Modding a security DVR's firmware

[motocrossmann]

Using FMK and binwalk, I was able to chop the header and footer off of my Swann DVR's firmware and then mod the Cramfs to update the root password.   When I reassemble it with FMK, and then run binwalk on it, it looks identical to the original with all sections ending/beginning in the sample places.   The contents of the Cramfs do make it a smidge larger, but it still fits into the original "boundaries".   When I go to flash the firmware though, it fails after thinking about it for some time.   I am guessing that there is a checksum somewhere, or some other security feature.   I have no idea how to proceed from here though.   Ideas???

[Coldblackice]

Any progress (or luck!) with this?

I would also guess it's a checksum issue.

[Jeremy Collake]

It does sound like it's probably a checksum / integrity check failure.

Resolution would require further evaluation.

Your best bet is to submit it as an issue at the Google Code site for the FMK.