A method comprising: configuring at least one of a first and a second security edge protection proxy elements (322, 312), wherein the first security edge protection proxy element of a first network is operatively coupled to the second security edge protection proxy element of a second network, to apply application layer security to one or more information elements in a received message from a network function before sending the received message to the other one of the first and second security edge protection proxy elements (322, 312); wherein the configuring comprises configuring the one of the first and second security edge protection proxy elements (322, 312) to apply different types of application layer security to different ones of the one or more information elements in the received message, characterised in that the applying different types of application layer security to different ones of the one or more information elements in the received message comprises: applying at least one of end-to-end encryption and a first type of end-to-end integrity protection to information elements of a first type; and applying a second type of end-to-end integrity protection to information elements of a second type, the second type of end-to-end integrity protection permitting verifiable modification of the information elements of the second type by one or more authorized nodes in the first network and/or second network. configuring at least one of a first and a second security edge protection proxy elements (322, 312), wherein the first security edge protection proxy element of a first network is operatively coupled to the second security edge protection proxy element of a second network, to apply application layer security to one or more information elements in a received message from a network function before sending the received message to the other one of the first and second security edge protection proxy elements (322, 312); wherein the configuring comprises configuring the one of the first and second security edge protection proxy elements (322, 312) to apply different types of application layer security to different ones of the one or more information elements in the received message, characterised in that the applying different types of application layer security to different ones of the one or more information elements in the received message comprises: applying at least one of end-to-end encryption and a first type of end-to-end integrity protection to information elements of a first type; and applying a second type of end-to-end integrity protection to information elements of a second type, the second type of end-to-end integrity protection permitting verifiable modification of the information elements of the second type by one or more authorized nodes in the first network and/or second network. applying at least one of end-to-end encryption and a first type of end-to-end integrity protection to information elements of a first type; and applying a second type of end-to-end integrity protection to information elements of a second type, the second type of end-to-end integrity protection permitting verifiable modification of the information elements of the second type by one or more authorized nodes in the first network and/or second network.