Maithili Narasimha Gene Tsudik Privacy-Preserving Revocation Checking with Modified CRLs. 18-33 2007 conf/europki/2007 EuroPKI http://dx.doi.org/10.1007/978-3-540-73408-6_2 db/conf/europki/europki2007.html#NarasimhaT07