Ludwig Seitz Erik Rissanen Babak Sadighi Firozabadi A Classification of Delegation Schemes for Attribute Authority. 158-169 2006 conf/ifip1-7/2006 Formal Aspects in Security and Trust http://dx.doi.org/10.1007/978-3-540-75227-1_11 db/conf/ifip1-7/fast2006.html#SeitzRF06