This policy setting allows you to filter a list of digital certificates for signing Excel 2007, PowerPoint 2007, and Word 2007 documents, based on the Key Usage field. The Key Usage field in a certificate is used to represent a series of basic constraints about the broad types of operations that can be performed with the certificate. Key usage filtering allows you to filter the list of installed certificates that can be used for signing documents. The filtered list will appear when users attempt to select a certificate for digitally signing a document.
If you enable this policy setting, only certificates with "digital signature" in the Key Usage field are listed as available certificates for signing documents.
If you disable this policy setting, you will not be able to filter the list of installed certificates that can be used for signing documents based on the Key Usage field.
If you do not configure this policy setting, the behavior is the equivalent of setting the policy to Enabled.