Way back in the early days of computers in the late 1960’s, the Department of Defense (DOD) commissioned a study on how to build a communications system that could survive a nuclear attack. Out of that study, and the many grants that followed, we now have the Internet and the DOD’s Defense Information System Network.

The Defense Information System Network (DISN) has two separate Internet Protocol Router (IPR) Networks: the Secret Internet Protocol Router Network (SIPRNET) and the Unclassified but sensitive Internet Protocol Network (NIPRNET). The SIPRNET is separated both physically and logically from other networks. Each access circuit and backbone trunk is encrypted to ensure integrity of information. SIPRNET uses several internetworking protocols including TCP/IP, FTP, Telnet, HTTP and SMTP. SIPRNET supports many important internal special programs, such as the Defense Message System (DMS), the Global Command and Control System (GCCS) and the Global Combat Support System (GCSS).

Ok, now that you have the textbook history lesson, let’s talk about specific issues that you can relate to any computer system you wish to keep secure. The SIPRNET is a closed loop system, meaning that it is completely separated from all other computer systems. This is done by using only dedicated lines - a combination of leased data lines from major international carriers such as MCI and AT&T and dedicated satellite up-links in various forms such as UHF, SHF, and EHF.

These communication lines are not only dedicated, but are encrypted using military grade hardware encryption. This means that the data signal is encrypted after leaving the computer by a separate machine loaded with a cryptographic key (commonly referred to as a black box). Hardware encryption is very different from its software counterparts, which are commonly used for financial transactions (bank ATM’s, e-commerce etc.). These keys are high level algorithms that change sometimes as often as daily, and in some situations as often as hourly. Even if you were able to crack these codes they would only be good until the key changed and you would have to start the process again. For you history buffs out there, these hardware encryption devices and the cryptographic keys were the material that John Walker was selling to the Russians in the early ’80s spy scandal.

Ok, now I know the next question you're going to ask is what about a back door, a dial-in connection. A few dial-in connections do exist within the system, but to access these you still need a hardware encryption device and the proper cryptographic key. The one most commonly used by DOD is the STU-III Telephone. With a special encryption key developed to the DOD’s standards, the STU-III is a telephone with a built in modem and encryption device used for secure voice and data transmissions. These dial-ins are rare and are very closely guarded. They are monitored for any possible problems and are mainly mail servers for high-level government types.

An issue I feel that the military addresses better than the civilian community is the use of good password discipline. This comes into play mainly on the SIPRNET. We all know how easy and how many times people have broken into the NIPRNET. Also, proper logging and intrusion detection software is very popular within the SIPRNET system. Another important lesson to learn from the SIPRNET is the use of Firewalls within the wide area network to further limit access. Even if physical access is gained to one area, it does not allow unlimited access to all other areas of the system.

Hopefully this sheds a bit of light on the mysteries surrounding this computer network. We can all learn some valuable lessons about proper security procedures from the Department of Defense.