This paper introduces a new expressive theory of types for the higher-order π-calculus and demonstrates its applicability via two security analyses for higher-order code mobility. The new theory significantly improves our previous one presented in [55] by the use of channel dependent/existential types. New dependent types control dynamic change of process accessibility via channel passing, while existential types guarantee safe scope-extrusion in higher-order process passing. This solves an open issue in [55], leading to significant enlargement of original typability. The resulting typing system is coherently integrated with the linear/affine typing disciplines as well as state, concurrency and distribution [53, 5, 56, 22], allowing precise analysis of software behaviour with higher-order mobility. As illustration of the usage of the typed calculus, two basic security concerns for mobile computation, secrecy for data confidentiality and role-based access control for authorised resources, are analysed in a uniform type-based framework, leading to the noninterference theorem and authority-error freedom in the presence of higher-order code mobility.
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