TUCTF 2018: APL

Description

Dr. W gave me an old program of his… Can you tell me what it does? (Difficulty: Easy)

We get a text file APL.txt that contains:

mx←7 0↓14 9⍴⍳132
a←mx[(3 3)(3 4)(1 4)(3 3)(1 7)(7 6)(7 2)(3 1)(5 6)(3 3)(5 2)(4 5)(2 7)(6 2)(2 4)(7 4)(4 5)(2 1)(6 7)(4 5)(1 9)(4 7)(3 1)(5 1)(4 5)(3 3)(6 3)(4 5)(3 1)(5 2)(1 2)(5 1)(7 8)]

Solution

After some research (and knowing the title of the challenge), we found out that this is a code interpretable in APL.

So we parsed the program on https://tryapl.org/. When we print the output of the variable a we got: 84 85 67 84 70 123 119 82 105 84 101 95 79 110 76 121 95 73 115 95 72 97 82 100 95 84 111 95 82 101 65 100 125

It looks like the flag in ASCII, when converting we retreived:

TUCTF{wRiTe_OnLy_Is_HaRd_To_ReAd}