Solution
You will be given the following files.
ende.pyflag.txt.enpw.txt
The ende.py is a simple encryption/decryption script.
$ python scripts/ende.py
Usage: scripts/ende.py (-e/-d) [file]
The flag.txt.en is an encrypted flag. I used the string in pw.txt as a password.
$ python scripts/ende.py -d scripts/flag.txt.en
Please enter the password:ac9bd0ffac9bd0ffac9bd0ffac9bd0ff
picoCTF{4p0110_1n_7h3_h0us3_ac9bd0ff}
Acknowledgement
Thank you, CMU security and privacy experts, for creating this challenge.