence: “Encryption keeps data safe because…” and one action: “To decrypt, you must…” Teacher collects for review.

Resources

• Slide/print cards with plain text and ciphertext examples
• ROT13 worksheet (includes a letter-shift mapping)
• XOR worksheet with either a simple character-to-number mapping or pre-provided lookup tables
• Student “encryption reasoning” table template (Plaintext/Ciphertext/Readable by/Why)
• Scenario handout (Wi‑Fi message + account protection prompt)
• Pens/pencils; scrap paper; exit ticket slips
• Teacher answer key for ROT13 and XOR tasks

Assessment

• Formative: teacher observation during ROT13 and XOR practice (correct method, accuracy, reasoning).
• Formative: guided table completion checked during circulation (linking encryption to who can read it and why).
• Summative (lightweight): exit ticket demonstrating accurate explanation of encryption and correct decryption idea.

Differentiation

• Support: provide sentence starters for the “encryption purpose” table (e.g., “Encryption changes…” “Without the key…”). Offer a worked example step-by-step for XOR at the start.
• Support for numeracy/SEN: use fewer characters in XOR messages and provide a partial lookup table; allow use of a checklist to apply the same key for encryption and decryption.
• Extension: ask students to compare ROT13 vs XOR in terms of “strength of secrecy” (not as a technical evaluation, but as a justification: ROT13 is limited to letters; XOR is based on a key and logic).
• EAL: allow responses using a word bank (encrypt, ciphertext, decrypt, key, secure, unauthorised) and pair oral rehearsal before writing.