Microsoft released a preview of the U-Prove cryptographic technology at this year’s RSA Conference. As part of the preview, Microsoft has released a C# reference implementation to allow testing/learning about this new technology.
The C# SDK can be found at : http://code.msdn.microsoft.com/uprovesdkcsharp
The CTP information can be found at: https://connect.microsoft.com/content/content.aspx?contentid=12505&siteid=642
The spec details can be found at: https://connect.microsoft.com/site642/Downloads/DownloadDetails.aspx?DownloadID=26953
This looks like an early CTP release that Microsoft is using to discover what the security community as a whole thinks about U-Prove and I am sure the SDK and the specs will change quite a bit. I am not sure what the road map for U-Prove and hence dont know what the time line looks towards a full-fledged release of the technology.