ACTION 181: Summary of EV certificate discussion, prototype recommendation

Extended Validation (EV) Certificates are X.509v3 certificates that are issued in accordance with minimum authentication criteria defined by the CA-Browser Forum, as demonstrated by a Web Trust audit of the issuer. 

When certain browsers (currently IE7 with the anti-phishing filter enabled or Firefox with a plug-in) visit a site secured with SSL and an EV certificate an enhanced user experience is presented. Currently in IE7 this user experience consists of the address bar turning green and the certificate subject and issuer being displayed alternately next to the address bar. Advertising and User education programs for EV certificates frequently use phrases such as 'Green for Go'.

The current CAB-Forum criteria are specified at: http://www.cabforum.org/EV_Certificate_Guidelines.pdf

The core principle of EV certificates is to assure the relying party that there is accountability. The EV issuing criteria require a certificate issuer to verify that the organization specified in the certificate subject exists as a legal entity, that the physical contact address is valid, that the party making the application is authorized to do so by the specified subject, that the applicant has control of the domain name specified in the certificate and that the applicant has possession of the private key corresponding to the specified public key.

If the issuance process should fail the certificate issuer is to be held accountable, hence the display of the issuer name in the EV security experience.

An EV certificate does not guarantee that a vendor selling a $3000 plasma TV will deliver a product that works or even that the TV will be delivered at all. But an EV certificate does guarantee that either the vendor can be held accountable for the default or the certificate issuer held accountable for the failure of their authentication program.

In addition to requiring minimum authentication standards and a WebTrust audit, the CABForum guidelines require CAs to implement certain technical measures. Certificates must conform to a specific profile of the X.509v3 and PKIX standards. Wildcard certificates are not permitted, the maximum validity interval is one year, a means of efficient revocation must be supported and certain minimum key sizes must be employed. These measures are generally consistent with community consensus amongst network security specialists.

Although the EV guidelines do not mandate support for publication of status information by OCSP, accountability of the certificate issuer creates a significant incentive to do so. 

While EV certificates are designed to be compatible with the existing deployed base of browsers the use of EV makes use of certain protocol extensions which are already highly desirable to be even more desirable. In particular support for the certificate host identification extension and OCSP token stapling. 

Although the EV security experience in IE7 is designed to resist certain types of attack it is impossible to provide absolute guarantees of security on a platform that is not considered trustworthy. For example the IE7 does not allow users to add EV signing certificates to the root store. IE7 only presents the EV security experience if a root certificate that is countersigned by a Certificate Trust List signed by an offline root. An attacker can only circumvent this requirement by compromising the IE7 executable.

Prototype recommendation:

Web clients SHOULD present a distinctive user experience in response to presentation of an EV certificate. Such a user experience SHOULD be guarded against emulation by browser content. The certificate subject and issuer SHOULD be displayed in the primary user experience.

In order to facilitate accessibility such a user experience SHOULD NOT use color alone, although if color is used the color green SHOULD NOT be used EXCEPT to indicate a positive condition and the color red SHOULD NOT be used except to indicate a negative condition.

In order to reduce the consuption of IPv4 addresses Web Clients SHOULD support the TLS host name identification extension on all SSL/TLS transactions regardless of whether an EV certificate is presented or not.

For efficiency, Web Clients SHOULD support the OCSP token stapling extension of TLS on all SSL/TLS transactions regardless of whether an EV certificate is presented or not.