Since commit:
commit a36082664e
Author: David Brown <david.brown@linaro.org>
Date: Thu Dec 12 15:35:31 2019 -0700
ecdsa: Allow ECDSA signatures to be actual length
MCUboot no longer requires ECDSA signatures to be padded to a fixed
length. This change makes imgtool, by default, also no longer add this
padding to images. There is an option `--pad-sig` that can be given to
the sign command to re-instate this padding. This flag will be needed
to make images that will work with older (pre 1.5.0) versions of
MCUboot.
Signed-off-by: David Brown <david.brown@linaro.org>