Default How can I know if donwloaded RUU is "OFFICIAL"?

It seems like everyone posted RUU on file hosting website.
Not like iOS, appldnld.apple.com/iOS7.1/031-4787.20140627.ggqmo/iPhone6,2_7.1.2_11D257_Restore.ipsw,
it's obvious on apple website, and many would post hash to validate if it's true.
Is any method I can tell if it's true "OFFICIAL"?