GNU Privacy Guard (GnuPG) Made Easy Python Bindings HOWTO (English)

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GNU Privacy Guard (GnuPG) Made Easy Python Bindings HOWTO (English)


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1 Introduction

Version:0.1.4
GPGME Version:1.12.1
Author:Ben McGinnes <ben@gnupg.org>
Author GPG Key:DB4724E6FA4286C92B4E55C4321E4E2373590E5D
Language:Australian English, British English
Language codes:en-AU, en-GB, en

This document provides basic instruction in how to use the GPGME Python bindings to programmatically leverage the GPGME library.


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1.1 Python 2 versus Python 3

Though the GPGME Python bindings themselves provide support for both Python 2 and 3, the focus is unequivocally on Python 3 and specifically from Python 3.4 and above. As a consequence all the examples and instructions in this guide use Python 3 code.

Much of it will work with Python 2, but much of it also deals with Python 3 byte literals, particularly when reading and writing data. Developers concentrating on Python 2.7, and possibly even 2.6, will need to make the appropriate modifications to support the older string and unicode types as opposed to bytes.

There are multiple reasons for concentrating on Python 3; some of which relate to the immediate integration of these bindings, some of which relate to longer term plans for both GPGME and the python bindings and some of which relate to the impending EOL period for Python 2.7. Essentially, though, there is little value in tying the bindings to a version of the language which is a dead end and the advantages offered by Python 3 over Python 2 make handling the data types with which GPGME deals considerably easier.


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1.2 Examples

All of the examples found in this document can be found as Python 3 scripts in the ‘lang/python/examples/howto’ directory.


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1.3 Unofficial Drafts

In addition to shipping with each release of GPGME, there is a section on locations to read or download draft editions of this document from at the end of it. These are unofficial versions produced in between major releases.


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1.4 What’s New

Full details of what is new are now available in the What’s New file and archives of the preceding What’s New sections are available in the What Was New file.


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1.4.1 New in GPGME 1·13·0

See the What’s New document for what is new in version 1.13.0.


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1.4.2 New in GPGME 1·12·0

See the What Was New document for what was new in version 1.12.0.


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2 GPGME Concepts


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2.1 A C API

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 with 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.


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2.2 Python bindings

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 generate that copy of ‘gpgme.h’.


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2.3 Difference between the Python bindings and other GnuPG Python packages

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.


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2.3.1 The python-gnupg package maintained by Vinay Sajip

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 in the past; most of which stemmed from using unsafe methods of accessing the command line via the ‘subprocess’ calls. While some effort has been made over the last two to three years (as of 2018) to mitigate this, particularly by no longer providing shell access through those subprocess calls, the wrapper is still somewhat limited in the scope of its GnuPG features coverage.

The python-gnupg package is available under the MIT license.


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2.3.2 The gnupg package created and maintained by Isis Lovecruft

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.

The naming and version numbering selected for this package, however, resulted in conflicts with the original python-gnupg and since its functions were called in a different manner to python-gnupg, 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 any later version).


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2.3.3 The PyME package maintained by Martin Albrecht

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 document.1

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 General Public License version 2.1 (or any later version).


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3 GPGME Python bindings installation


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3.1 No PyPI

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.

This is because the bindings use SWIG to dynamically generate C bindings against ‘gpgme.h’ and ‘gpgme.h’ is generated from ‘gpgme.h.in’ at compile time when GPGME is built from source. Thus to include a package in PyPI which actually built correctly would require either statically built libraries for every architecture bundled with it or a full implementation of C for each architecture.

See the additional notes regarding CFFI and SWIG at the end of this section for further details.


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3.2 Requirements

The GPGME Python bindings only have three requirements:

  1. A suitable version of Python 2 or Python 3. With Python 2 that means CPython 2.7 and with Python 3 that means CPython 3.4 or higher.
  2. SWIG.
  3. GPGME itself. Which also means that all of GPGME’s dependencies must be installed too.

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3.2.1 Recommended Additions

Though none of the following are absolute requirements, they are all recommended for use with the Python bindings. In some cases these recommendations refer to which version(s) of CPython to use the bindings with, while others refer to third party modules which provide a significant advantage in some way.

  1. If possible, use Python 3 instead of 2.
  2. Favour a more recent version of Python since even 3.4 is due to reach EOL soon. In production systems and services, Python 3.6 should be robust enough to be relied on.
  3. If possible add the following Python modules which are not part of the standard library: Requests, Cython, Pendulum and hkp4py.

Chances are quite high that at least the first one and maybe two of those will already be installed.

Note that, as with Cython, some of advanced use case scenarios will bring with them additional requirements. Most of these will be fairly well known and commonly installed ones, however, which are in many cases likely to have already been installed on many systems or be familiar to Python programmers.


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3.3 Installation

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’ executables 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’, ‘python3.7’, ‘python3.6’, ‘python3.5’ and ‘python3.4’.2

On systems where ‘python’ is actually ‘python3’ and not ‘python2’ it may be possible that ‘python2’ may be overlooked, but there have been no reports of that actually occurring as yet.

In the three months or so since the release of Python 3.7.0 there has been extensive testing and work with these bindings with no issues specifically relating to the new version of Python or any of the new features of either the language or the bindings. This has also been the case with Python 3.7.1rc1. With that in mind and given the release of Python 3.7.1 is scheduled for around the same time as GPGME 1.12.0, the order of preferred Python versions has been changed to move Python 3.7 ahead of Python 3.6.


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3.3.1 Installing GPGME

See the GPGME ‘README’ file for details of how to install GPGME from source.


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3.4 Known Issues

There are a few known issues with the current build process and the Python bindings. For the most part these are easily addressed should they be encountered.


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3.4.1 Breaking Builds

Occasionally when installing GPGME with the Python bindings included it may be observed that the ‘make’ portion of that process induces a large very number of warnings and, eventually errors which end that part of the build process. Yet following that with ‘make check’ and ‘make install’ appears to work seamlessly.

The cause of this is related to the way SWIG needs to be called to dynamically generate the C bindings for GPGME in the first place. So the entire process will always produce ‘lang/python/python2-gpg/’ and ‘lang/python/python3-gpg/’ directories. These should contain the build output generated during compilation, including the complete bindings and module installed into ‘site-packages’.

Occasionally the errors in the early part or some other conflict (e.g. not installing as root or su) may result in nothing being installed to the relevant ‘site-packages’ directory and the build directory missing a lot of expected files. Even when this occurs, the solution is actually quite simple and will always work.

That solution is simply to run the following commands as either the root user or prepended with ‘sudo -H3 in the ‘lang/python/’ directory:

/path/to/pythonX.Y setup.py build
/path/to/pythonX.Y setup.py build
/path/to/pythonX.Y setup.py install

Yes, the build command does need to be run twice. Yes, you still need to run the potentially failing or incomplete steps during the ‘configure’, ‘make’ and ‘make install’ steps with installing GPGME. This is because those steps generate a lot of essential files needed, both by and in order to create, the bindings (including both the ‘setup.py’ and ‘gpgme.h’ files).

  1. IMPORTANT Note

    If specifying a selected number of languages to create bindings for, try to leave Python last. Currently the majority of the other language bindings are also preceding Python of either version when listed alphabetically and so that just happens by default currently.

    If Python is set to precede one of the other languages then it is possible that the errors described here may interrupt the build process before generating bindings for those other languages. In these cases it may be preferable to configure all preferred language bindings separately with alternative ‘configure’ steps for GPGME using the ‘--enable-languages=$LANGUAGE’ option.


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3.4.2 Reinstalling Responsibly

Regardless of whether you’re installing for one version of Python or several, there will come a point where reinstallation is required. With most Python module installations, the installed files go into the relevant site-packages directory and are then forgotten about. Then the module is upgraded, the new files are copied over the old and that’s the end of the matter.

While the same is true of these bindings, there have been intermittent issues observed on some platforms which have benefited significantly from removing all the previous installations of the bindings before installing the updated versions.

Removing the previous version(s) is simply a matter of changing to the relevant ‘site-packages’ directory for the version of Python in question and removing the ‘gpg/’ directory and any accompanying egg-info files for that module.

In most cases this will require root or administration privileges on the system, but the same is true of installing the module in the first place.


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3.4.3 Multiple installations

For a variety of reasons it may be either necessary or just preferable to install the bindings to alternative installed Python versions which meet the requirements of these bindings.

On POSIX systems this will generally be most simply achieved by running the manual installation commands (build, build, install) as described in the previous section for each Python installation the bindings need to be installed to.

As per the SWIG documentation: the compilers, libraries and runtime used to build GPGME and the Python Bindings must match those used to compile Python itself, including the version number(s) (at least going by major version numbers and probably minor numbers too).

On most POSIX systems, including OS X, this will very likely be the case in most, if not all, cases.

Note that from GPGME 1.12.1 the default installation installs to each version of Python it can find first. That is that it will currently install for the first copies of Python versions 2.7, 3.4, 3.5, 3.6, 3.7 and 3.8 (dev branch) that it finds. Usually this will be in the same prefix as GPGME itself, but is dictated by the ‘$PATH’ when the installation is performed. The above instructions can still be performed on other python installations which the installer does not find, including alternative prefixes.


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3.4.4 Won’t Work With Windows

There are semi-regular reports of Windows users having considerable difficulty in installing and using the Python bindings at all. Very often, possibly even always, these reports come from Cygwin users and/or MinGW users and/or Msys2 users. Though not all of them have been confirmed, it appears that these reports have also come from people who installed Python using the Windows installer files from the Python website (i.e. mostly MSI installers, sometimes self-extracting ‘.exe’ files).

The Windows versions of Python are not built using Cygwin, MinGW or Msys2; they’re built using Microsoft Visual Studio. Furthermore the version used is considerably more advanced than the version which MinGW obtained a small number of files from many years ago in order to be able to compile anything at all. Not only that, but there are changes to the version of Visual Studio between some micro releases, though that is is particularly the case with Python 2.7, since it has been kept around far longer than it should have been.

