KL-7 (also known as ADONIS)

KL-7 (also known as ADONIS or Pollux) was a Cold War–era electromechanical cipher machine used by the U.S. National Security Agency (NSA) and NATO allies from the 1950s through the late 1970s.

Key points:

• Purpose: Secure high-level military and diplomatic communications.
• Type: Rotor-based encryption device, but more advanced than WWII-era machines like Enigma.
• Design:
  • Used eight rotors, with seven active in the cipher path and one controlling stepping.
  • Employed irregular rotor stepping, which made cryptanalysis significantly more difficult.
• Operation:
  • The message was typed in; plaintext was encoded into ciphertext by the rotating internal wiring.
  • The machine required operators to load a daily key list and rotor positions.
• Security:
  • Considered very secure for its time.
  • Remained in service until replaced by fully electronic systems such as the KL-51 in the late ’70s.