Wirebook › Glossary › Certificate
What is a certificate?
In one sentence: A digital ID card that proves a website is who it says it is. Your browser checks it before showing the padlock.
A little more
Anyone can build a website that claims to be your bank. A certificate stops that: it's a small file, signed by an organisation your device already trusts, that says "this key really belongs to this web address". Your browser checks the signature, the address and the expiry date before it shows the padlock.
Certificates don't say a site is honest or safe, only that you're really connected to the address in the bar.
It's a bit like… A passport: it doesn't prove someone is nice, but it proves who they are, and you trust it because of who issued it.
See it in action
- 1What happens when you open a web page?Follow one click from your keyboard to a server and back: DNS, the padlock handshake, HTTP, tunnels and painting the page.6 min · interactive
- 4Secret codes: encryption and hashingFrom Caesar's cipher to the AES-256 lock behind every padlock: encrypt and decrypt in your browser, crack a code by brute force, and watch one letter change a SHA-256 fingerprint completely..7 min · interactive