Cambridge IGCSE0478

The internet and the world wide web

Computer Science 0478 Chapter Notes

What this chapter covers

The internet and the world wide webDigital currencyCyber security

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In this chapter

1The internet and the world wide web
2Uniform resource locator (URL)
3HTTP and HTTPS
4The web browser
5Locating, retrieving and displaying a web page
6Cookies
7What a digital currency is
8Blockchain as a digital ledger
9Tracking transactions that cannot be altered
10Attacks on passwords, servers and data in transit
11Malware
12Phishing, pharming and social engineering
13Access levels and authentication
14Anti-malware, updates and careful checking
15Firewalls, proxy servers and SSL

1. The internet and the world wide web

The internet is the infrastructure. The world wide web is the collection of websites and web pages accessed using the internet.

They are not the same thing. The web is accessed using the internet. It is not the internet itself.

Pick one meaning for each term. An answer that says the web is both the infrastructure and the web pages contradicts itself.

Examiner insight

“Some candidates mixed up the term with that of the internet, describing it as the infrastructure that provided access to the website. Some candidates gave contradictory answers, stating that it was both the infrastructure and the web pages.”

Worked example 12 marks

Explain the difference between the internet and the world wide web.

1
The internet is the infrastructure [1]
2
The world wide web is the collection of websites and web pages accessed using the internet [1]

2. Uniform resource locator (URL)

A uniform resource locator (URL) is a text-based address for a web page. It is not the IP address.

