The Windows8-UpdateAssistant/Windows8-Setup programs download the files into C:\ESD\Windows. Most of the files in there have a file-date of 26-July-2012, but install.esd and boot.wim have a file-date of the download date. So I wonder whether they are especially made for you. If they are, there wont be a single value MD5 hash for the ISO, because the ISO is created from those files.
I had to download the files three times before I got a version that worked. So even though there is some verification process, it doesn't seem to work very well.
In the first two attempts I created a USB boot device but during setup I got an 0x8007025D error. I tried the same files to create an ISO to use in a VM, same problem.
After the third download it worked in a VM, but not with a USB device on a real machine. I tried a different USB device and finally got it to work.