There are two theoretical solutions to this issue:

  1. Compile and install the GnuPG stack, including GPGME and the Python bindings using the same version of Microsoft Visual Studio used by the Python Foundation to compile the version of Python installed.

    If there are multiple versions of Python then this will need to be done with each different version of Visual Studio used for those versions of Python.

  2. Compile and install Python using the same tools used by choice, such as MinGW or Msys2.

Do not use the official Windows installer for Python unless following the first method.

In this type of situation it may even be for the best to accept that there are less limitations on permissive software than free software and simply opt to use a recent version of the Community Edition of Microsoft Visual Studio to compile and build all of it, no matter what.

Investigations into the extent or the limitations of this issue are ongoing.

The following table lists the version of Microsoft Visual Studio which needs to be used when compiling GPGME and the Python bindings with each version of the CPython binary released for Windows:

CPythonMicrosoft product nameruntime filename
2.7.6Visual Studio 2008MSVCR90.DLL
3.4.0Visual Studio 2010MSVCR100.DLL
3.5.0Visual Studio 2015see below
3.6.0Visual Studio 2015see below
3.7.0Visual Studio 2017*see below

It is important to note that MingW and Msys2 ship with the Visual C runtime from Microsoft Visual Studio 2005 and are thus incompatible with all the versions of CPython which can be used with the GPGME Python bindings.

It is also important to note that from CPython 3.5 onwards, the Python Foundation has adopted the reworking of the Visual C runtime which was performed for Visual Studio 2015 and aimed at resolving many of these kinds of issues. Much greater detail on these issues and the correct file(s) to link to are available from Matthew Brett’s invaluable page, Using Microsoft Visual C with Python. It is also worth reading the Microsoft Developer Network blog post on the universal CRT and Steve Dower’s blog posts on Python extensions (part 1 and part 2).

The second of those two posts by Steve Dower contains the details of specific configuration options required for compiling anything to be used with official CPython releases. In addition to those configuration and compiler settings to use, the versions of Visual Studio prior to Visual Studio 2015 did not support 64-bit systems by default. So compiling a 64-bit version of these bindings for a 64-bit version of CPython 2.7 or 3.4 requires additional work.

In addition to the blog posts, the Windows compilers wiki page on the CPython wiki is another essential reference on the relevant versions of Visual Studio to use and the degree of compatibility with CPython releases.

Eventually someone will ask why there isn’t an installable binary for Windows, which the GPGME of the licenses do not preclude as long as the source code is available in conjunction with such a release.

The sheer number of versions of Visual Studio in conjunction with differing configuration options depending on the target Windows version and whether the architecture is 64-bit or 32-bit makes it difficult to provide a correct binary installer for Windows users. At the bare minimum doing so would require the GnuPG project compile ten different versions of the bindings with each release; both 32-bit and 64-bit versions for CPython 2.7 and 3.4, with 64-bit versions for both x86-64 (i.e. Intel and AMD) and ARM architectures for CPython 3.5, 3.6, 3.7 and later releases. That’s the bare minimum, it’d probably be higher.

Additionally, with only a binary installation used in conjunction with the CPython installer from ‘python.org’ the advanced options available which utilise Cython will not be able to be used at all. Cython depends on being able to compile the C code it generates and that too would need to utilise a matching runtime to both the installed version of CPython and these bindings in order to work with the bindings.

Considering all of that, what do we recommend?

  1. Use a recent version of CPython; at least 3.5, but ideally 3.6 or later.
  2. Use Visual Studio 2015 or the standalone build tools for Visual Studio 2017 (or later).
  3. Compile both CPython and GPGME with these bindings using the tools selected in step 2.
  4. Ignore MingW, Msys2 and the official CPython binary installers.
  5. Be thankful the answer to this question wasn’t simply to say something like, “install Linux” or “install FreeBSD” (or even Apple’s OS X).

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3.4.5 CFFI is the Best™ and GPGME should use it instead of SWIG

There are many reasons for favouring CFFI and proponents of it are quite happy to repeat these things as if all it would take to switch from SWIG to CFFI is repeating that list as if it were a new concept.

The fact is that there are things which Python’s CFFI implementation cannot handle in the GPGME C code. Beyond that there are features of SWIG which are simply not available with CFFI at all. SWIG generates the bindings to Python using the ‘gpgme.h’ file, but that file is not a single version shipped with each release, it too is generated when GPGME is compiled.

CFFI is currently unable to adapt to such a potentially mutable codebase. If there were some means of applying SWIG’s dynamic code generation to produce the Python/CFFI API modes of accessing the GPGME libraries (or the source source code directly), but such a thing does not exist yet either and it currently appears that work is needed in at least one of CFFI’s dependencies before any of this can be addressed.

So if you’re a massive fan of CFFI; that’s great, but if you want this project to switch to CFFI then rather than just insisting that it should, I’d suggest you volunteer to bring CFFI up to the level this project needs.

If you’re actually seriously considering doing so, then I’d suggest taking the ‘gpgme-tool.c’ file in the GPGME ‘src/’ directory and getting that to work with any of the CFFI API methods (not the ABI methods, they’ll work with pretty much anything). When you start running into trouble with "ifdefs" then you’ll know what sort of things are lacking. That doesn’t even take into account the amount of work saved via SWIG’s code generation techniques either.


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3.4.6 Virtualised Environments

It is fairly common practice amongst Python developers to, as much as possible, use packages like virtualenv to keep various things that are to be installed from interfering with each other. Given how much of the GPGME bindings is often at odds with the usual pythonic way of doing things, it stands to reason that this would be called into question too.

As it happens the answer as to whether or not the bindings can be used with virtualenv, the answer is both yes and no.

In general we recommend installing to the relevant path and matching prefix of GPGME itself. Which means that when GPGME, and ideally the rest of the GnuPG stack, is installed to a prefix like ‘/usr/local’ or ‘/opt/local’ then the bindings would need to be installed to the main Python installation and not a virtualised abstraction. Attempts to separate the two in the past have been known to cause weird and intermittent errors ranging from minor annoyances to complete failures in the build process.

As a consequence we only recommend building with and installing to the main Python installations within the same prefix as GPGME is installed to or which are found by GPGME’s configuration stage immediately prior to running the make commands. Which is exactly what the compiling and installing process of GPGME does by default.

Once that is done, however, it appears that a copy of the compiled module may be installed into a virtualenv of the same major and minor version matching the build. Alternatively it is possible to utilise a ‘sites.pth’ file in the ‘site-packages/’ directory of a virtualenv installation, which links back to the system installations corresponding directory in order to import anything installed system wide. This may or may not be appropriate on a case by case basis.

Though extensive testing of either of these options is not yet complete, preliminary testing of them indicates that both are viable as long as the main installation is complete. Which means that certain other options normally restricted to virtual environments are also available, including integration with pythonic test suites (e.g. pytest) and other large projects.

That said, it is worth reiterating the warning regarding non-standard installations. If one were to attempt to install the bindings only to a virtual environment without somehow also including the full GnuPG stack (or enough of it as to include GPGME) then it is highly likely that errors would be encountered at some point and more than a little likely that the build process itself would break.

If a degree of separation from the main operating system is still required in spite of these warnings, then consider other forms of virtualisation. Either a virtual machine (e.g. VirtualBox), a hardware emulation layer (e.g. QEMU) or an application container (e.g. Docker).

Finally it should be noted that the limited tests conducted thus far have been using the ‘virtualenv’ command in a new directory to create the virtual python environment. As opposed to the standard ‘python3 -m venv’ and it is possible that this will make a difference depending on the system and version of Python in use. Another option is to run the command ‘python3 -m virtualenv /path/to/install/virtual/thingy’ instead.


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4 Fundamentals

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.


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4.1 No REST

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 that this HOWTO deals with.


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4.2 Context

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 persistent 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.


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5 Working with keys


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5.1 Key selection

Selecting keys to encrypt to or to sign with will be a common occurrence when working with GPGMe and the means available for doing so are quite simple.

They do depend on utilising a Context; however once the data is recorded in another variable, that Context does not need to be the same one which subsequent operations are performed.

The easiest way to select a specific key is by searching for that key’s key ID or fingerprint, preferably the full fingerprint without any spaces in it. A long key ID will probably be okay, but is not advised and short key IDs are already a problem with some being generated to match specific patterns. It does not matter whether the pattern is upper or lower case.

So this is the best method:

import gpg

k = gpg.Context().keylist(pattern="258E88DCBD3CD44D8E7AB43F6ECB6AF0DEADBEEF")
keys = list(k)

This is passable and very likely to be common:

import gpg

k = gpg.Context().keylist(pattern="0x6ECB6AF0DEADBEEF")
keys = list(k)

And this is a really bad idea:

import gpg

k = gpg.Context().keylist(pattern="0xDEADBEEF")
keys = list(k)

Alternatively it may be that the intention is to create a list of keys which all match a particular search string. For instance all the addresses at a particular domain, like this:

import gpg

ncsc = gpg.Context().keylist(pattern="ncsc.mil")
nsa = list(ncsc)

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5.1.1 Counting keys

Counting the number of keys in your public keybox (‘pubring.kbx’), the format which has superseded the old keyring format (‘pubring.gpg’ and ‘secring.gpg’), or the number of secret keys is a very simple task.

import gpg

c = gpg.Context()
seckeys = c.keylist(pattern=None, secret=True)
pubkeys = c.keylist(pattern=None, secret=False)

seclist = list(seckeys)
secnum = len(seclist)

publist = list(pubkeys)
pubnum = len(publist)

print("""
  Number of secret keys:  {0}
  Number of public keys:  {1}
""".format(secnum, pubnum))

NOTE: The Cython introduction in the Advanced and Experimental section uses this same key counting code with Cython to demonstrate some areas where Cython can improve performance even with the bindings. Users with large public keyrings or keyboxes, for instance, should consider these options if they are comfortable with using Cython.


