Recently,　Yang　et　al.　proposed　a　kind　of　quantum　cryptographic　schemes　based　on　secret　sharing.　The　main　idea　is　drawn　from　the　case,　where　any　n　participants　who　share　a　secret　K　can　co-operate　as　K　does.　This　process　can　be　applied　to　encryption,　authentication,　signature　and　so　on.　Unfortunately,　since　there　is　no　identity　authentication　of　the　share＇s　holder,　these　schemes　inherit　the　limitation　of　secret　sharing　in　practice.　If　some　participants　do　not　follow　the　protocol,　the　protocol　would　be　a　failure　at　last.　Moreover,　these　schemes　encounter　another　serious　attack.　Any　two　participants　can　co-operate　to　defeat　the　schemes　by　sending　different　shares　to　the　parties　unknown　to　the　distributor　of　the　secret　K,　such　that　these　parties　can　execute　the　protocol　as　well.　The　attack　proves　that　it　is　not　enough　for　quantum　cryptographic　schemes　that　only　the　secret　key　is　secure.