A URL can contain the protocol, the domain name and the web page / file name. Take this one:

``` https://www.example.com/notes/index.html ```

The protocol is `https`. The domain name is `www.example.com`. The web page / file name is `notes/index.html`. The file name and the path are one part, not two.

Examiner insight

“A common misconception candidates had is that the URL is the IP address.” “Some candidates gave multiple names for the same part, for example the file name and the path as two separate parts.”

Worked example 12 marks

The web page has a uniform resource locator (URL). Identify two parts of a URL.

1
any one from: protocol, domain name, web page / file name // path [1]
2
a second, different part from the same list [1]

3. HTTP and HTTPS

Hypertext transfer protocol (HTTP) and hypertext transfer protocol secure (HTTPS) are protocols. The protocol is the first part of a URL. HTTPS is the secure one: it uses encryption to protect the data.

With HTTPS the web browser sends a request to the web server for its digital certificate. The web server sends the certificate to the browser. The browser authenticates it.

If the certificate is valid, the data is encrypted using public and private keys and sent.

Examiner insight

“Some responses inaccurately described the browser as sending the certificate to the server instead of the other way around.” “Another common error was describing the web server as asking the browser to identify itself, for example reversing the actions.”

Worked example 14 marks

Describe how a web browser and a web server use a digital certificate and encryption to send data securely.

1
The web browser sends a request to the web server for its digital certificate [1]
2
The web server sends the digital certificate to the web browser [1]
3
The web browser authenticates the certificate; data is sent only if it is valid [1]
4
The data is encrypted using public and private keys, to make any data sent meaningless [1]

4. The web browser

A web browser is a piece of software. Its main purpose is to render hypertext markup language (HTML) and display web pages. The purpose and the functions are different answers.

Functions include storing bookmarks and favourites, recording user history, allowing use of multiple tabs, storing cookies, providing navigation tools and providing an address bar.

Examiner insight

“Some candidates gave functions of a web browser, rather than its purpose.” “Some candidates stated that it allows a user to access a website, which was also provided as part of the question.”

Worked example 13 marks

Two functions of a web browser are to provide an address bar and to store cookies. Give three other functions of a web browser.

1
any one from: displays a web page // renders HTML, storing bookmarks / favourites, recording history, multiple tabs, navigation tools, can set a homepage [1]
2
a second, different function [1]
3
a third, different function [1]

5. Locating, retrieving and displaying a web page

The user enters a URL. The web browser sends the domain name from the URL to the domain name server (DNS). The DNS searches for the matching IP address and sends it back to the browser.

The browser then sends a request to the web server for the web page. The web server sends the data for the page back to the browser. The browser renders the HTML to display the page.

The request goes to the web server, not to the website. The website is a collection of files.

Examiner insight

“It would be beneficial for candidates to understand that the web browser sends the request to the web server and not the website.”

Worked example 14 marks

The URL is converted into an internet protocol (IP) address. Describe the purpose of an IP address. Explain how a URL is converted to an IP address.

1
purpose: to uniquely identify a device on a network / internet [1]
2
the browser sends the URL / domain name to the DNS [1]
3
the DNS stores a table of domain names and their matching IP addresses, and searches for the match; if not found, it is sent to a higher DNS until found [1]
4
the IP address is returned to the web browser [1]

6. Cookies

A cookie is a text file that stores data about the user's browsing activity on the computer. The web browser stores it. A session cookie is retained during the session. A persistent cookie is retained permanently.

Cookies are used for saving personal details, tracking user preferences, holding items in an online shopping cart and storing login details.

Examiner insight

“Some candidates gave examples of the use of cookies, for example storing login details, instead of stating what a cookie is.” “Many stated what a cookie stores, but few referred to it being a file.”

Worked example 13 marks

The website stores cookies on the user's computer. State what is meant by a cookie. Give one example of how a website can use a session cookie and one example of how a website can use a persistent cookie. Each example must be different.

1
a text file that stores data about user / browsing activities on the computer [1]
2
session cookie, one from: store shopping basket, store login details, enable live chat [1]
3
persistent cookie, a different one from: retain login, store bank / card details, store preferences [1]

Recap

The internet is the infrastructure. The world wide web is the collection of websites and web pages.
A URL is a text-based address. Parts: protocol, domain name, web page / file name.
A URL is not an IP address. An IP address uniquely identifies a device.
HTTPS: the web server sends a digital certificate, the browser authenticates it, then data is encrypted.
A web browser renders HTML and displays web pages. Learn its purpose and its functions.
Browser sends domain name to DNS, DNS returns the IP address, browser requests the page from the web server, browser renders the HTML.
A cookie is a text file. Session cookies and persistent cookies have different uses.

