How end-to-end encryption works: why even WhatsApp cannot read your messages
Encryption in transit: why a chat server can read messages that are locked on the way
Some chat apps lock a message only on its way to their server. There, the company unlocks it and can read it. So "encrypted" does not always mean that nobody else can read your messages.
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Rono's birthday is on Saturday, and you and Miva have found his gift: a ride in a hot-air balloon. You type the news to Miva in your chat app.
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Your phone does not send it straight to Miva. Every message goes first to the chat server, a computer of the company behind the app, and the server passes it on. Rono works at that company. He looks after this very server.
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Say your app locks the message only for the trip. Then nobody on your Wi-Fi, or anywhere along the cables, can read it on the way. This is called encryption in transit.
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But that lock comes off at the server, because the server holds the key of the trip. Your message would sit there in plain words, and Rono could read his own surprise.
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The server would lock it again for the trip to Miva. Two locked trips, and in the middle, one stop where the message is open to whoever runs the server, or whoever breaks into it.
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Many apps worked this way for years, and some still do for most chats. Yours works like WhatsApp and Signal, which do something else. You press send.
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Go further
Two things to know.