IGCSE Computer Science Paper 1 Definitions Worksheet: 2.3 Encryption and 3.1 Computer Architecture (Modules 204–217)
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Key terms
Write what each term means, in your own words.
1
private key
2
encrypt with recipient's public key
3
private key decryption
4
Encrypt with public key, decrypt with private key
5
symmetric vs asymmetric
6
plaintext, key, ciphertext
7
microprocessor
8
Von Neumann architecture
9
ALU
10
Control Unit (CU)
Answer Key
IGCSE Computer Science Paper 1 · Modules 204–217 · Student wording will vary for definitions
1private 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.
2encrypt 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.
3private 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.
4Encrypt 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.
5symmetric vs asymmetric — Use symmetric if both sides can already share a key safely; use asymmetric for strangers, such as a customer and a website. Justify the choice with 'because'.
6plaintext, 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.
7microprocessor — A CPU built as an integrated circuit on a single chip. It is only the processor, not the whole computer, and is found in PCs, phones and embedded devices.
8Von Neumann architecture — A computer design where instructions and data share the same main memory (RAM) and the CPU fetches them one at a time. This is the stored program concept, named after John von Neumann.
9ALU — Arithmetic logic unit: the part of the CPU that does calculations (add, subtract) and logic decisions (AND, OR, NOT, comparisons). Results are held in the accumulator.
10Control Unit (CU) — The part of the CPU that decodes instructions and sends control signals to coordinate the ALU, registers, memory and other parts during the fetch-decode-execute cycle.