1354 lines
42 KiB
Org Mode
1354 lines
42 KiB
Org Mode
#+TITLE: GNU Privacy Guard (GnuPG) Made Easy Python Bindings HOWTO (English)
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#+LATEX_COMPILER: xelatex
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#+LATEX_CLASS: article
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#+LATEX_CLASS_OPTIONS: [12pt]
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#+LATEX_HEADER: \usepackage{xltxtra}
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#+LATEX_HEADER: \usepackage[margin=1in]{geometry}
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#+LATEX_HEADER: \setmainfont[Ligatures={Common}]{Times New Roman}
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#+LATEX_HEADER: \author{Ben McGinnes <ben@gnupg.org>}
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* Introduction
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:PROPERTIES:
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:CUSTOM_ID: intro
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:END:
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| Version: | 0.0.1-alpha |
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| Author: | Ben McGinnes <ben@gnupg.org> |
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| Author GPG Key: | DB4724E6FA4286C92B4E55C4321E4E2373590E5D |
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| Language: | Australian English, British English |
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| xml:lang: | en-AU, en-GB, en |
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This document provides basic instruction in how to use the GPGME
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Python bindings to programmatically leverage the GPGME library.
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** Python 2 versus Python 3
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:PROPERTIES:
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:CUSTOM_ID: py2-vs-py3
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:END:
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Though the GPGME Python bindings themselves provide support for
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both Python 2 and 3, the focus is unequivocally on Python 3 and
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specifically from Python 3.4 and above. As a consequence all the
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examples and instructions in this guide use Python 3 code.
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Much of it will work with Python 2, but much of it also deals with
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Python 3 byte literals, particularly when reading and writing data.
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Developers concentrating on Python 2.7, and possibly even 2.6, will
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need to make the appropriate modifications to support the older
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string and unicode types as opposed to bytes.
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There are multiple reasons for concentrating on Python 3; some of
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which relate to the immediate integration of these bindings, some
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of which relate to longer term plans for both GPGME and the python
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bindings and some of which relate to the impending EOL period for
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Python 2.7. Essentially, though, there is little value in tying
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the bindings to a version of the language which is a dead end and
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the advantages offered by Python 3 over Python 2 make handling the
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data types with which GPGME deals considerably easier.
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* GPGME Concepts
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:PROPERTIES:
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:CUSTOM_ID: gpgme-concepts
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:END:
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** A C API
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:PROPERTIES:
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:CUSTOM_ID: gpgme-c-api
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:END:
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Unlike many modern APIs with which programmers will be more
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familiar with these days, the GPGME API is a C API. The API is
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intended for use by C coders who would be able to access its
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features by including the =gpgme.h= header file with their own C
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source code and then access its functions just as they would any
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other C headers.
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This is a very effective method of gaining complete access to the
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API and in the most efficient manner possible. It does, however,
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have the drawback that it cannot be directly used by other
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languages without some means of providing an interface to those
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languages. This is where the need for bindings in various
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languages stems.
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** Python bindings
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-bindings
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:END:
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The Python bindings for GPGME provide a higher level means of
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accessing the complete feature set of GPGME itself. It also
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provides a more pythonic means of calling these API functions.
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The bindings are generated dynamically with SWIG and the copy of =gpgme.h= generated when GPGME is compiled.
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This means that a version of the Python bindings is fundamentally
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tied to the exact same version of GPGME used to generate that copy
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of =gpgme.h=.
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** Difference between the Python bindings and other GnuPG Python packages
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-bindings-diffs
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:END:
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There have been numerous attempts to add GnuPG support to Python
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over the years. Some of the most well known are listed here, along
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with what differentiates them.
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*** The python-gnupg package maintained by Vinay Sajip
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:PROPERTIES:
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:CUSTOM_ID: diffs-python-gnupg
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:END:
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This is arguably the most popular means of integrating GPG with
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Python. The package utilises the =subprocess= module to implement
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wrappers for the =gpg= and =gpg2= executables normally invoked on
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the command line (=gpg.exe= and =gpg2.exe= on Windows).
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The popularity of this package stemmed from its ease of use and
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capability in providing the most commonly required features.
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Unfortunately it has been beset by a number of security issues,
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most of which stemmed from using unsafe methods of accessing the
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command line via the =subprocess= calls.
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The python-gnupg package is available under the MIT license.
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*** The gnupg package created and maintained by Isis Lovecruft
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:PROPERTIES:
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:CUSTOM_ID: diffs-isis-gnupg
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:END:
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In 2015 Isis Lovecruft from the Tor Project forked and then
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re-implemented the python-gnupg package as just gnupg. This new
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package also relied on subprocess to call the =gpg= or =gpg2=
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binaries, but did so somewhat more securely.
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However the naming and version numbering selected for this package
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resulted in conflicts with the original python-gnupg and since its
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functions were called in a different manner, the release of this
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package also resulted in a great deal of consternation when people
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installed what they thought was an upgrade that subsequently broke
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the code relying on it.
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The gnupg package is available under the GNU General Public
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License version 3.0 (or later).
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*** The PyME package maintained by Martin Albrecht
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:PROPERTIES:
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:CUSTOM_ID: diffs-pyme
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:END:
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This package is the origin of these bindings, though they are
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somewhat different now. For details of when and how the PyME
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package was folded back into GPGME itself see the /Short History/
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document[fn:1] in this Python bindings =docs= directory.[fn:2]
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The PyME package was first released in 2002 and was also the first
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attempt to implement a low level binding to GPGME. In doing so it
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provided access to considerably more functionality than either the =python-gnupg= or =gnupg= packages.
