Apple has introduced a new post-quantum cryptographic protocol called PQ3 for iMessage, which provides end-to-end encryption and protection against quantum attacks. The protocol uses a hybrid design that combines Elliptic Curve cryptography with post-quantum encryption and includes a periodic rekeying mechanism to self-heal from key compromise. PQ3 is considered to be the first large-scale messaging protocol to reach Level 3 security, providing protocol protections that surpass those in other widely deployed messaging apps. The new protocol will start rolling out with the public releases of iOS 17.4, iPadOS 17.4, macOS 14.4, and watchOS 10.4.