Gene Itkis Peng Xie Generalized Key-Evolving Signature Schemes or How to Foil an Armed Adversary. 151-168 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2846&spage=151 2003 conf/acns/2003 ACNS db/conf/acns/acns2003.html#ItkisX03