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The PyME package is only available for Python 2.6 and 2.7.
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Porting the PyME package to Python 3.4 in 2015 is what resulted in
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it being folded into the GPGME project and the current bindings
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are the end result of that effort.
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The PyME package is available under the same dual licensing as
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GPGME itself: the GNU General Public License version 2.0 (or any
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later version) and the GNU Lesser Public License version 2.1 (or
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any later version).
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* GPGME Python bindings installation
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-install
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:END:
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** No PyPI
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:PROPERTIES:
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:CUSTOM_ID: do-not-use-pypi
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:END:
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Most third-party Python packages and modules are available and
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distributed through the Python Package Installer, known as PyPI.
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Due to the nature of what these bindings are and how they work, it
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is infeasible to install the GPGME Python bindings in the same way.
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** Requirements
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-requirements
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:END:
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The GPGME Python bindings only have three requirements:
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1. A suitable version of Python 2 or Python 3. With Python 2 that
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means Python 2.7 and with Python 3 that means Python 3.4 or
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higher.
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2. SWIG.
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3. GPGME itself. Which also means that all of GPGME's dependencies
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must be installed too.
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** Installation
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:PROPERTIES:
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:CUSTOM_ID: installation
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:END:
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Installing the Python bindings is effectively achieved by compiling
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and installing GPGME itself.
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Once SWIG is installed with Python and all the dependencies for
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GPGME are installed you only need to confirm that the version(s) of
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Python you want the bindings installed for are in your =$PATH=.
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By default GPGME will attempt to install the bindings for the most
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recent or highest version number of Python 2 and Python 3 it
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detects in =$PATH=. It specifically checks for the =python= and =python3= executables first and then checks for specific version
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numbers.
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For Python 2 it checks for these executables in this order: =python=, =python2= and =python2.7=.
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For Python 3 it checks for these executables in this order: =python3=, =python3.6=, =python3.5= and =python3.4=.
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*** Installing GPGME
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:PROPERTIES:
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:CUSTOM_ID: install-gpgme
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:END:
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See the GPGME =README= file for details of how to install GPGME from
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source.
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* Fundamentals
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:PROPERTIES:
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:CUSTOM_ID: howto-fund-a-mental
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:END:
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Before we can get to the fun stuff, there are a few matters
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regarding GPGME's design which hold true whether you're dealing with
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the C code directly or these Python bindings.
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** No REST
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:PROPERTIES:
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:CUSTOM_ID: no-rest-for-the-wicked
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:END:
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The first part of which is or will be fairly blatantly obvious upon
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viewing the first example, but it's worth reiterating anyway. That
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being that this API is /*not*/ a REST API. Nor indeed could it
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ever be one.
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Most, if not all, Python programmers (and not just Python
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programmers) know how easy it is to work with a RESTful API. In
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fact they've become so popular that many other APIs attempt to
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emulate REST-like behaviour as much as they are able. Right down
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to the use of JSON formatted output to facilitate the use of their
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API without having to retrain developers.
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This API does not do that. It would not be able to do that and
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also provide access to the entire C API on which it's built. It
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does, however, provide a very pythonic interface on top of the
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direct bindings and it's this pythonic layer with which this HOWTO
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deals with.
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** Context
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:PROPERTIES:
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:CUSTOM_ID: howto-get-context
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:END:
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One of the reasons which prevents this API from being RESTful is
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that most operations require more than one instruction to the API
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to perform the task. Sure, there are certain functions which can
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be performed simultaneously, particularly if the result known or
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strongly anticipated (e.g selecting and encrypting to a key known
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to be in the public keybox).
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There are many more, however, which cannot be manipulated so
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readily: they must be performed in a specific sequence and the
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result of one operation has a direct bearing on the outcome of
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subsequent operations. Not merely by generating an error either.
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When dealing with this type of persistent state on the web, full of
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both the RESTful and REST-like, it's most commonly referred to as a
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session. In GPGME, however, it is called a context and every
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operation type has one.
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* Working with keys
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:PROPERTIES:
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:CUSTOM_ID: howto-keys
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:END:
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** Key selection
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:PROPERTIES:
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:CUSTOM_ID: howto-keys-selection
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:END:
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Selecting keys to encrypt to or to sign with will be a common
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occurrence when working with GPGMe and the means available for
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doing so are quite simple.
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They do depend on utilising a Context; however once the data is
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recorded in another variable, that Context does not need to be the
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same one which subsequent operations are performed.
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The easiest way to select a specific key is by searching for that
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key's key ID or fingerprint, preferably the full fingerprint
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without any spaces in it. A long key ID will probably be okay, but
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is not advised and short key IDs are already a problem with some
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being generated to match specific patterns. It does not matter
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whether the pattern is upper or lower case.
