The padlock in the browser
You open your bank in a browser. A padlock appears. How does the browser know the site is really the bank?
The bank shows a certificate. A trusted body signed it. That body is a certificate authority. A company can run its own, to protect its own servers and devices.
Key words
| Word | What it means | Example |
|---|---|---|
| Digital certificate | A file that links a name to a public key, like a passport for a website or a device. | |
| Certificate authority | A trusted body that checks who you are and signs your certificate. | CA |
| Public key | A key you can share freely. It locks data that only the matching private key can open. | |
| Private key | A key you keep secret. | |
| Chain of trust | A device trusts the CA, and the CA signs the certificate, so the device trusts the certificate. | |
| Expiry | The date a certificate stops being valid. | |
| Revoke | Cancel a certificate before its expiry. | |
| Server | A computer that gives data or services to other computers. | |
| Encryption | Scrambling data so only the right key can read it. |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can explain what a certificate authority does and list the steps to set one up and use it.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Cycle 1: how a CA works
A certificate says: "This public key belongs to this server." The certificate authority signs it, so nobody can forge one.
Every device has a list of CAs it trusts. If the CA that signed a certificate is on the list, the device trusts the certificate. That is the chain of trust.
An organisation can run its own CA. Its own devices trust it, so its own servers get certificates without paying a public CA.
Check: how it works
Have a go
Check: how it works
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.