Rating:
When I excute the file and attack debugger to it, I can find it was written by python.
So I use ```python-exe-unpacker```. There are so many package, but main logic is in ```emco``` file.
```emco``` has no signatue and extended, but I can simply read it by add signature on file header and add extend ```.pyc``` and decompile it.
Find another ```.pyc``` file, and compare it to ```emco``` file, and signature is ```03 F3 0D 0A 00 00 00 00```.(It may different on other project)
Make 2nd file like 1st file.
Add this signature on ```emco``` and rename it ```emco.pyc```, and use ```uncompyle6``` to decompile the pyc file.
Main logic is like this:
```python
def encrypt(file_path):
im = Image.open(file_path).convert('RGB')
width, height = im.size
pixels = list(im.getdata())
pixels = [ pixels[i * width:(i + 1) * width] for i in range(height) ]
binary_pixels = []
for item in pixels:
for pixel in item:
if pixel == (255, 255, 255):
binary_pixels.append('0')
else:
binary_pixels.append('1')
line = ''.join(binary_pixels)
n = 8
enc = [ int(line[i:i + n], 2) for i in range(0, len(line), n) ]
data = ''
enc_len = len(enc)
s = int(sqrt(enc_len))
for i in range(enc_len):
data += chr(125) + chr(0) + chr(enc[i])
im2 = Image.frombytes('RGB', (s, s), data.encode())
im2.save('encrypted.png', 'PNG')
```
I do some test and get sure that logic is only use for app and other package is just trick.(like all crypto, ssl, ftp and other.)
So I write decrypt function in python.
```python
def decrypt(file_path):
im = Image.open(file_path).convert('RGB')
pixels = list(im.getdata())
for i in range(100):
pixels.append((125,0,0))
data =[]
for pixel in pixels:
data.append(pixel[2])
line = ''
for p in data:
t = "{0:b}".format(p)
if len(t) < 8:
t = '0'*(8-len(t)) + t
line += t
original = []
for ch in line:
if ch == '0':
original.append((255,255,255))
else:
original.append((0,0,0))
res = b''
for o in original:
res += bytes([o[0]]) + bytes([o[1]]) + bytes([o[2]])
print(len(res), 40000)
im2 = Image.frombytes('RGB', (200, 200), res)
pixels = list(im2.getdata())
print(pixels)
im2.save("target.png", "PNG")
```
And run the code, I get QR code.
Flag is ```infernoCTF{w04h_3ncrypt3d_qr_d4yumnnn}```