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5.2 Get key

An alternative method of getting a single key via its fingerprint is available directly within a Context with ‘Context().get_key’. This is the preferred method of selecting a key in order to modify it, sign or certify it and for obtaining relevant data about a single key as a part of other functions; when verifying a signature made by that key, for instance.

By default this method will select public keys, but it can select secret keys as well.

This first example demonstrates selecting the current key of Werner Koch, which is due to expire at the end of 2018:

import gpg

fingerprint = "80615870F5BAD690333686D0F2AD85AC1E42B367"
key = gpg.Context().get_key(fingerprint)

Whereas this example demonstrates selecting the author’s current key with the ‘secret’ key word argument set to ‘True’:

import gpg

fingerprint = "DB4724E6FA4286C92B4E55C4321E4E2373590E5D"
key = gpg.Context().get_key(fingerprint, secret=True)

It is, of course, quite possible to select expired, disabled and revoked keys with this function, but only to effectively display information about those keys.

It is also possible to use both unicode or string literals and byte literals with the fingerprint when getting a key in this way.


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5.3 Importing keys

Importing keys is possible with the ‘key_import()’ method and takes one argument which is a bytes literal object containing either the binary or ASCII armoured key data for one or more keys.

The following example retrieves one or more keys from the SKS keyservers via the web using the requests module. Since requests returns the content as a bytes literal object, we can then use that directly to import the resulting data into our keybox.

import gpg
import os.path
import requests

c = gpg.Context()
url = "https://sks-keyservers.net/pks/lookup"
pattern = input("Enter the pattern to search for key or user IDs: ")
payload = {"op": "get", "search": pattern}

r = requests.get(url, verify=True, params=payload)
result = c.key_import(r.content)

if result is not None and hasattr(result, "considered") is False:
    print(result)
elif result is not None and hasattr(result, "considered") is True:
    num_keys = len(result.imports)
    new_revs = result.new_revocations
    new_sigs = result.new_signatures
    new_subs = result.new_sub_keys
    new_uids = result.new_user_ids
    new_scrt = result.secret_imported
    nochange = result.unchanged
    print("""
  The total number of keys considered for import was:  {0}

     Number of keys revoked:  {1}
   Number of new signatures:  {2}
      Number of new subkeys:  {3}
     Number of new user IDs:  {4}
  Number of new secret keys:  {5}
   Number of unchanged keys:  {6}

  The key IDs for all considered keys were:
""".format(num_keys, new_revs, new_sigs, new_subs, new_uids, new_scrt,
           nochange))
    for i in range(num_keys):
        print("{0}\n".format(result.imports[i].fpr))
else:
    pass

NOTE: When searching for a key ID of any length or a fingerprint (without spaces), the SKS servers require the the leading ‘0x’ indicative of hexadecimal be included. Also note that the old short key IDs (e.g. ‘0xDEADBEEF’) should no longer be used due to the relative ease by which such key IDs can be reproduced, as demonstrated by the Evil32 Project in 2014 (which was subsequently exploited in 2016).


Next: , Up: Importing keys   [Contents]

5.3.1 Working with ProtonMail

Here is a variation on the example above which checks the constrained ProtonMail keyserver for ProtonMail public keys.

import gpg
import requests
import sys

print("""
This script searches the ProtonMail key server for the specified key and
imports it.
""")

c = gpg.Context(armor=True)
url = "https://api.protonmail.ch/pks/lookup"
ksearch = []

if len(sys.argv) >= 2:
    keyterm = sys.argv[1]
else:
    keyterm = input("Enter the key ID, UID or search string: ")

if keyterm.count("@") == 2 and keyterm.startswith("@") is True:
    ksearch.append(keyterm[1:])
    ksearch.append(keyterm[1:])
    ksearch.append(keyterm[1:])
elif keyterm.count("@") == 1 and keyterm.startswith("@") is True:
    ksearch.append("{0}@protonmail.com".format(keyterm[1:]))
    ksearch.append("{0}@protonmail.ch".format(keyterm[1:]))
    ksearch.append("{0}@pm.me".format(keyterm[1:]))
elif keyterm.count("@") == 0:
    ksearch.append("{0}@protonmail.com".format(keyterm))
    ksearch.append("{0}@protonmail.ch".format(keyterm))
    ksearch.append("{0}@pm.me".format(keyterm))
elif keyterm.count("@") == 2 and keyterm.startswith("@") is False:
    uidlist = keyterm.split("@")
    for uid in uidlist:
        ksearch.append("{0}@protonmail.com".format(uid))
        ksearch.append("{0}@protonmail.ch".format(uid))
        ksearch.append("{0}@pm.me".format(uid))
elif keyterm.count("@") > 2:
    uidlist = keyterm.split("@")
    for uid in uidlist:
        ksearch.append("{0}@protonmail.com".format(uid))
        ksearch.append("{0}@protonmail.ch".format(uid))
        ksearch.append("{0}@pm.me".format(uid))
else:
    ksearch.append(keyterm)

for k in ksearch:
    payload = {"op": "get", "search": k}
    try:
        r = requests.get(url, verify=True, params=payload)
        if r.ok is True:
            result = c.key_import(r.content)
        elif r.ok is False:
            result = r.content
    except Exception as e:
        result = None

    if result is not None and hasattr(result, "considered") is False:
        print("{0} for {1}".format(result.decode(), k))
    elif result is not None and hasattr(result, "considered") is True:
        num_keys = len(result.imports)
        new_revs = result.new_revocations
        new_sigs = result.new_signatures
        new_subs = result.new_sub_keys
        new_uids = result.new_user_ids
        new_scrt = result.secret_imported
        nochange = result.unchanged
        print("""
The total number of keys considered for import was:  {0}

With UIDs wholely or partially matching the following string:

        {1}

   Number of keys revoked:  {2}
 Number of new signatures:  {3}
    Number of new subkeys:  {4}
   Number of new user IDs:  {5}
Number of new secret keys:  {6}
 Number of unchanged keys:  {7}

The key IDs for all considered keys were:
""".format(num_keys, k, new_revs, new_sigs, new_subs, new_uids, new_scrt,
           nochange))
        for i in range(num_keys):
            print(result.imports[i].fpr)
        print("")
    elif result is None:
        print(e)

Both the above example, pmkey-import.py, and a version which prompts for an alternative GnuPG home directory, pmkey-import-alt.py, are available with the other examples and are executable scripts.

Note that while the ProtonMail servers are based on the SKS servers, their server is related more to their API and is not feature complete by comparison to the servers in the SKS pool. One notable difference being that the ProtonMail server does not permit non ProtonMail users to update their own keys, which could be a vector for attacking ProtonMail users who may not receive a key’s revocation if it had been compromised.


Next: , Previous: , Up: Importing keys   [Contents]

5.3.2 Importing with HKP for Python

Performing the same tasks with the hkp4py module (available via PyPI) is not too much different, but does provide a number of options of benefit to end users. Not least of which being the ability to perform some checks on a key before importing it or not. For instance it may be the policy of a site or project to only import keys which have not been revoked. The hkp4py module permits such checks prior to the importing of the keys found.

import gpg
import hkp4py
import sys

c = gpg.Context()
server = hkp4py.KeyServer("hkps://hkps.pool.sks-keyservers.net")
results = []

if len(sys.argv) > 2:
    pattern = " ".join(sys.argv[1:])
elif len(sys.argv) == 2:
    pattern = sys.argv[1]
else:
    pattern = input("Enter the pattern to search for keys or user IDs: ")

try:
    keys = server.search(pattern)
    print("Found {0} key(s).".format(len(keys)))
except Exception as e:
    keys = []
    for logrus in pattern.split():
        if logrus.startswith("0x") is True:
            key = server.search(logrus)
        else:
            key = server.search("0x{0}".format(logrus))
        keys.append(key[0])
    print("Found {0} key(s).".format(len(keys)))

for key in keys:
    import_result = c.key_import(key.key_blob)
    results.append(import_result)

for result in results:
    if result is not None and hasattr(result, "considered") is False:
        print(result)
    elif result is not None and hasattr(result, "considered") is True:
        num_keys = len(result.imports)
        new_revs = result.new_revocations
        new_sigs = result.new_signatures
        new_subs = result.new_sub_keys
        new_uids = result.new_user_ids
        new_scrt = result.secret_imported
        nochange = result.unchanged
        print("""
The total number of keys considered for import was:  {0}

   Number of keys revoked:  {1}
 Number of new signatures:  {2}
    Number of new subkeys:  {3}
   Number of new user IDs:  {4}
Number of new secret keys:  {5}
 Number of unchanged keys:  {6}

The key IDs for all considered keys were:
""".format(num_keys, new_revs, new_sigs, new_subs, new_uids, new_scrt,
           nochange))
        for i in range(num_keys):
            print(result.imports[i].fpr)
        print("")
    else:
        pass

Since the hkp4py module handles multiple keys just as effectively as one (‘keys’ is a list of responses per matching key), the example above is able to do a little bit more with the returned data before anything is actually imported.


Previous: , Up: Importing keys   [Contents]

5.3.3 Importing from ProtonMail with HKP for Python

Though this can provide certain benefits even when working with ProtonMail, the scope is somewhat constrained there due to the limitations of the ProtonMail keyserver.

For instance, searching the SKS keyserver pool for the term "gnupg" produces hundreds of results from any time the word appears in any part of a user ID. Performing the same search on the ProtonMail keyserver returns zero results, even though there are at least two test accounts which include it as part of the username.

The cause of this discrepancy is the deliberate configuration of that server by ProtonMail to require an exact match of the full email address of the ProtonMail user whose key is being requested. Presumably this is intended to reduce breaches of privacy of their users as an email address must already be known before a key for that address can be obtained.

  1. Import from ProtonMail via HKP for Python Example no. 1

    The following script is available with the rest of the examples under the somewhat less than original name, ‘pmkey-import-hkp.py’.

    import gpg
    import hkp4py
    import os.path
    import sys
    
    print("""
    This script searches the ProtonMail key server for the specified key and
    imports it.
    
