Description

Do you know unzip?

• flag.zip

(Warmup, 40 points)

So, we are given the flag.zip archive with recursive including another archive. The goal is to fetch the flag.txt file from isnide.

I noticed repeating pattern that all off the included archives are named flag.zip and executed the simple unzip command inside endless loop.

$ while true; do unzip -o 'flag.zip'; done;
Archive:  flag.zip
  inflating: flag.txt                
Archive:  flag.zip
  inflating: flag.txt                
Archive:  flag.zip
  inflating: flag.txt                
Archive:  flag.zip
  inflating: flag.txt                
Archive:  flag.zip
  inflating: flag.txt                
Archive:  flag.zip
  inflating: flag.txt                
^C

Thanks to -o flag, the loop will recursively overwrite original flag.zip archive with the extracted one. The loop has no end so we have to terminate it by hand when the flag.txt is beeing extracted over and over.

Here is the flag: HarekazeCTF{(\lambda f. (\lambda x. f (x x)) (\lambda x . f (x x))) zip}