The Challenge

Name: Python Wrangling
Description: Python scripts are invoked kind of like programs in the Terminal... Can you run this Python script using this password to get the flag?

The Solution

With python installed, use the following command in a terminal
```
> cat pw.txt | python ende.py -d flag.txt.en
```

The Steps

The Source Code

Having some knowledge of Python helps to review the source code. Let's interpret it in chunks:
```
import sys
import base64
from cryptography.fernet import Fernet
```
- We're importing the sys library which looks like it's used to handle the CLI arguments.
- The base64 library, which looks to encode some sort of password
- And Fernet which seems to be an easy to use symmetric encryption class.
```
usage_msg = "Usage: "+ sys.argv[0] +" (-e/-d) [file]"
help_msg = usage_msg + "\n" +\
		"Examples:\n" +\
		"  To decrypt a file named 'pole.txt', do: " +\
		"'$ python "+ sys.argv[0] +" -d pole.txt'\n"

if len(sys.argv) < 2 or len(sys.argv) > 4:
	print(usage_msg)
	sys.exit(1)
```
- We have a usage message and a help message. The help message looks... helpful, and provides instruction to decrypt what I assume is the encrypted flag.txt.en flag.
- It looks like the usage message prints when either too few or too many CLI arguments are passed to the program.
```
if sys.argv[1] == "-e":
	...
	data_c = c.encrypt(data)
	sys.stdout.write(data_c.decode())


elif sys.argv[1] == "-d":
	...
	data_c = c.decrypt(data.encode())
	sys.stdout.buffer.write(data_c)
```
- The -e option encrypts the data, the -d option decrypts.

The Terminal Bits

After verifying the source code is magically harmless let's run it and see what happens.
```
> python ende.py
Usage: ende.py (-e/-d) [file]
```
- As expected the usage string prints.

Let's try following the help message. We can read it better by passing in the flag -h.

> python ende.py -h
Usage: ende.py (-e/-d) [file]
Examples:
  To decrypt a file named 'pole.txt', do: '$ python ende.py -d pole.txt'

Now let's try passing in our encrypted flag file

> python ende.py -d flag.txt.en
Please enter the password:

Now we can copy and paste the password from the pw.txt file or:
```
> cat pw.txt | python ende.py -d flag.txt.en
```
- The flag prints out to the terminal.