Year 11 · Computer Science · Autumn 2

The internet and its uses · Lesson 4 of 5

Keeping data safe

Theory5.3 Cyber security

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

You will learn to

  • Explain how each security solution helps keep data safe.
  • Describe how a firewall and a proxy server each protect a network.
  • Describe how SSL sets up a secure connection, in three steps.
  • Evaluate which defence best stops a given threat, and justify the choice.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Success criteria

You have got it when you can say:

  • I can match each threat to at least one defence that stops it.
  • I can label a diagram showing where a firewall and a proxy server sit.
  • I can describe SSL in three steps, including the digital certificate.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Retrieval starter

Questions from before. Write your answers, then show them.

  1. Last lesson

    The World Wide Web is…

    A The same thing as the internetB The cables and routersC Pages that use the internet via HTTP

    C. Pages that use the internet via HTTP

  2. Last unit

    Which of these is system software?

    A The operating systemB A word processorC A game

    A. The operating system

  3. Earlier this unit

    A proxy server…

    A Is the same as a routerB Sits between users and the internet, filtering and cachingC Stores the DNS

    B. Sits between users and the internet, filtering and caching

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Key words (1 of 5)

Internet
The worldwide network of connected computer networks: the physical infrastructure.
URL
Uniform resource locator: the text address of a web page, made of protocol, domain name and file name.
HTTP / HTTPS
The rules for sending web pages; HTTPS adds encryption using SSL.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Key words (2 of 5)

Web browser
Application software that fetches web pages and renders HTML so you can see them.
DNS
Domain Name System: servers that find the IP address that matches a domain name.
IP address
A number that identifies a device on a network, such as 151.101.0.81.
Digital currency
Money that exists only electronically.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Key words (3 of 5)

Brute-force attack
Trying every possible password or key until the right one is found.
DDoS
Distributed denial of service: flooding a server with requests from many computers so real users cannot reach it.
Malware
Software designed to cause harm, such as a virus, worm, Trojan horse, spyware, adware or ransomware.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Key words (4 of 5)

Phishing
A fake message that tricks the user into clicking a link and giving personal details on a fake site.
Pharming
Malicious code or a tampered DNS server redirects the user to a fake website, even if they type the correct URL.
Social engineering
Manipulating people into breaking normal security rules.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Key words (5 of 5)

Firewall
Hardware or software that checks traffic in and out against rules and blocks anything that breaks them.
Proxy server
A server between the user and the internet that filters requests, hides the user's IP address and caches pages.
SSL
Secure Sockets Layer: a protocol that uses certificates and encryption to secure data between browser and server.

The explanation · step 1 of 14 · part 1 of 3

Brute-force attack

A brute-force attack is when a criminal tries every possible password (or key) until one works. Software tries millions of guesses each second.

The aim is to get into an account or system, then steal data or cause harm.

Longer passwords with a mix of character types have far more possible combinations, so they take much longer to crack.

The explanation · step 1 of 14 · part 2 of 3

Brute-force attack (continued)

e.g.Example
A 4-digit PIN: 10 choices per digit. 10 × 10 × 10 × 10 = 10,000 possible PINs. An 8-character password using a–z, A–Z and 0–9: 62 choices per character. 62^8 = 218,340,105,584,896 possible passwords (about 218 million million).
?Why?

Each extra character multiplies the number of guesses needed. That is why length matters more than anything else.

The explanation · step 1 of 14 · part 3 of 3

Brute-force attack (continued)

!Watch out

Defences: long, complex passwords; locking the account after a few failed attempts; two-step verification.

The explanation · step 2 of 14 · part 1 of 2

Data interception

Data interception is when data is stolen while it is being sent, for example over Wi-Fi or across the internet.

A criminal can use a packet sniffer, a program that captures and examines data packets as they pass. On an unsecured public Wi-Fi network this is easy.

The aim is to read passwords, card numbers or private messages.

The explanation · step 2 of 14 · part 2 of 2

Data interception (continued)

e.g.Example
In a café, someone on the same free Wi-Fi captures the packets from your laptop. If a website uses plain HTTP, they can read the password you typed.
!Watch out

Defences: encryption (HTTPS/SSL so captured data cannot be read); avoid public Wi-Fi for banking, or use a VPN; use strong Wi-Fi encryption at home.

