“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
you can use this code to extract color codes too :
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
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
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 :
With admin hints :) we could find the flag, i cant remember exactly but it should be the flag
The flag was :