Help with Ctera stock firmware format decoding (strange md5 sum calculation)

Hi all,

I work with support for Ctera C200 NAS. Device is old kirkwood, so it was easy. But I struggle with factory images because bootloader is blocked and Ctera ignored my u-boot GPL source request..

What is the problem:

Ctera firmware is a simple tar archive. Every part of image contains header file with some text data, image and trailer file with MD5 sum. And here start the problem: I can't figure out how they calculate md5 sum. I can't reproduce original calculations.

Could someone take a second look and help me?

Here is original and working stock file: