A system for providing communications security and authentication to a plurality of computerized devices is disclosed. In one embodiment, the system is useful with an untrusted network, and comprises security apparatus adapted to create associations with a plurality of security devices on the network. Traffic between the associated devices may be encrypted and residue-protected for e.g., data confidentiality and integrity protection. In one variant, the security apparatus of the system comprises a software entity disposed at least partly within the software stack of a host. A security card may also be used as part of the security apparatus system. The computerized devices of the system may be untrusted (e.g., have an untrusted operating system) and also be physically unsecure.