That's because the ISO includes two versions: "Windows 8 Core" and "Windows 8 Pro". So the install process needs a key to know what version to install.
Originally Posted by pparks1
When you integrate a "ei.cfg" file into the ISO folder "/sources" (hint: install from USB stick) then you see the key input screen - but can skipped. Windows installs then with a default key.
ei.cfg for "Windows 8 Pro":
ei.cfg for "Windows 8 Core":
I can post the two default keys for "Core" and "Pro" - then the "ei.cfg" files are not necessary. They were included in an earlier version in the "product.ini" file. But I don't know if that's allowed in this forum.