This is the IOS binary image packing and unpacking program capable of calculating a correct checksum for these images. Cisco is using it's own modified version of the ZIP archivator, and if you don't have it, simply supplement the unpacked image body with an empty bit (0xff) in your favourite hex editor, if the image length is a fraction after packing with ZIP (see the length in the tool output in brackets before "words"). Then use ciscopack.pl to repack the image and the correct checksum would be calculated. Please read the --help output for the options available. Don't forget that you need ZIP installed to use ciscopack.pl.

If you do need to employ this tool, you know what is it for :-)