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So this is the best method:
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#+begin_src python
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import gpg
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k = gpg.Context().keylist(pattern="258E88DCBD3CD44D8E7AB43F6ECB6AF0DEADBEEF")
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keys = list(k)
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#+end_src
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This is passable and very likely to be common:
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#+begin_src python
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import gpg
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k = gpg.Context().keylist(pattern="0x6ECB6AF0DEADBEEF")
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keys = list(k)
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#+end_src
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And this is a really bad idea:
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#+begin_src python
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import gpg
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k = gpg.Context().keylist(pattern="0xDEADBEEF")
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keys = list(k)
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#+end_src
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Alternatively it may be that the intention is to create a list of
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keys which all match a particular search string. For instance all
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the addresses at a particular domain, like this:
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#+begin_src python
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import gpg
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ncsc = gpg.Context().keylist(pattern="ncsc.mil")
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nsa = list(ncsc)
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#+end_src
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*** Counting keys
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:PROPERTIES:
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:CUSTOM_ID: howto-keys-counting
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:END:
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Counting the number of keys in your public keybox (=pubring.kbx=),
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the format which has superseded the old keyring format
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(=pubring.gpg= and =secring.gpg=), or the number of secret keys is
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a very simple task.
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#+begin_src python
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import gpg
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c = gpg.Context()
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seckeys = c.keylist(pattern=None, secret=True)
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pubkeys = c.keylist(pattern=None, secret=False)
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seclist = list(seckeys)
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secnum = len(seclist)
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publist = list(pubkeys)
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pubnum = len(publist)
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print("""
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Number of secret keys: {0}
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Number of public keys: {1}
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""".format(secnum, pubnum)
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#+end_src
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** Get key
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:PROPERTIES:
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:CUSTOM_ID: howto-get-key
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:END:
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An alternative method of getting a single key via its fingerprint
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is available directly within a Context with =Context().get_key=.
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This is the preferred method of selecting a key in order to modify
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it, sign or certify it and for obtaining relevant data about a
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single key as a part of other functions; when verifying a signature
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made by that key, for instance.
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By default this method will select public keys, but it can select
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secret keys as well.
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This first example demonstrates selecting the current key of Werner
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Koch, which is due to expire at the end of 2018:
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#+begin_src python
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import gpg
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fingerprint = "80615870F5BAD690333686D0F2AD85AC1E42B367"
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key = gpg.Context().get_key(fingerprint)
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#+end_src
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Whereas this example demonstrates selecting the author's current
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key with the =secret= key word argument set to =True=:
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#+begin_src python
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import gpg
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fingerprint = "DB4724E6FA4286C92B4E55C4321E4E2373590E5D"
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key = gpg.Context().get_key(fingerprint, secret=True)
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#+end_src
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It is, of course, quite possible to select expired, disabled and
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revoked keys with this function, but only to effectively display
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information about those keys.
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It is also possible to use both unicode or string literals and byte
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literals with the fingerprint when getting a key in this way.
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* Basic Functions
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:PROPERTIES:
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:CUSTOM_ID: howto-the-basics
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:END:
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The most frequently called features of any cryptographic library
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will be the most fundamental tasks for encryption software. In this
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section we will look at how to programmatically encrypt data,
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decrypt it, sign it and verify signatures.
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** Encryption
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption
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:END:
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Encrypting is very straight forward. In the first example below
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the message, =text=, is encrypted to a single recipient's key. In
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the second example the message will be encrypted to multiple
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recipients.
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*** Encrypting to one key
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption-single
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:END:
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The text is then encapsulated in a GPGME Data object as =plain= and
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the =cipher= object is created with another Data object. Then we
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create the Context as =c= and set it to use the ASCII armoured
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OpenPGP format. In later examples there will be alternative
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methods of setting the OpenPGP output to be ASCII armoured.
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Next we prepare a keylist object in our Context and follow it with
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specifying the recipients as =r=. Note that the configuration in
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one's =gpg.conf= file is honoured, so if you have the options set
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to encrypt to one key or to a default key, that will be included
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with this operation.
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This is followed by a quick check to be sure that the recipient is
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actually selected and that the key is available. Assuming it is,
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the encryption can proceed, but if not a message will print stating
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the key was not found.
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The encryption operation is invoked within the Context with the =c.op_encrypt= function, loading the recipients (=r=), the message
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(=plain=) and the =cipher=. The =cipher.seek= uses =os.SEEK_SET=
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to set the data to the correct byte format for GPGME to use it.
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At this point we no longer need the plaintext material, so we
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delete both the =text= and the =plain= objects. Then we write the
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encrypted data out to a file, =secret_plans.txt.asc=.
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#+begin_src python
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import gpg
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import os
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rkey = "0x12345678DEADBEEF"
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text = """
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Some plain text to test with. Obtained from any input source Python can read.
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It makes no difference whether it is string or bytes, but the bindings always
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produce byte output data. Which is useful to know when writing out either the
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encrypted or decrypted results.
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"""
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plain = gpg.core.Data(text)
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cipher = gpg.core.Data()
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c = gpg.core.Context()
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c.set_armor(1)
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c.op_keylist_start(rkey, 0)
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r = c.op_keylist_next()
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if r == None:
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print("""The key for user "{0}" was not found""".format(rkey))
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else:
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try:
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c.op_encrypt([r], 1, plain, cipher)
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cipher.seek(0, os.SEEK_SET)
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del(text)
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del(plain)
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afile = open("secret_plans.txt.asc", "wb")
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afile.write(cipher.read())
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afile.close()
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except gpg.errors.GPGMEError as ex:
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print(ex.getstring())
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#+end_src
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*** Encrypting to multiple keys
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption-multiple
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:END:
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Encrypting to multiple keys, in addition to a default key or a key
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configured to always encrypt to, is a little different and uses a
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slightly different call to the =op_encrypt call= demonstrated in the
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previous section.
