Marcin Gomulkiewicz Marek Klonowski Miroslaw Kutylowski Onions Based on Universal Re-encryption - Anonymous Communication Immune Against Repetitive Attack. 400-410 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3325&spage=400 2004 conf/wisa/2004 WISA db/conf/wisa/wisa2004.html#GomulkiewiczKK04