How Signal Instant Messaging Protocol Works (& WhatsApp etc) - Computerphile?

Signal is like having a secret conversation where only you and your friend can understand what’s being said, even if someone else is listening in.

Imagine you and your best friend have a special code that changes every day, like a password to unlock your messages. You write a note, use the code to hide it, and send it to your friend. They use their copy of the same code to read the message, and no one else can figure out what you said, even if they catch the note in the mail.

Signal uses keys, like invisible locks and keys that only you and your friend have. When you start a conversation, both of you get special keys. These keys help make sure that only you two can read each other’s messages, no one else can snoop around.

Apps like WhatsApp use this same idea but with a twist. It's like having multiple friends who all have different codes for different conversations. Every time you talk to someone new, you both get new keys just for that chat. This way, even if one friend’s code is broken, your other chats stay safe, it’s like having several secret hideouts instead of just one.

This makes sure your messages are private and safe, even when lots of people are using the app at the same time.