The US government relies on its National Security Agent (NSA) for ensuring the security of its communication and information systems. NSA worries about confidentiality and authentication of any messages sent over government networks. NSA algorithms are usually classified, especially those algorithms used to protect classified information. The HAIPE encryption mentioned in this chapter is sometimes referred to as Type I encryption by the NSA. In 2003, the NSA took a major step (the first in its history) of publishing the Skipjack and AES algorithms, categorized as Type I encryption.
The NSA created many security techniques for computer networking, including link encryption, key management, and access of encrypted communications. They also ensured the compatibility between defense and commercial networks, while also establishing compatibility with communications of US allies (such as NATO countries).
For over 60 years, the NSA has been developing encryption systems, starting with electromechanical systems introduced in the 1950s. These were built on the legacy of World War II systems (built by the NSA) that used rotor machines for encryption. These systems used distribution paper key lists, that changed daily, which described to the operator how to manage the rotor (changed every day).
With the use of vacuum tubes came a new generation of electronic encryption systems that used logic or algorithms based on feedback shift registers. Encryption keys were ...