#+TITLE: GNU Privacy Guard (GnuPG) Made Easy Python Bindings HOWTO (English) #+LATEX_COMPILER: xelatex #+LATEX_CLASS: article #+LATEX_CLASS_OPTIONS: [12pt] #+LATEX_HEADER: \usepackage{xltxtra} #+LATEX_HEADER: \usepackage[margin=1in]{geometry} #+LATEX_HEADER: \setmainfont[Ligatures={Common}]{Times New Roman} #+LATEX_HEADER: \author{Ben McGinnes } * Introduction :PROPERTIES: :CUSTOM_ID: intro :END: Version: 0.0.1-alpha [2018-03-07 Wed] Author: Ben McGinnes Author GPG Key: DB4724E6FA4286C92B4E55C4321E4E2373590E5D This document provides basic instruction in how to use the GPGME Python bindings to programmatically leverage the GPGME library. * GPGME Concepts :PROPERTIES: :CUSTOM_ID: gpgme-concepts :END: ** A C API :PROPERTIES: :CUSTOM_ID: gpgme-c-api :END: Unlike many modern APIs with which programmers will be more familiar with these days, the GPGME API is a C API. The API is intended for use by C coders who would be able to access its features by including the =gpgme.h= header file eith their own C source code and then access its functions just as they would any other C headers. This is a very effective method of gaining complete access to the API and in the most efficient manner possible. It does, however, have the drawback that it cannot be directly used by other languages without some means of providing an interface to those languages. This is where the need for bindings in various languages stems. ** Python bindings :PROPERTIES: :CUSTOM_ID: gpgme-python-bindings :END: The Python bindings for GPGME provide a higher level means of accessing the complete feature set of GPGME itself. It also provides a more pythonic means of calling these API functions. The bindings are generated dynamically with SWIG and the copy of =gpgme.h= generated when GPGME is compiled. This means that a version of the Python bindings is fundamentally tied to the exact same version of GPGME used to gemerate that copy of =gpgme.h=. ** Difference between the Python bindings and other GnuPG Python packages :PROPERTIES: :CUSTOM_ID: gpgme-python-bindings-diffs :END: There have been numerous attempts to add GnuPG support to Python over the years. Some of the most well known are listed here, along with what differentiates them. *** The python-gnupg package maintained by Vinay Sajip :PROPERTIES: :CUSTOM_ID: diffs-python-gnupg :END: This is arguably the most popular means of integrating GPG with Python. The package utilises the =subprocess= module to implement wrappers for the =gpg= and =gpg2= executables normally invoked on the command line (=gpg.exe= and =gpg2.exe= on Windows). The popularity of this package stemmed from its ease of use and capability in providing the most commonly required features. Unfortunately it has been beset by a number of security issues, most of which stemmed from using unsafe methods of accessing the command line via the =subprocess= calls. The python-gnupg package is available under the MIT license. *** The gnupg package created and maintained by Isis Lovecruft :PROPERTIES: :CUSTOM_ID: diffs-isis-gnupg :END: In 2015 Isis Lovecruft from the Tor Project forked and then re-implemented the python-gnupg package as just gnupg. This new package also relied on subprocess to call the =gpg= or =gpg2= binaries, but did so somewhat more securely. However the naming and version numbering selected for this package resulted in conflicts with the original python-gnupg and since its functions were called in a different manner, the release of this package also resulted in a great deal of consternation when people installed what they thought was an upgrade that subsequently broke the code relying on it. The gnupg package is available under the GNU General Public License version 3.0 (or later). *** The PyME package maintained by Martin Albrecht :PROPERTIES: :CUSTOM_ID: diffs-pyme :END: This package is the origin of these bindings, though they are somewhat different now. For details of when and how the PyME package was folded back into GPGME itself see the [[Short_History.org][Short History]] document in this Python bindings =docs= directory. The PyME package was first released in 2002 and was also the first attempt to implement a low level binding to GPGME. In doing so it provided access to considerably more functionality than either the =python-gnupg= or =gnupg= packages. The PyME package is only available for Python 2.6 and 2.7. Porting the PyME package to Python 3.4 in 2015 is what resulted in it being folded into the GPGME project and the current bindings are the end result of that effort. The PyME package is available