I think you mean the phone vendors, as they are the ones holding the unencrypted chat history in the users cloud storage. Facebook themselves do not have access to the chat logs (unless they are compelled to inject keys).
To be clear I’m not suggesting this is absolutely happening. I’m merely pointing out it’s entirely possible from a technological perspective given it’s closed source software owned by Facebook. That’s not a recipe for privacy.
I'd love for iOS and android to add some sort of OS-level application hash or something. "This app was compiled with xcode version X / llvm version Y with this set of options. The resulting binary hashes to ZZZ". That way with the source code you could verify that the binary on your phone is unchanged.
(Another approach would be to get apple / google to do the compilation themselves from the project on github. If apple builds my project, they could put some signed metadata in the bundle saying "We (apple) compiled this from git SHA XXX")
On iOS it's a lot more difficult to get the required certificates from Apple but you can run your own build in Xcode and deploy it to your personal device if you are a registered Apple developer.
While reproducible builds are obviously the gold standard, for apps you install from the Play Store or the App Store, developers sign the apps that get distributed with their own private keys. As Google and Apple don’t have access to these it should be verifiable that the apps are not tampered with.
There is an exception here with the Play Store, where there is an opt-in option for Google to sign the app on your behalf [1], but I think we can safely assume Signal are manually signing with their own private keys.
In any case it's easy to just grab an APK from an Android device and check signatures for yourself.
For iOS though, no surprises here it’s locked down. Although from what I gather reading Apple’s security documentation, it confirms that apps must be signed by developers with their private keys. [2] But unlike Android there’s sadly no way I can tell for the user to independently verify this without jailbreaking.
But ultimately, short of building each version yourself, all this is moot if you distrust the developers.
[1] https://developer.android.com/studio/publish/app-signing [2] https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app...
You can build the iOS version too for development: https://github.com/signalapp/Signal-iOS/blob/master/BUILDING...
I haven't done it before but you should even be able to deploy that build to your phone in theory: https://codewithchris.com/deploy-your-app-on-an-iphone/
It's unclear to me if there are any restrictions on iOS that would prevent you from doing that.
You can certainly get your own build working (without notifications and other features). But personally I found it prohibitively difficult to do so.
https://github.com/signalapp/Signal-Android/tree/master/repr...
It's an issue with Play Store as a delivery channel, the individual app in question can't do much about that.
Reproducible builds help if you: - download the APK separately (includng from the Signal website, or some of the other sources) - install the file locally via sideload - disable updates (!)
https://github.com/signalapp/Signal-Android/tree/master/repr...
But reverse engineering is a skill in itself and modern day smartphone OS's use a lot of code obfuscation when apps are compiled. This effectively means even those talented hackers are going through the reverse engineering process pulling at threads until they get lucky.
Reverse engineering (in this context, at least) doesn't just show you the code as the developer wrote it. And FB hires a lot of very clever people including cybersecurity experts who could sneak these things in using innocent looking code scrambled around the app. Even open source projects are at risk of having backdoors put in that pass review and simply look like innocent bugs if they get discovered, let alone closed source apps that have to be reverse engineered.
Again not going conspiracy nut and saying that's what FB is doing. Just saying it'd be very easy for FB to hide it if they were doing it.
To me the biggest confirmed weakness of WhatsApp is the cloud backups. E2EE is pointless when the message database is synced up to iCloud or Google Drive. WhatsApp even tells you this itself. When you enable cloud backups (and they keep bugging you until you do it) it literally tells you the backups aren't secured by E2EE. [1] Because, well, of course they aren't.
[1] https://faq.whatsapp.com/iphone/chats/how-to-back-up-to-iclo...
"Media and messages you back up aren't protected by WhatsApp end-to-end encryption while in iCloud."
This is just bullshit. If you have access to the binaries you can find out what the software does.
If I wanted to I could install a fork of Signal that doesn't require Google Play [1] and run it on any non-Google Android build. I would do if it wasn't for the fact I'm currently using an iPhone.
The auto update functionality just tells you that an update is available, you can choose not to install it. You can also independently verify that the sha256 sum matches the one given on the website, and that the binary that sha256 sum corresponds to is produced via the reproducible build instructions. There are occasional bugs (I'd estimate a couple times a year, though it's less and less frequent) that causes the reproducible build to not match the provided build, and it's quickly noticed by someone and an issue opened in the issue tracker. If there were no explanation or no quick resolution, people would publicly raise a stink about it.
There is a time bomb in there and servers will kick you out regularly unless you have updated.
If you get a patched client running you could probably change whatever string is required but some sort of action is required on the client side.
It makes it impractical to actually audit the code you're running, because you're forced to re-audit on Signal's schedule. And it makes those audits mostly meaningless: what are you going to do if you decide a given code change is suspicious? You can't keep using the version of the code you were happy with, so you'd better have a plan in place for moving off Signal quickly - but in that case how much can you gain from using it at all?
Not saying this happens, one possibility can always be to send encrypted traffic to WhatsApp servers while opening a second unencrypted channel to govt servers if a govt asks for it.