The picoCTF Challenge ‘The Numbers’ is worth 50 points, so let’s jump straight into it.

The hint on this Challenge only tells us to remember the format to submit the flag: picoCTF{ }
Behind the given link there is a .png file called ‘the_numbers.png’ . You can access it by simply clicking on the link or using the wget command.

The picture i obtained is shown below. It only consists of individual numbers separated by spaces and curly braces.

The partition of the numbers and the curly braces was an indication for me, that the transformation needed is simple. In fact, the hardest part was to figure out, how this kind of transformation is named. A small google request told me, that this chiffre is called A1Z26-chiffre. That’s pretty straight forward as the transformation used on the flag simply was to substitute each character of the flag with the corresponding number on the alphabet. (A = 1, B = 2 ….. Z = 26)

Instead of doing the transformation by hand i used cyberchef again. With selecting A1Z26 Cipher Decode (delimiter: space) you can type in the numbers from the picture (without the braces) and get the result (the flag!) in clear text.

before we submit the flag we need to apply the common format for picoCTF and voilá – here we go!

picoCTF{thenumbersmason}