do_keys() {
  # create directory
  install -d ${KEYS_OUTDIR}
  openssl genrsa -out ${KEYS_OUTDIR}/uboot_sign.key 4096
  openssl req -batch -new -x509 -key ${KEYS_OUTDIR}/uboot_sign.key -out ${KEYS_OUTDIR}/uboot_sign.crt
}
addtask keys before do_bundle_initramfs_dtb

do_bundle_initramfs_dtb[prefuncs] += " do_keys"