Begin extracting the following files from your ipsw
Notice we aren't extracting a ramdisk, even though the upgrade routine requires this file. I will explain this later.
I usually being with decrypting the rootfs first so we can being decrypting with dmg.
./dmg extract rootfs.dmg output.dmg -k
This is going to decrypt and grow to real size, so we need to repack, but still keep the dmg decrypted.
./dmg build rootfs.dmg output.dmg
Now is when we start to use reimagine. Start decrypting applelogo and kernelcache.
./reimagine Firmware/all_flash/all_flash."device".production/applelogo... applelogo -iv -k
./reimagine kernelcache.release."device" kernelcache -iv -k
Now for the others, it's the same process but we need to strip the files of the their tags with -r parameter.
./reimagine Firmware/all_flash/all_flash."device".production/DeviceTree."device".img3 dtre.raw -iv -k -r
./reimagine Firmware/dfu/iBEC/iBSS."device".RELEASE.dfu iBEC/iBSS.raw -iv -k -r