Signal Protocol is becoming the standard for ETEE

To comply with DMA, WhatsApp and Messenger will become interoperable via Signal protocol
https://techcrunch.com/2024/03/06/to-comply-with-dma-whatsapp-and-messenger-will-become-interoperable-via-signal/?guccounter=1

The Signal Protocol is a non-federated cryptographic protocol that offers end-to-end encryption for voice and instant messaging conversations. It includes the Double Ratchet Algorithm, which ensures secure message exchange between parties by deriving new keys for each message and incorporating Diffie-Hellman calculations into the key derivation process. The protocol has been widely adopted by various messaging apps like Signal, Wire, and WhatsApp for its robust security features and encryption capabilities.