Step 1 of 6 How encryption works
Scrambled messages
Encryption scrambles a message so that only someone with the right key can read it. One of the oldest methods shifts every letter a fixed number of places along the alphabet: with a key of 3, A becomes D and B becomes E. The same key, turned back, unscrambles it.
This message was scrambled with a secret key: . Turn the wheel until it makes sense.
How many different keys does this wheel have, apart from not shifting at all?
Step 2 of 6 How encryption works
Bigger keys
Modern keys are numbers measured in bits (lesson 08 shows what a bit is). Every extra bit doubles the number of possible keys. Attackers can't read the message, so their only hope is to try every key, and with long enough keys that becomes impossible.
Make the key long enough that trying every key, at a trillion guesses a second, would take longer than the age of the universe.
Is a 256-bit key twice as strong as a 128-bit key?
Step 3 of 6 How encryption works
A padlock anyone can close
How do two strangers share a secret key without anyone overhearing? With public-key encryption. Picture Sara handing out open padlocks to anyone who asks: that's her public key. Anyone can snap one shut on a box, but only Sara's private key, which she never shares, can open it.
Send a box that only Sara can open. A thief is waiting on the way.
Everyone can see Sara's padlock. Why can't the thief work out her key from it?
Step 4 of 6 How encryption works
The padlock in your browser
When a web address starts with https and shows a padlock, your browser and the website have used these keys to set up a private connection. What you type is sealed on its way, so the café Wi-Fi, or anyone else in between, sees only scrambled data.
Send your password to the bank so the café's Wi-Fi router can't read it.
A site shows the padlock. Does that mean the site is genuine?
Step 5 of 6 How encryption works
End to end
Chat messages pass through the chat company's servers. With end-to-end encryption, only the phones at each end hold the keys: the server passes on sealed boxes it can't open. Without it, the server can read what passes through.
Send a message the chat company's server can't read.
With end-to-end encryption, why might your old chats be lost if you lose your phone without a backup?
Step 6 of 6 How encryption works
Fingerprints, not passwords
A hash turns text into a fixed-length fingerprint that can't be turned back. Websites store your password's fingerprint, never the password, and compare fingerprints when you sign in.
Use any word, not a real password. Nothing is saved or sent.
Fingerprint a word, then change one letter and fingerprint it again. How much changes?
A website leaks its password fingerprints. Why does a long, unique password still protect you?
Quiz How encryption works
Check what you know
Six questions, 5 points each. One answer per question.
Done How encryption works
Lesson complete
Now you know what the padlock means and what it doesn't, why long keys can't be guessed, how strangers share secrets with padlocks anyone can close, and why websites never need to know your password.
MARIFA · Nothing you do here leaves this device.