# Lithp
Misc

## Challenge

My friend gave me this program but I couldn't understand what he was saying - what was he trying to tell me?

Author: fireholder

[lithp.lisp.txt](lithp.lisp.txt)

## Solution

The code

> [lithp.lisp.txt](lithp.lisp.txt)

I debugged the functions in an online compiler

- https://rextester.com/l/common_lisp_online_compiler

This is my understanding of the code

function (whats-this x y)
- returns x*y

function (multh plain)
- plain is a list
- returns a list of -a*a, for each a in list.

function (owo inpth)
- reorder the list according to the index given at *reorder*

function (enc plain)
- calls (owo (multh plain))
- remove the negative sign for each item in list
- print flag

So I simply reversed the process in a script

$ python3 solve.py
_{_fmvtlpthelpahee_i_Iac_h}a
actf{help_me_I_have_a_lithp}

## Flag

actf{help_me_I_have_a_lithp}

Original writeup (https://github.com/zst-ctf/angstromctf-2019-writeups/tree/master/Solved/Lithp).