    Usage:  pmkey-import-hkp.py [search strings]
    """)
    
    c = gpg.Context(armor=True)
    server = hkp4py.KeyServer("hkps://api.protonmail.ch")
    keyterms = []
    ksearch = []
    allkeys = []
    results = []
    paradox = []
    homeless = None
    
    if len(sys.argv) > 2:
        keyterms = sys.argv[1:]
    elif len(sys.argv) == 2:
        keyterm = sys.argv[1]
        keyterms.append(keyterm)
    else:
        key_term = input("Enter the key ID, UID or search string: ")
        keyterms = key_term.split()
    
    for keyterm in keyterms:
        if keyterm.count("@") == 2 and keyterm.startswith("@") is True:
            ksearch.append(keyterm[1:])
            ksearch.append(keyterm[1:])
            ksearch.append(keyterm[1:])
        elif keyterm.count("@") == 1 and keyterm.startswith("@") is True:
            ksearch.append("{0}@protonmail.com".format(keyterm[1:]))
            ksearch.append("{0}@protonmail.ch".format(keyterm[1:]))
            ksearch.append("{0}@pm.me".format(keyterm[1:]))
        elif keyterm.count("@") == 0:
            ksearch.append("{0}@protonmail.com".format(keyterm))
            ksearch.append("{0}@protonmail.ch".format(keyterm))
            ksearch.append("{0}@pm.me".format(keyterm))
        elif keyterm.count("@") == 2 and keyterm.startswith("@") is False:
            uidlist = keyterm.split("@")
            for uid in uidlist:
                ksearch.append("{0}@protonmail.com".format(uid))
                ksearch.append("{0}@protonmail.ch".format(uid))
                ksearch.append("{0}@pm.me".format(uid))
        elif keyterm.count("@") > 2:
            uidlist = keyterm.split("@")
            for uid in uidlist:
                ksearch.append("{0}@protonmail.com".format(uid))
                ksearch.append("{0}@protonmail.ch".format(uid))
                ksearch.append("{0}@pm.me".format(uid))
        else:
            ksearch.append(keyterm)
    
    for k in ksearch:
        print("Checking for key for: {0}".format(k))
        try:
            keys = server.search(k)
            if isinstance(keys, list) is True:
                for key in keys:
                    allkeys.append(key)
                    try:
                        import_result = c.key_import(key.key_blob)
                    except Exception as e:
                        import_result = c.key_import(key.key)
            else:
                paradox.append(keys)
                import_result = None
        except Exception as e:
            import_result = None
        results.append(import_result)
    
    for result in results:
        if result is not None and hasattr(result, "considered") is False:
            print("{0} for {1}".format(result.decode(), k))
        elif result is not None and hasattr(result, "considered") is True:
            num_keys = len(result.imports)
            new_revs = result.new_revocations
            new_sigs = result.new_signatures
            new_subs = result.new_sub_keys
            new_uids = result.new_user_ids
            new_scrt = result.secret_imported
            nochange = result.unchanged
            print("""
    The total number of keys considered for import was:  {0}
    
    With UIDs wholely or partially matching the following string:
    
            {1}
    
       Number of keys revoked:  {2}
     Number of new signatures:  {3}
        Number of new subkeys:  {4}
       Number of new user IDs:  {5}
    Number of new secret keys:  {6}
     Number of unchanged keys:  {7}
    
    The key IDs for all considered keys were:
    """.format(num_keys, k, new_revs, new_sigs, new_subs, new_uids, new_scrt,
               nochange))
            for i in range(num_keys):
                print(result.imports[i].fpr)
            print("")
        elif result is None:
            pass
    
  2. Import from ProtonMail via HKP for Python Example no. 2

    Like its counterpart above, this script can also be found with the rest of the examples, by the name pmkey-import-hkp-alt.py.

    With this script a modicum of effort has been made to treat anything passed as a ‘homedir’ which either does not exist or which is not a directory, as also being a pssible user ID to check for. It’s not guaranteed to pick up on all such cases, but it should cover most of them.

    import gpg
    import hkp4py
    import os.path
    import sys
    
    print("""
    This script searches the ProtonMail key server for the specified key and
    imports it.  Optionally enables specifying a different GnuPG home directory.
    
    Usage:  pmkey-import-hkp.py [homedir] [search string]
       or:  pmkey-import-hkp.py [search string]
    """)
    
    c = gpg.Context(armor=True)
    server = hkp4py.KeyServer("hkps://api.protonmail.ch")
    keyterms = []
    ksearch = []
    allkeys = []
    results = []
    paradox = []
    homeless = None
    
    if len(sys.argv) > 3:
        homedir = sys.argv[1]
        keyterms = sys.argv[2:]
    elif len(sys.argv) == 3:
        homedir = sys.argv[1]
        keyterm = sys.argv[2]
        keyterms.append(keyterm)
    elif len(sys.argv) == 2:
        homedir = ""
        keyterm = sys.argv[1]
        keyterms.append(keyterm)
    else:
        keyterm = input("Enter the key ID, UID or search string: ")
        homedir = input("Enter the GPG configuration directory path (optional): ")
        keyterms.append(keyterm)
    
    if len(homedir) == 0:
        homedir = None
        homeless = False
    
    if homedir is not None:
        if homedir.startswith("~"):
            if os.path.exists(os.path.expanduser(homedir)) is True:
                if os.path.isdir(os.path.expanduser(homedir)) is True:
                    c.home_dir = os.path.realpath(os.path.expanduser(homedir))
                else:
                    homeless = True
            else:
                homeless = True
        elif os.path.exists(os.path.realpath(homedir)) is True:
            if os.path.isdir(os.path.realpath(homedir)) is True:
                c.home_dir = os.path.realpath(homedir)
            else:
                homeless = True
        else:
            homeless = True
    
    # First check to see if the homedir really is a homedir and if not, treat it as
    # a search string.
    if homeless is True:
        keyterms.append(homedir)
        c.home_dir = None
    else:
        pass
    
    for keyterm in keyterms:
        if keyterm.count("@") == 2 and keyterm.startswith("@") is True:
            ksearch.append(keyterm[1:])
            ksearch.append(keyterm[1:])
            ksearch.append(keyterm[1:])
        elif keyterm.count("@") == 1 and keyterm.startswith("@") is True:
            ksearch.append("{0}@protonmail.com".format(keyterm[1:]))
            ksearch.append("{0}@protonmail.ch".format(keyterm[1:]))
            ksearch.append("{0}@pm.me".format(keyterm[1:]))
        elif keyterm.count("@") == 0:
            ksearch.append("{0}@protonmail.com".format(keyterm))
            ksearch.append("{0}@protonmail.ch".format(keyterm))
            ksearch.append("{0}@pm.me".format(keyterm))
        elif keyterm.count("@") == 2 and keyterm.startswith("@") is False:
            uidlist = keyterm.split("@")
            for uid in uidlist:
                ksearch.append("{0}@protonmail.com".format(uid))
                ksearch.append("{0}@protonmail.ch".format(uid))
                ksearch.append("{0}@pm.me".format(uid))
        elif keyterm.count("@") > 2:
            uidlist = keyterm.split("@")
            for uid in uidlist:
                ksearch.append("{0}@protonmail.com".format(uid))
                ksearch.append("{0}@protonmail.ch".format(uid))
                ksearch.append("{0}@pm.me".format(uid))
        else:
            ksearch.append(keyterm)
    
    for k in ksearch:
        print("Checking for key for: {0}".format(k))
        try:
            keys = server.search(k)
            if isinstance(keys, list) is True:
                for key in keys:
                    allkeys.append(key)
                    try:
                        import_result = c.key_import(key.key_blob)
                    except Exception as e:
                        import_result = c.key_import(key.key)
            else:
                paradox.append(keys)
                import_result = None
        except Exception as e:
            import_result = None
        results.append(import_result)
    
    for result in results:
        if result is not None and hasattr(result, "considered") is False:
            print("{0} for {1}".format(result.decode(), k))
        elif result is not None and hasattr(result, "considered") is True:
            num_keys = len(result.imports)
            new_revs = result.new_revocations
            new_sigs = result.new_signatures
            new_subs = result.new_sub_keys
            new_uids = result.new_user_ids
            new_scrt = result.secret_imported
            nochange = result.unchanged
            print("""
    The total number of keys considered for import was:  {0}
    
    With UIDs wholely or partially matching the following string:
    
            {1}
    
       Number of keys revoked:  {2}
     Number of new signatures:  {3}
        Number of new subkeys:  {4}
       Number of new user IDs:  {5}
    Number of new secret keys:  {6}
     Number of unchanged keys:  {7}
    
    The key IDs for all considered keys were:
    """.format(num_keys, k, new_revs, new_sigs, new_subs, new_uids, new_scrt,
               nochange))
            for i in range(num_keys):
                print(result.imports[i].fpr)
            print("")
        elif result is None:
            pass
    

Previous: , Up: Working with keys   [Contents]

5.4 Exporting keys

Exporting keys remains a reasonably simple task, but has been separated into three different functions for the OpenPGP cryptographic engine. Two of those functions are for exporting public keys and the third is for exporting secret keys.


