I clicked the app-store link "get macos high sierra" in [support.apple.com/en-us/HT208969], then [Open] in the app store, but the popup box said: "This copy of the Install macOS High Sierra.app application is damaged, and can‘t be used to install macOS".
Why is apple's own file "damaged"?
How can I circumvent this obstacle?
Don't use Firefox for this link...
https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=12
If you get a corrupted message...
Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...
Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS High Sierra App in Applications, so expired Certificates are not expired.
Or... trash the Install MacsOS High Sierra.app in Applications then a new copy more recent version can be downloaded.
Don't use Firefox for this link...
https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=12
If you get a corrupted message...
Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...
Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS High Sierra App in Applications, so expired Certificates are not expired.
Or... trash the Install MacsOS High Sierra.app in Applications then a new copy more recent version can be downloaded.
Yes, the problem was related to "expired Certificate" and was solved promptly, thank you very much!
I found further that, beside setting back the Date, one could also delete the [installInfo.plist] (?) from one of the folders associated with the macOS High Sierra app (under Applications)!
Solution was simple; the message about something being "damaged" was / is indeed misleading;
Great news, god work on your part too, take care my friend. :)
High Sierra macOS upgrade from Sierra - howto
