> For the complete documentation index, see [llms.txt](https://ir0nstone.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ir0nstone.gitbook.io/notes/writeups/picogym/cryptography/credstuff.md).

# Credstuff

We found a leak of a blackmarket website's login credentials. Can you find the password of the user cultiris and successfully decrypt it? Download the leak here.

Opening up `usernames.txt` and `passwords.txt` in Pycharm, we see `cultiris` is on line `378` of `usernames.txt` so we go to line `378` of `passwords.txt` and find an encrypted password:

```
cvpbPGS{P7e1S_54I35_71Z3}
```

The `{}` are in place, implying that it's some sort of transposition cipher for the letters. We've done it numerous times, but we try a caesar cipher decode:

```python
from string import ascii_lowercase, ascii_uppercase

enc_flag = 'cvpbPGS{P7e1S_54I35_71Z3}'

for shift in range(26):
    flag = ''

    for c in enc_flag:
        if c in ascii_lowercase:
            flag += ascii_lowercase[(ascii_lowercase.index(c) + shift) % 26]
        elif c in ascii_uppercase:
            flag += ascii_uppercase[(ascii_uppercase.index(c) + shift) % 26]
        else:
            flag += c

    print(flag)

# picoCTF{C7r1F_54V35_71M3}

```

In fact the shift is 13, so it's just a ROT13.


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