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S4 ICT: Network Security and Encryption (Paper 1 (basics))
S4 ICT: Network Security and Encryption (Paper 1 (basics))
Paper 1 (basics): ten network security and encryption questions with answers and one-line notes.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 ICT: Network Security and Encryption |
| Level | S4 |
02 Questions (10 items)
- FoundationIn a Caesar cipher shifting letters three places forward, which letter does C become?
- FoundationThe ciphertext is D and encryption shifted three places forward; which letter is the plaintext?
- FoundationA Caesar cipher uses a shift from 0 to 25; how many possible keys exist?
- IntermediateIn symmetric encryption the sender and receiver share one key; how many distinct keys are needed in total?
- IntermediateIn asymmetric encryption, which key should A use to encrypt a confidential message for B?
- IntermediateAn AES-192 key is 192 bits long; how many bytes is that?
- ChallengeA SHA-256 digest is 256 bits long; how many bytes is that?
- ChallengeA letter is shifted forward 13 places twice in a Caesar cipher; what is the result?
- ChallengeThe browser shows a padlock and https; which technology protects the data in transit?
- Error redoA student says an encrypted file must be smaller because the content can no longer be seen. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | F | Three places after C gives D, then E, then F. |
| 2 | A | Decryption runs the other way, three letters back from D to A. |
| 3 | 26 | Shifts from 0 to 25 count as one key each, giving 26 keys. |
| 4 | One key | Symmetric encryption uses a single key that both sides must share over a secure channel first. |
| 5 | B’s public key | The public key may be handed out freely, and only B’s private key can decrypt the result. |
| 6 | 24 bytes | 192 divided by 8 gives 24 bytes. |
| 7 | 32 bytes | 256 divided by 8 gives 32 bytes, a fixed length whatever the input size. |
| 8 | The original letter | 13 plus 13 makes 26, one full cycle of the alphabet. |
| 9 | TLS encryption | https is HTTP over TLS, which adds encryption, server authentication and integrity checking. |
| 10 | Encryption does not compress; padding and headers usually make the file slightly larger | Hiding content and shrinking a file are separate jobs, and only compression touches size. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Encryption serves three aims: hiding content, proving origin and detecting tampering, and each aim uses a different tool. A Caesar cipher has only 26 keys and falls to brute force or frequency analysis, while modern systems exchange a session key with asymmetric encryption and then send data with fast symmetric encryption, using a hash plus a private key for digital signatures. Count keys, bits and bytes carefully before calculating.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.
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