End-to-end encrypted messaging: what it protects, and what it doesn’t

5 min read · White Sun

Almost every messaging app now says its messages are encrypted. That can mean very different things, and the difference decides who can read what. This guide explains end-to-end encryption in plain terms, and just as importantly, what it does not cover.

What end-to-end encryption does

With end-to-end encryption, a message is locked on the sender’s phone and only unlocked on the recipient’s phone. The company’s servers carry the locked message between the two, but they do not hold the keys, so they cannot read it. Photos and files can be protected the same way. This is different from an app that only encrypts the connection to its servers, where the company can still read the message once it arrives.

What it does not hide

Encrypting the content is not the same as hiding everything around it. Depending on how a messenger is built, a service may still be able to see things such as:

• that an account exists, and when a phone connects;
• roughly how large a message is;
• which account a message is addressed to, though some designs hide the sender;
• the network address a phone connects from.

Your internet provider can also see that you are connecting to the service. None of this is a flaw to be embarrassed about, but an honest messenger should say what it can see rather than claim to be anonymous. If an app says it is untraceable, treat that as a warning sign.

The weak points are usually outside the encryption

• Your phone: anyone who can unlock it can read your chats, so a screen lock matters.
• The other person: they can screenshot or forward anything you send.
• Backups: a chat history copied to an unprotected cloud backup is only as private as that backup.
• Lost access: some apps let the company reset your account; others, by design, cannot. If only you hold the recovery phrase, losing it can mean losing the account.

Questions worth asking any messenger

• Does it need my phone number or email to sign up?
• What does it store about me, and for how long?
• Has the design had an independent security audit, or is it still early?
• What does a notification reveal on my lock screen?

For transparency, WSMsg is an example of the trade-offs above. It is in early testing, has not had an independent security audit, and does not claim to be anonymous.