Disk Image Formats

iPhone Firmware (ipsw) files contain .dmg disk images beside other files.

The main filesystem .dmg disk image (the largest .dmg file) is decrypted to an UDZO .dmg disk image.

UDZO Image Format

The UDZO Image is an UDIF zlib-compressed read-only image which can be mounted on Mac OSX. UDZO Images can be converted to read/write UDRW Images with the hdiutil on Mac OSX:

hdiutil convert -format UDRW -o udrw.dmg udzo.dmg

To add checksums of the data in the provided UDZO Image and store them in the image the asr tool on Mac OSX can be used:

asr -imagescan udzo.dmg

UDRW Image Format

The UDRW Image is an UDIF read/write image which can be mounted on Mac OSX. UDRW Images can be converted to zlib-compressed read-only UDZO Images with the hdiutil on Mac OSX:

hdiutil convert -format UDZO udrw.dmg -o udzo.dmg