For anyone who can't install macOS because "the Installer is Damaged"

This kept me up late, I tried a couple of different flash drives with versions of Sierra, High Sierra, from the App Store and the Google Drive. I could boot into the installer without a hitch and do stuff in disk utility, Terminal, etc. Then, I'd click "Install macOS" and it would pop up This copy of the install maOS [High] Sierra application is damaged and can't be used to install macOS. I'd done my imaging through Terminal using the createInstallMedia that's inside of the .app installer so I was pulling my hair out, I tried multiple flash drives and no one in the Discord knew what to do. Finally, I decided I'd set the time and date properly in BOTH my motherboard and inside of the installer. I don't know if this is necessary but setting through Terminal in the installer definitely helped.

First, run date in the terminal and double check that the output date looks correct. It defaults to PST because Apple are weird californians. If that's incorrect and you have an internet connection, you can proceed to type in ntpdate -u time.apple.com and it'll set the date from the Apple time server. If you don't have internet, MacWorld! has a little walkthrough of manually doing Unix time and setting manually by the date app.

But after that, I doubled checked the date and voila! Without even rebooting the installer, I was able to proceed and run through it.