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Support for netscape / html5 SPKAC client certificate request
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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.


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


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

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