The U-Prove SDK has the following comment: (link)

// 1: CA-RA split (a party trusted by the issuer provides the gamma value)

Given that the Gamma value (if provided) overrides the Attributes value, does that mean the issuer can be separated into two IdPs that can have dedicated purposes?


  1. One secure IdP to verify the attributes
  2. A second IdP generate the UProve token with no knowledge of the attributes

... and the only communication between the IdPs is the "gamma" value?


I try to answer your question (hope I understood it correctly, if not please let me know). I did not find the comment in the given link.

First of all in U-Prove you are able to use a blinded gamma (I guess that's what you ment). The blinded gamma comes from the Attribute Authority (AA). With this blinded gamma the Issuer is not able to see the attributes and there values which he puts into the token. But if you have this situation, the Issuer must fully trust the AA. How the blinded gamma works, please see U-Prove Collaborative Issuance Extension.

To your two examples, the gamma is calculated from the AA itself and sent to the Issuer and Prover (he gets the unblinding information too, to verify if the attributes are correct). If you want to have more than just the attributes from one AA you have to collect them somewhere before calculating the blinded gamma (I wouldnt recommend this, because this is nearly the same as

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