The method comprising, in a network based on a chain of individual Service Functions, SFs, that are composed to implement Network Services, NSs: assigning, at an ingress node of a network architecture, to at least one data packet received by said ingress node from the network, a unique cryptographic tag; processing said assigned unique cryptographic tag using a cryptographic function specific to each Service Function, SF; and verifying, at a given point of the network architecture, said processed unique cryptographic tag by applying a cryptographic verification function composed by the inverse functions of the cryptographic functions associated to the SFs traversed by the at least one data packet.