IMac OSX el capitan bootable installer failing

[Noby]

After my Mac from 2011 suddenly not starting only white screen apple support told me to do a usb bootable installer for OS X El Capitan. Using the installer i get prompted with el capitan can't be verified it may be damaged when downloadet. using 4 different usb memory sticks and all giving the same error code I'm convinced its nothing wrong with the download. Of course i run system diagnose and attempted to reinstall the usual way ctrl-r with no success plus the system having no faults found. I am desperate to get this boot disc working. Apple support first willing giving me the necessary command suddenly backed out and told its secret and can't be told. Go figure.  

[Telly82]

Apple has used a certificate that expired. You need to do a fresh download. http://updates-http.cdn-apple.com/2019/cert/061-41424-20191024-218af9ec-cf50-4516-9011-228c78eda3d2/InstallMacOSX.dmg

[Stereotypen]

Change date in Terminal:

 

shut off wiFi/Internet

 

Open Terminal

 

Write:

 

date 080808082019 

hit enter

 

close Terminal and proceed installation.