End to end encryption with Firestore

Question

Is there any recommended way to encrypt data in Firestore? Even though Firestore, by default, encrypts data before it writes to the disk, admins still can read data in the console. I am looking to make the data readable only by users who are allowed decrypt it. So it will be unreadable in the console.

One way I think it may be possible is to use cloud functions but I can't find how to modify the data before it gets saved to the disk (beforeWrite hook).

Answer 1

The only way to control all access to all data in Firestore (or Realtime Database for that matter) is to perform encryption on the raw data itself before it's even passed to the client APIs or SDKs that perform the write.

It's not possible to hook writes before they actually commit to storage with Cloud Functions. A function will only receive an event after the data is successfully written.

Also, bear in mind that if you encrypt data before it reaches the API, you will be unable to search and sort using that data, because it will no longer represent the original data in any way. All you would be able to do is access a document/location by its unique key (assuming that key is also not encrypted, or the encrypted id is (cryptographically) shared between both parties through another secure channel.

Answer 2

You'll need to encrypt data on the client devices before you write them into Firestore. When the other device reads up the data, decrypt it.

Key management is what you'll need to spend some time with to implement: Users on both devices need to have private keys locally and public keys accessible to the other users to encrypt messages with. Then you'll need to create a data encryption key to encrypt/decrypt messages in the chat room. This data encryption key, you'll encrypt with the participating users' public keys. And all keys, store in Firebase, encrypted.

Check out these 2 sample apps for a Firestore chat app example:

• iOS: https://github.com/VirgilSecurity/demo-firebase-ios
• Android: https://github.com/VirgilSecurity/demo-firebase-android

David