Subject: [OAUTH-WG] Interesting paper on Anonymous Delegation

From: Lucy Lynch <[email-masked]>
Date: Thu, 10 Dec 2009 08:03:09 -0800 (PST)

may be old news to some of you...

Randomizable Proofs and Delegatable Anonymous Credentials

http://eprint.iacr.org/2008/428 or
http://cseweb.ucsd.edu/~hovav/papers/bcckls09.html

Abstract

We construct an e cient delegatable anonymous credentials system. Users can 
anonymously and unlinkably obtain credentials from any authority, delegate 
their credentials to other users, and prove possession of a credential L levels 
away from a given authority. The size of the proof (and time to compute it) is 
O(Lk), where k is the security parameter. The only other construction of 
delegatable anonymous credentials (Chase and Lysyanskaya, Crypto 2006) relies 
on general non-interactive proofs for NP-complete languages of size k (2L). We 
revise the entire approach to constructing anonymous credentials and identify 
randomizable zero-knowledge proof of knowledge systems as the key building 
block. We formally dene the notion of randomizable non-interactive 
zero-knowledge proofs, and give the rst instance of controlled rerandomization 
of non-interactive zero-knowledge proofs by a third-party. Our construction 
uses Groth-Sahai proofs (Eurocrypt 2008).

- Lucy