← IGCSE Computer Science Paper 1

Secure socket layer (SSL) protocol

Secure Socket Layer: a security protocol that encrypts data between a browser and web server, so intercepted data cannot be read. Used for logins and payments. TLS is its successor.

Part of: IGCSE Computer Science 0478 — 5.3 Cyber Security — Module 45, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 88, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 96, WA Computer Science ATAR Year 11 — Cyber Security — Module 94

Understanding Secure socket layer (SSL) protocol in IGCSE Computer Science Paper 1

What it does: The plain text is encrypted by SSL, so a hacker who intercepts it only sees scrambled ciphertext. A checkout page that takes card details uses https:// so SSL protects the payment data during the session. SSL scrambles the data into ciphertext. An attacker who intercepts it cannot read it without the key. The 's' in https stands for secure. It shows the browser and server are using an encrypted SSL/TLS session. SSL protects data travelling across a network between the user's browser and the web server. Logins and online payments send sensitive data such as passwords and card numbers, so they need SSL/TLS encryption.

Common mistakes: "https://" is 8 characters long. Taking only 5 gives "https", which never equals "https://", so the SSL check fails. It should be LEFT(url, 8). The card number was encrypted on the previous line but the plain text is sent instead. Anyone intercepting it could read it. It should send the encrypted value: SEND encrypted TO server.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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Learning
Duo
What does SSL do to data sent between a browser and a web server?
It deletes the data after it has been sentIt encrypts the data so it cannot be understood if intercepted
Matches
A hacker intercepts SSL data and reads the password easily
↓
SSL encrypts the data, so intercepted data is scrambled and cannot be understood without the decryption key
Applying
Meanings
Term
SSL
Meaning
Secure Socket Layer: a security protocol that encrypts data between a browser and web server, so intercepted data cannot be read. Used for logins and payments. TLS is its successor.
Practice
BROWSER connects to https://shop.com
Testing
Gaps
://www.mybank.com/login
Check Answer
Spots
1url ← "https://bank.com"
2prefix ← LEFT(url, 5)

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Quick Questions

1. What does SSL do to data sent between a browser and a web server?
A. It encrypts the data so it cannot be understood if intercepted ✓
B. It deletes the data after it has been sent
SSL scrambles the data into ciphertext. An attacker who intercepts it cannot read it without the key.
2. Which web address shows that a site is using an SSL/TLS secure connection?
A. http://www.mybank.com
B. https://www.mybank.com ✓
The 's' in https stands for secure. It shows the browser and server are using an encrypted SSL/TLS session.
3. SSL creates an encrypted session between which two devices?
A. A keyboard and a monitor
B. A browser and a web server ✓
SSL protects data travelling across a network between the user's browser and the web server.
4. Which activity should always use SSL to protect the data?
A. Entering card details to pay online ✓
B. Reading a printed timetable at school
Logins and online payments send sensitive data such as passwords and card numbers, so they need SSL/TLS encryption.
5. What is the relationship between SSL and TLS?
A. TLS is the newer successor to SSL ✓
B. TLS is a type of malware that attacks SSL
TLS (Transport Layer Security) replaced SSL and is more secure. People still often use the name SSL for both.

Match the Pairs

https://www.myschool.com/login → The https:// at the start shows the page uses SSL/TLS, so data sent between the browser and the server is encrypted
SSL -> TLS → SSL has been replaced by its newer, more secure successor, TLS, though people still say SSL
SSL encrypts data sent between a browser and a web server, so intercepted data cannot be understood → Sent: password123 -> Intercepted: x9Fq#2LpZ8
SSL is used where sensitive data is sent, such as logins and online payments → https://shop.com/checkout?card=enter
A hacker intercepts SSL data and reads the password easily → SSL encrypts the data, so intercepted data is scrambled and cannot be understood without the decryption key
http://mybank.com/login (secure SSL page) → http:// does not use SSL, so the data is not encrypted. A secure SSL page should start with https://

Key Term

SSL
Secure Socket Layer: a security protocol that encrypts data between a browser and web server, so intercepted data cannot be read. Used for logins and payments. TLS is its successor.

Fill in the Blanks

1. https://www.mybank.com/login
Hint: Type the URL prefix that shows the connection is secured with SSL/TLS.
2. SSL stands for Secure Socket Layer
Hint: Type the middle word of the protocol's full name.
3. SSL encrypts data between browser and server
Hint: Type the verb for what SSL does to the data so intercepted data cannot be read.
4. SSL was replaced by its successor, TLS
Hint: Type the acronym of the newer protocol that took over from SSL.
5. Data is sent in an encrypted session
Hint: Type the word for the secure connection set up between the browser and the web server.

Spot the Error

Question 1
A url ← "https://bank.com"
B prefix ← LEFT(url, 5)
C IF prefix = "https://" THEN
D OUTPUT "SSL is protecting you"
Line B — "https://" is 8 characters long. Taking only 5 gives "https", which never equals "https://", so the SSL check fails. It should be LEFT(url, 8).
Question 2
A OUTPUT "Enter card number"
B INPUT card
C encrypted ← SSL_ENCRYPT(card)
D SEND card TO server
Line D — The card number was encrypted on the previous line but the plain text is sent instead. Anyone intercepting it could read it. It should send the encrypted value: SEND encrypted TO server.
Question 3
A session ← START_SSL(server)
B key ← session.KEY
C data ← DECRYPT(msg, key)
D SEND data TO server
Line C — Data must be encrypted before it is sent. DECRYPT would try to unscramble a plain message. It should be ENCRYPT(msg, key).
Question 4
A IF url STARTS "http://" THEN
B OUTPUT "SSL in use"
C ELSE
D OUTPUT "Data not encrypted"
Line A — A URL starting with http:// is not protected by SSL/TLS. The SSL check must test for "https://", where the s means secure.
Question 5
A old ← "SSL"
B successor ← "DNS"
C OUTPUT old, "replaced by", successor
D OUTPUT "Both encrypt data"
Line B — The successor to SSL is TLS (Transport Layer Security). DNS translates domain names to IP addresses and is not an encryption protocol. It should be successor ← "TLS".

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