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Linked Local Names: An Overview

By Christopher Allen -

How do you identify someone online? Traditionally, the answer has been to use a centralized naming system. Trusted authorities act as the root of a global name space that connects names with public keys to certify who people are.

Unfortunately, this classic setup has problems. The earliest complaints focused on the 1988 x.509 standard and said that it was overly complex and overly formal. However, as the internet grew, people soon realized that there was a bigger problem: in a global name space, names quickly failed as a means of unique identity. If someone is verified by a certificate authority (CA) as Christopher Allen, who are they, really? Is it the psychic medium? The UCSF assistant professor? The security technologist? A traditional certificate can’t tell you. CA-based systems also require validation and revocation which recent SSL attacks like HeartBleed have proven have not adequately deployed or scaled to meet security requirements. Other aspects in the centrality of architecture in CA-based systems have also made them vulnerable to new forms of attacks.

An alternative to X.509-based certificates, 1991's PGP offered a web-of-trust model. In its ideal form this is a decentralized approach, but in practice identity depends on unique email addresses that are rooted in centralized systems, and as a whole the system was dependent for discovery of public keys through centralized key servers.

In 1996, Ronald L. Rivest & Butler Lampson proposed a different sort of system: linked local names, which they included as part of their “Simple Distributed Security Infrastructure”. SDSI was intended to put the power of certificate authority in everyone’s hands. Each individual attaches personal labels to public key credentials, creating “local names”. More importantly, individuals could also connect to the local names created by other people. Thus you might have a local name for Christopher Allen that you label “Christopher”. It in turn could be used to create a more complex chain like “Christopher’s Shannon’s wife”. This would refer to a person labeled “wife” by the person labeled “Shannon” by the person labeled “Christopher” who is labeled by you: you define Christopher who defines Shannon who defines wife.

That same year, Carl Ellison was also working on local names and how to avoid the use of global certificate authorities. He eventually combined his work with SDSI in an IETF work group that defined the simple public-key infrastructure (SPKI). It takes an orthogonal look at these problems by linking authorizations to keys instead of just names. It also does away with CAs by creating webs of certificates between individuals and allows for the creation of cryptographic Access Control Lists (ACLs).

SDSI/SPKI continued to expand in the years since Ellison’s RFCs, as seen in Ninghui Li’s 2000 paper “Local Names In SPKI/SDSI”. However, the SPKI RFCs never deployed--the specifications remain troubled by some of the same issues as older systems, particularly when representing complex information in a semantic graph. Finally, usage was limited in part due to an inability for anyone to monetize the infrastructure itself.

Marc Stiegler independently addressed the problem of global name spaces by expanding on Zooko’s Triangle — a list of requirements for global naming. It suggests that global names must be memorable, securely unique, and (obviously) global. Taking away any one criteria produces a more limited sort of identifier, such as a key (which is not memorable) or a nickname (which is not securely unique). Stiegler’s equivalent of the local name is a PetName (which is not global). Nick Szabo also worked on some proofs to demonstrate a solution for Zooko's Triangle can be created using blockchain technologies, for which Zooko now concurs is possible.

OpenID similarly tacked the topic of how people could identify and authenticate themselves to a relying party without having to use a single central authority. The OpenID community's original solution was to use a resolvable global name in the form of URL, and more recently, in OpenID Connect, an email address. This global name was then resolved to an associated OpenID identity provider to provide an authentication assertion (which may also include various identity attributes).

Although some large identity providers, such as Google, Wordpress, and Flickr, offer OpenID service, the OpenID community has not yet been able to achieve adoption beyond a few large identity providers. This challenge has been especially acute because the primary alternative to OpenID has become the social logins provided by the large social networks like Facebook and Twitter that already have very large namespaces and users that authenticate with these networks regularly.

More recently at OASIS, the XDI Technical Committee has developed an addressable semantic graph model and graph interchange protocol that requires identifiers and identifier resolution. Although early work on XDI identifiers was focused on centralized XDI identifier registries (called i-name and i-number registries), more recent work has prioritized specifying how the XDI protocol can be used for a fully decentralized registry for identifier assignment, resolution, and authentication. One of the features of this new effort are "relative name" identifiers.

Thus over the last two decades there has been plenty of interest in local names as tool to support decentralized name discovery, however, to date there have been no big successes. The biggest obstacle is combing through all of this disparate work to find out what’s worked and what hasn’t. Then, we can we push forward toward new, more polished implementations of this recurring security theme.


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