What is encryption? A simple guide

A locked box for your information

Encryption means scrambling information so that it looks like nonsense to anyone without the key. The scrambled version is called ciphertext. The readable version is called plaintext. A key is a long secret number used to lock and unlock it.

Imagine posting a letter in a locked box. The postal workers can carry the box, but they cannot read what is inside. Only the person with the key can open it. Encryption does the same for data travelling across the internet or sitting on your phone.

Where you already use it

• Websites: the padlock and https:// in your browser mean the connection is encrypted, so others on the network cannot read what you type.
• Messaging apps: many use end-to-end encryption, which means only the sender and the receiver can read messages, not even the company running the app.
• Wi-Fi: your home network password protects encryption between your devices and the router.
• Phones and laptops: modern devices encrypt their storage, so a thief who takes the device cannot simply copy your files.
• Card payments: card details are encrypted between the shop, the payment company and the bank.

Two kinds of key

There are two main approaches, and most systems use both together:

• One shared key (symmetric encryption): the same key locks and unlocks. It is very fast, but both sides need the key.
• A key pair (asymmetric encryption): a public key that anyone can use to lock something for you, and a private key that only you hold to unlock it. This solves the problem of sharing keys safely.

Our comparison Symmetric vs asymmetric encryption shows the difference with an animation.

What encryption does not do

Encryption is powerful, but it is not magic:

• It does not stop you from typing your password into a fake website. A scam site can have a padlock too.
• It does not protect a device that is unlocked and in someone else's hands.
• It is only as strong as the password protecting the key. A weak password weakens everything.

Tip: The padlock means "this connection is private", not "this website is honest". Always check the website name as well.

What you should do

1. Set a screen lock (PIN, fingerprint or face) on every phone and laptop. On most modern devices this also switches on storage encryption.
2. Use messaging apps with end-to-end encryption for private conversations.
3. Use WPA2 or WPA3 security with a strong password on your home Wi-Fi.
4. Use strong, unique passwords, ideally with a password manager. See Strong passwords made easy.

Want the technical version? Read our note on cryptography or try the hash tool.

Why governments and companies argue about it

You may hear debates about encryption in the news. Police and some governments want ways to read criminals' messages. Security experts point out that a hidden "back door" for one group can be found and used by others too, which would weaken protection for everyone. It is a genuine policy argument with reasonable people on both sides. For everyday users, the practical point is simple: the encryption built into mainstream apps and devices is there to protect you, and you should keep it switched on.