As evidence, the lawsuit cites unnamed “courageous whistleblowers” who allege that WhatsApp and Meta employees can request to view a user’s messages through a simple process, thus bypassing the app’s end-to-end encryption. “A worker need only send a ‘task’ (i.e., request via Meta’s internal system) to a Meta engineer with an explanation that they need access to WhatsApp messages for their job,” the lawsuit claims. “The Meta engineering team will then grant access – often without any scrutiny at all – and the worker’s workstation will then have a new window or widget available that can pull up any WhatsApp user’s messages based on the user’s User ID number, which is unique to a user but identical across all Meta products.”
“Once the Meta worker has this access, they can read users’ messages by opening the widget; no separate decryption step is required,” the 51-page complaint adds. “The WhatsApp messages appear in widgets commingled with widgets containing messages from unencrypted sources. Messages appear almost as soon as they are communicated – essentially, in real-time. Moreover, access is unlimited in temporal scope, with Meta workers able to access messages from the time users first activated their accounts, including those messages users believe they have deleted.” The lawsuit does not provide any technical details to back up the rather sensational claims.
Your threat model seems to be an app whose published source code doesn’t match the published app, and whose published version uses a side channel not in the source code to leak messages in plaintext to a server. If that’s what we’re worried about then decentralization of the app’s main messaging channel makes no difference. The sneaky side channel could still be there in any app, centralised or decentralized.
That’s a theoretical worry to be mitigated through integrity checks on published open-source apps. The worry with Meta and WhatsApp is much more immediate: a known bad actor with a closed-source app, many domains they could use to leak keys or unencrypted messages, and a fawning relationship with the fascist and surveillance-hungry US Government. I’d still put significantly more trust in Signal even though it is centralised.
You’re right decentralization would help because you could isolate yourself from the corporate server sending the instructions for you to leak the messages.
But ultimately you’re right integrity checks of apps are a better way to address this and fortunately it seems Signal do produce reproducible builds. https://github.com/signalapp/Signal-Android/blob/main/reproducible-builds/README.md so is secure from this kind of attack (unless there is a backdoor in the published code)