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The following example encrypts a message (=text=) to everyone with
|
|
an email address on the =gnupg.org= domain,[fn:3] but does /not/ encrypt
|
|
to a default key or other key which is configured to normally
|
|
encrypt to.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
text = b"""Oh look, another test message.
|
|
|
|
The same rules apply as with the previous example and more likely
|
|
than not, the message will actually be drawn from reading the
|
|
contents of a file or, maybe, from entering data at an input()
|
|
prompt.
|
|
|
|
Since the text in this case must be bytes, it is most likely that
|
|
the input form will be a separate file which is opened with "rb"
|
|
as this is the simplest method of obtaining the correct data
|
|
format.
|
|
"""
|
|
|
|
c = gpg.Context(armor=True)
|
|
rpattern = list(c.keylist(pattern="@gnupg.org", secret=False))
|
|
logrus = []
|
|
|
|
for i in range(len(rpattern)):
|
|
if rpattern[i].can_encrypt == 1:
|
|
logrus.append(rpattern[i])
|
|
|
|
cipher = c.encrypt(text, recipients=logrus, sign=False, always_trust=True)
|
|
|
|
afile = open("secret_plans.txt.asc", "wb")
|
|
afile.write(cipher[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
All it would take to change the above example to sign the message
|
|
and also encrypt the message to any configured default keys would
|
|
be to change the =c.encrypt= line to this:
|
|
|
|
#+begin_src python
|
|
cipher = c.encrypt(text, recipients=logrus, always_trust=True,
|
|
add_encrypt_to=True)
|
|
#+end_src
|
|
|
|
The only keyword arguments requiring modification are those for
|
|
which the default values are changing. The default value of =sign= is =True=, the default of =always_trust= is =False=, the
|
|
default of =add_encrypt_to= is =False=.
|
|
|
|
If =always_trust= is not set to =True= and any of the recipient
|
|
keys are not trusted (e.g. not signed or locally signed) then the
|
|
encryption will raise an error. It is possible to mitigate this
|
|
somewhat with something more like this:
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
afile = open("secret_plans.txt", "rb")
|
|
text = afile.read()
|
|
afile.close()
|
|
|
|
c = gpg.Context(armor=True)
|
|
rpattern = list(c.keylist(pattern="@gnupg.org", secret=False))
|
|
logrus = []
|
|
|
|
for i in range(len(rpattern)):
|
|
if rpattern[i].can_encrypt == 1:
|
|
logrus.append(rpattern[i])
|
|
|
|
try:
|
|
cipher = c.encrypt(text, recipients=logrus, add_encrypt_to=True)
|
|
except gpg.errors.InvalidRecipients as e:
|
|
for i in range(len(e.recipients)):
|
|
for n in range(len(logrus)):
|
|
if logrus[n].fpr == e.recipients[i].fpr:
|
|
logrus.remove(logrus[n])
|
|
else:
|
|
pass
|
|
try:
|
|
cipher = c.encrypt(text, recipients=logrus, add_encrypt_to=True)
|
|
except:
|
|
pass
|
|
|
|
afile = open("secret_plans.txt.asc", "wb")
|
|
afile.write(cipher[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
This will attempt to encrypt to all the keys searched for, then
|
|
remove invalid recipients if it fails and try again.
|
|
|
|
**** Encrypting to one key using the second method
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-encryption-monogamous
|
|
:END:
|
|
|
|
This example re-creates the first encryption example except it
|
|
uses the same =encrypt= method used in the subsequent examples
|
|
instead of the =op_encrypt= method. This means that, unlike the =op_encrypt= method, it /must/ use byte literal input data.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
rkey = "0x12345678DEADBEEF"
|
|
text = b"""Some text to test with.
|
|
|
|
Since the text in this case must be bytes, it is most likely that
|
|
the input form will be a separate file which is opened with "rb"
|
|
as this is the simplest method of obtaining the correct data
|
|
format.
|
|
"""
|
|
|
|
c = gpg.Context(armor=True)
|
|
rpattern = list(c.keylist(pattern=rkey, secret=False))
|
|
logrus = []
|
|
|
|
for i in range(len(rpattern)):
|
|
if rpattern[i].can_encrypt == 1:
|
|
logrus.append(rpattern[i])
|
|
|
|
cipher = c.encrypt(text, recipients=logrus, sign=False, always_trust=True)
|
|
|
|
afile = open("secret_plans.txt.asc", "wb")
|
|
afile.write(cipher[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
With one or two exceptions, this method will probably prove to be
|
|
easier to implement than the first method and thus it is the
|
|
recommended encryption method. Though it is even more likely to
|
|
be used like this:
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
rkey = "0x12345678DEADBEEF"
|
|
|
|
afile = open("secret_plans.txt", "rb")
|
|
text = afile.read()
|
|
afile.close()
|
|
|
|
c = gpg.Context(armor=True)
|
|
rpattern = list(c.keylist(pattern=rkey, secret=False))
|
|
logrus = []
|
|
|
|
for i in range(len(rpattern)):
|
|
if rpattern[i].can_encrypt == 1:
|
|
logrus.append(rpattern[i])
|
|
|
|
cipher = c.encrypt(text, recipients=logrus, sign=False, always_trust=True)
|
|
|
|
afile = open("secret_plans.txt.asc", "wb")
|
|
afile.write(cipher[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
|
|
** Decryption
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-encryption
|
|
:END:
|
|
|
|
Decrypting something encrypted to a key in one's secret keyring is
|
|
fairly straight forward.
