Where are Wi-Fi passwords stored? Are encrypted Wi-Fi passwords stored in /Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist? If yes, which string? 

I know we can view wireless passwords using the Keychain GUI or using security in Terminal. But where are Wi-Fi passwords actually physically stored in macOS?
Wi-Fi passwords are physically stored in the System keychain at /Library/Keychains/System.keychain