Convergence was a proposed strategy for replacing
SSL certificate authorities, first put forth by
Moxie Marlinspike in August 2011 while giving a talk titled "SSL and the Future of Authenticity" at the
Black Hat security conference. It was demonstrated with a
Firefox addon
For Mozilla software, an add-on is a software component that extends the functionality of the Firefox web browser and related application software, applications although most are browser extensions. Mozilla provides add-ons to users via its offic ...
and a server-side notary
daemon.
In the talk, Marlinspike proposed that all of the current problems with the certificate authority (CA) system could be reduced to a single missing property, which he called "trust agility" and which Convergence aimed to provide. The strategy claimed to be agile, secure, and distributed.
As of 2013, Marlinspike was focused on an
IETF
The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...
proposal called TACK, which was designed to be an uncontroversial first step that advocates for dynamic certificate pinning instead of full CA replacement and reduces the number of times a third party needs to be trusted.
Development of Convergence was continued in a "Convergence Extra" fork until about 2014.
Background
Convergence was based on previous work from the Perspectives Project at
Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania, United States. The institution was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools. In 1912, it became the Carnegie Institu ...
. Like Perspectives, Convergence authenticated connections by contacting external notaries, but unlike Perspectives, Convergence notaries could use a number of different strategies beyond network perspective in order to reach a verdict.
Convergence in comparison to conventional SSL
The purpose of a
certificate authority in the conventional
SSL system is to vouch for the identity of a site, by checking its SSL certificate. Without some vouchsafing, one is open to a
man-in-the-middle attack. A single site is vouched for by only a single certificate authority (CA), and this CA has to be trusted by the user. Web browsers typically include a list of default trusted CAs and display a warning about an "untrusted connection" when a site cannot be vouchsafed by a trusted CA. A problem with this system is that if a user (or browser vendor) loses trust in a CA, removing the CA from the browser's list of trusted authorities means losing trust in all the sites that used that CA. This happened when major browsers lost trust in the
DigiNotar CA and sites registered with this CA had to get new certificate authorities (see ''
Certificate authority#CA compromise'' for more examples of trust breaches).
With Convergence, however, there was a level of
redundancy, and no
single point of failure
A single point of failure (SPOF) is a part of a system that would Cascading failure, stop the entire system from working if it were to fail. The term single point of failure implies that there is not a backup or redundant option that would enab ...
. Several ''notaries'' could vouch for a single site. A user could choose to trust several notaries, most of which would vouch for the same sites. If the notaries disagreed on whether a site's identity was correct, the user could choose to go with the
majority vote, or err on the side of caution and demand that all notaries agree, or be content with a single notary (the voting method was controlled with a setting in the browser addon). If a user chose to distrust a certain notary, a non-malicious site could still be trusted as long as the remaining trusted notaries trusted it; thus there was no longer a single point of failure.
In September 2011,
Qualys
Qualys, Inc. is an American technology firm based in Foster City, California, specializing in cloud security, compliance and related services.
Qualys has over 10,300 customers in more than 130 countries. The company has strategic partnerships ...
announced it would run two notary servers. As of June, 2016 these servers appeared to be down. A list of notaries was maintained on the Convergence wiki.
Alternatives
* The
Monkeysphere Project tries to solve the same problem by using the
PGP web of trust model to assess the authenticity of https certificates.
*
HTTP Public Key Pinning is a security mechanism which allows HTTPS websites to resist impersonation by attackers using mis-issued or otherwise fraudulent certificates.
*
Certificate Transparency is an attempt to solve the problem by
verifiable append-only public logs.
References
External links
*
Convergence project pageat GitHub
{{SSL/TLS
Computer security accreditations
Transport Layer Security