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Light-Weight Identity (LID) is a set of protocols and software implementations created by Johannes Ernst of NetMesh Inc. for representing and using digital identities on the Internet in a light-weight manner, without relying on any central authority. LID is the original URL-based identity protocol, and part of the OpenID movement. LID supports digital identities for humans, human organizations and non-humans (e.g. software agents, things, websites, etc.) It implements Yadis, a meta-data discovery service and is pluggable on all levels.

LID uses standard URLs as identifiers. For example, the URL http://lid.netmesh.org/liddemouser/ is the LID identifier for a hypothetical individual called Mr. LID Demo User. Anybody can host LID digital identities at a URL of their choosing, as long as they have control over the URL and the ability to run a program (CGI script) at that URL. For URLs where that is not possible, Yadis delegation allows a LID URL to point at one or more identity services hosted by different sites.

Unlike other digital identity systems, LID is organized in a base protocol called MinimumLID, and an ever-growing list of services on top of it. This enables LID to be a foundation for digital-identity related innovation by many parties. Any implementor chooses which or how many LID profiles to support to meet their needs.

Some of the already-defined profiles include:

• LID single sign-on
• LID for controlled profile data exchange using vCards -- define subsets of information for different clients
• LID for controlled, decentralized social networking using FOAF -- different subsets of information for different clients
• LID for authenticated messaging and blogging -- no more forged return addresses

LID relies on existing technologies to the maximum extent possible:

• XML and XPath (but not WS-*)
• REST
• PGP / GPG
• standard browsers without requiring plug-ins or extensions
• LID also supports OpenID authentication

Several implementations are available (including open source).

• OpenID
• Yadis

LID originally was a late-night wild idea to solve a particular customer problem and only that: we were observing what the users of an enterprise customer of ours (NetMesh) were doing with a mobile application they had built using NetMesh InfoGrid, and we noticed that "people" were primary entities in the system, not just "data" and "services" etc. We wanted to give the users more capabilities for those "people objects" in the system, in particular "social"/"collaborative" features. I joked to my wife Tammy Ernst (who is technical as well) that we needed something simple and quick, and maybe we could "just give everybody a URL and be done with it". (That was essentially all the planning that was done for LID V1...) A few days later, she hacked a bit of Perl and we figured, hmm, it just about contradicts every established truth in digital identity (radically decentralized, radically cheap, no new namespaces etc. ...) but there might be a 'there' there ... which turned out to be a correct hunch.

(and edited a bit by Johannes Ernst for readability)

• Light-Weight Digital Identity (LID) - official site, LID-enabled itself
• Yadis - official Yadis site, LID-enabled
• Demo LID user
• mylid.net - a hosted LID service