From The Apple Wiki

This tool is used to create Image3 files from arbitrary data. Additionally, it supports image versioning, setting the chip/security epoch, ECID, and so on for images.

AES functionality is not implemented yet, and neither is certificate stitching.


Usage: image3maker [options]

Generate an Image3 file.

  -c, --certificateBlob [file]        Use file as a certificate to add to the image.
  -f, --dataFile [file]               Use file as an input. (required)
  -t, --imageTag [tag]                4-byte ASCII tag for image (required)
  -s, --imageSecurityEpoch [epoch]    Set epoch
                                      Valid epochs are: s5l8920x, s5l8922x, s5l8930x
                                                        s5l8940x, s5l8942x, s5l8947x
                                                        s5l8950x, s5l8955x, s5l8747x
  -v, --imageVersion [version]        Set version string
  -d, --imageDomain [securityDomain]  Set specified security domain (manufacturer/Darwin)
  -p, --imageProduction [prodValue]   Mark image production value (production/development)
  -h, --hardwareEpoch [epoch]         Set chip epoch
  -y, --chipType [chipType]           Set chip type
  -b, --boardType [boardType]         Set board type
  -e, --uniqueIdentifier [uniqueID]   Set ECID for image
  -a, --aesKey [aesKey]               Set AES key for image encryption (implies -i/--aesIv)
  -i, --aesIv [aesIv]                 Set AES IV for image encryption (implies -a/--aesKey)
  -o, --outputFile [file]             Output image3 file

Only AES256 keybags are supported by this program right now.
Have fun using this thingy. (ALL VALUES FOR THINGS SHOULD BE IN HEX!!!)