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The KL-7,
codenamed ADONIS or POLLUX, is an off-line rotor
cipher machine that was developed in the late
1940's by the American National Security Agency
(NSA) as a successor of the SIGABA. The machine
entered service in 1952. ADONIS and POLLUX were
two different encryption procedures for the KL-7.
The American ADONIS procedure applied an
encrypted message key to preset the initial
startposition of the rotors, whereas the
‘export version’ POLLUX procedure used
far less secure non-encrypted message keys. The
KL-7 was compromised by John Walker who sold
technical information and key lists to the
Soviets. The KL-7 was used by the US and many of
its Allies and retired in 1983. Output of the KL-7 was printed on a
paper ribbon and some versions had a paper
puncher for 5-bit code output. The KL-7 has eight
rotors (the fourth from the left was stationary)
with 36 contacts each. During its service time,
the rotors were recalled and re-wired regularly.
The rotors are placed in a rotor basket, called
KLK-7 which can be removed from the machine base
KLB-7. Each rotor is placed in a plastic outer
ring with cams. Microswitches, controlled by
these cams, engage electro-magnets which in turn
step the rotors. This resulted in a highly
irregular stepping of the rotors. The 26 inputs
and outputs of the rotor basket are used to
encrypt the letters. The 10 remaining inputs and
outputs are looped back through the rotors,
resulting in a very complex signal path for the
26 letters. The machine was non-reciprocal. This
was achieved by a sliding permutor board
underneath the keyboard which swapped all input
and output contacts of the rotor encryption. The
exact details about rotor and stepping unit
wiring are still unknown. