The invention provides methods, devices (102, 110, 124, 136) and communication systems (100) for establishing end-to-end secure connections and for securely communicating data packets. Such a communication system (100) comprises a first device (124, 136), an intermediate device (110) and a second device (102). The first device (124, 136) communications via a first network (120), which is based on a first transport protocol and a first transport security protocol with the intermediate device (110). The second device (102) communications via a second network, which is based on a second transport protocol and a second transport security protocol with the intermediate device (110). The intermediate device (110) modifies packets received via first network to packets suitable for communication via the second network, and vice versa. The first device (124, 136) is able to reconstruct a header of a received packet as if the packet was sent via the second network (108) and its transport and security protocols. Further, the first device (124) is able to verify, on basis of the reconstructed header, verification fields which are generated on basis of the second transport security protocol.