In short: Signal uses DRM to prevent Windows Recall (spyware) from capturing what's inside the app. It's similar to how Netflix prevents piracy.
That's an interesting use-case of web DRM.
There are other details in the article, for example about Recall forces users to use biometrics to then permit them to authenticate using a PIN code. That's an interesting observation.
mmozeiko · 10h ago
I don't know why Signal calls it "DRM" because the do not use DRM for this. Typically DRM means encryption & keys are involved (which is what Netflix & others are doing with Widevine or PlayReady).
And that "simple Windows API" call is pretty much absolute, since it's across the stack.
yupyupyups · 9h ago
Thanks for the insight, I thought they took advantage of the whole DRM stack (including HDCP in monitors) to encrypt the UI and let the monitor decrypt it.
That's an interesting use-case of web DRM.
There are other details in the article, for example about Recall forces users to use biometrics to then permit them to authenticate using a PIN code. That's an interesting observation.
All Signal does is just a simple Windows API call to exclude window from screen capture. SetWindowDisplayAffinity function with WDA_EXCLUDEFROMCAPTURE argument: https://learn.microsoft.com/en-us/windows/win32/api/winuser/...
https://learn.microsoft.com/en-us/windows/client-management/...
And that "simple Windows API" call is pretty much absolute, since it's across the stack.