Consumer Messaging Platform — WhatsApp-Class System · View 12 of 23

End-to-End Encryption Architecture

From device key material through asynchronous session setup to per-message ratcheting — and where the platform sits, which is outside the trust boundary.

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Protocol choices

X3DH for asynchronous session setup so a peer need not be online
Double Ratchet for forward secrecy and post-compromise recovery per message
Sender Keys for groups, media keys per blob, all under the same identity key

Key management

Identity keys are long-lived and hardware-backed where the device supports it
Signed prekeys rotate weekly; one-time prekeys are consumed once and replenished
Key Distribution stores public material only and can be fully rebuilt from devices

Threat position

A full compromise of the platform yields ciphertext and metadata, not messages
Safety numbers give users an out-of-band check against a key substitution attack
A key change raises a visible warning rather than being silently accepted