was often limited to running a diagnostic mode and replacing a complete bad unit with a spare, the defective box being sent to a depot for repair. Keys were loaded through a connector on the front panel. NSA adopted the same type of connector that the military used for field radio handsets as its fill connector. Keys were initially distributed as strips of punched paper tape that could be pulled through a hand held reader (KOI-18) connected to the fill port. Other, portable electronic fill devices (KYK-13, etc.) were available as well. Fourth generation: electronic key distribution Fourth generation systems (1990s) use more commercial packaging and electronic key distribution. Integrated circuit technology allowed backward compatibility with third generation systems. Security tokens, such as the KSD-64 crypto ignition key (CIK) were introduced. Secret splitting technology allows encryptors and CIKs to be treated as unclassified when they were separated. Later the Fortezza card, originally introduced as part of the controversial Clipper chip proposal, were employed as tokens. Cryptoperiods were much longer, at least as far as the user was concerned. Users of secure telephones like the STU-III only have to call a special phone number once a year to have their encryption updated. Public key methods (FIREFLY) were introduced for electronic key management (EKMS). Keys could now be generated by individual commands instead of coming from NSA by courier. A common handheld fill device (the AN/CYZ-10) was introduced to replace the plethora of devices used to load keys on the many third generation systems that were still widely used. Encryption support was provided for commercial standards such as Ethernet, IP (originally developed by DOD's ARPA), and optical fiber multiplexing. Classified networks, such as SIPRNet (Secret Internet Protocol Router Network) and JWICS (Joint Worldwide Intelligence Communications System), were built using commercial Internet technology with secure communications links between "enclaves" where classified data was processed. Care had to be taken to ensure that there were no insecure connections between the classified networks and the public Internet. Fifth generation: network-centric systems In the twenty-first century, communication is increasingly based on computer networking. Encryption is just one aspect of protecting sensitive information on such systems, and far from the most challenging aspect. NSA's role will increasingly be to provide guidance to commercial firms designing systems for government use. HAIPE solutions are examples of this type of product (e.g., KG-245A and KG-250 ). Other agencies, particularly NIST,