This plugin provides Enigform Secure Login support for WordPress. Works in similar way to HTTP Authentication by dwc.
Enigform is a Firefox Add-On which uses OpenPGP to digitally sign outgoing HTTP requests and Securely login to remote web sites, as long as the remote web server is Enigform-compliant. There is an Apache module called mod_openpgp which needs to be configured. I recommend you read the Enigform Definitive Guide at http://wiki.buanzo.org/index.php?n=Main.Wp-enigform-authentication THEN come back here... if you still need it :)
The Definitive Guide shows how to create a client and server OpenPGP Keypair using the GNU Privacy Guard (GnuPG) suite, how to install Enigform and mod_openpgp, and finally how to install this plugin and tweak your WordPress template (only one change required).
This is an experimental, still in research technology. Your support is LOVED. :)