Using PGPy to encrypt and decrypt files and messages

 PGPy is a library for python that enables the creation, storage, and encryption/decryption of PGP keys and files in python. Recently, in a small project to reacquaint myself with python, I used PGPy for key generation and encryption and decryption. That project can be found in my github at https://github.com/lpowell. The goal of the project was to use command-line switches to control the program, and to provide basic encryption and decryption capabilities, along with rot13 and base64 encoding. 

First, to load in a key use key, _ = pgpy.PGPKey.from_file(keyfilename). This loads the key from either a binary or ASCII armored file. You can swap out .from_file for .from_blob, if you plan on using a key stored in a string or bytes object rather than a file. In my example code, I pull the key from a file, as I found it to be the simpler method. 

Next, you'll need to open a file or create a string or bytes object that contains the message you wish to encrypt. We'll call this file_message. To open a message from a file, you will want to do something like this, file_message = pgpy.PGPMessage.new(message_file_location, file=True). This will create a PGPMessage object called file_message. You can also import from a string or bytes object string_message = pgpy.PGPMessage.new("string or string object here"). To encrypt this message, encrypted_file_message = key.encrypt(file_message). This uses the key we opened early to encrypt the file or message. This will give an error if a private key is loaded, so make sure that the key object is loaded with a public key.  Outputting this is easy enough, output_file.write(str(encrypted_file_message). This will convert the encrypted message to a string, and store it inside a file. I recommend writing to PGP files.

To decrypt this message, make sure that the key you have open is the matching private key to the public key that was used to encrypt the original message. To open the encrypted message, encrypted_message = pgpy.PGPMessage.from_file(encrypted_message_file_location). This opens the encrypted message file we made earlier as a PGPMessage object. You can also run this with .from_blob and use a string or bytes object. 

Now that the encrypted message is open, we need to decrypt it. We can decrypt it using key.decrypt. decrypted_message = key.decrypt(encrypted_message). This creates a new object containing the decrypted message. This cannot be written directly to a file, as it is still an encrypted object. To get the decrypted message from the object, we need to use decrypted_message.message. This will give us access to the decrypted message. It sounds a bit silly, but this took me ages to figure out. Fully written out, this looks like str_decrypted_message = decrypted_message.message. To write this to a file, we do output_file.write(str_decrypted_message). I believe you could do output_file.write(decrypted_message.message), but I didn't do this myself.

More info on PGPy can be found on their website, https://pgpy.readthedocs.io/en/latest/api.html