Revisiting this rather helpful issue and adding a bit of additional information which might be helpful.
My task was to extend a Win32 application that uses passwords to authenticate with an online service with a "save password" functionality. The idea was to protect the password using Windows Hello (UserConsentVerifier). I was under the impression that Windows surely has something comparable to the macOS keychain.
If you use the Windows Credential Manager APIs (CredReadA, CredWriteA), another application can simply enumerate the credentials and if it knows what to look for (the target name), it will be able to read the credential.
I also explored using DPAPI where you are in charge of storing the encrypted blob yourself, typically in a file. Again, there seems to be no way (except obfuscation) to prevent another application from finding and reading that file. Supplying additional entropy to CryptProtectData and CryptUnprotectData again poses the question of where to store the entropy (typically I assume it would be hard-coded and perhaps obfuscated in the application: this is security by obscurity).
As it turns out, neither DPAPI (CryptProtectData, CryptUnprotectData) nor Windows Credential Manager APIs (CredRead, CredWrite) can prevent another application running under the same user from reading a secret.
What I was actually looking for was something like the macOS keychain, which allows applications to store secrets, define ACLs on those secrets, enforce biometric authentication on accessing the secret, and critically, prevents other applications from reading the secrets.
As it turns out, Windows has a PasswordVault which claims to isolate apps from each other, but its only available to UWP apps:
Represents a Credential Locker of credentials. The contents of the locker are specific to the app or service. Apps and services don't have access to credentials associated with other apps or services.
Is there a way for a Win32 Desktop application to access this functionality? I realize that if a user can be brought to install and run a random app, that app could probably mimic the original application and just prompt the user to enter the secret, but still, it's a little disappointing that there is no app-level separation by default.