Next: , Up: Exporting keys   [Contents]

5.4.1 Exporting public keys

There are two methods of exporting public keys, both of which are very similar to the other. The default method, ‘key_export()’, will export a public key or keys matching a specified pattern as normal. The alternative, the ‘key_export_minimal()’ method, will do the same thing except producing a minimised output with extra signatures and third party signatures or certifications removed.

import gpg
import os.path
import sys

print("""
This script exports one or more public keys.
""")

c = gpg.Context(armor=True)

if len(sys.argv) >= 4:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = sys.argv[3]
elif len(sys.argv) == 3:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = input("Enter the GPG configuration directory path (optional): ")
elif len(sys.argv) == 2:
    keyfile = sys.argv[1]
    logrus = input("Enter the UID matching the key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")
else:
    keyfile = input("Enter the path and filename to save the secret key to: ")
    logrus = input("Enter the UID matching the key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")

if homedir.startswith("~"):
    if os.path.exists(os.path.expanduser(homedir)) is True:
        c.home_dir = os.path.expanduser(homedir)
    else:
        pass
elif os.path.exists(homedir) is True:
    c.home_dir = homedir
else:
    pass

try:
    result = c.key_export(pattern=logrus)
except:
    result = c.key_export(pattern=None)

if result is not None:
    with open(keyfile, "wb") as f:
        f.write(result)
else:
    pass

It should be noted that the result will only return ‘None’ when a search pattern has been entered, but has not matched any keys. When the search pattern itself is set to ‘None’ this triggers the exporting of the entire public keybox.

import gpg
import os.path
import sys

print("""
This script exports one or more public keys in minimised form.
""")

c = gpg.Context(armor=True)

if len(sys.argv) >= 4:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = sys.argv[3]
elif len(sys.argv) == 3:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = input("Enter the GPG configuration directory path (optional): ")
elif len(sys.argv) == 2:
    keyfile = sys.argv[1]
    logrus = input("Enter the UID matching the key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")
else:
    keyfile = input("Enter the path and filename to save the secret key to: ")
    logrus = input("Enter the UID matching the key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")

if homedir.startswith("~"):
    if os.path.exists(os.path.expanduser(homedir)) is True:
        c.home_dir = os.path.expanduser(homedir)
    else:
        pass
elif os.path.exists(homedir) is True:
    c.home_dir = homedir
else:
    pass

try:
    result = c.key_export_minimal(pattern=logrus)
except:
    result = c.key_export_minimal(pattern=None)

if result is not None:
    with open(keyfile, "wb") as f:
        f.write(result)
else:
    pass

Next: , Previous: , Up: Exporting keys   [Contents]

5.4.2 Exporting secret keys

Exporting secret keys is, functionally, very similar to exporting public keys; save for the invocation of ‘pinentry’ via ‘gpg-agent’ in order to securely enter the key’s passphrase and authorise the export.

The following example exports the secret key to a file which is then set with the same permissions as the output files created by the command line secret key export options.

import gpg
import os
import os.path
import sys

print("""
This script exports one or more secret keys.

The gpg-agent and pinentry are invoked to authorise the export.
""")

c = gpg.Context(armor=True)

if len(sys.argv) >= 4:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = sys.argv[3]
elif len(sys.argv) == 3:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = input("Enter the GPG configuration directory path (optional): ")
elif len(sys.argv) == 2:
    keyfile = sys.argv[1]
    logrus = input("Enter the UID matching the secret key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")
else:
    keyfile = input("Enter the path and filename to save the secret key to: ")
    logrus = input("Enter the UID matching the secret key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")

if len(homedir) == 0:
    homedir = None
elif homedir.startswith("~"):
    userdir = os.path.expanduser(homedir)
    if os.path.exists(userdir) is True:
        homedir = os.path.realpath(userdir)
    else:
        homedir = None
else:
    homedir = os.path.realpath(homedir)

if os.path.exists(homedir) is False:
    homedir = None
else:
    if os.path.isdir(homedir) is False:
        homedir = None
    else:
        pass

if homedir is not None:
    c.home_dir = homedir
else:
    pass

try:
    result = c.key_export_secret(pattern=logrus)
except:
    result = c.key_export_secret(pattern=None)

if result is not None:
    with open(keyfile, "wb") as f:
        f.write(result)
    os.chmod(keyfile, 0o600)
else:
    pass

Alternatively the approach of the following script can be used. This longer example saves the exported secret key(s) in files in the GnuPG home directory, in addition to setting the file permissions as only readable and writable by the user. It also exports the secret key(s) twice in order to output both GPG binary (‘.gpg’) and ASCII armoured (‘.asc’) files.

import gpg
import os
import os.path
import subprocess
import sys

print("""
This script exports one or more secret keys as both ASCII armored and binary
file formats, saved in files within the user's GPG home directory.

The gpg-agent and pinentry are invoked to authorise the export.
""")

if sys.platform == "win32":
    gpgconfcmd = "gpgconf.exe --list-dirs homedir"
else:
    gpgconfcmd = "gpgconf --list-dirs homedir"

a = gpg.Context(armor=True)
b = gpg.Context()
c = gpg.Context()

if len(sys.argv) >= 4:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = sys.argv[3]
elif len(sys.argv) == 3:
    keyfile = sys.argv[1]
    logrus = sys.argv[2]
    homedir = input("Enter the GPG configuration directory path (optional): ")
elif len(sys.argv) == 2:
    keyfile = sys.argv[1]
    logrus = input("Enter the UID matching the secret key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")
else:
    keyfile = input("Enter the filename to save the secret key to: ")
    logrus = input("Enter the UID matching the secret key(s) to export: ")
    homedir = input("Enter the GPG configuration directory path (optional): ")

if len(homedir) == 0:
    homedir = None
elif homedir.startswith("~"):
    userdir = os.path.expanduser(homedir)
    if os.path.exists(userdir) is True:
        homedir = os.path.realpath(userdir)
    else:
        homedir = None
else:
    homedir = os.path.realpath(homedir)

if os.path.exists(homedir) is False:
    homedir = None
else:
    if os.path.isdir(homedir) is False:
        homedir = None
    else:
        pass

if homedir is not None:
    c.home_dir = homedir
else:
    pass

if c.home_dir is not None:
    if c.home_dir.endswith("/"):
        gpgfile = "{0}{1}.gpg".format(c.home_dir, keyfile)
        ascfile = "{0}{1}.asc".format(c.home_dir, keyfile)
    else:
        gpgfile = "{0}/{1}.gpg".format(c.home_dir, keyfile)
        ascfile = "{0}/{1}.asc".format(c.home_dir, keyfile)
else:
    if os.path.exists(os.environ["GNUPGHOME"]) is True:
        hd = os.environ["GNUPGHOME"]
    else:
        try:
            hd = subprocess.getoutput(gpgconfcmd)
        except:
            process = subprocess.Popen(gpgconfcmd.split(),
                                       stdout=subprocess.PIPE)
            procom = process.communicate()
            if sys.version_info[0] == 2:
                hd = procom[0].strip()
            else:
                hd = procom[0].decode().strip()
    gpgfile = "{0}/{1}.gpg".format(hd, keyfile)
    ascfile = "{0}/{1}.asc".format(hd, keyfile)

try:
    a_result = a.key_export_secret(pattern=logrus)
    b_result = b.key_export_secret(pattern=logrus)
except:
    a_result = a.key_export_secret(pattern=None)
    b_result = b.key_export_secret(pattern=None)

if a_result is not None:
    with open(ascfile, "wb") as f:
        f.write(a_result)
    os.chmod(ascfile, 0o600)
else:
    pass

if b_result is not None:
    with open(gpgfile, "wb") as f:
        f.write(b_result)
    os.chmod(gpgfile, 0o600)
else:
    pass

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5.4.3 Sending public keys to the SKS Keyservers

As with the previous section on importing keys, the ‘hkp4py’ module adds another option with exporting keys in order to send them to the public keyservers.

The following example demonstrates how this may be done.

import gpg
import hkp4py
import os.path
import sys

print("""
This script sends one or more public keys to the SKS keyservers and is
essentially a slight variation on the export-key.py script.
""")

c = gpg.Context(armor=True)
server = hkp4py.KeyServer("hkps://hkps.pool.sks-keyservers.net")

if len(sys.argv) > 2:
    logrus = " ".join(sys.argv[1:])
elif len(sys.argv) == 2:
    logrus = sys.argv[1]
else:
    logrus = input("Enter the UID matching the key(s) to send: ")

if len(logrus) > 0:
    try:
        export_result = c.key_export(pattern=logrus)
    except Exception as e:
        print(e)
        export_result = None
else:
    export_result = c.key_export(pattern=None)

if export_result is not None:
    try:
        try:
            send_result = server.add(export_result)
        except:
            send_result = server.add(export_result.decode())
        if send_result is not None:
            print(send_result)
        else:
            pass
    except Exception as e:
        print(e)
else:
    pass

An expanded version of this script with additional functions for specifying an alternative homedir location is in the examples directory as ‘send-key-to-keyserver.py’.

The ‘hkp4py’ module appears to handle both string and byte literal text data equally well, but the GPGME bindings deal primarily with byte literal data only and so this script sends in that format first, then tries the string literal form.


Next: , Previous: , Up: Top   [Contents]

6 Basic Functions

The most frequently called features of any cryptographic library will be the most fundamental tasks for encryption software. In this section we will look at how to programmatically encrypt data, decrypt it, sign it and verify signatures.


Next: , Up: Basic Functions   [Contents]

6.1 Encryption

Encrypting is very straight forward. In the first example below the message, ‘text’, is encrypted to a single recipient’s key. In the second example the message will be encrypted to multiple recipients.


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6.1.1 Encrypting to one key

Once the the Context is set the main issues with encrypting data is essentially reduced to key selection and the keyword arguments specified in the ‘gpg.Context().encrypt()’ method.

