Mira Belenkiy Jan Camenisch Melissa Chase Markulf Kohlweiss Anna Lysyanskaya Hovav Shacham Randomizable Proofs and Delegatable Anonymous Credentials. 108-125 2009 CRYPTO http://dx.doi.org/10.1007/978-3-642-03356-8_7 conf/crypto/2009 db/conf/crypto/crypto2009.html#BelenkiyCCKLS09