9618Paper 3 · Advanced Theory§17.1

17. Security

Asymmetric encryption, digital signatures and certificates, SSL/TLS, quantum cryptography.

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Statometer33OccasionalNext Paper 372%

Marks a paper4.2 · 6%Rank#8 of 8 · #6 on P3Trend · last 12→Full stats

Everything for this topic — study hub

A2 Level · 9618 · Paper 3

Statometer — what 32 real papers say about this topic and each of its 2 syllabus bullets

Occasional · #8 of 8 in A2 Level · recomputed with every new session

Occasional#8 of 8 in A2 Level#6 on Paper 3→ Steady

Rotated in now and then — learn it last, but never skip it: Cambridge sets everything eventually.

Next Paper 3: 72%; 7 in 10 chance it is set
Marks a paper: 4.2 / 75; 6% of Paper 3 · fair share 17%
Appeared in: 22 / 32; Paper 3 sittings 2021–2026
Last set: May/Jun 2026; 9618/33 · Q8 · 6 marks · 3-series streak

Marks in each of the last 12 Paper 3 sittingsOct/Nov 24 → May/Jun 26

What the papers say

Set in 22 of 32 Paper 3 sittings — about 7 papers in 10.
Worth about 4.2 marks a paper (6% of Paper 3, well under its fair share of 17%).
Last set May/Jun 2026 · 9618/33 · Q8 for 6 marks — in the most recent series.
Steady at around 4.3 marks a paper year on year.
Lives on “Explain” and “Describe” — 73% of its questions: full sentences with a reason, not one-word answers.
Its biggest question so far: 10 marks (May/Jun 2022 · 9618/32 · Q7).
Inside the topic, §17.1 Encryption carries the most marks (57%) and §17.1 Encryption protocols and digital certificates the least (43%).
It is examined almost entirely as AO1 (Knowledge & understanding, 100%) — definitions and descriptions in syllabus words score.
The examiner has commented on 13 of its questions — read “What the examiner said” before you practise.

Command words

Share of questions using the word (a question can use several). What each wants →

Question shapes

≤ 6 mk16
7–9 mk5
10–12 mk1
13–15 mk0
16+ mk0

Average 6 marks a question · 0% with a figure or table · 0% with code · biggest 10 marks

Assessment objectives — how it is examined

Every part of every current-syllabus question filed under Cambridge's AO1 / AO2 / AO3 (from its command word and what it asks you to do), so you know whether this topic pays for definitions, for applying, or for judging and building.

AO1 100%

AO1 Knowledge & understanding
AO2 Apply & analyse
AO3 Design, program & evaluate

Paper 3 as a whole

Paper 3	Syllabus	Measured
AO1 Knowledge & understanding	60%	54%
AO2 Apply & analyse	40%	46%
AO3 Design, program & evaluate	0%	0%

Syllabus = Cambridge's grid; measured = the bank's current-syllabus papers.

Inside the topic — every syllabus bullet, measured

Each part of each question is filed under the bullet it examines; the numbers are per Paper 3 sitting, exactly like the topic's. Open a bullet for its own Statometer.

