Check the service menu: dial *#*#7378423#*#* (i.e. *#*#SERVICE#*#*) and choose 'Service tests' > 'Security'. If your DRM keys are okay, both MARLIN and WMLA will show up as [Key OK]. If they are erased, they would show up as [Unknown Error].
DRM keys are unique for each device, so they are not contained in any firmware download. Once they are erased, there is no way to get them back, unless you made a backup of the Trim Area (TA) before unlocking your bootloader.