Authentication of a bitstream is different from all other partitions. The FSBL can be wholly contained within the OCM, and therefore authenticated and decrypted inside of the device. For the bitstream, the size of the file is so large that it cannot be wholly contained inside the device and external memory must be used. The use of external memory creates a challenge to maintain security because an adversary may have access to this external memory.
The following section describes how the bitstream is authenticated securely using external memory.