|
|
|
|
In this example code, however, preconfiguring either =gpg.Context()= or =gpg.core.Context()= as =c= is unnecessary
|
|
because there is no need to modify the Context prior to conducting
|
|
the decryption and since the Context is only used once, setting it
|
|
to =c= simply adds lines for no gain.
|
|
|
|
#+begin_src python
|
|
import os.path
|
|
import gpg
|
|
|
|
if os.path.exists("/path/to/secret_plans.txt.asc") is True:
|
|
ciphertext = "/path/to/secret_plans.txt.asc"
|
|
elif os.path.exists("/path/to/secret_plans.txt.gpg") is True:
|
|
ciphertext = "/path/to/secret_plans.txt.gpg"
|
|
else:
|
|
ciphertext = None
|
|
|
|
if ciphertext is not None:
|
|
afile = open(ciphertext, "rb")
|
|
plaintext = gpg.Context().decrypt(afile)
|
|
afile.close()
|
|
newfile = open("/path/to/secret_plans.txt", "wb")
|
|
newfile.write(plaintext[0])
|
|
newfile.close()
|
|
print(plaintext[0])
|
|
plaintext[1]
|
|
plaintext[2]
|
|
del(plaintext)
|
|
else:
|
|
pass
|
|
#+end_src
|
|
|
|
The data available in plaintext in this example is the decrypted
|
|
content as a byte object in =plaintext[0]=, the recipient key IDs
|
|
and algorithms in =plaintext[1]= and the results of verifying any
|
|
signatures of the data in =plaintext[0]=.
|
|
|
|
|
|
** Signing text and files
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-signing
|
|
:END:
|
|
|
|
The following sections demonstrate how to specify
|
|
|
|
*** Signing key selection
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-signing-signers
|
|
:END:
|
|
|
|
By default GPGME and the Python bindings will use the default key
|
|
configured for the user invoking the GPGME API. If there is no
|
|
default key specified and there is more than one secret key
|
|
available it may be necessary to specify the key or keys with
|
|
which to sign messages and files.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
logrus = input("Enter the email address or string to match signing keys to: ")
|
|
hancock = gpg.Context().keylist(pattern=logrus, secret=True)
|
|
sig_src = list(hancock)
|
|
#+end_src
|
|
|
|
The signing examples in the following sections include the
|
|
explicitly designated =signers= parameter in two of the five
|
|
examples; once where the resulting signature would be ASCII
|
|
armoured and once where it would not be armoured.
|
|
|
|
While it would be possible to enter a key ID or fingerprint here
|
|
to match a specific key, it is not possible to enter two
|
|
fingerprints and match two keys since the patten expects a string,
|
|
bytes or None and not a list. A string with two fingerprints
|
|
won't match any single key.
|
|
|
|
*** Normal or default signing messages or files
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-signing-normal
|
|
:END:
|
|
|
|
The normal or default signing process is essentially the same as
|
|
is most often invoked when also encrypting a message or file. So
|
|
when the encryption component is not utilised, the result is to
|
|
produce an encoded and signed output which may or may not be ASCII
|
|
armoured and which may or may not also be compressed.
|
|
|
|
By default compression will be used unless GnuPG detects that the
|
|
plaintext is already compressed. ASCII armouring will be
|
|
determined according to the value of =gpg.Context().armor=.
|
|
|
|
The compression algorithm is selected in much the same way as the
|
|
symmetric encryption algorithm or the hash digest algorithm is
|
|
when multiple keys are involved; from the preferences saved into
|
|
the key itself or by comparison with the preferences with all
|
|
other keys involved.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
text0 = """Declaration of ... something.
|
|
|
|
"""
|
|
text = text0.encode("utf-8")
|
|
|
|
c = gpg.Context(armor=True, signers=sig_src)
|
|
signed = c.sign(text, mode=0)
|
|
|
|
afile = open("/path/to/statement.txt.asc", "w")
|
|
for line in signed[0]:
|
|
afile.write("{0}\n".format(line.decode("utf-8")))
|
|
afile.close()
|
|
#+end_src
|
|
|
|
Though everything in this example is accurate, it is more likely
|
|
that reading the input data from another file and writing the
|
|
result to a new file will be performed more like the way it is done
|
|
in the next example. Even if the output format is ASCII armoured.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
tfile = open("/path/to/statement.txt", "rb")
|
|
text = tfile.read()
|
|
tfile.close()
|
|
|
|
c = gpg.Context()
|
|
signed = c.sign(text, mode=0)
|
|
|
|
afile = open("/path/to/statement.txt.sig", "wb")
|
|
afile.write(signed[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
*** Detached signing messages and files
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-signing-detached
|
|
:END:
|
|
|
|
Detached signatures will often be needed in programmatic uses of
|
|
GPGME, either for signing files (e.g. tarballs of code releases)
|
|
or as a component of message signing (e.g. PGP/MIME encoded
|
|
email).
