Kouichi Itoh Tetsuya Izu Wakaha Ogata Takeshi Shimoyama Masahiko Takenaka Forgery Attacks on Time-Stamp, Signed PDF and X.509 Certificate. 67-75 2009 92-A IEICE Transactions 1 http://search.ieice.org/bin/summary.php?id=e92-a_1_67&category=A&year=2009&lang=E&abst= db/journals/ieicet/ieicet92a.html#ItohIOST09