- Server uses deduplication to save space
- Since duplicate data is not stored, the quota value tells us whether newly stored data is a duplicate of existing data
- By checking the quota value, we can determine whether any arbitrary string is a substring of the flag

[Full Writeup](https://zeyu2001.gitbook.io/ctfs/2021/google-ctf-2021/filestore)

Original writeup (https://zeyu2001.gitbook.io/ctfs/2021/google-ctf-2021/filestore).