How the Double Ratchet Algorithm Secures Your Messages on Signal & WhatsApp 🔒

How do text messaging services like Signal and WhatsApp keep your text messages secure? The Double Ratchet algorithm.

Let’s say Alice wants to send Bob an end-to-end encrypted message. She uses a key to lock up the message and Bob uses the same key to unlock the message. But what if they want to send a bunch of messages back and forth? Using the same key the whole time is not very secure. It would be better to have a unique key for each message. The Double Ratchet algorithm cranks out a new key each time you send a message by combining a key derivation function and a Diffie-Hellman calculation.


Resources:
Diffie-Hellman (with numbers): https://www.youtube.com/watch?v=ESPT_36pUFc
Diffie-Hellman (with colors): https://www.youtube.com/watch?v=NmM9HA2MQGI
Signal Specifications: https://signal.org/docs/specifications/doubleratchet/

Created by Kelsey Houston-Edwards
Sponsored by Wire https://wire.com