Thread: *.gma - What's inside?!

Hi all,

I have a .gma file within the Garmin Folder on my SD card. Does anyone know whats this file for and what exactly it relates too i.e the map image or the sd card id?

Also on the SD card is an .UNL file - im guessing this is the unlock code for the map?

I can open the UNL file - its just a bunch of regular numbers and letters, but the GMA file is a whole bunch of mess!

Thanks to all..

The GMA (Garmin Map Activation) can be viewed as a signature file co-existing with the current unlock codes from UNL. Its main purpose is to validate the current unlock codes are indeed generated by Garmin.
GMA is encrypted with the RSA-2048 algorithm.

Originally Posted by Cnfhbr

The GMA (Garmin Map Activation) can be viewed as a signature file co-existing with the current unlock codes from UNL.

For me, it seems the GMA mechanism is designed to facilitate many usage scenarios and it's up to map vendor which one to choose. If the vendor's intention is to implement a region-specific unlocking then yes, both an unlock code for that region and the device-specific .gma certificate can be required. While in another scenario, the .gma file just supersedes the unlocking code file ( .unl), not "validates" it. So the details are up to a map vendor

Originally Posted by Swall

For me, it seems the GMA mechanism is designed to facilitate many usage scenarios and it's up to map vendor which one to choose.

GMA was designed to counter forged unlock codes obtained using JetMouse's keygen.

Originally Posted by Swall

While in another scenario, the .gma file just supersedes the unlocking code file ( .unl), not "validates" it.

It's not like that.
GMA file of course contains unlock codes, the validity of which is confirmed by a digital signature in the file. The main thing in this file is a valid signature.

Here's the official Overview by Garmin:

Code:

Please Login or Register to see the links

Originally Posted by Cnfhbr

It's not like that.
GMA file of course contains unlock codes, the validity of which is confirmed by a digital signature in the file. The main thing in this file is a valid signature.

Shure it's some kind of signature. Anyway that's my experience. Some time ago my vendor said that starting from the next map version current "license" is no more valid (as the map's FID value has increased) so each customer have to "renew" it individually according to the procedure. So I'd sent them ID of my unit and the vendor did responded with the .gma file generated. Actually, in order to get the map working, all I have to do is to place that .gma file next to gmapsupp.img in the ext. storage media. There are no other related files like .unl, etc. The .gma file missing results in auth error so the map is indeed protected. And that .gma file is the sole mean to unlock the map. I've no idea if that's right or wrong but it in my case it works in that manner.

Thanks for the quote from the official Overview. Could you provide a direct link to the related Garmin page?

Originally Posted by Swall

Some time ago my vendor said that starting from the next map version current "license" is no more valid (as the map's FID value has increased) so each customer have to "renew" it individually according to the procedure. So I'd sent them ID of my unit and the vendor did responded with the .gma file generated. Actually, in order to get the map working, all I have to do is to place that .gma file next to gmapsupp.img in the ext. storage media. There are no other related files like .unl, etc. The .gma file missing results in auth error so the map is indeed protected. And that .gma file is the sole mean to unlock the map. I've no idea if that's right or wrong but it in my case it works in that manner.

No wonder.
An additional GMA-check was added to the firmware of modern devices for maps with FID > 2200.
As I mentioned before, the GMA file contains unlock codes that are digitally signed, so it was enough in your case.
However, many legacy devices don't have additional GMA-check and don't support GMA files at all, only UNL.

Originally Posted by Swall

Thanks for the quote from the official Overview. Could you provide a direct link to the related Garmin page?

Garmin does not publish such overviews on its pages available to the public.

The GMA file is pretty much impossible to crack, or generate a GMA code of our own due to the extremely sophisticated encryption algorithm.

Others had figured out how to get around the GMA file check, but I have no idea how it was done.

And Garmin has added another layer of protection to their most recent firmware/software versions.

Originally Posted by timp4411

Others had figured out how to get around the GMA file check, but I have no idea how it was done.

By disassembling a firmware, locating the routine that performs the check, and bypassing it.
It’s done by changing only four bytes, which is probably one or two instructions for a 16 bit processor.

Another update and I have to admit the .unl file is actually necessary. For the first time anyway. Garmin loves cashing very much