Note that the feature is for premium (paid) users only.
There's no mention of whether or not this will also be available in iOS or Android apps as well. Information on this would be appreciated.
Also: Available to everyone with a Plus, Professional, or Visionary plan
Hopefully there is a big mobile update coming soon now that ProtonMail 4.0 is out of beta.
Protonmail doesn’t stop you from migrating, they’re stopping you from *indefinitely using their domain and servers, for free*. GMail has an incentive-they’ll scan your emails for information about you and use it to target you on their other platforms. Proton has no such incentive, and no obligation as far as I can see.
I activated the feature today, and my Indexed DB for mail.protonmail.com now has a table "messages", and each message has an ID, a time, and an "aesGcmCiphertext" object with 2 child objects of keys "iv" and "ciphertext". The "iv" object has 12 integer keys from 0-11, with integer values between 0-255. I don't see any data in the "ciphertext" object at all.
I am not well versed in indexeddb so can't shed more light.
This means that when you have search message content enabled, but your web browser is closed, an attacker with physical access to your device cannot read the contents of the index file. If you are logged in with your ProtonMail tab open, a decrypted version is stored in memory, but at this point, they would have direct access to your emails, anyway.
