Attached is a small util which will check the sboot.bin file and give you some info, such as if it appears on the Samsung blacklist, if it's new which means boot downgrade will not be possible or if it does not appear in the blacklist which means it can be used for bootloader downgrade and you should PM me with details
I have checked all the sboot.bin files I have and they are all blacklisted, some of these sboot.bin files are ones which have never appeared in the internet and I have gotten from my various sources, these include engineering boots and debug versions.
The blacklist is built on the date the EBL was compiled and its possible no older sboot.bin files will be missing from the blacklist, but we have to try
It's also worth noting here that this boot enforcement is also in the latest boots on the M440s, N7100 (XXDLL7), N7102, E210s (KSJLL6) and will probably spread to other models in the near future.
Enjoy and happying hunting the nice sboot.
How to downgrade boots on XXELLA or XXELLC and bypass the blacklist (or any other boot in existence as of this post)
(USE THESE COMMANDS AT YOUR OWN RISK)
> adb push sboot.bin /sdcard/sboot.bin
> adb push tz.img /sdcard/tz.img
> adb push param.bin /sdcard/param.bin
> adb shell
# dd if=/sdcard/sboot.bin of=/dev/block/mmcblk0p1
# dd if=/sdcard/tz.img of=/dev/block/mmcblk0p2
# dd if=/sdcard/param.bin of=/dev/block/mmcblk0p4
# rm /sdcard/sboot.bin
# rm /sdcard/tz.img
# rm /sdcard/param.bin
# reboot fota_bl
tz.img and param.bin are not required, but since they are part of AP_BOOT I included them for completeness.
You will not lose any data, since no wipe is performed or needs to be performed using this method.
Its tested method and no, I will not release any automated method.