# [EN] Rev C 2
###### tags:`Writeup` `Reverse` `English`
> [name=FlyDragon]

## Step.1
By observing `output.txt` and executing the code, it can be inferred that the program `flag.exe` will output the flag after shuffling it.
## Step.2
By examining `main()` using Ghidra, it can be discovered that this program reads in the contents of `flag.txt` and outputs them after performing specific swaps in a particular order.



order = [5, 13, 0, 12, 1, 16, 3, 2, 8, 7, 15, 4, 6, 17, 11, 10, 9]

The for loop's condition is `local_20 < 0x12`, but the length of `order[]` is only 0x11 (missing 14). So, add an extra zero at the end.

order = [5, 13, 0, 12, 1, 16, 3, 2, 8, 7, 15, 4, 6, 17, 11, 10, 9, 0]

## Step.3

Writing a program to reverse the swap order and obtain the flag

output = list("4_e_foyeXE__ouryCs")
order = [5, 13, 0, 12, 1, 16, 3, 2, 8, 7, 15, 4, 6, 17, 11, 10, 9, 0]

for i in reversed(range(len(order))):
    temp = output[i]
    output[i] = output[order[i]]
    output[order[i]] = temp

print("".join(output))

{%hackmd M1bgOPoiQbmM0JRHWaYA1g %}