Avoiding Pollution of Extended Validation SSL Contexts with Channel Trust Chaining
By Sid Stamm (sid at mozilla dot com)

Extended Validation SSL certificates (EV certificates) have been proposed by the Certification Authority/Browser Forum and widely implemented with the cooperation of many SSL certificate authorities. These new certificates are more difficult for an entity to obtain, requiring more proof of identity on the requester's part in the hopes of minimizing the risk that a phisher or other type of attacker could obtain a certificate for a domain they do not legitimately control.

Sotirov and Zusman[1] have pointed out that although a site may have been served with an EV certificate, it may not have control over all of the resources embedded into its context (such as ads, stylesheets or scripts), which could ultimately affect the site's behavior or appearance.

EV-SSL TrustList is a trust-chaining mechanism that allows the owner of an EV certificate to better control which HTTPS channels are used to embed resources such as images, scripts and stylesheets on his page; this is accomplished by specifying a list of trusted SSL certificates that may be used in encryption channels for other hosts that provide content for his site. A signed trust file specified in an extension of the EV SSL certificate provides a white list of other certificates and is tamper-proof. The policy is enforced on the client side when loading ad rendering the EV site, and any violations of the policy cause the browser to cancel any EV badging or UI indicators.

Separated into a few pieces, here are links to the theoretical and practical perspectives of EVSSL Trust Chaining:


  1. Sotirov, A. and Zusman, M., "Subprime PKI and SSL Rebinding", Internet blog posting http://schmoil.blogspot.com/2009/03/suprime-pki-and-ssl-rebinding.html. March, 2009.
  2. Jackson, C. and Barth, A., "Beware of Finer-Grained Origins", in proceedings of Web 2.0 Security and Privacy (W2SP 2008), 2008. http://crypto.stanford.edu/websec/origins/fgo.pdf