We saw the Motorola Atrix get rooted several days before availability, surprising many who thought the locked bootloader design would make this more difficult. Now the filesystems have been dumped from the device, and it was discovered that while they are not encrypted (they are dumpable), they are signed.
Both the base filesystems and the recovery are signed, meaning that the bootloader will not accept a flash that is not signed with Motorola’s private certificate. This blocks custom ROM development for now as there is no way to deploy the ROM to the device.
This doesn’t block ROM development completely however, as the system partition can still be modified on a running device after rooting. The bootloader signature checks only come into play when flashing an entire system image at once, via the bootloader.
This type of image signing is nothing new, as HTC has implemented the same type of signature for years on Windows Mobile with their “SPL”. The signature checks were worked around by a hacked SPL named “HardSPL”, enabling custom ROMs. The signature checks for Motorola Atrix will likely be worked around in a similar manner.
Update: A post by a Motorola employee surfaced over at getsatisfaction stating that the Motorola Atrix 4G has a locked and encrypted bootloader, and that more bootloader announcements would be forthcoming.