What is end-to-end encryption, and why only two people can read your messages

You've probably seen “messages are end-to-end encrypted” in plenty of apps. But what does it actually mean, and how is it different from an ordinary “secure” website?

Ordinary encryption vs end-to-end encryption

When you visit a site with a padlock in the address bar (HTTPS), data is encrypted in transit between you and the server. But once it reaches the server, it's decrypted, and the server can read it.

End-to-end encryption goes further: a message is encrypted on the sender's device and decrypted only on the recipient's device. Everything in between, including the server passing the message along, sees only meaningless characters.

Public keys and private keys

Imagine everyone has a mailbox with two kinds of key:

• The public key is like the mail slot: anyone can use it to drop a letter into your box.
• The private key opens the box. Only you hold it, and it never leaves your device.

When two people are matched on Người Lạ Ơi, their devices exchange public keys. You encrypt your message with the other person's public key, and only their private key can open it.

What this means for you

• The server can't read your messages. We pass messages along and hold them briefly in encrypted form, but we don't have the key to open them.
• There's no archive to leak. Once both people leave a chat, its messages are deleted from the server.
• New device, old messages unreadable. Because the private key lives on your device, if you reinstall the app or clear your browser data, older messages encrypted for the old key show “This message can't be read on this device”. That's the small price of privacy.

Encryption doesn't replace caution

Encryption protects messages on the way and on the server, but it can't stop the recipient from taking a screenshot or telling someone else. Truly private details, like your phone number, address or sensitive photos, are still best kept to yourself, especially with someone you've just met.