nrfutil create DFU zip file

[deadpoolcode]

Hello 

I am following example on :

examples/dfu/secure_dfu_test_images/ble/nrf52832

when flashing: 

sd_s132_bootloader_buttonless_with_setting_page_dfu_secure_ble_debug_without_bonds.hex

and then performing DFU with presigned .zip: hrs_application_s132.zip 
update works as expected

but when I try creating my own DFU image: 

nrfutil pkg generate --debug-mode --application hrs_application_s132.hex app_dfu_package.zip --hw-version 52

update fails 

please advice

[deadpoolcode]

I think I have found the reason.

using nrfutil pkg display and comparing the pre-generated "hrs_application_s132.zip" I have composed the following command: 

nrfutil pkg generate --debug-mode --application hrs_application_s132.hex app_dfu_package.zip --hw-version 52 --sd-req 0xCAFE,0xAF --application-version 1 --app-boot-validation NO_VALIDATION

but, it seems that the "hrs_application_s132.zip" was signed with .pem key.

in order to create a reference zip file I need that key, where is it located? 

thank you