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4. Secure File Loading
Castles implemented an interface named User Loader (ULD) to provide secure file loading to
system memory. Loading of user application, kernel firmware, font and others must use User
Loader.
The loading process is secure by signing the files using ULD Key System.
4.1. ULD Key System
The ULD Key System uses two key sets for securely managing the kernel updating
and application downloading. Each key set contains two RSA key pairs. One is
used for key encryption and the other is used for signature. These two key sets are
specified as below:
ULD Manufacturer Key Set
ULD Manufacturer Key Encryption Key (RSA)
ULD Manufacturer Signature Key (RSA)
ULD User Key Set
ULD User Key Encryption Key (RSA)
ULD User Signature Key (RSA)
For UPT1000F, the RSA key length is 2048bits.
4.1.1. ULD Manufacturer Key
The system consists of several kernel modules. These kernel modules
are provided by the Manufacturer, and released in CAP format file with
encryption and signing via ULD Manufacturer Keys.
The ULD Manufacturer keys are managed and maintained by the
manufacturer. The manufacturer uses these keys to generate kernel CAP
files for updating the system. However, the system is not permitted to be
updated with these kernel CAP files directly generated by the
manufacturer. This is because only the user can have the privilege to
decide whether the system is to be updated. Therefore, before system
