How to generate .ruc file?

I am using RA2A1 MCU for my product and want to use UNIQUE ID code  for security purpose and restrict the debugging without ID code.

While flashing from Renesas Flash Programmer(RFP-3.09.01) we required to provide security key which should be store in .ruc file.

My problems is that how to generate .ruc file.

I try to save the code in simple .txt and change the file extension from .txt to .ruc. But that method is not working and showing file is not readable (Error00000302)