page_title: NSA encryption systems
section_title: First generation: electromechanical
hierarchical_section_title: NSA encryption systems / Five generations of NSA encryption / First generation: electromechanical
caption_attribution_description: KL-7 cipher machine on display on the HMS Belfast ship museum, London.
context_page_description: The National Security Agency took over responsibility for all U.S. Government encryption systems when it was formed in 1952. The technical details of most NSA-approved systems are still classified, but much more about its early systems have become known and its most modern systems share at least some features with commercial products.
  Rotor machines from the 1940s and 1950s were mechanical marvels. The first generation electronic systems were quirky devices with cantankerous punched card readers for loading keys and failure-prone, tricky-to-maintain vacuum tube circuitry. Late 20th century systems are just black boxes, often literally. In fact they are called blackers in NSA parlance because they convert plaintext classified signals into encrypted unclassified ciphertext signals. They typically have electrical connectors for the red signals, the black signals, electrical power, and a port for loading keys.
context_section_description: First generation NSA systems were introduced in the 1950s and were built on the legacy of NSA's World War II predecessors and used rotor machines derived from the SIGABA design for most high level encryption; for example, the KL-7. Key distribution involved distribution of paper key lists that described the rotor arrangements, to be changed each day (the cryptoperiod) at midnight, GMT. The highest level traffic was sent using one-time tape systems, including the British 5-UCO, that required vast amounts of paper tape keying material.
caption: KL-7 at NSA Museum.
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