This is a great article and I have been talking about it for several months when presenting about digital identity. It was written by Drummond Reed and Eve Maler and I read it in December.(I am doing this more and more now). It has finally been published here is the abstract but it actually costs $19 - uggg.
Digital identities can be associated with everything from people to software applications to entire companies, but human digital identities prove the most interesting and challenging. Human digital identities can simplify network usage and enable new classes of applications, but they also introduce security and privacy risks. Federated identity management addresses scenarios in both enterprise and consumer contexts by defining how to dynamically distribute identity information and delegate identity tasks across security domains. This article explains federated identity's components, discusses security and privacy risks and architectural challenges, surveys the SAML, OpenID, and InfoCard protocols, and reviews new developments in federated identity management.
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Eve recently noted on her blog ( http://www.xmlgrrl.com/blog/archives/2008/04/10/the-venn-in-article-form/) that she will be making this available for free.
Hi Kaliya-- Thanks for the kind words! It was a blast working with Drummond so closely on this.
Note that I should be able to make the article available online for free soon -- I'm just waiting to get the PDF file. Keep an eye on my Publications page or my blog entry about the article for an update.