Gildas Avoine Serge Vaudenay Optimistic Fair Exchange Based on Publicly Verifiable Secret Sharing. 74-85 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3108&spage=74 2004 conf/acisp/2004 ACISP db/conf/acisp/acisp2004.html#AvoineV04