What Is the Signal Encryption Protocol?

This is a very approachable overview of the Signal protocol. I wasn't aware of how often it rotated keys.

The Signal protocol, however, uses a so-called "ratchet" system that changes the key after every message. It does this by generating a collection of temporary key pairs for each user, in addition to the permanent keys. When someone sends a message to a contact over an app using the Signal protocol, the app combines the temporary and permanent pairs of public and private keys for both users to create a shared secret key that's used to encrypt and decrypt that message. Since generating this secret key requires access to the users' private keys, it exists only on their two devices. And the Signal protocol's system of temporary keys—which it constantly replenishes for each user—allows it to generate a new shared key after every message.

That is incredibly secure! 🔒