You are not checksumming the InstallESD.dmg but the dmg of the app itself. (And the copy that is floating arround the internet, since the mas receipt should vary between users.)
People are trying to find the InstallESD.dmg checksum, the 7b4f.. hash has some google matches from 4chan hardly trustworthy.
OK
7b4f4b188f13dd3eabdd86a1cbc433632bf41882