Golden Shield Wargame 1 Writeup

In the first problem, a picture is given and ask you to decode it.

It's trivial to rotate 45 degree and remove useless part.Then we can observe that this QR code has opposite color, so we can change the colors. I write a small python program use PIL to rote picture.

import PIL
im = Image.open("QR1.jpg")
new_im = im.rotate(45)
new_im.save("QR2.jpg')

Use online QR code decoder, we can decode that
"恭喜您，解開了QRcode。請到 http://www.multiupload.nl/25BD9YIRO0，下載Golden Shield.apk，KEY就在裡面。"
Then we can goto website download the apk file.
After download the file, we use dex2jar convert the hex file to jar. Then we can use java decompiler to decompile the class file in jar back to java code.

The decompile result

 Then the string "@@@@您累了嗎? 來聽首歌好嗎?@@@@@" is the key.