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 Post subject: Christmas puzzle
PostPosted: Mon Dec 19, 2011 3:42 pm 
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I just made this today. It looks difficult, but after figuring out the first step, the rest will follow through quite smoothly. You'll know when you've solved it.


Attachments:
christmaspuzzles3.png
christmaspuzzles3.png [ 7.67 KiB | Viewed 889 times ]
christmaspuzzles2.png
christmaspuzzles2.png [ 7.67 KiB | Viewed 889 times ]
christmaspuzzles1.png
christmaspuzzles1.png [ 7.67 KiB | Viewed 889 times ]

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 4:41 pm 
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I always drink my Ovaltine :wink: .

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 4:42 pm 
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Hey Jorbs3210,

Solved. That was great, thank you.

I don't want to spoil it for others, so I won't say much... With this link, Jorbs3210 will know that I solved it... Others, click at your own risk: http://goo.gl/1sdEP

Skarabajo.

EDIT: Damn! bmenrigh beat me to it (by seconds!) :lol: :lol: :lol:

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 4:53 pm 
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:shock: That was quick. How hard was it to take the answer to the first step and convert it into usable data? Did you have to do anything to it?

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 4:56 pm 
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Jorbs3210 wrote:
:shock: That was quick. How hard was it to take the answer to the first step and convert it into usable data? Did you have to do anything to it?


Well the first step seemed obvious and I've had a need to process images in that way many times before so I can hack up a perl script to do it in no time flat.

I spent a lot of time on your first version cleaning up noise to try to be able to process the result without any luck. Your second version without the noise was easy.

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 4:59 pm 
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bmenrigh wrote:
Well the first step seemed obvious and I've had a need to process images in that way many times before so I can hack up a perl script to do it in no time flat.


Really? How does it work?

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:04 pm 
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Jorbs3210 wrote:
bmenrigh wrote:
Well the first step seemed obvious and I've had a need to process images in that way many times before so I can hack up a perl script to do it in no time flat.


Really? How does it work?


Code:
brenrigh@lambda ~ $ pngtopnm -plain download/christmaspuzzles1.png > xmas_1.txt
brenrigh@lambda ~ $ pngtopnm -plain download/christmaspuzzles2.png > xmas_2.txt
brenrigh@lambda ~ $ pngtopnm -plain download/christmaspuzzles3.png > xmas_3.txt
brenrigh@lambda ~ $ ./xorpnm.pl xmas_1.txt xmas_2.txt > xmas_12.txt
brenrigh@lambda ~ $ ./xorpnm.pl xmas_12.txt xmas_3.txt > xmas_123.txt
brenrigh@lambda ~ $ cat xmas_123.txt | pnmtopng > xmas.png


EDIT: a friend of mine and I compete in the defcon CTF quals each year and the forensics category generally has problems similar to this (although usually much more complicated). He uses python and when we've had challenges like this in the past he uses Python with something like "import Image" or something like that and just reads out the image values directly. I tend to go the netpbm route.

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Last edited by Brandon Enright on Mon Dec 19, 2011 5:08 pm, edited 1 time in total.

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:06 pm 
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Wow bmernrigh, that's some coding you got there, very efficient. :D

I actually combined all three images in Photoshop and noticed that they made a QR code, then I used Zxing decoder to convert the QR code to numbers. Since I was looking for an English message, I figured the numbers were ASCII code and manually replaced them. Total time from start to finish: 4 minutes. :wink:

Skarabajo.

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:13 pm 
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I spent a few minutes staring at the screen expecting something 3D to pop up, and then I simply gave up. I did think of QR codes but turned that one down because it didn't look remotely like one. Very nice!

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:16 pm 
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This is actually quite a common problem that comes up in the "real world" when people don't understand the crypto that they are using. If you re-use the stream from a stream cipher (salsa20, RC4, any block cipher in CTR or OFB or CFB mode, etc) the problem is reduced to that of XOR.

The same is true for pad-based encryption where the "key" is short and gets repeated. Think XOR by 0x01234567 where the key is repeated every 32 bits. XORing the various parts together makes the stream drop out. I have plenty of code to automate various aspects of this.

There are more broken/abused cryptosystems than ones implemented correctly.

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:19 pm 
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This will look a little better.


Attachments:
christmaspuzzle22.png
christmaspuzzle22.png [ 7.68 KiB | Viewed 808 times ]
christmaspuzzle21.png
christmaspuzzle21.png [ 7.71 KiB | Viewed 808 times ]

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 Post subject: Re: Christmas puzzle
PostPosted: Mon Dec 19, 2011 5:40 pm 
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I went ahead and tried something else.


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yes5.png
yes5.png [ 7.69 KiB | Viewed 793 times ]
yes4.png
yes4.png [ 7.71 KiB | Viewed 793 times ]
yes3.png
yes3.png [ 7.69 KiB | Viewed 793 times ]
yes2.png
yes2.png [ 7.69 KiB | Viewed 793 times ]
yes1.png
yes1.png [ 7.7 KiB | Viewed 793 times ]

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