Hi

“colors” was third crypto challange in APAIUT-CERT CTF which had 40 points . they gave us this file with 11 circles .

I had nothing in my mind till CTF admins gave a hint

Look at colors codes.

then i tried to extract color codes with Photoshop or GIMP our codes had lot of Zero’s trying to find a way to decode that codes they gave another hints

Remove Extra Zero’s.

finally it was our codes

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63 84 189 238 45 112 175 140 56 189 98

you can use this code to extract color codes too :

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import Image
im = Image.open('chall.png')
(h, w) = im.size
code = []
def unique( seq ):
    seen = set()
    for item in seq:
        if item not in seen:
            seen.add( item )
            yield item
for x in range(h):
 for y in range(w):
  rgb_im = im.convert('RGB')
  r, g, b = rgb_im.getpixel((x, y))
  if (r,g,b) != (255,255,255) and r == 0 or g == 0 or b == 0 :
   if r != 0 or g != 0 or b != 0  :
    fin = r or g or b
    code.append(str(fin))
code[:] = unique(code)
print code

i tested ascii-table , Hex , Decimal , and …. or decodeing these codes but nothing changed because these codes had'nt special base aand Radix.

i went to mathematics :) so decided to find Greatest common divisor of all numbers first 2 by 2 tested each number till 45 no divisor found with other numbers but other numbers had divisor , then deleted 45 and test for divisor of all numbers to gether the result was “7” …

divided all numbers to 7 except 45 this was the result

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9 12 24 34 ? 16 25 20 8 24 14

these numbers had a base and radix between 0-36 after testing lot of classic ciphers i found Letter Number cipher but with a small diffrence letter number is a-z similar to 0-27 but our codes were like this a-z+0-9 similar to 1-26+27-36 in perl language it is like this :

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@char{("a".."z")} = (1..26);

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@num{("0".."9")} = (27..36);

With admin hints :) we could find the flag, i cant remember exactly but it should be the flag

The flag was :

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il073pyth0n

Cheers <3