A network security apparatus adapted to provide for secure communications across data networks, including untrusted networks. In one embodiment, the security apparatus comprises one or more components disposed within the software stack of a computerized device, the components including an association process adapted to establish security associations between devices on the network, and an encryption key generation process adapted to generate one or more encryption keys. In one variant, the keys are specifically for use with temporary or ad hoc security associations. The one or more keys are exchanged according to a key exchange protocol after the device is authenticated or authenticates another device. In one implementation, the device comprises a portable device such as a laptop computer.