How can I implement end-to-end encryption for chat messages in a Flutter + Firebase app?

[Ziauddin-developer]

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I’m using Firebase (Auth, Firestore, Cloud Storage, FCM) for a chat app. I want messages (including media) to be readable only by the sender and intended recipients even if Firebase is compromised.
What’s a production-grade approach for key management, message encryption, and group chats? Code pointers in Dart would help.

[Manahiltareen]

You can implement end-to-end encryption (E2EE) in a Flutter + Firebase chat app by encrypting messages on the client before sending them to Firestore/Realtime DB and decrypting only on the recipient’s device.

A common approach:
Use a key exchange protocol (e.g., Diffie-Hellman) to generate shared keys between users.
Encrypt/decrypt messages with AES (for speed) and RSA/ECC (for key exchange).
Store only encrypted data in Firebase; Firebase should never see plaintext messages.

Libraries like encrypt
in Dart can handle AES/RSA.

This ensures Firebase acts as a transport/storage layer only, while message privacy stays intact.