Every time you open a page, your browser and a web server hold a short conversation following agreed rules: HTTP. Add encryption and it becomes HTTPS. Then the browser turns the HTML it receives into the page you see.
Hypertext transfer protocol (HTTP) is the set of rules for transferring web pages between a web browser (the client) and a web server: the browser sends a request, the server sends a response containing the files. HTTPS is HTTP made secure: the data is encrypted using the SSL/TLS protocol, so if it is intercepted it cannot be understood. The main purpose of a web browser is to render HTML and display web pages.
Fig. 1: the browser requests a page and the web server responds
Section 01
HTTP: request and response.
In the lab, watch the request leave the browser and the response come back from the web server. Then switch between HTTP and HTTPS and look at what someone intercepting the data would see.
Purpose of HTTP: a protocol (set of rules) that lets a browser and a web server communicate, so that web pages can be requested and transferred.
Request: the browser sends an HTTP request to the web server asking for a page or file.
Response: the server sends back the requested files (HTML, images, scripts) or an error message, such as 404 Not Found.
Without encryption: with plain HTTP the data travels as plain text, so anyone who intercepts it can read it.
Section 02
HTTPS: the secure version.
HTTPS works in the same request and response way, but it adds security on top.
Encryption: HTTPS uses the secure socket layer (SSL) protocol, or its newer version TLS, to encrypt all data sent between browser and server.
Authentication: the server proves it is genuine with a digital certificate, so the browser knows it is talking to the real website.
Where it matters: any page where users enter personal details, passwords or payment card numbers.
How to tell: the URL begins https:// and the browser shows a padlock in the address bar.
Examiner trap
HTTPS does not stop data being intercepted. It means that intercepted data is encrypted, so it is meaningless without the key. Write "cannot be understood", not "cannot be stolen".
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
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What is the purpose of HTTP?
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In the lab, what does an eavesdropper see when the page is sent using HTTPS?
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What is the main purpose of a web browser?
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Which browser function lets a user return to a page they saved earlier?
Section 03
What a browser does.
A web browser is application software. Its main job is to render HTML: read the HTML code and turn it into the formatted page on screen. It has several other functions that the syllabus lists.
Function
What it does for the user
Storing bookmarks and favourites
Saves the URLs of pages so they can be revisited with one click
Recording user history
Keeps a list of pages visited, so a page can be found again
Allowing multiple tabs
Several web pages can be open at once in one window
Storing cookies
Keeps small files from websites, e.g. login details or a shopping basket
Providing navigation tools
Back, forward, refresh and home buttons; following hyperlinks
Providing an address bar
Where the user types or sees the URL of the page
Examiner trap
A web browser is not a search engine. The browser displays pages; a search engine is a website that you visit using a browser.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 1 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
How does HTTPS differ from HTTP?
Exam style+20 XP
Which of these is a function of a web browser?
Exam style+20 XP
Which website should certainly use HTTPS?
Exam style+20 XP
A browser receives a file of HTML from a web server. What does the browser do with it?
Skill unlocked
HTTP, HTTPS and web browsers, mastered.
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