However, while certificate pinning is a step forward, the solution isn't perfect. First of all, it only works for HTTPS, leaving out other secure protocols used for email communication or instant messaging, like SMTP over SSL, POP over SSL, IMAP over SSL, and XMPP.
Other criticisms are that certificate pinning lacks a coherent revocation mechanism and doesn't prevent attacks against users who connect for the first time to a domain name.
According to the EFF, the Sovereign Keys extension addresses all of these problems.
In addition, the SK specification is compatible with DANE (DNS-Based Authentication of Named Entities), a protocol used to associate certificates with domain names via DNSSEC, and can be be used to cross-sign DANE keys in order to prevent DNS-based attacks.
The Sovereign Keys system is said to addresses the false-positive and false-negative issues raised by Convergence, a system designed by SSL security researcher Moxie Marlinkspike, which aims to slowly replace the CA model.
With Convergence, a browser trying to establish an HTTPS connection asks a number of trusted third-party notary servers to also query the domain. If the digital certificates received by the notaries and the browser are different, then a man-in-the-middle attack is most likely in progress and the connection is refused.
Marlinspike is skeptical regarding the success of Sovereign Keys because it requires too many changes to current SSL/TLS implementations. "The deployment of 'Sovereign Keys' would require a major internet migration, changing both the way that every webserver deploys SSL today, as well as the way that every SSL client processes server certificates," he said.
"My feeling is that this migration would be unlikely to happen, as it requires the use of client technologies that web browsers are disinclined to integrate, as well as commitments and mechanics that the operators of SSL websites are disinclined to make," he added.
Even though people and organizations have different ideas about how the security of the Internet public key infrastructure should be improved, they all seem to agree that the CA model needs to be replaced or strengthened.
Marlinspike believes that the solution which will eventually be accepted will most likely be the one that requires less changes from those involved in the process. "As we've seen from years of talk about the deficiencies of the CA system, the hard part of this work is not coming up with an idea, but getting it done," he said.