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
text0 = """Declaration of ... something.
|
|
|
|
"""
|
|
text = text0.encode("utf-8")
|
|
|
|
c = gpg.Context(armor=True)
|
|
signed = c.sign(text, mode=1)
|
|
|
|
afile = open("/path/to/statement.txt.asc", "w")
|
|
for line in signed[0].splitlines():
|
|
afile.write("{0}\n".format(line.decode("utf-8")))
|
|
afile.close()
|
|
#+end_src
|
|
|
|
As with normal signatures, detached signatures are best handled as
|
|
byte literals, even when the output is ASCII armoured.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
tfile = open("/path/to/statement.txt", "rb")
|
|
text = tfile.read()
|
|
tfile.close()
|
|
|
|
c = gpg.Context(signers=sig_src)
|
|
signed = c.sign(text, mode=1)
|
|
|
|
afile = open("/path/to/statement.txt.sig", "wb")
|
|
afile.write(signed[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
*** Clearsigning messages or text
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-signing-clear
|
|
:END:
|
|
|
|
Though PGP/in-line messages are no longer encouraged in favour of
|
|
PGP/MIME, there is still sometimes value in utilising in-line
|
|
signatures. This is where clear-signed messages or text is of
|
|
value.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
text0 = """Declaration of ... something.
|
|
|
|
"""
|
|
text = text0.encode("utf-8")
|
|
|
|
c = gpg.Context()
|
|
signed = c.sign(text, mode=2)
|
|
|
|
afile = open("/path/to/statement.txt.asc", "w")
|
|
for line in signed[0].splitlines():
|
|
afile.write("{0}\n".format(line.decode("utf-8")))
|
|
afile.close()
|
|
#+end_src
|
|
|
|
In spite of the appearance of a clear-signed message, the data
|
|
handled by GPGME in signing it must still be byte literals.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
|
|
tfile = open("/path/to/statement.txt", "rb")
|
|
text = tfile.read()
|
|
tfile.close()
|
|
|
|
c = gpg.Context()
|
|
signed = c.sign(text, mode=2)
|
|
|
|
afile = open("/path/to/statement.txt.asc", "wb")
|
|
afile.write(signed[0])
|
|
afile.close()
|
|
#+end_src
|
|
|
|
|
|
** Signature verification
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: howto-basic-verification
|
|
:END:
|
|
|
|
Essentially there are two principal methods of verification of a
|
|
signature. The first of these is for use with the normal or
|
|
default signing method and for clear-signed messages. The second is
|
|
for use with files and data with detached signatures.
|
|
|
|
The following example is intended for use with the default signing
|
|
method where the file was not ASCII armoured:
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
import time
|
|
|
|
filename = "statement.txt"
|
|
gpg_file = "statement.txt.gpg"
|
|
|
|
c = gpg.Context()
|
|
|
|
try:
|
|
verified = c.verify(open(gpg_file))
|
|
except gpg.errors.BadSignatures as e:
|
|
verified = None
|
|
print(e)
|
|
|
|
if verified is not None:
|
|
for i in range(len(verified[1].signatures)):
|
|
sign = verified[1].signatures[i]
|
|
print("""Good signature from:
|
|
{0}
|
|
with key {1}
|
|
made at {2}
|
|
""".format(c.get_key(sign.fpr).uids[0].uid,
|
|
sign.fpr, time.ctime(sign.timestamp)))
|
|
else:
|
|
pass(e)
|
|
#+end_src
|
|
|
|
Whereas this next example, which is almost identical would work
|
|
with normal ASCII armoured files and with clear-signed files:
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
import time
|
|
|
|
filename = "statement.txt"
|
|
asc_file = "statement.txt.asc"
|
|
|
|
c = gpg.Context()
|
|
|
|
try:
|
|
verified = c.verify(open(asc_file))
|
|
except gpg.errors.BadSignatures as e:
|
|
verified = None
|
|
print(e)
|
|
|
|
if verified is not None:
|
|
for i in range(len(verified[1].signatures)):
|
|
sign = verified[1].signatures[i]
|
|
print("""Good signature from:
|
|
{0}
|
|
with key {1}
|
|
made at {2}
|
|
""".format(c.get_key(sign.fpr).uids[0].uid,
|
|
sign.fpr, time.ctime(sign.timestamp)))
|
|
else:
|
|
pass
|
|
#+end_src
|
|
|
|
In both of the previous examples it is also possible to compare the
|
|
original data that was signed against the signed data in =verified[0]= to see if it matches with something like this:
|
|
|
|
#+begin_src python
|
|
afile = open(filename, "rb")
|
|
text = afile.read()
|
|
afile.close()
|
|
|
|
if text == verified[0]:
|
|
print("Good signature.")
|
|
else:
|
|
pass
|
|
#+end_src
|
|
|
|
The following two examples, however, deal with detached signatures.
|
|
With his method of verification the data that was signed does not
|
|
get returned since it is already being explicitly referenced in the
|
|
first argument of =c.verify=. So =verified[0]= is None and only
|
|
the data in =verified[1]= is available.
