Hi Bob, thank for a good review. I appreciate your response.
According to your question you can read following article : https://threatpost.com/android-keystore-encryption-scheme-broken-researchers-say/119092/
As mentioned in this article: “An attacker could have exploited the vulnerability in Android 4.3 and earlier devices to gain access to a device’s lock credentials, encrypted and decrypted master keys, and so on.”
As we (developers) still support 4.3 and lower so i think it’s important to know about that.