TL;DR: Multiple concatenated zip files with the following EOCD records (end of central directory)

```
abcdefghijklmnopqrstuvwxyz{CTF0137}_
TF0137}_
F0137}_
0137}_
abcdefghijklmnopqrstuvwxyz{CTF0137}_
CTF0137}_
qrstuvwxyz{CTF0137}_
137}_
tuvwxyz{CTF0137}_
}_
nopqrstuvwxyz{CTF0137}_
137}_
efghijklmnopqrstuvwxyz{CTF0137}_
7}_
stuvwxyz{CTF0137}_
opqrstuvwxyz{CTF0137}_

{CTF0137}_
37}_
qrstuvwxyz{CTF0137}_
_
```
The 0th is a dictionary, the other lines are substrings of it, encoding the letter before it, so `TF0137}_` -> C, `F0137}_` -> T...

[Full writeup](http://sigflag.at/blog/2022/writeup-googlectf2022-appnote/)

Original writeup (http://sigflag.at/blog/2022/writeup-googlectf2022-appnote/).