7. What a digital currency is

A digital currency is one that only exists electronically. It has no physical form, so there are no coins or notes.

A digital currency is used to make transactions. It is a decentralised system. Decentralised means it is not controlled from one central place.

Examiner insight

“Many candidates were able to describe what is meant by a digital currency.”

Worked example 12 marks

Give two features of a digital currency.

1
It only exists electronically. [1]
2
It is a decentralised system. [1]

8. Blockchain as a digital ledger

Blockchain, in its basic form, is a digital ledger. A ledger is a record of transactions.

The ledger is a time-stamped series of records. Each record carries the time it was made, so the order of the transactions can be read from the time stamps.

Examiner insight

“Many candidates were able to recognise that the name of the process described was blockchain.”

Worked example 12 marks

The table gives part of a digital ledger for a digital currency.

State the name of the process used to keep this ledger. Give one feature of the ledger that the table demonstrates.

Time stamp	From	To	Amount
09:00:12	Asha	Ben	2
09:04:51	Ben	Chen	1
09:10:30	Chen	Dara	1

1
Blockchain [1]
2
It is a time-stamped series of records: every record has a time stamp. [1]

9. Tracking transactions that cannot be altered

Blockchain is used to track digital currency transactions. Each transaction is a record in the ledger.

The records cannot be altered. Once a transaction has been recorded, its record cannot be changed.

Worked example 13 marks

A shop accepts payment in a digital currency. Explain how blockchain is used to track the payment.

1
The blockchain is a digital ledger, and the payment is a record in it. [1]
2
The record is time-stamped, so the ledger holds when the payment was made. [1]
3
The records cannot be altered, so the payment cannot be changed later. [1]

Recap

A digital currency only exists electronically.
A digital currency is a decentralised system.
Blockchain, in its basic form, is a digital ledger.
The ledger is a time-stamped series of records that cannot be altered.
Blockchain is used to track digital currency transactions.

10. Attacks on passwords, servers and data in transit

A brute-force attack is where a third party repeatedly tries to crack a password by entering different combinations. Hacking is where a person gains unauthorised / illegal access to a user's device, account or system.

A distributed denial of service (DDoS) attack is where multiple computers send a large number of requests to a web server with the aim of crashing it. The attack prevents access to the web server. It is not installed onto it.

Data interception is where software is used to analyse data packets during transmission. Any packets that look useful are sent to a malicious third party.

Examiner insight

“It would be beneficial for candidates to understand that a DoS attack prevents access to a webserver, but it is not installed onto one.” “Many just stated that it denies the user of a service, which was not accurate enough for a mark.”

Worked example 15 marks

Cyber security threats are a problem when using the internet.

Complete the table by writing the missing terms and descriptions about cyber security threats.

Each term and description must be different.

term	description
........	An attack where a third party repeatedly tries to crack a password by entering different combinations.
hacking	........
........	An attack where multiple computers send a large number of requests to a web server with the aim of crashing it.
spyware	........
........	A security threat where software is used to analyse data packets during transmission. Any packets that look useful are sent to a malicious third party.

1
row 1: brute-force attack [1]
2
row 2: a person gains unauthorised / illegal access to a user's device, account or system [1]
3
row 3: distributed denial of service attack (DDoS) [1]
4
row 4: malware that is used to record the keypresses from a user's device [1]
5
row 5: data interception (packet sniffing) [1]

11. Malware

The syllabus lists six types of malware: virus, worm, Trojan horse, spyware, adware and ransomware. Hacking and phishing are not malware.

A virus replicates itself to corrupt the data on a hard disk drive or use up memory. A worm also replicates itself, but the aim is to use up the bandwidth of a network. A Trojan horse is used to disguise malware. Once it is downloaded it releases the malware it contains.

Spyware records the keypresses from a user's device. Ransomware is downloaded with the aim of encrypting data so that the user cannot get access to it. There is often a demand for payment before access is given back.

Examiner insight

“a worm replicates over a network, whilst a virus replicates within a computer.” “Some candidates inaccurately identified hacking as being malware – which might make use of malware but not necessarily.”

Worked example 15 marks

Cyber security threats are a concern for any company that stores data using a network.

Complete the statements about cyber security threats. Use the terms from the list. Some of the terms in the list will not be used. You should only use a term once.

adware · bandwidth · components · data · decrypting · encrypting · keylogger · pharming · phishing · sharing · spyware · trojan horse · virus · worm

A ........ is used to disguise malware. Once it is downloaded onto a computer, it releases the malware that it contains.

A ........ replicates itself to corrupt the data stored on a user's hard disk drive or use up the available memory.

A ........ also replicates itself but the aim is to use up all the ........ of a network.

Ransomware is downloaded onto a computer with the aim of ........ data to stop the user gaining access to it. There is often a demand for payment before the user is given access to the data again.

1
gap 1: trojan horse [1]