Those keyword arguments are: ‘recipients’, a list of keys encrypted to (covered in greater detail in the following section); ‘sign’, whether or not to sign the plaintext data, see subsequent sections on signing and verifying signatures below (defaults to ‘True’); ‘sink’, to write results or partial results to a secure sink instead of returning it (defaults to ‘None’); ‘passphrase’, only used when utilising symmetric encryption (defaults to ‘None’); ‘always_trust’, used to override the trust model settings for recipient keys (defaults to ‘False’); ‘add_encrypt_to’, utilises any preconfigured ‘encrypt-to’ or ‘default-key’ settings in the user’s ‘gpg.conf’ file (defaults to ‘False’); ‘prepare’, prepare for encryption (defaults to ‘False’); ‘expect_sign’, prepare for signing (defaults to ‘False’); ‘compress’, compresses the plaintext prior to encryption (defaults to ‘True’).

import gpg

a_key = "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)
rkey = list(c.keylist(pattern=a_key, secret=False))
ciphertext, result, sign_result = c.encrypt(text, recipients=rkey, sign=False)

with open("secret_plans.txt.asc", "wb") as afile:
    afile.write(ciphertext)

Though this is even more likely to be used like this; with the plaintext input read from a file, the recipient keys used for encryption regardless of key trust status and the encrypted output also encrypted to any preconfigured keys set in the ‘gpg.conf’ file:

import gpg

a_key = "0x12345678DEADBEEF"

with open("secret_plans.txt", "rb") as afile:
    text = afile.read()

c = gpg.Context(armor=True)
rkey = list(c.keylist(pattern=a_key, secret=False))
ciphertext, result, sign_result = c.encrypt(text, recipients=rkey, sign=True,
                                            always_trust=True,
                                            add_encrypt_to=True)

with open("secret_plans.txt.asc", "wb") as afile:
    afile.write(ciphertext)

If the ‘recipients’ parameter is empty then the plaintext is encrypted symmetrically. If no ‘passphrase’ is supplied as a parameter or via a callback registered with the ‘Context()’ then an out-of-band prompt for the passphrase via pinentry will be invoked.


Previous: , Up: Encryption   [Contents]

6.1.2 Encrypting to multiple keys

Encrypting to multiple keys essentially just expands upon the key selection process and the recipients from the previous examples.

The following example encrypts a message (‘text’) to everyone with an email address on the ‘gnupg.org’ domain,4 but does not encrypt to a default key or other key which is configured to normally encrypt to.

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])

ciphertext, result, sign_result = c.encrypt(text, recipients=logrus,
                                            sign=False, always_trust=True)

with open("secret_plans.txt.asc", "wb") as afile:
    afile.write(ciphertext)

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:

ciphertext, result, sign_result = c.encrypt(text, recipients=logrus,
                                            always_trust=True,
                                            add_encrypt_to=True)

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:

import gpg

with open("secret_plans.txt.asc", "rb") as afile:
    text = afile.read()

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:
        ciphertext, result, sign_result = 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:
            ciphertext, result, sign_result = c.encrypt(text,
                                                        recipients=logrus,
                                                        add_encrypt_to=True)
            with open("secret_plans.txt.asc", "wb") as afile:
                afile.write(ciphertext)
        except:
            pass

This will attempt to encrypt to all the keys searched for, then remove invalid recipients if it fails and try again.


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6.2 Decryption

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.

import gpg

ciphertext = input("Enter path and filename of encrypted file: ")
newfile = input("Enter path and filename of file to save decrypted data to: ")

with open(ciphertext, "rb") as cfile:
    try:
        plaintext, result, verify_result = gpg.Context().decrypt(cfile)
    except gpg.errors.GPGMEError as e:
        plaintext = None
        print(e)

if plaintext is not None:
    with open(newfile, "wb") as nfile:
            nfile.write(plaintext)
    else:
        pass

The data available in ‘plaintext’ in this example is the decrypted content as a byte object, the recipient key IDs and algorithms in ‘result’ and the results of verifying any signatures of the data in ‘verify_result’.

If ‘gpg.Context().decrypt(cfile, verify=False)’ is called instead, then ‘verify_result’ will be returned as ‘None’ and the rest remains as described here.


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6.3 Signing text and files

The following sections demonstrate how to specify keys to sign with.


Next: , Up: Signing text and files   [Contents]

6.3.1 Signing key selection

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.

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)

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.


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6.3.2 Normal or default signing messages or files

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.

import gpg

text0 = """Declaration of ... something.

"""
text = text0.encode()

c = gpg.Context(armor=True, signers=sig_src)
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.NORMAL)

with open("/path/to/statement.txt.asc", "w") as afile:
    afile.write(signed_data.decode())

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.

import gpg

with open("/path/to/statement.txt", "rb") as tfile:
    text = tfile.read()

c = gpg.Context()
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.NORMAL)

with open("/path/to/statement.txt.sig", "wb") as afile:
    afile.write(signed_data)

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6.3.3 Detached signing messages and files

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).

import gpg

text0 = """Declaration of ... something.

"""
text = text0.encode()

c = gpg.Context(armor=True)
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.DETACH)

with open("/path/to/statement.txt.asc", "w") as afile:
    afile.write(signed_data.decode())

As with normal signatures, detached signatures are best handled as byte literals, even when the output is ASCII armoured.

import gpg

with open("/path/to/statement.txt", "rb") as tfile:
    text = tfile.read()

c = gpg.Context(signers=sig_src)
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.DETACH)

with open("/path/to/statement.txt.sig", "wb") as afile:
    afile.write(signed_data)

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6.3.4 Clearsigning messages or text

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.

import gpg

text0 = """Declaration of ... something.

"""
text = text0.encode()

c = gpg.Context()
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.CLEAR)

with open("/path/to/statement.txt.asc", "w") as afile:
    afile.write(signed_data.decode())

In spite of the appearance of a clear-signed message, the data handled by GPGME in signing it must still be byte literals.

import gpg

with open("/path/to/statement.txt", "rb") as tfile:
    text = tfile.read()

c = gpg.Context()
signed_data, result = c.sign(text, mode=gpg.constants.sig.mode.CLEAR)

with open("/path/to/statement.txt.asc", "wb") as afile:
    afile.write(signed_data)

Previous: , Up: Basic Functions   [Contents]

6.4 Signature verification

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:

import gpg
import time

filename = "statement.txt"
gpg_file = "statement.txt.gpg"

c = gpg.Context()

try:
    data, result = c.verify(open(gpg_file))
    verified = True
except gpg.errors.BadSignatures as e:
    verified = False
    print(e)

if verified is True:
    for i in range(len(result.signatures)):
        sign = result.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

Whereas this next example, which is almost identical would work with normal ASCII armoured files and with clear-signed files:

import gpg
import time

filename = "statement.txt"
asc_file = "statement.txt.asc"

c = gpg.Context()

try:
    data, result = c.verify(open(asc_file))
    verified = True
except gpg.errors.BadSignatures as e:
    verified = False
    print(e)

if verified is True:
    for i in range(len(result.signatures)):
        sign = result.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

In both of the previous examples it is also possible to compare the original data that was signed against the signed data in ‘data’ to see if it matches with something like this:

with open(filename, "rb") as afile:
    text = afile.read()

if text == data:
    print("Good signature.")
else:
    pass

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 ‘data’ is ‘None’ and only the information in ‘result’ is available.

import gpg
import time

filename = "statement.txt"
sig_file = "statement.txt.sig"

c = gpg.Context()

try:
    data, result = c.verify(open(filename), open(sig_file))
    verified = True
except gpg.errors.BadSignatures as e:
    verified = False
    print(e)

if verified is True:
    for i in range(len(result.signatures)):
        sign = result.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
import gpg
import time

filename = "statement.txt"
asc_file = "statement.txt.asc"

c = gpg.Context()

try:
    data, result = c.verify(open(filename), open(asc_file))
    verified = True
except gpg.errors.BadSignatures as e:
    verified = False
    print(e)

if verified is True:
    for i in range(len(result.signatures)):
        sign = result.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

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7 Creating keys and subkeys

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.

In the following examples a key will be created for the world’s greatest secret agent, Danger Mouse. Since Danger Mouse is a secret agent he needs to be able to protect information to ‘SECRET’ level clearance, so his keys will be 3072-bit keys.

The pre-configured ‘gpg.conf’ file which sets cipher, digest and other preferences contains the following configuration parameters:

expert
allow-freeform-uid
allow-secret-key-import
trust-model tofu+pgp
tofu-default-policy unknown
enable-large-rsa
enable-dsa2
cert-digest-algo SHA512
default-preference-list TWOFISH CAMELLIA256 AES256 CAMELLIA192 AES192 CAMELLIA128 AES BLOWFISH IDEA CAST5 3DES SHA512 SHA384 SHA256 SHA224 RIPEMD160 SHA1 ZLIB BZIP2 ZIP Uncompressed
personal-cipher-preferences TWOFISH CAMELLIA256 AES256 CAMELLIA192 AES192 CAMELLIA128 AES BLOWFISH IDEA CAST5 3DES
personal-digest-preferences SHA512 SHA384 SHA256 SHA224 RIPEMD160 SHA1
personal-compress-preferences ZLIB BZIP2 ZIP Uncompressed

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7.1 Primary key

Generating a primary key uses the ‘create_key’ method in a Context. It contains multiple arguments and keyword arguments, including: ‘userid’, ‘algorithm’, ‘expires_in’, ‘expires’, ‘sign’, ‘encrypt’, ‘certify’, ‘authenticate’, ‘passphrase’ and ‘force’. The defaults 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 is no default for ‘userid’.

If ‘passphrase’ is left as ‘None’ then the key will not be generated with a passphrase, if ‘passphrase’ is set to a string then that will be the passphrase and if ‘passphrase’ is set to ‘True’ then gpg-agent will launch pinentry to prompt for a passphrase. For the sake of convenience, these examples will keep ‘passphrase’ set to ‘None’.

import gpg

c = gpg.Context()

c.home_dir = "~/.gnupg-dm"
userid = "Danger Mouse <dm@secret.example.net>"

dmkey = c.create_key(userid, algorithm="rsa3072", expires_in=31536000,
                     sign=True, certify=True)

One thing to note here is the use of setting the ‘c.home_dir’ parameter. This enables generating the key or keys in a different location. In this case to keep the new key data created for this example in a separate location rather than adding it to existing and active key store data. As with the default directory, ‘~/.gnupg’, any temporary or separate directory needs the permissions set to only permit access by the directory owner. On posix systems this means setting the directory permissions to 700.

The ‘temp-homedir-config.py’ script in the HOWTO examples directory will create an alternative homedir with these configuration options already set and the correct directory and file permissions.

