The padlock and the missing email
A student types a password on a Wi-Fi café page. A friend says: "Look for the padlock first." Later the student reads email on a phone. The laptop at home shows the same email as new.
Two ideas hide here: how a page is kept private, and how email reaches many devices.
Key words
| Word | What it means | Example |
|---|---|---|
| HTTP | hypertext transfer protocol: the rules for asking for and sending web pages | |
| HTTPS | HTTP with encryption added, so nobody on the way can read it | |
| Encryption | scrambling data so only the right people can read it | |
| SMTP | simple mail transfer protocol: the rules for sending email | |
| POP | post office protocol: it downloads email to one device | |
| IMAP | internet message access protocol: it keeps email on the server for many devices | |
| Status code | a number in a web reply that says how it went | 404 |
| Protocol | a set of rules computers follow to talk to each other | |
| Network | devices joined so they can share things |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can say what HTTP, HTTPS, SMTP, POP and IMAP are used for.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
HTTP asks, the server answers
HTTP is how a browser asks for a web page. The browser sends a request. The web server sends back a reply with a status code, such as 200 for "here it is" or 404 for "not found". Then it sends the page.
HTTP is plain text. Anyone sharing your Wi-Fi may read it.
Try it: a request and a reply
request = "GET /timetable.html HTTP/1.1"
reply = "HTTP/1.1 200 OK"
print("Browser sends:", request)
print("Server replies:", reply)
# Change the request to /menu.html.
# Change the reply to 404 Not Found. Press Run.HTTPS adds a lock
HTTPS is HTTP with encryption. The server also proves who it is with a certificate. The padlock in the browser shows this.
On HTTPS, a person on the same Wi-Fi sees only scrambled data. Use it for logins, shopping and banking. Most sites now use it for everything.
HTTP and HTTPS compared
| Feature | HTTP | HTTPS |
|---|---|---|
| Encrypted? | No | Yes |
| Proves the server is real? | No | Yes, with a certificate |
| Shown in the browser as | Not secure | A padlock |
| Fit for passwords and payments? | No | Yes |
The cells students fill in are left blank in this preview.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.