2.9 KiB
Seeing Stars
Category: Astronomy, Astrophysics, Astrometry, Astrodynamics, AAAA Points (final): 23 Solves: 213
Here is the output from a CCD Camera from a star tracker, identify as many stars as you can! (in image reference coordinates) Note: The camera prints pixels in the following order (x,y): (0,0), (1,0), (2,0)... (0,1), (1,1), (2,1)…
Note that top left corner is (0,0)
Write-up
The CCD image given by the netcat is a 128x128 matrix of comma-separated values.
We read the data into a NumPy array, and pass that into OpenCV.
data = []
for line in rawdat.strip().split('\n'):
data.append([int(x) for x in line.split(',')])
x = np.array(data, dtype='uint8').T
im = x
We then run a filter on the data, only grabbing values in [127, 255] to filter
out data that is obviously not stars.
We then run two dilates on the image post-filter, because otherwise
we end up with a division by zero on centroid finding later for M["m00"].
Finally, we grabbed the contour of every object visible in the image.
ret, thresh = cv2.threshold(im.copy(), 127, 255, 0)
kernel = np.ones((5, 5), np.uint8)
dilated = cv2.dilate(thresh.copy(), kernel, iterations = 2)
cnts, hier = cv2.findContours(dilated.copy(), \
cv2.RETR_TREE, \
cv2.CHAIN_APPROX_NONE)
For each contour, we grabbed its centroid:
solve = ''
for c in cnts:
M = cv2.moments(c)
cX = int(M["m10"] / M["m00"])
cY = int(M["m01"] / M["m00"])
solve += (str(cX) + "," + str(cY)+'\n')
return solve
We then automated this entire process using pwnlib to connect to the server and read the data.
Full code
Run it:
λ has-writeup/aaaa/seeing-stars python seeing-stars.py
b'flag{juliet73678uniform:GDy7YZdtCL9mcLgYuLceK_zwgwSAoT6ui5aMGo1IMYcic9tiI8EXUHLfQDcUsjjt5KqsIvOWUYeM8IS6631Vppw}\n'
Traceback (most recent call last):
File "seeing-stars.py", line 42, in <module>
rawdat = r.recvuntil('Enter', drop=True)
File "/usr/lib/python3.8/site-packages/pwnlib/tubes/tube.py", line 310, in recvuntil
res = self.recv(timeout=self.timeout)
File "/usr/lib/python3.8/site-packages/pwnlib/tubes/tube.py", line 82, in recv
return self._recv(numb, timeout) or b''
File "/usr/lib/python3.8/site-packages/pwnlib/tubes/tube.py", line 160, in _recv
if not self.buffer and not self._fillbuffer(timeout):
File "/usr/lib/python3.8/site-packages/pwnlib/tubes/tube.py", line 131, in _fillbuffer
data = self.recv_raw(self.buffer.get_fill_size())
File "/usr/lib/python3.8/site-packages/pwnlib/tubes/sock.py", line 56, in recv_raw
raise EOFError
EOFError