End-to-end encryption, explained in plain English
Many messaging apps say they're "end-to-end encrypted". It's a strong promise, but it's easy to misunderstand what it covers. This guide explains how it works without the maths, what it protects, what it leaves open, and what you can do to stay safe.
Encryption in one paragraph
Encryption scrambles a message so that it looks like random noise to anyone without the right key. With the key, the message turns back into readable text. Modern encryption is strong enough that guessing the key isn't realistic. In practice, the question is always who holds the keys.
Ordinary encryption vs end-to-end
Encryption in transit protects a message on its way between your phone and a company's server, like the padlock you see on websites. Once it reaches the server, the company can read it. Many services work this way, and it does protect you from people on the same Wi-Fi.
End-to-end encryption goes further. The message is locked on the sender's phone and can only be unlocked on the recipient's phone. The server passes it along but only ever sees the scrambled version. The company running the service can't read it, even if it wanted to.
How the keys work
End-to-end systems use a pair of keys for each person or device:
- A public key, which can be shared openly. Anyone can use it to lock a message for you.
- A private key, which never leaves your phone. Only it can unlock messages locked with your public key.
Think of a padlock you hand out freely. Anyone can snap it shut on a box addressed to you, but only you have the key that opens it. Apps combine this with other techniques so that each conversation, and often each message, uses fresh keys.
What end-to-end encryption protects
- The content of your messages: text, photos, voice notes and files.
- Calls, when the app encrypts calls end to end as well. Not every app does, so check.
- Protection from the server. If the company's servers are hacked, the attacker gets scrambled data, not readable chats.
What it doesn't protect
- Metadata. The server usually still needs to know that a message went from one account to another, when, and roughly how big it was. Good apps keep as little of this as possible, but some is needed to deliver messages at all.
- Your phone itself. Messages are readable on your device once they arrive. If someone unlocks your phone, they can read your chats. A screen lock and an app PIN matter.
- The person you're talking to. Encryption can't stop a recipient from taking a screenshot or forwarding a message.
- Backups. Some apps back up chats to cloud storage in a form that isn't end-to-end encrypted. Check how backups are protected.
- Scams. A fraudster in an encrypted chat is still a fraudster. Encryption protects the line, not your judgement.
Checking you're talking to the right person
There's one weakness end-to-end encryption can't fix by itself: making sure the public key really belongs to your friend and not to someone pretending to be them. Secure messengers let you verify a contact by comparing a code or scanning a QR code when you're together in person. Once verified, you'll know if their key ever changes unexpectedly.
It takes ten seconds and is worth doing for the people you talk to most.
How WhisperLite handles it
In WhisperLite, our messenger, messages are encrypted on your phone before they're sent. The server only relays scrambled data it can't read. Your account is protected on the phone by a PIN, no phone number or email is needed to sign up, and you can verify a contact by scanning their QR code. More detail is in the WhisperLite help centre and the website privacy page.
Checklist for any messaging app
- Does it say chats and calls are end-to-end encrypted?
- Can you verify contacts with a code or QR scan?
- How are backups protected?
- Does it ask for more personal data than it needs?
- Is your phone locked, and does the app have its own lock?