Popular encrypted messaging app Signal is facing criticism over a security issue in its desktop application. Researchers and app users are raising
As mentioned in the comments, plain text keys aren't bad because they are necessary. You have to have at least one plain text key in order to be able to use encryption
That said, let’s compare how it works on the phone to how it could work on MacOS and how it actually works on MacOS. In each scenario, we’ll suppose you installed an app that has hidden malware - we’ll call it X (just as a placeholder name) - and compare how much data that app has access to. Access to session data allows the app to spoof your client and send+receive messages
On the phone, your data is sandboxed. X cannot access your Signal messages or session data. ✅ Signal may also encrypt the data and store an encryption key in the database, but this wouldn’t improve security except in very specific circumstances (basically it would mean that if exploits were being used to access your data, you’d need more exploits if the key were in the keychain). Downside: On iOS at least, you also don’t have access to this data.
On MacOS, it could be implemented using sandboxed data. Then, X would not be able to access your Signal messages or spoof your session unless you explicitly allowed it to (it could request access to it and you would be shown a modal). ✅ Downside: the UX to upload attachments is worse.
It could also be implemented by storing the encryption key in the keychain instead of in plaintext on disk. Then, X would not be able to access your Signal messages and session data. It might be able to request access - I’m not sure. As a user, you can access the keychain but you have to re-authenticate. ✅ Downside: None.
It’s actually implemented by storing the encryption key in plaintext, collocated with the encrypted database file. X can access your messages and session data. ❌
Is it foolproof? No, of course not. But it’s an easy step that would probably take an hour of dev time to refactor. They’re even already storing a key, just not one that’s used for this. And this has been a known issue that they’ve refused to fix for several years. Because of their hostile behavior towards forks, the FOSS community also cannot distribute a hardened version that fixes this issue.
If I'm not mistaken you can save keys in these chips so that they can not be extracted. You can only use the key to encrypt/decrypt/sign/verify by asking the chip to do these operations with your key.
You would probably use a recovery key that exists exclusively elsewhere like on paper in a vault. Like bitlocker.
I have no idea if signal uses TPM or not but generally keys in TPM are non-exportable which is a very good thing and IMO the primary reason to use TPM at all.
It is. A password is generated that you have to write down. It must've been a compromise because they knew most people would just pick a shitty password if they didn't generate one and it would end up on a piece of paper or in some digital form anyway.