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
import time
|
|
|
|
filename = "statement.txt"
|
|
sig_file = "statement.txt.sig"
|
|
|
|
c = gpg.Context()
|
|
|
|
try:
|
|
verified = c.verify(open(filename), open(sig_file))
|
|
except gpg.errors.BadSignatures as e:
|
|
verified = None
|
|
print(e)
|
|
|
|
if verified is not None:
|
|
for i in range(len(verified[1].signatures)):
|
|
sign = verified[1].signatures[i]
|
|
print("""Good signature from:
|
|
{0}
|
|
with key {1}
|
|
made at {2}
|
|
""".format(c.get_key(sign.fpr).uids[0].uid,
|
|
sign.fpr, time.ctime(sign.timestamp)))
|
|
else:
|
|
pass
|
|
#+end_src
|
|
|
|
#+begin_src python
|
|
import gpg
|
|
import time
|
|
|
|
filename = "statement.txt"
|
|
asc_file = "statement.txt.asc"
|
|
|
|
c = gpg.Context()
|
|
|
|
try:
|
|
verified = c.verify(open(filename), open(asc_file))
|
|
except gpg.errors.BadSignatures as e:
|
|
verified = None
|
|
print(e)
|
|
|
|
if verified is not None:
|
|
for i in range(len(verified[1].signatures)):
|
|
sign = verified[1].signatures[i]
|
|
print("""Good signature from:
|
|
{0}
|
|
with key {1}
|
|
made at {2}
|
|
""".format(c.get_key(sign.fpr).uids[0].uid,
|
|
sign.fpr, time.ctime(sign.timestamp)))
|
|
else:
|
|
pass
|
|
#+end_src
|
|
|
|
|
|
* Creating keys and subkeys
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: key-generation
|
|
:END:
|
|
|
|
The one thing, aside from GnuPG itself, that GPGME depends on, of
|
|
course, is the keys themselves. So it is necessary to be able to
|
|
generate them and modify them by adding subkeys, revoking or
|
|
disabling them, sometimes deleting them and doing the same for user
|
|
IDs.
|
|
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In the following examples a key will be created for the world's
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greatest secret agent, Danger Mouse. Since Danger Mouse is a secret
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agent he needs to be able to protect information to =SECRET= level
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clearance, so his keys will be 3072-bit keys.
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The pre-configured =gpg.conf= file which sets cipher, digest and
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other preferences contains the following configuration parameters:
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#+begin_src conf
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expert
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allow-freeform-uid
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allow-secret-key-import
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trust-model tofu+pgp
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tofu-default-policy unknown
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# no-auto-check-trustdb
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enable-large-rsa
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enable-dsa2
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# no-emit-version
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# no-comments
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# cert-digest-algo SHA256
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cert-digest-algo SHA512
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default-preference-list TWOFISH CAMELLIA256 AES256 CAMELLIA192 AES192 CAMELLIA128 AES BLOWFISH IDEA CAST5 3DES SHA512 SHA384 SHA256 SHA224 RIPEMD160 SHA1 ZLIB BZIP2 ZIP Uncompressed
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personal-cipher-preferences TWOFISH CAMELLIA256 AES256 CAMELLIA192 AES192 CAMELLIA128 AES BLOWFISH IDEA CAST5 3DES
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personal-digest-preferences SHA512 SHA384 SHA256 SHA224 RIPEMD160 SHA1
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personal-compress-preferences ZLIB BZIP2 ZIP Uncompressed
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#+end_src
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** Primary key
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:PROPERTIES:
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:CUSTOM_ID: keygen-primary
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:END:
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Generating a primary key uses the =create_key= method in a Context.
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It contains multiple arguments and keyword arguments, including: =userid=, =algorithm=, =expires_in=, =expires=, =sign=, =encrypt=, =certify=, =authenticate=, =passphrase= and =force=. The defaults
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for all of those except =userid=, =algorithm=, =expires_in=, =expires= and =passphrase= is =False=. The defaults for =algorithm= and =passphrase= is =None=. The default for =expires_in= is =0=. The default for =expires= is =True=. There
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is no default for =userid=.
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If =passphrase= is left as =None= then the key will not be
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generated with a passphrase, if =passphrase= is set to a string
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then that will be the passphrase and if =passphrase= is set to =True= then gpg-agent will launch pinentry to prompt for a
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passphrase. For the sake of convenience, these examples will keep =passphrase= set to =None=.
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#+begin_src python
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import gpg
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c = gpg.Context()
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c.home_dir = "/tmp/dmgpg"
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userid = "Danger Mouse <dm@secret.example.net>"
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dmkey = c.create_key(userid, algorithm = "rsa3072", expires_in = 31536000,
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sign = True, certify = True)
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#+end_src
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One thing to note here is the use of setting the =c.home_dir=
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parameter. This enables generating the key or keys in a different
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location. In this case to keep the new key data created for this
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example in a separate location rather than adding it to existing
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and active key store data.
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The successful generation of the key can be confirmed via the
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returned =GenkeyResult= object, which includes the following data:
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#+begin_src python
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print("""
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Fingerprint: {0}
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Primary Key: {1}
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Public Key: {2}
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Secret Key: {3}
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Sub Key: {4}
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User IDs: {5}
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""".format(dmkey.fpr, dmkey.primary, dmkey.pubkey, dmkey.seckey, dmkey.sub,
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dmkey.uid))
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#+end_src
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Alternatively the information can be confirmed using the command
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line program:
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#+begin_src shell
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bash-4.4$ gpg --homedir /tmp/dmgpg -K
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/tmp/dmgpg/pubring.kbx
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----------------------
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sec rsa3072 2018-03-15 [SC] [expires: 2019-03-15]
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177B7C25DB99745EE2EE13ED026D2F19E99E63AA
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uid [ultimate] Danger Mouse <dm@secret.example.net>
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|
bash-4.4$
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#+end_src
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As with generating keys manually, to preconfigure expanded
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preferences for the cipher, digest and compression algorithms, the =gpg.conf= file must contain those details in the home directory in
|
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which the new key is being generated. I used a cut down version of
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my own =gpg.conf= file in order to be able to generate this:
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|
|
#+begin_src shell
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bash-4.4$ gpg --homedir /tmp/dmgpg --edit-key 177B7C25DB99745EE2EE13ED026D2F19E99E63AA showpref quit
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Secret key is available.
