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[mkgmap-dev] Recent Garmin Firmware "cannot authenticate maps" when they are unicode

From Franco Bez franco.bez at freenet.de on Sat Aug 26 20:53:30 BST 2017

Hi Gerd and Andrzej,

I do not see any reason why GARMIN should only require UNICODE maps to
be signed, while LATIN1 maps can remain unsigned.

I suspect that there is a flag in the file header, maybe a new and
undocumented one, that marks the file as "check for signature".
When the Oregon checks the signature, and finds out that there is none,
it states that the check failed.

Maybe mkgmap accidentally marks the file as "to be checked for
signature" when it writes out a unicode map.

Does this soud plausible to you ?

I uploaded a sample map that produces the error, it just contains
administrative border lines as an overlay layer. I'm not sure whether it
contains an index or not .

I can do a little testing if you can provide me with test cases.


Am 26.08.2017 um 06:59 schrieb Gerd Petermann:
> Hi Franco,
> my understanding is that this is not a bug, but a limitation implemented by Garmin.
> My mothers Nüvi also doesn't load unicode maps.
> One reason might be that some indexes don't work with unicode and mkgmap doesn't
> write the needed ones. I cannot try that now.
> If the 750 loads a unicode map without an index we may have a chance by doing more reverse
> engeneering of old maps.
> On the other hand, I wonder how long they will the support the old img format written by mkgmap,
> maybe this is the first step to drop this support.
> Gerd
> ________________________________________
Am 26.08.2017 um 11:51 schrieb Andrzej Popowski:
> Hi,
> > my understanding is that this is not a bug, but a limitation
> > implemented by Garmin.
> This is true. Garmin maps can be digitally signed. Many new GPS
> require, that Unicode map include signature. Signature is a protection
> against tampering, which is reasonable for commercial maps, but it
> exclude support for 3-rd party maps.

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