Current　key　management　schemes　only　consider　the　security　of　newly　deployed　nodes　in　wireless　sensor　networks,　whereas　the　security　of　mobile　nodes　is　ignored.　In　order　to　ensure　data　transfer　secure　in　node　mobility　scenarios,　we　propose　a　composite　security　mechanism　based　on　the　elliptic　curve　digital　signature　algorithm　to　help　nodes　in　the　mobile　scenarios　to　authenticate　their　identities　and　establish　the　pairwise　keys.　Analysis　shows　that　this　scheme　is　very　low　in　storage,　computation,　and　communication　overhead.