The User Experience
Let us consider a hypothetical user expierence: A user navigates to Google and enters a company name. They are presented with a listing of search results, often including the official company web site, other web sites for companies with a similar name, sites reviewing products by the company and sometimes sites maskarading as the official site.
In the search results listing, each site where the identity of the organization that controls the site has been verified includes a special icon known as a "trust mark". This icon indicates that Google has established a chain of trust that allows the identity of the organization responsible for the content on that site to be verified.
Figure 1: An example UI from Safari indicating the validity of a certificate.
The green check icon is a good example of a visual representation of a trust mark.
The presence of the trust mark may be sufficient for the user to navigate to the site in confidence, or they may click on the trust mark, showing a page containing legal information about the entity, including their location (using Google Maps, of course). This information would especially be useful for disambiguating different companies with similar names.
Standard web certificates are already used for secure transactions and providing information about the authenticity of a secured web site. But these are limited to the secure sections of web sites, such as pages for authentication and payment processing. Most web sites do not use SSL/TLS for the bulk of their web site due to the computational cost of processing HTTPS transactions when compared to standard HTTP.
However, the same certificates used to provide HTTPS could also be used for indicating a degree of trust. By placing the certificate as a file in the root path of the web site, the Google crawler could retrieve a "certificates.txt" file, much like the current "robots.txt" file. As most certificates contain the top level domain name, Google would be able to verify the chain of trust of the certificate, check to make sure that the URL it was crawling matched the URL in the certificate, and then display the trust mark and associated information.
As this approach leverages existing infrastructure, does not require any new protocols, and allows web sites operators with existing certificates to immediately use them for this purpose, this would facilitate rapid adoption of this technique.