esp-idf/components/bootloader_support/Makefile.projbuild

$(SECURE_BOOT_SIGNING_KEY):
	@echo "Need to generate secure boot signing key."
	@echo "One way is to run this command:"
	@echo "$(ESPSECUREPY) generate_signing_key $@"
	@echo "Keep key file safe after generating."
	@echo "(See secure boot documentation for risks & alternatives.)"
	@exit 1