The successful generation of the key can be confirmed via the returned ‘GenkeyResult’ object, which includes the following data:

print("""
 Fingerprint:  {0}
 Primary Key:  {1}
  Public Key:  {2}
  Secret Key:  {3}
 Sub Key:  {4}
User IDs:  {5}
""".format(dmkey.fpr, dmkey.primary, dmkey.pubkey, dmkey.seckey, dmkey.sub,
           dmkey.uid))

Alternatively the information can be confirmed using the command line program:

bash-4.4$ gpg --homedir ~/.gnupg-dm -K
~/.gnupg-dm/pubring.kbx
----------------------
sec   rsa3072 2018-03-15 [SC] [expires: 2019-03-15]
      177B7C25DB99745EE2EE13ED026D2F19E99E63AA
uid           [ultimate] Danger Mouse <dm@secret.example.net>

bash-4.4$

As with generating keys manually, to preconfigure expanded preferences for the cipher, digest and compression algorithms, the ‘gpg.conf’ file must contain those details in the home directory in which the new key is being generated. I used a cut down version of my own ‘gpg.conf’ file in order to be able to generate this:

bash-4.4$ gpg --homedir ~/.gnupg-dm --edit-key 177B7C25DB99745EE2EE13ED026D2F19E99E63AA showpref quit
Secret key is available.

sec  rsa3072/026D2F19E99E63AA
     created: 2018-03-15  expires: 2019-03-15  usage: SC
     trust: ultimate      validity: ultimate
[ultimate] (1). Danger Mouse <dm@secret.example.net>

[ultimate] (1). Danger Mouse <dm@secret.example.net>
     Cipher: TWOFISH, CAMELLIA256, AES256, CAMELLIA192, AES192, CAMELLIA128, AES, BLOWFISH, IDEA, CAST5, 3DES
     Digest: SHA512, SHA384, SHA256, SHA224, RIPEMD160, SHA1
     Compression: ZLIB, BZIP2, ZIP, Uncompressed
     Features: MDC, Keyserver no-modify

bash-4.4$

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7.2 Subkeys

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.

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.

import gpg

c = gpg.Context()
c.home_dir = "~/.gnupg-dm"

key = c.get_key(dmkey.fpr, secret=True)
dmsub = c.create_subkey(key, algorithm="rsa3072", expires_in=15768000,
                        encrypt=True)

As with the primary key, the results here can be checked with:

print("""
 Fingerprint:  {0}
 Primary Key:  {1}
  Public Key:  {2}
  Secret Key:  {3}
 Sub Key:  {4}
User IDs:  {5}
""".format(dmsub.fpr, dmsub.primary, dmsub.pubkey, dmsub.seckey, dmsub.sub,
           dmsub.uid))

As well as on the command line with:

bash-4.4$ gpg --homedir ~/.gnupg-dm -K
~/.gnupg-dm/pubring.kbx
----------------------
sec   rsa3072 2018-03-15 [SC] [expires: 2019-03-15]
      177B7C25DB99745EE2EE13ED026D2F19E99E63AA
uid           [ultimate] Danger Mouse <dm@secret.example.net>
ssb   rsa3072 2018-03-15 [E] [expires: 2018-09-13]

bash-4.4$

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7.3 User IDs


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7.3.1 Adding User IDs

By comparison to creating primary keys and subkeys, adding a new user ID to an existing key is much simpler. The method used to do this is ‘key_add_uid’ and the only arguments it takes are for the ‘key’ and the new ‘uid’.

import gpg

c = gpg.Context()
c.home_dir = "~/.gnupg-dm"

dmfpr = "177B7C25DB99745EE2EE13ED026D2F19E99E63AA"
key = c.get_key(dmfpr, secret=True)
uid = "Danger Mouse <danger.mouse@secret.example.net>"

c.key_add_uid(key, uid)

Unsurprisingly the result of this is:

bash-4.4$ gpg --homedir ~/.gnupg-dm -K
~/.gnupg-dm/pubring.kbx
----------------------
sec   rsa3072 2018-03-15 [SC] [expires: 2019-03-15]
      177B7C25DB99745EE2EE13ED026D2F19E99E63AA
uid           [ultimate] Danger Mouse <danger.mouse@secret.example.net>
uid           [ultimate] Danger Mouse <dm@secret.example.net>
ssb   rsa3072 2018-03-15 [E] [expires: 2018-09-13]

bash-4.4$

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7.3.2 Revoking User IDs

Revoking a user ID is a fairly similar process, except that it uses the ‘key_revoke_uid’ method.

import gpg

c = gpg.Context()
c.home_dir = "~/.gnupg-dm"

dmfpr = "177B7C25DB99745EE2EE13ED026D2F19E99E63AA"
key = c.get_key(dmfpr, secret=True)
uid = "Danger Mouse <danger.mouse@secret.example.net>"

c.key_revoke_uid(key, uid)

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7.4 Key certification

Since key certification is more frequently referred to as key signing, the method used to perform this function is ‘key_sign’.

The ‘key_sign’ method takes four arguments: ‘key’, ‘uids’, ‘expires_in’ and ‘local’. The default value of ‘uids’ is ‘None’ and which results in all user IDs being selected. The default value of both ‘expires_in’ and ‘local’ is ‘False’; which results in the signature never expiring and being able to be exported.

The ‘key’ is the key being signed rather than the key doing the signing. To change the key doing the signing refer to the signing key selection above for signing messages and files.

If the ‘uids’ value is not ‘None’ then it must either be a string to match a single user ID or a list of strings to match multiple user IDs. In this case the matching of those strings must be precise and it is case sensitive.

To sign Danger Mouse’s key for just the initial user ID with a signature which will last a little over a month, do this:

import gpg

c = gpg.Context()
uid = "Danger Mouse <dm@secret.example.net>"

dmfpr = "177B7C25DB99745EE2EE13ED026D2F19E99E63AA"
key = c.get_key(dmfpr, secret=True)
c.key_sign(key, uids=uid, expires_in=2764800)

Up: Key certification   [Contents]

7.4.1 Verifying key certifications

import gpg
import time

c = gpg.Context()
dmfpr = "177B7C25DB99745EE2EE13ED026D2F19E99E63AA"
keys = list(c.keylist(pattern=dmuid, mode=gpg.constants.keylist.mode.SIGS))
key = keys[0]

for user in key.uids:
    for sig in user.signatures:
        print("0x{0}".format(sig.keyid), "", time.ctime(sig.timestamp), "",
              sig.uid)

Which for Danger Mouse displays the following:

0x92E3F6115435C65A  Thu Mar 15 13:17:44 2018  Danger Mouse <dm@secret.example.net>
0x321E4E2373590E5D  Mon Nov 26 12:46:05 2018  Ben McGinnes <ben@adversary.org>

The two key signatures listed are for the self-certification of Danger Mouse’s key made when the key was created in March, 2018; and the second is a signature made by the author and set to expire at the end of the year. Note that the second signature was made with the following code (including the preceding code to display the output of the certifications or key signatures):

import gpg
import math
import pendulum
import time

hd = "/home/dm/.gnupg"
c = gpg.Context()
d = gpg.Context(home_dir=hd)
dmfpr = "177B7C25DB99745EE2EE13ED026D2F19E99E63AA"
dmuid = "Danger Mouse <dm@secret.example.net>"
dkeys = list(c.keylist(pattern=dmuid))
dmkey = dkeys[0]

c.key_import(d.key_export(pattern=None))

tp = pendulum.period(pendulum.now(tz="local"), pendulum.datetime(2019, 1, 1))
ts = tp.total_seconds()
total_secs = math.ceil(ts)
c.key_sign(dmkey, uids=dmuid, expires_in=total_secs)

d.key_import(c.key_export(pattern=dmuid))
keys = list(c.keylist(pattern=dmuid, mode=gpg.constants.keylist.mode.SIGS))
key = keys[0]

for user in key.uids:
    for sig in user.signatures:
        print("0x{0}".format(sig.keyid), "", time.ctime(sig.timestamp), "",
              sig.uid)

Note that this final code block includes the use of a module which is not part of Python’s standard library, the pendulum module. Unlike the standard datetime module, pendulum makes working with dates and times significantly easier in Python; just as the requests module makes working with HTTP and HTTPS easier than the builtin modules do.

Though neither requests nor pendulum are required modules for using the GPGME Python bindings, they are both highly recommended more generally.


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8 Advanced or Experimental Use Cases


Up: Advanced or Experimental Use Cases   [Contents]

8.1 C plus Python plus SWIG plus Cython

In spite of the apparent incongruence of using Python bindings to a C interface only to generate more C from the Python; it is in fact quite possible to use the GPGME bindings with Cython. Though in many cases the benefits may not be obvious since the most computationally intensive work never leaves the level of the C code with which GPGME itself is interacting with.

Nevertheless, there are some situations where the benefits are demonstrable. One of the better and easier examples being the one of the early examples in this HOWTO, the key counting code. Running that example as an executable Python script, ‘keycount.py’ (available in the ‘examples/howto/’ directory), will take a noticeable amount of time to run on most systems where the public keybox or keyring contains a few thousand public keys.

