Macbook Pro 13' 2015 with OS X Yosemite on board. I've been trying to install OS X El Capitan, but always get the following message: 'This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading.' By the way this is not a date time issue, date is correct on my computer. As explained here, OS X 10.11 'El Capitan' fails to install because it is too old (the technical reason being that the signing certificate is no longer valid). But you can trick the OS X installer into thinking that it is 2017 and it will happily run without any errors.
How to fix 'This copy of the install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading.
Many Hackintosh users running Mac OS X Lion have been unable to login to the Mac App Store, instead receiving the error, 'Your device or computer could not be verified. Contact support for assistance.' The verification issue appears to have affected the several legitimate Macs as well, though on less wide of a scale. There is no single, definite solution to this issue, but several possible workarounds are available. Read past the break to find out how to fix the error.There are several solutions to the login error.
1. Go to /Extra in your main hard drive and open the text file org.Chameleon.boot.plist with TextEdit. This is the configuration file for the Chimera bootloader (which UserDSDT uses). Add this string to the part of the file between <dict> and </dict>:
<key>EthernetBuiltIn</key>
<string>Yes</string>
Then reboot. If this doesn't solve the errors, proceed to the next solution.
2. Open org.Chameleon.boot.plist again. Add the following string:
<key>PCIRootUID</key>
<string>1</string>
If this string is currently set to 0, change it to 1. Reboot.
El Capitan Can't Be Verified
3. If neither of the above solutions fix the issue, open the System Preferences app and go to the Network section. On the left-hand column in the Network section, select each of the items and remove it by clicking the minus sign on the bottom of the column.
Then, go to /Library/Preferences/SystemConfiguration in your main hard drive and delete NetworkInterfaces.plist. Or alternatively, drag it to the desktop (as a backup, in case things go wrong).
By removing all of the Network items in System Preferences and deleting NetworkInterfaces.plist, you have effectively reset the network configuration for Mac OS X. Reboot (you may have to reconfigure your internet connection afterwards).