17.1Encryption#10 of 14 on Paper 3Regular · 4052% next paper2.5 marks15/32 sittings↗ May/Jun 2026Regular · 4052%
2.5 · 57% of topic15/32May/Jun 2026latest series · ↗
Set most sessions for a few marks; know the definition and one example.Syllabus: plain text and cipher text; symmetric and asymmetric cryptography; public and private keys for private and for verified messages; quantum cryptography
Next Paper 3
52%
5 in 10
Marks a paper
2.5
3% of the paper · 57% of the topic
Asked in
15 / 32
Paper 3 sittings · 15 questions
Last asked
May/Jun 2026
9618/33 · Q8 · 6 marks · 3-series streak
Asked in 15 of 32 Paper 3 sittings — roughly one paper in 2.
About 2.5 marks a paper (3% of Paper 3; 57% of the topic's marks across its 2 bullets).
Last asked May/Jun 2026 · 9618/33 · Q8 (6 marks) — in the most recent series.
Rising: 2.2 → 2.8 marks a paper.
Usually “Describe” or “State”: full sentences with a reason, not one-word answers.
Biggest chunk of marks so far: 7 in May/Jun 2026 · 9618/32 · Q8.
It is examined almost entirely as AO1 (Knowledge & understanding, 100%) — definitions and descriptions in syllabus words score.
Last 12 sittings↗ Rising
Assessment objectives
AO1 100%
AO1 Knowledge & understanding
AO2 Apply & analyse
AO3 Design, program & evaluate
Describe40%
State40%
Explain40%
Outline27%
Practise its 15 questions Biggest: 7 marks · May/Jun 2026
17.1Encryption protocols and digital certificates#13 of 14 on Paper 3Occasional · 2841% next paper1.6 marks13/32 sittings→ Oct/Nov 2025Occasional · 2841%
1.6 · 43% of topic13/32Oct/Nov 20251 series ago · →
Rotated in occasionally — the bullet students skip and then meet.Syllabus: purpose and use of SSL/TLS in client-server communication; acquiring a digital certificate and using it to produce digital signatures
Next Paper 3
41%
2 in 4
Marks a paper
1.6
2% of the paper · 43% of the topic
Asked in
13 / 32
Paper 3 sittings · 13 questions
Last asked
Oct/Nov 2025
9618/33 · Q9 · 2 marks · 1 series ago
Asked in 13 of 32 Paper 3 sittings — roughly one paper in 2.
About 1.6 marks a paper (2% of Paper 3; 43% of the topic's marks across its 2 bullets).
Last asked Oct/Nov 2025 · 9618/33 · Q9 (2 marks), 1 series ago.
Usually “Explain” or “Describe”: full sentences with a reason, not one-word answers.
Biggest chunk of marks so far: 8 in May/Jun 2022 · 9618/32 · Q7.
It is examined almost entirely as AO1 (Knowledge & understanding, 100%) — definitions and descriptions in syllabus words score.
Last 12 sittings→ Steady
Assessment objectives
AO1 100%
AO1 Knowledge & understanding
AO2 Apply & analyse
AO3 Design, program & evaluate
Explain77%
Describe46%
State39%
Identify15%
Practise its 13 questions Biggest: 8 marks · May/Jun 2022

3% of the topic's marks sit in question parts that belong to another topic (scenario questions cross sections) or that no bullet claims; they count for the topic, not for a bullet.

Marks a paper, year by year

212223242526

By exam series

May/Jun14/18 · 4.6 mk
Oct/Nov8/14 · 3.4 mk

Practise 22 real questions Smart Notes Quiz Flashcards Every topic on the Statometer

What you need to know2syllabus §17.1

17.1Encryption — plain text and cipher text; symmetric and asymmetric cryptography; public and private keys for private and for verified messages; quantum cryptography
17.1Encryption protocols and digital certificates — purpose and use of SSL/TLS in client-server communication; acquiring a digital certificate and using it to produce digital signatures

Video lectures2ZAK's YouTube channel · play here

A220182.6K views
O LevelASA22018630 views

Open in the video library ZAK's channel

Infographics2draw these the way the examiner expects · download as PNG

Asymmetric encryption & digital signatures

Digital certificates & the TLS handshake

Browse all infographics →

Key terms9use these exact words in the exam

asymmetric encryptionpublic keyprivate keydigital signaturedigital certificatehashingSSLTLSquantum cryptography

Dotted terms are defined in the glossary.

Code help1referenced to the Cambridge pseudocode guide

Simple hash + signature verification idea

pseudocode §5.5, §8.2 Run in Playground

FUNCTION Hash(S : STRING) RETURNS INTEGER
   DECLARE i, H : INTEGER
   H ← 7
   FOR i ← 1 TO LENGTH(S)
      H ← (H * 31 + ASC(MID(S, i, 1))) MOD 1000003
   NEXT i
   RETURN H
ENDFUNCTION
DECLARE Msg : STRING
DECLARE Digest : INTEGER
Msg ← "Pay Ali 100"
Digest ← Hash(Msg)
OUTPUT "Digest sent: ", Digest
// receiver recomputes and compares
OUTPUT "Tampered? ", Hash("Pay Ali 900") <> Digest

💡 Real signatures encrypt the digest with the sender's private key; the receiver decrypts with the public key and compares.

Playground examples1runnable program for this topic

Caesar cipher — encrypt & decrypt
Shift letters with ASC and CHR, wrapping with MOD 26. Same key both ways = symmetric encryption.
O LevelASA2PseudocodeString handling §5.5 · 2210 §5 / 9618 §6.2 security
Run

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Quiz: Security (A2) (34)🃏 Flashcards: mix this topic (30)🔐 Encryption, signatures, certificates & TLS (13)📜 Digital signatures, certificates & TLS (17)Past-paper questions (22)🔐 RSA, signatures & the TLS handshake