IGCSE Computer Science 0478 — 2.3 Encryption Hangman

The 19 key terms

1interception

When someone copies data as it travels across a network through routers and other devices, so unprotected data can be read by anyone who intercepts it, for example on public Wi-Fi.

2data in transit

Data moving across a network, such as email or web traffic. It is protected by encrypting it (e.g. HTTPS or a VPN) so intercepted data cannot be read.

3plaintext

The original, readable data (text, file, image or message) before it is encrypted. Decrypting ciphertext with the correct key turns it back into plaintext.

4ciphertext

The scrambled, unreadable data made when plaintext is encrypted. It is what gets sent across a network and looks meaningless without the key.

5Encryption

Turning a readable message into a scrambled, unreadable message using a key, so it can only be read again with decryption.

6encryption key

A secret value used by the encryption algorithm to scramble data into ciphertext and unscramble it again. A different key gives different ciphertext, and a longer key is harder to guess.

7Caesar cipher

A cipher that encrypts a message by shifting each letter forward by a fixed number, and decrypts it by shifting each letter back by the same number.

8unreadable without the key

Encryption cannot stop data being intercepted, but the interceptor sees only ciphertext and cannot get the plaintext without the key, so passwords and bank details stay safe.

9Symmetric encryption

Using the exact same secret key to both lock and unlock a message.

11shared secret key

In symmetric encryption, the receiver can only decrypt if they hold the same key as the sender, so the key must be shared before any data is sent.

12key interception

If an attacker intercepts a symmetric key while it is being shared, they can decrypt every message that uses that key, so the encryption is defeated.

13Asymmetric encryption

Encryption that uses a linked pair of keys: a public key to encrypt data and a private key to decrypt it, with no shared secret key needed.

14public key

The half of a key pair that the owner shares openly. Anyone can use it to encrypt data sent to the owner, but it cannot decrypt that data. Only the matching private key can.

15private key

The secret half of a key pair. Only the owner keeps it, never sends it, and uses it to decrypt data that was encrypted with their public key.

16encrypt with recipient's public key

To send a secure message, the sender encrypts the plaintext using the receiver's public key, not their own. Only the receiver's private key can decrypt the ciphertext.

17private key decryption

Only the recipient's private key can decrypt a message encrypted with their public key. The private key stays secret on the recipient's device, so interceptors cannot read it.

18Encrypt with public key, decrypt with private key

The receiver shares their public key, the sender encrypts with it, and only the receiver's private key can decrypt it. No secret key is shared, so an interceptor sees only ciphertext.

19symmetric vs asymmetric

Symmetric: one shared secret key, fast but hard to share safely. Asymmetric: public and private key pair, no secret to share but slower. Often combined.

21plaintext, key, ciphertext

A full-mark answer uses the key terms correctly and gives the steps in order: plaintext is encrypted with a key into ciphertext. Encryption does not stop interception.