Help - Other QR code - Can it be reverse engineered?

Despite the performance of doing such a thing I don't think it's a good idea in order to publish it in the level section. Maybe as a proof of concept in the forum section, but not as an official level. @meko made a joke once but it was a fake . If you've found levels that seem suspect please report them, but I am not sure it will be obvious to prove that.

If I were Martin I would thought about encrypting the content (even weakly) so that it can be decode from the software only. You can encapsulate data in QR Code but it is not garanted that these data are "readable" without the needed key. I admit that I didn't invest my time in such a way despite I find this subject really interesting.

 

Thanks @Martin for your reply.

That would be great! But as this forum is kind of a generic one (the XenForo platform), I am not sure it is possible to do so unless by developing a plugin with the agreement of its owner and studying how to do that on this platform... On another hand, cards need to be rendered in order to be shown in the website (but maybe it doesn't need to be as big as those uploaded). So pictures has to be stored somewhere, otherwise if the image is recreated each time the card is requested, it could heavily loads the server

What could be also interesting from the server side is a way to check that the QR Code is valid and is readable each time it is uploaded. That could save a lot of time. But I don't see how to do that without a proper webserver with a dedicated development to do that

Hmmm... That intrigues me... Thanks for the tip... Maybe I'll check that one day as a challenge

 

@Gepeto Looks like we'll need to link the forum to the game to do it, then (for the game to scan and render the cards on your device, and not the sever), to prevent server overloading. Sadly, it doesn't look like something like that is going to happen soon (or anytime in the future, for that matter). Oh well...

P.S. I hope that what I said made sense . I'm not an expert in these stuff.

 

Maybe you're right but then, we are not mandatory to a QR Code interface... It could be any requests exchanges method between both parts. But that would need a real dedicated webserver software linked to the client application... That's a huge work from server and client side .

QR Codes still a "friendly" way to exchange cards. It is also is a really great way for a universal exchange method and that's well considered. Cards can be exchanged everywhere (FB, Personnal websites, this forum,...), people look at them such as kids exchanging and collecting cards as they want at schools playgrounds. Myself I have got a big collection of cards in a folder of my device

Things have to move on everytime but despite the fact that we have few details on Martin's projects, I am sure he's doing everything for the good of the game

 

So working with Java... Fine. I'll check that when I can but not sure it is soon
I also tried to see differences in the data with nothing then one block of stone, metal, etc. and I have seen that the result was totally different so I gave up. I was waiting for some byte changes but no.

 

I just wanna add that I like to hack things but not for bad purposes. Curiosity is a good temper but not if it leads to bad manners. That's my opinion. If at the end we'll see hacked levels published in the forum as original ones I would disagree. If we'll share hacked level in the forum section (not the levels one) as a curiosity with evidences on the method used I would find this as interesting and fun. Everything depends on the way it is presented

 

I suppose that you've worked with Python 2.7, as unicode and string encoding is a mess to manipulate. That's why I've moved to Python 3 for most new developements that do not require the use of OpenCV or other libraries that hasn't yet been ported to this version.

I didn't try to develop something about QR Code with python but I've seen some interesting references to start with (qrtools, PyQRCode, PyXing and ZBar - I've already used this last at work for Code128 barcode).

 

Agreed.

That would be phenomenal. I'm sure many designers would like that. Except that I don't think anyone could succeed at it. I suspect that the level picture in the card image is generated in the app and then stored as straight data on the card image (and QR code). To change the level picture, you'd have to find a new way to render it and then save it into the QR code. Not likely possible - particularly not simply by cracking the QR code.

Nice. That is what I found as well. Except that I found that padding at the end of the QR code.

What I tried was simply adding the character '7' after New Level (so that it read "New Level7"). I figured that this change would probably be the absolute smallest change from one QR code to another. Adding a checkmark to a card does not change the QR code as the checkmark resides in a lookup table on the respective device. Adding any block would add all kinds of information like what block, where located, what orientation, what shading, how does it look on the final level picture on the card image, etc.

Like you, I was hoping that the card title and author would be a simple hex entry for the ASCII equivalents. No such luck, indicating - as you say - likely compression of the data prior to QR code encoding. The first task then would be to see if the compression algorithm could be determined. This is where I'm going to stop. I suspect that it'll be some form of lossless compression, but I haven't touched code since school.

Good luck!

 

Yesterday I have made some investigations on the chunk data from the QR Code.

From what I have seen I am pretty sure that the data has been compressed with a Zlib compression or kind of. As PNG format uses the Deflate algorithm (which is the same algorithm used in the zlib compression library), Martin could have used the PNG library to compress the data, extract the IDAT part and package it in a suitable format (maybe with a custom signature?). I guess this because the PNG images generated from the game has an IDAT which begins with 0x78, 0x01 (the zlib with no/low compression signature) then some data that seems to be the size or else and looks like the structure I have found in the QR Code.

I don't know yet if that could lead somewhere but that seems to be a good start to me.

Here is the PNG Wikipedia page where the zlib compression is named (in english)

 

Wow, that's great! I have stopped before as the zlib.decompress method returned an "unknown compression method" but the header seemed to be accepted. Maybe tonight I'll dig on that.