Earlier in the evening, prior to starting this section, I ran that script on my laptop; as I tend to do periodically and timed it using ‘time’ utility, with the following results:

bash-4.4$ time keycount.py

Number of secret keys:  23
Number of public keys:  12112


real        11m52.945s
user        0m0.913s
sys        0m0.752s

bash-4.4$

Sometime after that I imported another key and followed it with a little test of Cython. This test was kept fairly basic, essentially lifting the material from the Cython Basic Tutorial to demonstrate compiling Python code to C. The first step was to take the example key counting code quoted previously, essentially from the importing of the ‘gpg’ module to the end of the script:

import gpg

c = gpg.Context()
seckeys = c.keylist(pattern=None, secret=True)
pubkeys = c.keylist(pattern=None, secret=False)

seclist = list(seckeys)
secnum = len(seclist)

publist = list(pubkeys)
pubnum = len(publist)

print("""
    Number of secret keys:  {0}
    Number of public keys:  {1}

""".format(secnum, pubnum))

Save that into a file called ‘keycount.pyx’ and then create a ‘setup.py’ file which contains this:

from distutils.core import setup
from Cython.Build import cythonize

setup(
    ext_modules = cythonize("keycount.pyx")
)

Compile it:

bash-4.4$ python setup.py build_ext --inplace
bash-4.4$

Then run it in a similar manner to ‘keycount.py’:

bash-4.4$ time python3.7 -c "import keycount"

Number of secret keys:  23
Number of public keys:  12113


real        6m47.905s
user        0m0.785s
sys        0m0.331s

bash-4.4$

Cython turned ‘keycount.pyx’ into an 81KB ‘keycount.o’ file in the ‘build/’ directory, a 24KB ‘keycount.cpython-37m-darwin.so’ file to be imported into Python 3.7 and a 113KB ‘keycount.c’ generated C source code file of nearly three thousand lines. Quite a bit bigger than the 314 bytes of the ‘keycount.pyx’ file or the full 1,452 bytes of the full executable ‘keycount.py’ example script.

On the other hand it ran in nearly half the time; taking 6 minutes and 47.905 seconds to run. As opposed to the 11 minutes and 52.945 seconds which the CPython script alone took.

The ‘keycount.pyx’ and ‘setup.py’ files used to generate this example have been added to the ‘examples/howto/advanced/cython/’ directory The example versions include some additional options to annotate the existing code and to detect Cython’s use. The latter comes from the Magic Attributes section of the Cython documentation.


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9 Miscellaneous extras and work-arounds

Most of the things in the following sections are here simply because there was no better place to put them, even though some are only peripherally related to the GPGME Python bindings. Some are also workarounds for functions not integrated with GPGME as yet. This is especially true of the first of these, dealing with group lines.


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9.1 Group lines

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.

import subprocess
import sys

if sys.platform == "win32":
    gpgconfcmd = "gpgconf.exe --list-options gpg"
else:
    gpgconfcmd = "gpgconf --list-options gpg"

try:
    lines = subprocess.getoutput(gpgconfcmd).splitlines()
except:
    process = subprocess.Popen(gpgconfcmd.split(), stdout=subprocess.PIPE)
    procom = process.communicate()
    if sys.version_info[0] == 2:
        lines = procom[0].splitlines()
    else:
        lines = procom[0].decode().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 = []
group_lists = []

for i in range(len(groups)):
    group_lines.append(groups[i].split("="))
    group_lists.append(groups[i].split("="))

for i in range(len(group_lists)):
    group_lists[i][1] = group_lists[i][1].split()

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 list.

A demonstration of using the ‘groups.py’ module is also available in the form of the executable ‘mutt-groups.py’ script. This second script reads all the group entries in a user’s ‘gpg.conf’ file and converts them into crypt-hooks suitable for use with the Mutt and Neomutt mail clients.


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9.2 Keyserver access for Python

The hkp4py module by Marcel Fest was originally a port of the old python-hkp module from Python 2 to Python 3 and updated to use the requests module instead. It has since been modified to provide support for Python 2.7 as well and is available via PyPI.

Since it rewrites the ‘hkp’ protocol prefix as ‘http’ and ‘hkps’ as ‘https’, the module is able to be used even with servers which do not support the full scope of keyserver functions.5 It also works quite readily when incorporated into a Cython generated and compiled version of any code.


Up: Keyserver access for Python   [Contents]

9.2.1 Key import format

The hkp4py module returns key data via requests as string literals (‘r.text’) instead of byte literals (‘r.content’). This means that the retrurned key data must be encoded to UTF-8 when importing that key material using a ‘gpg.Context().key_import()’ method.

For this reason an alternative method has been added to the ‘search’ function of ‘hkp4py.KeyServer()’ which returns the key in the correct format as expected by ‘key_import’. When importing using this module, it is now possible to import with this:

for key in keys:
    if key.revoked is False:
        gpg.Context().key_import(key.key_blob)
    else:
        pass

Without that recent addition it would have been necessary to encode the contents of each ‘hkp4py.KeyServer().search()[i].key’ in ‘hkp4py.KeyServer().search()’ before trying to import it.

An example of this is included in the Importing Keys section of this HOWTO and the corresponding executable version of that example is available in the ‘lang/python/examples/howto’ directory as normal; the executable version is the ‘import-keys-hkp.py’ file.


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9.3 GPGME version checking

For various reasons it may be necessary to check which version of GPGME the bindings have been built against; including whether a minimum required version of GPGME is in use.

For the most part the ‘gpg.version.versionstr’ and ‘gpg.version.versionlist’ methods have been quite sufficient. The former returns the same string as ‘gpgme-config --version’, while the latter returns the major, minor and patch values in a list.

To check if the installed bindings have actually been built against the current installed libgpgme version, this check can be performed:

import gpg
import subprocess
import sys

gpgme_version_call = subprocess.Popen(["gpgme-config", "--version"],
                                      stdout=subprocess.PIPE,
                                      stderr=subprocess.PIPE)
gpgme_version_str = gpgme_version_call.communicate()

if sys.version_info[0] == 2:
    gpgme_version = gpgme_version_str[0].strip()
elif sys.version_info[0] >= 3:
    gpgme_version = gpgme_version_str[0].decode().strip()
else:
    gpgme_version = None

if gpgme_version is not None:
    if gpgme_version == gpg.version.versionstr:
        print("The GPGME Python bindings match libgpgme.")
    else:
        print("The GPGME Python bindings do NOT match libgpgme.")
else:
    print("Upgrade Python and reinstall the GPGME Python bindings.")

For many developers, however, the preferred checking means checking for a minimum version or point release. This is now readily available via the ‘gpg.version.versionintlist’ method (added in version ‘1.12.1-beta79’). It is also now possible to easily check whether the installed GPGME Python bindings were built from a development or beta branch of the GPGME source code.

The following code demonstrates how both of those methods may be used:

import gpg

try:
    if gpg.version.is_beta is True:
        print("The installed GPGME Python bindings were built from beta code.")
    else:
        print("The installed GPGME Python bindings are a released version.")
except Exception as e:
    print(e)

try:
    if gpg.version.versionintlist[0] == 1:
        if gpg.version.versionintlist[1] == 12:
            if gpg.version.versionintlist[2] == 1:
                print("This is the minimum version for using versionintlist.")
            elif gpg.version.versionintlist[2] > 1:
                print("The versionintlist method is available.")
            else:
                pass
        elif gpg.version.versionintlist[1] > 12:
            print("The versionintlist method is available.")
        else:
            pass
    elif gpg.version.versionintlist[0] > 1:
        print("The versionintlist method is available.")
    else:
        pass
except Exception as e:
    print(e)

The points where ‘pass’ is used in the above example will most likely also produce an ‘Exception’ error since those results should only occur in versions which do not have the ‘gpgme.version.is_beta’ and ‘gpgme.version.versionintlist’ methods available.


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10 Copyright and Licensing


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10.1 Copyright

Copyright © The GnuPG Project, 2018.

Copyright (C) The GnuPG Project, 2018.


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10.2 Draft Editions of this HOWTO

Draft editions of this HOWTO may be periodically available directly from the author at any of the following URLs:

All of these draft versions except for one have been generated from this document via GNU Emacs Org mode and GNU Texinfo. Though it is likely that the specific file version used will be on the same server with the generated output formats.

The GNU Texinfo and reStructured Text versions ship with the software, while the GNU Emacs Info verseion is generated from the Texinfo version using GNU Texinfo or GNU Makeinfo. The Texinfo format is generated from the original Org mode source file in Org mode itself either within GNU Emacs or via the command line by invoking Emacs in batch mode:

emacs gpgme-python-howto.org --batch -f org-texinfo-export-to-texinfo --kill
emacs gpgme-python-howto --batch -f org-texinfo-export-to-texinfo --kill

The reStructuredText format is also generated from the Org-mode source file, except it is generated using Pandoc with either of the following commands:

pandoc -f org -t rst+smart -o gpgme-python-howto.rst gpgme-python-howto.org
pandoc -f org -t rst+smart -o gpgme-python-howto.rst gpgme-python-howto

In addition to these there is a significantly less frequently updated version as a HTML WebHelp site (AWS S3 SSL); generated from DITA XML source files, which can be found in an alternative branch of the GPGME git repository.

Various generated output formats may occasionally be found in subdirectories of the gpgme-python directory. In particular within the DITA, reStructuredText and Texinfo subdirectories. The ‘rst’ directory contains output files generated with Sphix and may include a considerable number of its possible output formats.

These draft editions are not official documents and the version of documentation in the master branch or which ships with released versions is the only official documentation. Nevertheless, these draft editions may occasionally be of use by providing more accessible web versions which are updated between releases. They are provided on the understanding that they may contain errors or may contain content subject to change prior to an official release.


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10.3 License GPL compatible

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

(1)

short-history’ and/or ‘short-history.html’.

(2)

With no issues reported specific to Python 3.7, the release of Python 3.7.1 at around the same time as GPGME 1.12.0 and the testing with Python 3.7.1rc1, there is no reason to delay moving 3.7 ahead of 3.6 now. Production environments with more conservative requirements will always enforce their own policies anyway and installation to each supported minor release is quite possible too.

(3)

Yes, even if you use virtualenv with everything you do in Python. If you want to install this module as just your user account then you will need to manually configure, compile and install the entire GnuPG stack as that user as well. This includes libraries which are not often installed that way. It can be done and there are circumstances under which it is worthwhile, but generally only on POSIX systems which utilise single user mode (some even require it).

(4)

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.

(5)

Such as with ProtonMail servers. This also means that restricted servers which only advertise either HTTP or HTTPS end points and not HKP or HKPS end points must still be identified as as HKP or HKPS within the Python Code. The ‘hkp4py’ module will rewrite these appropriately when the connection is made to the server.