Well, I guess it’s common now to see this when trying to install OS X. My example happened when I tried to install El Capitan, fresh (no upgrade) on a newly formatted SSD – and had me scratching my bean.
I got this:
This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading
People have identified the need to set the clock back via Terminal, right before you install the OS after boot-up.
I checked my time & it was spot on (although it thought I was on the Left Coast, which I’m not).
I COULD have ran the infamous date command (date MMDDHHmmYY), but elected not to.
I deleted the installer and downloaded El Capitan yet again. Guess what? It worked.
Here is what I’m thinking. If you download & set it aside for a while, you need to roll your clock back. If not, you’re good to go.
So if you don’t have the luxury of downloading the OS again, see what the time/date stamp shows up as and set the date back to a week later than that and you should be all set.
So, if you see this (for example):
But it’s April, 2016 now … run:
Exit the Terminal App and try the install again.