A system adapted to provide communication security between computerized devices in, for example, an ad hoc or temporary networked environment. In one embodiment, the network comprises an untrusted network, and the system includes network security apparatus adapted to create security associations between devices on the network, including mutual authentication. Traffic between the associated devices may be encrypted for e.g., data confidentiality and integrity protection. In one variant, the network security apparatus comprises a software entity disposed at least partly within the software stack of the devices. The associated devices may be for example fixed or portable, and may be untrusted (e.g., have an untrusted operating system).