[zz]WHQL and Digital Signature

For full article, please visit  http://www.touch-base.com/documentation/WHQL.htm

 

Signing procedure

In very basic terms the WHQL hardware compatibility testsare downloaded and installed and are run against a driver and controllercombination. The tests have to be undertaken on a system that has passed WHQLand will not cause any conflicts during testing. Tests are performed for both32 and 64 bit drivers.

 

The tests generate logs which are processed and aresubmitted for review and approval.  Theycan only be submitted by companies that have obtained a VeriSign Class 3code-signing ID. Once approved a .cat file, containing the digital signature,is returned for distribution with the driver and controller combination.

 

Thereafter, the operating system performs signature detection wheneveran INF file is referenced to install hardware from a device class that issubject to signature detection: that is, during any Plug and Play operation,when the user runs the Add New Hardware wizard in the Control Panel, and so on.

The system always installs the driver that is the closest match for thehardware, whether or not that driver is signed; however, given drivers of equalrank, the system installs the signed driver rather than the unsigned driver.

During driver installation, Windows compares the hashes contained inthe driver's CAT file with the computed hash of the driver binaries todetermine whether the binaries have changed since the CAT file was created. Ifa driver fails the signature check or there is no CAT file the driver isconsidered unsigned. Given this, once signed, no changes can be made to anybinaries used in the signing process. For this reason most companies that offersigned drivers also offer the unsigned drivers with the latest development.

Further information about the signing procedure can be foundon the web and a good place to start is the WHQL Getting Startedweb page.

 

Given the level of knowledge required to undertake thesigning procedure many companies use a third party WHQL services company toundertake this work.