Shoko Yonezawa Goichiro Hanaoka Junji Shikata Hideki Imai Traceability Schemes for Signed Documents. 257-271 2002 conf/isw/2002 ISC http://link.springer.de/link/service/series/0558/bibs/2433/24330257.htm db/conf/isw/isc2002.html#YonezawaHSI02