In my view... U-Prove is the equivalent in the privacy world of RSA in the security space. It does things we wouldn’t have otherwise thought possible.
— Kim Cameron

On 6 March 2008 Microsoft acquired Credentica, a Montreal-based company with some remarkable cryptography technology called U-Prove. The technology allows a user to disclose the absolute minimum information required in any given situation. U-Prove has been developed by Stefan Brands over the past two decades. In addition to acquiring the U-Prove technology and patent portfolio, Stefen Brands, and his colleagues Christian Paquin and Greg Thompson have joined Microsoft's Identity and Access Group. The U-Prove technology will be integrated in Microsoft's user-centric CardSpace identity metasystem and Windows Communication Foundation.

Stefan Brands, who ignored several previous offers, is excited about the Microsoft acquisition.

In turn, Microsoft's identity architect, Kim Cameron, is notably delighted with the acquisition.

Our goal is that Minimal Disclosure Tokens will become base features of identity platforms and products, leading to the safest possible Internet.  I don’t think the point here is ultimately to make a dollar.  It’s about building a system of identity that can withstand the ravages that the Internet will unleash. That will be worth billions.
— Kim Cameron

Kim has several blog posts related to the acquisition, which I link to and quote from here:

Microsoft to adopt Stefan Brands’ Technology (6 March 2008)

In my view... U-Prove is the equivalent in the privacy world of RSA in the security space. It does things we wouldn’t have otherwise thought possible.  At one time “public key” was considered an oxymoron - but the properties of RSA were so compelling they completely changed our thinking about keys.

The same, I think, is true of the zero knowledge proofs and “blinded signatures” Stefan has perfected. When you first hear about their capabilities, you say, “Well, that’s impossible.” But if you look into the math, it's not. It actually works.

If you are inclined to look into the math, Stephan Brands's book, Rethinking Public Key Infrastructures and Digital Certificates; Building in Privacy (MIT Press, 2000, ISBN 0-262-02491-8) is available in PDF form. Like most dense and chewy material, I do better reading my mathematics better in a dead tree format.

Know your need (6 March 2008). Need to know, know your need, need for security and privacy now.

Reactions to Credentica acquisition (9 March 2008). A reaction rodeo round-up.

Ralf Bendrath on the Credentica acquisition (9 March 2008)

Ralf Bendrath is a person who thinks about privacy deeply...

"Microsoft has acquired... Credentica. While that probably means nothing to most of you out there, it is one of the most important and promising developments in the digital identity world."

Microsoft says, “U-Prove it” (10 March 2008). Quotes Joe Wilcox at length, addressing some of Ralf Bendrath's comments.

Brendon Lynch, Microsoft Director of Privacy Strategy, helps explain what it all means.

In the great world beyond Redmond, Burton Group Identity Blog observes that Microsoft acquires Credentica, and there has been considerable press coverage by Washington Post, Network World, PC World, and eWeek's Microsoft Watch ("This is a damn, exciting acquisition." Hey, Joe, what is that comma doing there?)

I am working on getting my head around zero-knowledge proofs and minimal disclosure tokens. It is clear that I've got some deep reading ahead. Exciting times.