tut request: gps map encryption (navigator sw reversing)

[giulio8]

As I'm suggesting in my topic's description (navigator sw reversing), I think it's the same old story of what happened with decss: the reversers' group reportedly disassembled the object code of a player to obtain a player key http://en.wikipedia.org/wiki/DeCSS

I also posted a similar request in another forum: http://forum.mobilism.org/viewtopic.php?f=15&t=78827

Basically the tutorial should show how an application (the gps navigator) reads an encrypted file (the map) and elaborate data (finding a route). As a wrap-up it should show how to edit the file (the map) changing some encrypted data (changing one-way street to the opposite direction) in order to get a different behaviour of the application (the navigator picking up a different route).
By far and large unpacking a target is almost an automatic task with tons of tuts already available, this tutorial would reveal the real genius of a reverse engineer: if analysing a program to discover a new encryption algorithm and bettern its functionalities is not the aim of reverse engineering, what else?

Look forward to hearing from you
TFL

[Git]

What work have you done towards solving this problem yourself, or do you expect others to just give you the finished answer on a silver plate?

Git

[giulio8]

I'm not expecting the finsihed answer on a silver plate simply because you have not that silver plate yet. I don't even need the work done or the explanation, just tell me if you can do it or you can not or if you are not interested - honestly. Maybe you can't admit that a task is too difficult or nobody is able to perform it?

Btw, what I've done is 1) found the target for x86 so that I can debug and reverse it on pc instead of a ppc device or emulator 2) found the point where the target reads the map file 3) intercepted the info regarding a particular one way street, 4) but I couldn't reverse the algorithm and find out how to save the opposite direction to the map.