HOW CHAT ENCRYPTION WORKS

Only the ends
can read it.

Your message passes through many computers on its way.

Two people at a café table, seen from behind and at a distance, each holding a phone, with soft window light and space on one side — AI-generated image, not a photograph of a real person or place.

Content is scrambled
Metadata still shows
The ends are the weak point
Strong lock, open envelope

With end-to-end encryption, it is scrambled on your phone and only unscrambled on the recipient's. The app's own servers pass it along without being able to read it. That is a lot of protection, but not all of it.

Updated 16 October 2026

THE SHORT ANSWER

A sealed letter,
not a secret meeting.

Encryption hides what you said.
It does not always hide that you said it.

THE CONTENT

Scrambled on the phone

End-to-end encryption turns a message into gibberish on the sender's device, and only the final recipient can decode it. Even the app's servers cannot listen in.

Who can read it?

THE KEYS

Check who you are talking to

Apps let you compare a fingerprint or scan a QR code to confirm the key belongs to your friend, which guards against a machine-in-the-middle.

How to check

THE LIMITS

Metadata and backups

The service may still see when messages are sent and your IP address. Cloud backups need their own encryption to stay protected.

See the numbers

A QUICK CHECK

Who can see
an encrypted chat?

Pick someone along the way to see what end-to-end encryption hides from them. The bar shows how much of the conversation they could still get.

Based on the Electronic Frontier Foundation's Surveillance Self-Defense guides. General information about how the technology works.

Who can see it

Choose who is lookingSomeone on the same Wi-FiThe app's own serversA cloud backupThe person you send toSomeone who has hacked a phone

Someone on the same Wi-FiScrambled text

Eavesdroppers on the network only see the scrambled message. They may still see metadata such as who is talking to whom and when.

The app's own serversNot the words

The app company cannot read the content, but it may collect some metadata, like what time a message was sent or your IP address.

A cloud backupCheck it

If chats are backed up to the cloud automatically, the EFF says to check that the backups are encrypted too, so the messages are protected at rest as well.

The person you send toEverything

The message is decrypted for them. They can take screenshots or keep logs of the conversation, and encryption cannot stop that.

Someone who has hacked a phoneEverything

If an endpoint, the device itself, is compromised, encrypted communications on it can be compromised too.

Source: EFF Surveillance Self-Defense, What Should I Know About Encryption? and A Deep Dive on End-to-End Encryption (reviewed 2025).

TWO NUMBERS WORTH KNOWING

Almost everyone chats,
groups included.

One figure on how many people message online,
one on how big an encrypted group can be.

94–96%

Internet users who send messages or make calls online

Ofcom's 2025 adults' media use report (2024 fieldwork) found 94% of male and 96% of female internet users use sites and apps to send messages or make calls.

UK USE · OFCOM

2 to thousands

Group sizes the MLS standard is built for

The Messaging Layer Security standard, published in July 2023, sets out how a group can agree on encryption keys even when members are not online at the same time.

GROUP CHATS · IETF RFC 9420

RFC 9420 explains that keys are hard to set up for group chats because more than two devices must agree on one, and some may be offline.

A phone lying face up on a wooden desk next to a laptop and a cup, its screen dark, in calm morning light — AI-generated image, not a photograph of a real person or place.

FOUR THINGS TO KNOW

Use the lock
the way it is meant.

These come from how the technology works, not from any one app. Settings differ from app to app.

Know which kind you have
Transport-layer encryption lets the service see messages on its servers; end-to-end encryption does not.
Verify a contact's key
Compare the fingerprint or scan each other's QR code, ideally in person, to rule out a machine in the middle.
Look at your backups
If chats back up to the cloud, check whether those backups are encrypted as well.
Remember the other end
Whoever receives a message can screenshot or save it. Encryption protects the journey, not what happens after.

HOW THE KEYS WORK

Two keys,
one lock.

End-to-end tools rely on public key cryptography. Each person has a public key that can be shared freely and a private key that stays on the device. A message locked with your public key can only be opened with your matching private key.

Modern chat apps swap public keys for you, so there is nothing to set up. The same pair of keys also lets a message be signed, which shows it came from the right person and was not changed on the way.

Hands holding two phones side by side as if comparing the same pattern on both screens, the screens softly blurred — AI-generated image, not a photograph of a real person or place.

Questions

Questions people ask

What does end-to-end encryption mean?

A message is encrypted by its original sender and decrypted only by its final recipient. No one in between, including the app's servers, can read it.

Can the app company see my messages?

Not the content, if the chat is end-to-end encrypted. The EFF notes the company may still collect some metadata, such as when a message was sent and your IP address.

Is HTTPS the same as end-to-end encryption?

No. HTTPS is transport-layer encryption: it protects data on the way to the service, but the service itself can see the data you send it.

What is a safety number or security code?

It is a way of checking a public key fingerprint, by comparing characters or scanning a QR code, so you know the key really belongs to the person you are talking to.

Are disappearing messages the same as encryption?

No. The EFF says features like disappearing messages can make a chat feel secure without giving the protection you need. Encryption is what stops others reading it.

Only the ends
can read it.