under the same dual licensing as GPGME itself: the GNU General Public License version 2.0 (or any later version) and the GNU Lesser Public License version 2.1 (or any later version). * GPGME Python bindings installation :PROPERTIES: :CUSTOM_ID: gpgme-python-install :END: ** No PyPI :PROPERTIES: :CUSTOM_ID: do-not-use-pypi :END: Most third-party Python packages and modules are available and distributed through the Python Package Installer, known as PyPI. Due to the nature of what these bindings are and how they work, it is infeasible to install the GPGME Python bindings in the same way. ** Requirements :PROPERTIES: :CUSTOM_ID: gpgme-python-requirements :END: The GPGME Python bindings only have three requirements: 1. A suitable version of Python 2 or Python 3. With Python 2 that means Python 2.7 and with Python 3 that means Python 3.4 or higher. 2. SWIG. 3. GPGME itself. Which also means that all of GPGME's dependencies must be installed too. ** Installation :PROPERTIES: :CUSTOM_ID: installation :END: Installing the Python bindings is effectively achieved by compiling and installing GPGME itself. Once SWIG is installed with Python and all the dependencies for GPGME are installed you only need to confirm that the version(s) of Python you want the bindings installed for are in your =$PATH=. By default GPGME will attempt to install the bindings for the most recent or highest version number of Python 2 and Python 3 it detects in =$PATH=. It specifically checks for the =python= and =python3= executabled first and then checks for specific version numbers. For Python 2 it checks for these executables in this order: =python=, =python2= and =python2.7=. For Python 3 it checks for these executables in this order: =python3=, =python3.6=, =python3.5= and =python3.4=. *** Installing GPGME :PROPERTIES: :CUSTOM_ID: install-gpgme :END: See the [[../../../README][GPGME README file]] for details of how to install GPGME from source. * Fundamentals :PROPERTIES: :CUSTOM_ID: howto-fund-a-mental :END: Before we can get to the fun stuff, there are a few matters regarding GPGME's design which hold true whether you're dealing with the C code directly or these Python bindings. ** No REST :PROPERTIES: :CUSTOM_ID: no-rest-for-the-wicked :END: The first part of which is or will be fairly blatantly obvious upon viewing the first example, but it's worth reiterating anyway. That being that this API is /*not*/ a REST API. Nor indeed could it ever be one. Most, if not all, Python programmers (and not just Python programmers) know how easy it is to work with a RESTful API. In fact they've become so popular that many other APIs attempt to emulate REST-like behaviour as much as they are able. Right down to the use of JSON formatted output to facilitate the use of their API without having to retrain developers. This API does not do that. It would not be able to do that and also provide access to the entire C API on which it's built. It does, however, provide a very pythonic interface on top of the direct bindings and it's this pythonic layer with which this HOWTO deals with. ** Context :PROPERTIES: :CUSTOM_ID: howto-get-context :END: One of the reasons which prevents this API from being RESTful is that most operations require more than one instruction to the API to perform the task. Sure, there are certain functions which can be performed simultaneously, particularly if the result known or strongly anticipated (e.g selecting and encrypting to a key known to be in the public keybox). There are many more, however, which cannot be manipulated so readily: they must be performed in a specific sequence and the result of one operation has a direct bearing on the outcome of subsequent operations. Not merely by generating an error either. When dealing with this type of persistant state on the web, full of both the RESTful and REST-like, it's most commonly referred to as a session. In GPGME, however, it is called a context and every operation type has one. * Copyright and Licensing :PROPERTIES: :CUSTOM_ID: copyright-and-license :END: ** Copyright (C) The GnuPG Project, 2018 :PROPERTIES: :CUSTOM_ID: copyright :END: Copyright © The GnuPG Project, 2018. ** License GPL compatible :PROPERTIES: :CUSTOM_ID: license :END: This file is free software; as a special exception the author gives unlimited permission to copy and/or distribute it, with or without modifications, as long as this notice is preserved. This file is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY, to the extent permitted by law; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.