Data Transmission · 4 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 4% of your exam marks.
Symmetric vs asymmetric encryption questions are growing as cybersecurity becomes more prominent.
When data crosses a network, anyone who can intercept the cable or radio signal could potentially read it. stops that by scrambling the data into a form that only the intended recipient can unscramble.
Encryption is the process of converting (readable data) into (unreadable, scrambled data) using an algorithm and a , so that only someone with the correct key can convert the ciphertext back into plaintext.
The five terms that matter most:
| Term | Meaning |
|---|---|
| Plaintext | The original, readable data before encryption |
| Ciphertext | The scrambled, unreadable data after encryption |
| Encryption algorithm | The mathematical procedure that turns plaintext into ciphertext (and back) |
| Key | A piece of secret information (usually a binary string of a fixed length) that controls how the algorithm scrambles the data |
| Decryption | The reverse process: turning ciphertext back into plaintext using the key |
Encryption does not stop an attacker from intercepting the data. It only stops them from understanding it.
State the purpose of encryption
What comes up: a 1-mark question asking you to state the purpose of, or the reason for, encrypting data before transmission.
Write: If the data is intercepted, it cannot be understood by the person who intercepted it, because they do not have the key needed to decrypt it.
Watch out: A common dropped mark is saying encryption "prevents" data from being intercepted or stolen — it does not. The data can still be captured; encryption only makes it meaningless to whoever captures it.
Both wired and wireless networks need encryption, but wireless networks are especially exposed because the signal travels through the air and can be picked up by any nearby radio receiver. Anyone within range of a Wi-Fi access point can in principle capture the radio waves. On a wired network, an attacker would have to physically tap into the cable to intercept anything.
Wireless networks therefore use dedicated security protocols such as WPA2 (Wi-Fi Protected Access 2) to encrypt all traffic between the device and the access point.
A typical wireless connection works like this: