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Subject: Gmini Firmware question
From: Laurent Giroud (laurent.giroud_at_libertysurf.fr)
Date: 2003-12-30


Hi,

I have acheived a first part of the Gmini's firmware analysis, it's not over yet as two points still need some work but it's a first step.

The first missing point is figuring the compression algorithm. Gzip can't compress the firmware file by more than 2 or 3 percents which is a good indicator and there's a 'CCOD' chunk which might stand for "Compressed code" and one 32 bits field yields a value which is approx 2 times bigger than each firmware file and would be a very good candidate for the decompressed firmware size.

Second point is the firmware signature, there's a 'SIGN' chunk which might contain a cryptographic signature of either the whole firmware file or the uncompressed code. It should be easy to guess which one is true by modifying a few bytes within the string containing the firmware's name. Guessing the signing algorithm might be tricky as would be the cracking of the key used to sign the firmware. Having access to the gmini's ROM would be useful for this task but I don't know yet if it's physically feasible.

I am willing to publish the firmware's format on the list for others to comment and work on.
Of course, I will accept full responsability for doing so and the mailing lists maintainers shall not be legally held accountable for it, but I'd prefer to have your permission first since Archos seems to have threatened some people here of legal action and some might think it's not a wise thing to do :)

Regards,

Laurent



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