A portable computerized device useful within a network and adapted to provide communication security. In one embodiment, the network comprises an untrusted network, and the portable device comprises network security apparatus adapted to create associations with other network security devices on the network. 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 a host computer. A card-like hardware structure may also be used as part of the security apparatus. The host computer may be untrusted (e.g., have an untrusted operating system).