← IGCSE Computer Science Paper 1

Interception of data on a network

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.

Part of: IGCSE Computer Science 0478 — 2.3 Encryption — Module 1, IGCSE Computer Science 0478 — 5.3 Cyber Security — Module 14, ACARA Digital Technologies Years 7–8 — Networks and Cyber Threats — Module 22, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 74, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities — Module 36, WA Computer Science ATAR Year 11 — Cyber Security — Module 29

Understanding Interception of data on a network in IGCSE Computer Science Paper 1

What it does: The arrows show that data passes through several devices between sender and receiver, and each one is a point where it could be intercepted. On open public Wi-Fi, unprotected data such as a password can be copied by anyone else on the network and read. Interception happens on the network, in transit. The attacker does not need access to the sender's or receiver's device. Interception is copying data in transit. Scrambling data is encryption, which is a way of protecting against interception. The mistake is believing there are no devices in between. Every one of those devices is a chance for interception.

Common mistakes: Data passes through routers and other devices on its way, and any of them could copy it. The line should say router1 CAN COPY packet. On public Wi-Fi other people can connect and intercept data that is not protected. The output should say the data can be copied, not that it is private.

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This module's key terms are also in a printable crossword (Modules 189–203) and word search (Modules 189–217).

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Learning

Duo

Data sent from your laptop to a website travels directly, so no other device ever handles it.

True: data goes straight from sender to receiverFalse: data passes through routers and other devices on the way

Matches

Data goes straight from sender to receiver, so nobody else can see it

↓

Data does not travel directly. It passes through routers and other devices, where it can be intercepted and copied.

Applying

Meanings

Term

interception

Meaning

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.

Practice

message ← "password123"

Testing

Gaps

Check Answer

Spots

2SEND packet TO router1

3router1 CANNOT COPY packet

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Quick Questions

1. Data sent from your laptop to a website travels directly, so no other device ever handles it.

A. False: data passes through routers and other devices on the way ✓

B. True: data goes straight from sender to receiver

Data is split into packets that pass through several routers and other devices. Each of these is a point where someone could intercept it.

2. What is an eavesdropper doing when they intercept data on a network?

A. Deleting the packets so they never arrive

B. Copying packets as they travel across the network ✓

Interception means copying the data as it travels. The sender and receiver may not notice anything has happened.

3. A hacker captures unprotected data sent across a network. What can they do with it?

A. Read it, because it is not protected ✓

B. Nothing, because data in transit cannot be read

Unprotected data (plaintext) can be read by anyone who intercepts it. This is why data in transit needs protecting.

4. Which place is the bigger risk for interception?

A. A private home network with a strong password

B. Public Wi-Fi in a cafe ✓

Anyone can join public Wi-Fi, so an eavesdropper on the same network may be able to copy the data other people send. It is a much higher risk than a private network.

5. Intercepting data means the eavesdropper must break into the sender's computer.

A. False: they copy data while it is travelling across the network ✓

B. True: they must take control of the sender's device

Interception happens on the network, in transit. The attacker does not need access to the sender's or receiver's device.

Match the Pairs

interception → Someone copies data as it travels across a network, so unprotected data can be read by them

eavesdropper = copy(packets) → An eavesdropper captures and copies packets as they pass through a router on their way to the receiver

Data crosses routers and other devices on its journey, so any of them could be used to copy it → sender -> router -> router -> receiver

Public Wi-Fi is risky because anyone connected to the network can intercept unprotected data → wifi = 'Free_Cafe_WiFi'; send(password)

Data goes straight from sender to receiver, so nobody else can see it → Data does not travel directly. It passes through routers and other devices, where it can be intercepted and copied.

Intercepted data cannot be read, even when it is not protected → Unprotected data can be read by anyone who intercepts it. Only protection such as encryption makes it unreadable.

Key Term

interception

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.

Fill in the Blanks

1. IF network = "public" THEN OUTPUT "Risk of interception" ENDIF

Hint: Type the keyword that closes an IF statement.

2. encrypted ← FALSE readable ← NOT encrypted

Hint: Type the logical operator that reverses a Boolean value, so unprotected data counts as readable.

3. packet ← "data" OUTPUT "Eavesdropper copied the packet"

Hint: Type the pseudocode keyword that displays a message.

4. network ← "public Wi-Fi" OUTPUT network

Hint: Type the pseudocode assignment symbol that stores a value in a variable.

5. IF public = TRUE AND secure = FALSE THEN OUTPUT "Anyone can read it" ENDIF

Hint: Type the logical operator that needs both conditions to be true.

Spot the Error

Question 1

A packet ← 'password123'

B SEND packet TO router1

C router1 CANNOT COPY packet

Line C — Data passes through routers and other devices on its way, and any of them could copy it. The line should say router1 CAN COPY packet.

Question 2

A network ← 'public Wi-Fi'

B OUTPUT 'Others can connect'

C OUTPUT 'Data is private'

Line C — On public Wi-Fi other people can connect and intercept data that is not protected. The output should say the data can be copied, not that it is private.

Question 3

A data ← 'bank details'

B encrypted ← FALSE

C SEND data ACROSS network

D interceptorCanRead ← FALSE

Line D — The data is not encrypted, so anyone who intercepts it can read it. interceptorCanRead should be TRUE.

Question 4

A path ← [router1, router2]

B FOR EACH device IN packet

C device FORWARDS packet

D NEXT device

Line B — The loop should go through the devices on the path that the data travels along, not through the packet. It should be FOR EACH device IN path.

Question 5

A wifi ← 'public'

B users ← 'only trusted people'

C risk ← 'interception'

Line B — Anyone can join public Wi-Fi, including an eavesdropper. That is why it is a risk. The users value should say anyone can connect.

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