The encyclopedia · Software & IT · Technical decision · 2013–2016
Signal's Double Ratchet made end-to-end encryption the default for a billion people
Open Whisper Systems' Double Ratchet derives new keys per message; WhatsApp switched it on by default in 2016, making it the world's most-deployed encryption.
Open Whisper Systems
the move
Until the mid-2010s, most messaging apps encrypted traffic only between phone and server, leaving messages readable at the provider. Truly private chat required users to trust the company operating the servers.
Open Whisper Systems' Signal Protocol, built on the Double Ratchet designed by Trevor Perrin and Moxie Marlinspike, derived fresh keys for every message and mixed Diffie-Hellman outputs into the chain. Even if long-term keys were later compromised, past and future messages stayed protected.
In 2015 WhatsApp announced a partnership to integrate the protocol, and on 5 April 2016 the rollout completed: end-to-end encryption became the default for every chat, group chat, attachment and call. Signal reported over a billion monthly active users on the protocol.
why it works
- Forward secrecy meant one stolen key did not decrypt history.
- Default-on encryption required zero user effort or trust.
- An open, specified protocol could be audited and ported.
- WhatsApp's scale made it the industry baseline.
what transfers
For a security standard to win at scale, it must work silently by default; WhatsApp made the Signal Protocol default-on, so a billion users got forward secrecy without understanding it.
what came after
The Signal Protocol became the de facto standard for end-to-end messaging, also used by Google Messages and Facebook Messenger's secret conversations; its ratchet design is now the reference model for secure chat.
references
- The Double Ratchet Algorithm (specification)
- WhatsApp's Signal Protocol integration is now complete
- WhatsApp adds end-to-end encryption
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