Thanks PC_Arcade for your Tutorial,
but I've a question about decrypt and checksum of the firmware.
If I open an encrypted firmaware with KDX 1.5 it tell me that the firmware is
encrypted so I need to decrypt with firmcrypt d myfirmware.bin.
after that I can read my KEY and copy and paste to xtreme_proper.bin
After that before to encrypt the firmware I need to update the checksum???
or simply encrypt the firmaware with firmcrypt e myxtreme.bin

?
Thanks for you reply and sorry for my english.
I can't help, I didn't use KDX as I diddn't see the point given how easy it is to just use a hex editor to copy and paste