2
gap 2: virus [1]
3
gap 3: worm [1]
4
gap 4: bandwidth [1]
5
gap 5: encrypting [1]

13. Access levels and authentication

Access levels limit a user's access to data by giving users different permissions, such as read only, read-write, no access, execute or administrator. An attacker then reaches only the data that the user can reach.

The syllabus lists three kinds of authentication: a username and password, biometrics and two-step verification. A biometric password is unique to a person and cannot be shared.

Examiner insight

“Better candidates then went on to describe what was different, for example ‘biometric passwords are unique to a person and cannot be shared’.” “The most common error was describing a retina/iris scanner as an eye scanner.”

Worked example 15 marks

Explain how access levels are used to help prevent a cyber security attack being successful.

1
they limit / restrict a user's access to data [1]
2
by giving users different permissions, e.g. read only, read-write, no access, execute or administrator [1]
3
so an attacker will only have access to the data that the user has access to [1]
4
to stop an attacker deleting, editing or corrupting data [1]
5
prevents an attacker installing malware, as they do not have administrator permissions [1]

14. Anti-malware, updates and careful checking

Anti-malware includes anti-virus and anti-spyware. Anti-virus software scans a computer to identify and remove viruses. It does not stop every virus being downloaded, and it is not a suitable method to prevent hacking or a DoS attack.

Software updates can be automated. Users can also check the URL attached to a link, check the spelling and tone of communications, and use privacy settings.

Examiner insight

“Some candidates demonstrated a misconception that anti-virus software will stop any viruses being downloaded.” “It would improve their understanding to know that antivirus software is not a suitable security method to prevent hacking or a DoS attack.”

Worked example 13 marks

A member of staff receives an email that asks them to click a link.

(a) State two checks they can make before clicking the link.

(b) They say the checks are not needed because anti-virus software will stop any virus being downloaded. State why they are wrong.

1
(a) check the URL attached to the link [1]
2
(a) check the spelling and tone of the email [1]
3
(b) anti-virus software will not stop every virus being downloaded [1]

15. Firewalls, proxy servers and SSL

A firewall monitors incoming and outgoing traffic and blocks signals that do not meet the criteria. The user can set the criteria, and a firewall can block specific ports. It can be software or hardware.

A proxy server can hide a user's IP address. The secure socket layer (SSL) protocol makes a secure connection and uses encryption so that data cannot be understood. The web server sends the digital certificate to the browser.

Examiner insight

“It would be beneficial for candidates to understand that a firewall will only stop traffic that it has been set to identify as malicious.” “Some responses inaccurately described the browser as sending the certificate to the server instead of the other way around.”

Worked example 14 marks

Explain how a firewall helps to prevent hacking.

1
it monitors incoming and outgoing traffic [1]
2
it checks the traffic against criteria set by the user [1]
3
it blocks traffic that does not meet the criteria [1]
4
it can block specific ports for entry or exit [1]

Recap

Brute-force: repeatedly tries to crack a password with different combinations.
DDoS: multiple computers send a large number of requests to a web server to crash it.
Data interception: software analyses data packets and sends useful ones to a third party.
Virus replicates within a computer. Worm replicates over a network and uses up bandwidth.
Phishing needs a click on a link or attachment. Pharming redirects to a fake website.
Access levels limit what each user can reach. Biometrics are unique to a person.
A firewall only stops traffic it is set to identify as malicious. Encryption protects data in transit.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

State which of the internet and the world wide web is the infrastructure.1 mark
State what is meant by the world wide web.1 mark
A web page has this URL: ``` https://www.example.com/shop/basket.html ``` Write down the protocol and the domain name.2 marks
State the main purpose of a web browser. Then name the browser function that keeps a list of the web pages a user visited yesterday.2 marks
A student says that a URL and an IP address are the same thing. State what a URL is and state the purpose of an IP address.2 marks
A bank's web page address begins with https. Describe one way HTTPS protects data sent between the web browser and the web server.2 marks
A web browser connects to a web server using HTTPS. Describe, in order, the first three steps.3 marks
A user types www.example.com. The first DNS the browser contacts does not hold this domain name. Explain how the browser gets the IP address.4 marks
A quiz website asks 20 questions over several web pages. The player's score so far is retained only during the session. The player's username is still filled in when the player returns a week later. (a) State what is meant by a cookie. (b) Identify the type of cookie that holds the score so far and the type that holds the username. Give a reason for each. (c) A student writes: "The web server stores the cookie on the web server." Rewrite the sentence so that it is correct.6 marks
A user enters `https://www.bank.com/login.html` into the address bar. A student writes five statements about what happens. Each statement contains one mistake. (a) Rewrite each statement so that it is correct. (b) After the corrected statement D, describe what the web browser does next and what happens to the data. | | Student's statement | | --- | --- | | A | The web browser sends the IP address to the DNS. | | B | The DNS searches for the matching web page and sends it back to the web browser. | | C | The web browser sends a request to the website for the web page. | | D | The web browser sends its digital certificate to the web server. | | E | The web server renders the HTML to display the web page. |7 marks
