Support for netscape / html5 SPKAC client certificate request

pip install pyspkac==0.7


pyspkac: Routines for supporting netscape / html5 SPKAC

Author: Ralf Schlatterbeck <>

This library supports the format of browser-generated SPKAC certificate requests.

The HTML keygen tag which previously was supported by most Mozilla-based browsers is now in the HTML-5 standard. The keygen tag is used in a HTML form element and displays a key generation widget to the user. When submitted, the browser locally generates a public key pair, locally stores the private key, and submits the public key to the web server in the SPKAC format.

When generating a form with a keygen element, the web server can include a challenge string in the form. This challenge string is returned in the SPKAC generated by the browser. It is signed together with the public key by the private key retained by the browser.

This package is intended for server-side support of SPKAC. It uses a submitted SPKAC and checks for correct challenge string and that the public key and challenge are properly signed by the browser. It supports a method for generating a certificate from the data in the SPKAC and additional data supplied by the web application.

The generated certificate can then typically be used for client authentication to a web application and is therefore called a client certificate. The web browser (or other client-side application) supplies the certificate in the SSL handshake and proves it is in the posession of the necessary private key.

When building certificates it is also a good idea to have a certificate revocation list (CRL). The package provides routines to generate a revocation list from scratch using a list of certificate serial numbers and revocation dates.


Install using the standard python mechanism, e.g.:

python install --prefix=/usr/local

You need pyasn1 and M2Crypto installed for this package to work.


For a usage example see the doctests in and

Notes for Building

When doing a release the following commands should be issued:

python clean --all
python sdist --manifest-only
git status
python sdist --quiet
git status
python register
python sdist upload --sign

The interleaved git status commands work around a bug in older git versions that, when git describe with --dirty option is used, will erroneously detect dirty status when the directory is stat-dirty. Since sdist will create symlinks this will make the directory stat-dirty.

The --manifest-only will re-create the MANIFEST file even if neither nor have changed.


Version 0.7: Bug fixes

Fix github issues

  • Fix Github issue 2 problems with version number format, we now use a numeric value but leave the tag format as before (starting with 'V-').
  • Merge pull request for Opera Workaround in Github issue 3

Version 0.6: Bug fix

Release now contains missing files from 0.5.

  • Add Notes for Building section and document release procedure to avoid missing files in the future
  • Remove relative import statements
  • Add version import to

Version 0.5: Major feature enhancements

Implement Certificate Revocation Lists (CRL)

  • Implementation of CRL (with MD5 hash, this probably needs to be fixed later on, don't know yet if there is a format with a stronger hash)
  • factor pem_object
  • Fix timezone of default valid_from for generated certificate: We used a timezone correction on a timestamp which is already UTC.

Version 0.4: Bug fix

Fix incompatibility with newer versions of pyasn1.

  • BitString serialisation in pyasn1 changed method names, the old inofficial serialisation method with '_' is now official without the '_'.

Version 0.3: Bug fix

Import of failed if dependecies were missing. This prevented a pip install from succeeding in case of missing dependencies.

  • Guard import in to not fail for missing dependencies

Version 0.2: Minor feature additions

Move example from end of into a doctest. Change of API: set_email no longer supported. Now extensions can be given as unnamed arguments in the constructor. Named arguments are interpreted as subject parameters for the resulting certificate. All this is shown in the doctest.

  • Remove set_email
  • Change constructor: Allow extensions as args and subject parameters as keyword args
  • Add doctest
  • Fix to include install_requires to auto-install required packages
  • Easier import: from pyspkac import SPKAC works now.

Version 0.1: Initial Release