The　surging　interest　in　cryptocurrency　has　revitalized　the　research　for　digital　signature　schemes　with　strong　security.　In　particular,　signature　schemes　are　investigated　to　resist　the　malleability　attacks　in　cryptocurrency　platforms.　However,　existing　signature　schemes　only　conquer　partial　malleability　attacks　due　to　various　sources　of　attacks.　Other　solutions　of　new　transaction　realizations　cannot　simultaneously　avoid　the　malleability　attacks　on　both　standard　and　contract　transactions.　Furthermore,　the　malleability　attack　becomes　more　stubborn　in　fast　clearing　applications.　In　this　paper,　we　propose　SigNT,　an　accessional　signature　scheme　with　unmalleable　transaction　implementations.　The　key　of　SigNT　is　an　improved　interactive　signature　scheme　for　securely　instant　confirmation　of　transactions.　Unlike　standard　signatures,　this　signature　is　generated　by　the　owner　and　block　producers.　Combining　it　with　several　other　optimizations　(i.e.,　hash　execution　of　intermediate　transactions　and　secret-based　claiming　conditions),　SigNT　achieves　complete　resistance　against　malleability　attacks　in　both　the　standard　and　contract　transactions.　As　an　example,　we　show　an　implementation　in　Bitcoin　with　the　＇providing　a　deposit＇　protocol.　The　security　analysis　and　comparative　experiments　demonstrate　that　SigNT　has　the　best　resistance　against　malleability　attacks　than　previous　malleability　solutions.　Besides,　better　performance　is　achieved　than　other　schemes.　©　2005-2012　IEEE.