State what is meant by a digital currency.1 mark
A digital currency is held as coins and notes in a purse. State whether this is true or false.1 mark
Give the name of the process used to track digital currency transactions.1 mark
Blockchain, in its basic form, is a digital ledger. State what is meant by a digital ledger.1 mark
A ledger lists three payments with the times 10:15, 10:02 and 10:09. State the order in which the payments happened.1 mark
A candidate is asked for two features of a digital currency. The candidate writes: 'It is not physical' and 'It only exists electronically'. Explain why this answer earns one mark only, and give a second feature.2 marks
A student says: 'A payment recorded in a blockchain can be deleted if the buyer changes their mind.' Explain why the student is wrong.2 marks
A café starts to take a digital currency. Describe how its payments are tracked.3 marks
A school gives reward points that only exist electronically. The points are tracked in a blockchain. A student copies four of its records into the table, not in order. Ravi has 0 points before these records. (a) Write the four time stamps in the order the transactions happened. (b) Work out how many points Ravi has immediately after the transaction time-stamped 11:45:30. (c) Ravi says the 11:42:10 record should have been for 4 points and asks for it to be changed. State whether the record can be changed. Give a reason. | Time stamp | From | To | Points | | --- | --- | --- | --- | | 11:42:10 | Ravi | Sam | 5 | | 11:40:55 | School | Ravi | 8 | | 11:47:03 | Sam | Ravi | 2 | | 11:45:30 | Ravi | Tia | 3 |4 marks
A games company sells 'gems' that players spend inside its games. Gems only exist electronically. The company alone controls the gems. It keeps every gem payment in one file. Each record in the file holds the payer, the receiver and the amount, but no time. Staff can edit or delete any record. The company says: 'Gems are a digital currency and we track them with blockchain.' Give one point that supports this claim and three points against it.4 marks
Name the type of malware that is downloaded with the aim of encrypting a user's data and then demands payment before access is given back.1 mark
State one difference between a virus and a worm.2 marks
A user opens a phishing email but does not click anything. Explain why they are not yet taken to the fake website.2 marks
Describe how a brute-force attack is carried out.3 marks
A company stores its website on a web server. Give three cyber security threats to the web server.3 marks
A firewall is used on a school network. A student says that it will stop all malicious traffic. Explain why the student is wrong.2 marks
A student writes "eye scanner" as an example of a biometric device. Give two accurate names the student could have used for a device that scans part of the eye.2 marks
A firewall and a proxy server are both used to protect a network. Give one similarity and one difference between a firewall and a proxy server.3 marks
A clinic keeps patient records on one laptop. The laptop is never connected to any network. A technician suggests four security solutions: a firewall, a biometric device, access levels and the secure socket layer (SSL) protocol. (a) Identify the two solutions that are unnecessary for this laptop. Give a reason for each. (b) The receptionist's account has read only permission for appointment records and no access to medical records. An attacker logs in with the receptionist's account. Explain what the access levels stop the attacker doing.7 marks
An online ticket shop runs a web server. Monday: the web server stops responding after many computers send it a large number of requests. Tuesday: a customer receives a legitimate-looking email. They open it, click a link in it and type their password into a fake website. Wednesday: a third party uses software to analyse the data packets sent between a customer and the web server. (a) Name the threat on each day. (b) State the action on Tuesday that took the customer to the fake website. (c) The manager says that anti-virus software will stop Monday's attack and that a firewall will keep Wednesday's data safe. Explain why the manager is wrong about each. Name a method that does keep Wednesday's data safe and state how.8 marks

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Read the notes

1. The internet and the world wide web#

2. Uniform resource locator (URL)#

3. HTTP and HTTPS#

4. The web browser#

5. Locating, retrieving and displaying a web page#

6. Cookies#

7. What a digital currency is#

8. Blockchain as a digital ledger#

9. Tracking transactions that cannot be altered#

10. Attacks on passwords, servers and data in transit#

11. Malware#

12. Phishing, pharming and social engineering#

13. Access levels and authentication#

14. Anti-malware, updates and careful checking#

15. Firewalls, proxy servers and SSL#

End-of-chapter exercise

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Chapter at a Glance

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Related chapters

1. The internet and the world wide web

2. Uniform resource locator (URL)

3. HTTP and HTTPS

4. The web browser

5. Locating, retrieving and displaying a web page

6. Cookies

7. What a digital currency is

8. Blockchain as a digital ledger

9. Tracking transactions that cannot be altered

10. Attacks on passwords, servers and data in transit

11. Malware

12. Phishing, pharming and social engineering

13. Access levels and authentication

14. Anti-malware, updates and careful checking

15. Firewalls, proxy servers and SSL