The explanation · step 3 of 14 · part 1 of 3

Distributed denial of service (DDoS)

A denial of service (DoS) attack floods a web server with so many requests that it cannot cope. Real users cannot reach the website.

In a distributed DoS (DDoS), the requests come from thousands of computers at once. These are often ordinary devices infected with malware and controlled by the criminal. This group is called a botnet.

The aim is to take a website offline, often to cause loss of sales or to demand money.

The explanation · step 3 of 14 · part 2 of 3

Distributed denial of service (DDoS) (continued)

e.g.Example
On the morning concert tickets go on sale, a botnet of 50,000 infected computers and cameras sends requests to the ticket website. The server is overloaded and real fans see an error page.
?Why?

Requests from so many different places are hard to block, because they look like normal visitors.

The explanation · step 3 of 14 · part 3 of 3

Distributed denial of service (DDoS) (continued)

!Watch out

Defences: a proxy server or firewall that filters out the flood of traffic; anti-malware on your own devices so they do not join a botnet.

The explanation · step 4 of 14 · part 1 of 2

Hacking

Hacking is gaining unauthorised access to a computer system. Unauthorised means without permission.

A hacker may steal, change or delete data, or install malware. This is illegal in most countries.

Ethical hacking is different: a company pays an expert to try to break in, so weaknesses can be found and fixed.

The explanation · step 4 of 14 · part 2 of 2

Hacking (continued)

!Watch out

Defences: firewalls, strong passwords and authentication, access levels, and keeping software updated so known weaknesses are fixed.

The explanation · step 5 of 14 · part 1 of 2

Malware: virus, worm and Trojan horse

Malware (malicious software) is any software written to cause harm. Cambridge lists six types. The first three spread or get in; the last three do specific damage.

TypeHow it worksExample of harm
VirusAttaches itself to a program or file. Needs a user to run that file. Then copies itself to other files.Deletes or corrupts files; makes the computer crash
WormA standalone program that copies itself across a network on its own. No user action needed.Uses up bandwidth and slows networks; can carry other malware
Trojan horseDisguised as useful, legitimate software. The user installs it willingly.Once installed, it lets in other malware such as spyware, or gives the criminal remote access

The explanation · step 5 of 14 · part 2 of 2

Malware: virus, worm and Trojan horse (continued)

e.g.Example
A student downloads a free "game cheat" from an unknown site. It works, but it also installs spyware. That download was a Trojan horse.
!Watch out

Virus versus worm: a virus needs a host file and a user to run it. A worm spreads by itself across a network.

The explanation · 9 more steps

More on the lesson page

The lesson page has the rest of the explanation, step by step:

  • Malware: spyware, adware and ransomware
  • Phishing and pharming
  • Social engineering
  • Solutions: access levels, anti-malware and authentication
  • Solutions: updates, checking messages and links
  • Solutions: firewalls and privacy settings
  • Solutions: proxy servers
  • Solutions: SSL
  • Matching threats to defences

Open the lesson page

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Quick quiz · 1 of 3

DNS…

  1. A Turns a domain name into an IP address
  2. B Encrypts the page
  3. C Stores cookies

A. Turns a domain name into an IP address

The phone book of the internet.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Quick quiz · 2 of 3

A session cookie…

  1. A Lasts for years
  2. B Is a type of virus
  3. C Is deleted when the browser closes

C. Is deleted when the browser closes

A persistent cookie stays. A session cookie goes with the session.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Quick quiz · 3 of 3

Pharming is…

  1. A Being sent to a fake website even when you type the right address
  2. B Guessing every password
  3. C A fake email asking for a password

A. Being sent to a fake website even when you type the right address

Phishing needs you to click. Pharming redirects you, often through poisoned DNS.

Year 11 · Computer Science · The internet and its uses · Lesson 4 of 5

Exit ticket

Answer on paper before you go. Then check.

  1. A DDoS attack…

    A Encrypts your files for moneyB Guesses passwordsC Floods a server with requests from many machines

    C. Floods a server with requests from many machines Distributed denial of service: so many requests the server cannot answer real ones.

  2. Each block in a blockchain contains…

    A Only a passwordB A pictureC A hash of the previous block, so any change shows

    C. A hash of the previous block, so any change shows Change one block and every hash after it stops matching.