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|
|
sec rsa3072/026D2F19E99E63AA
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created: 2018-03-15 expires: 2019-03-15 usage: SC
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trust: ultimate validity: ultimate
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[ultimate] (1). Danger Mouse <dm@secret.example.net>
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[ultimate] (1). Danger Mouse <dm@secret.example.net>
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Cipher: TWOFISH, CAMELLIA256, AES256, CAMELLIA192, AES192, CAMELLIA128, AES, BLOWFISH, IDEA, CAST5, 3DES
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Digest: SHA512, SHA384, SHA256, SHA224, RIPEMD160, SHA1
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|
Compression: ZLIB, BZIP2, ZIP, Uncompressed
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|
Features: MDC, Keyserver no-modify
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|
|
bash-4.4$
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#+end_src
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|
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|
** Subkeys
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|
:PROPERTIES:
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|
:CUSTOM_ID: keygen-subkeys
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|
:END:
|
|
|
|
Adding subkeys to a primary key is fairly similar to creating the
|
|
primary key with the =create_subkey= method. Most of the arguments
|
|
are the same, but not quite all. Instead of the =userid= argument
|
|
there is now a =key= argument for selecting which primary key to
|
|
add the subkey to.
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|
|
In the following example an encryption subkey will be added to the
|
|
primary key. Since Danger Mouse is a security conscious secret
|
|
agent, this subkey will only be valid for about six months, half
|
|
the length of the primary key.
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|
|
#+begin_src python
|
|
import gpg
|
|
|
|
c = gpg.Context()
|
|
c.home_dir = "/tmp/dmgpg"
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|
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key = c.get_key(dmkey.fpr, secret = True)
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|
dmsub = c.create_subkey(key, algorithm = "rsa3072", expires_in = 15768000,
|
|
encrypt = True)
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#+end_src
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As with the primary key, the results here can be checked with:
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|
|
#+begin_src python
|
|
print("""
|
|
Fingerprint: {0}
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|
Primary Key: {1}
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|
Public Key: {2}
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|
Secret Key: {3}
|
|
Sub Key: {4}
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|
User IDs: {5}
|
|
""".format(dmsub.fpr, dmsub.primary, dmsub.pubkey, dmsub.seckey, dmsub.sub,
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dmsub.uid))
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|
#+end_src
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|
As well as on the command line with:
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|
|
#+begin_src shell
|
|
bash-4.4$ gpg --homedir /tmp/dmgpg -K
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|
/tmp/dmgpg/pubring.kbx
|
|
----------------------
|
|
sec rsa3072 2018-03-15 [SC] [expires: 2019-03-15]
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|
177B7C25DB99745EE2EE13ED026D2F19E99E63AA
|
|
uid [ultimate] Danger Mouse <dm@secret.example.net>
|
|
ssb rsa3072 2018-03-15 [E] [expires: 2018-09-13]
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|
|
|
bash-4.4$
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|
#+end_src
|
|
|
|
|
|
** User IDs
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: keygen-uids
|
|
:END:
|
|
|
|
|
|
** Key preferences
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: keygen-prefs
|
|
:END:
|
|
|
|
|
|
** Key certification
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: keygen-certify
|
|
:END:
|
|
|
|
|
|
* Miscellaneous work-arounds
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: cheats-and-hacks
|
|
:END:
|
|
|
|
** Group lines
|
|
:PROPERTIES:
|
|
:CUSTOM_ID: group-lines
|
|
:END:
|
|
|
|
There is not yet an easy way to access groups configured in the
|
|
gpg.conf file from within GPGME. As a consequence these central
|
|
groupings of keys cannot be shared amongst multiple programs, such
|
|
as MUAs readily.
|
|
|
|
The following code, however, provides a work-around for obtaining
|
|
this information in Python.
|
|
|
|
#+begin_src python
|
|
import subprocess
|
|
|
|
lines = subprocess.getoutput("gpgconf --list-options gpg").splitlines()
|
|
|
|
for i in range(len(lines)):
|
|
if lines[i].startswith("group") is True:
|
|
line = lines[i]
|
|
else:
|
|
pass
|
|
|
|
groups = line.split(":")[-1].replace('"', '').split(',')
|
|
|
|
group_lines = groups
|
|
for i in range(len(group_lines)):
|
|
group_lines[i] = group_lines[i].split("=")
|
|
|
|
group_lists = group_lines
|
|
for i in range(len(group_lists)):
|
|
group_lists[i][1] = group_lists[i][1].split()
|
|
#+end_src
|
|
|
|
The result of that code is that =group_lines= is a list of lists
|
|
where =group_lines[i][0]= is the name of the group and =group_lines[i][1]= is the key IDs of the group as a string.
|
|
|
|
The =group_lists= result is very similar in that it is a list of
|
|
lists. The first part, =group_lists[i][0]= matches =group_lines[i][0]= as the name of the group, but =group_lists[i][1]= is the key IDs of the group as a string.
|
|
|
|
|
|
* 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.
|
|
|
|
|
|
* Footnotes
|
|
|
|
[fn:1] =Short_History.org= and/or =Short_History.html=.
|
|
|
|
[fn:2] The =lang/python/docs/= directory in the GPGME source.
|
|
|
|
[fn:3] You probably don't really want to do this. Searching the
|
|
keyservers for "gnupg.org" produces over 400 results, the majority of
|
|
which aren't actually at the gnupg.org domain, but just included a
|
|
comment regarding the project in their key somewhere.
|