Traditional　access　control　models　are　suitable　for　centralized　and　static　environments,　but　can　hardly　meet　the　requirements　of　open　and　dynamic　environments　because　subjects　and　objects　are　not　always　known　in　advance.　As　an　important　consideration　for　security,　trust　can　be　applied　to　security　management,　especially　in　access　control.　In　trust-based　access　control,　mapping　between　trust　values　and　access　permissions　is　an　important　issue.　In　this　paper,　we　present　a　trust　quantification　algorithm　based　on　grey　fuzzy　theory　and　propose　a　new　trust-based　dynamic　access　control　model.　In　the　model,　we　use　the　arcsine　function　to　construct　an　algorithm　to　perform　mapping　between　trust　values　and　access　permissions　for　effective　access　control.　Simulation　results　show　that　our　model　is　suitable　for　access　control　in　open　and　dynamic　environments　with　a　high　degree　of　scalability.　©　2010　Binary　Information　Press.