This thesis deals with the question of the nature of international humanitarian law (IHL) as a permissive or restrictive regime. It is often said that the primary purpose of IHL is to place restrictions on the actions of parties to armed conflicts, and to impose obligations on them in order to protect the victims thereof. Nevertheless, IHL is also increasingly used to claim the existence of an authority to resort to certain conducts that would be deemed unlawful during peace time. Using deontic logic and the function of public international law, the thesis determines that IHL initially developed as a restrictive regime, which nevertheless contains some rare strong permissions granting States an authorization to act. It also applies this general result to the more specific questions of the existence of an authority to intern and an authority to target persons, during both international and non-international armed conflict.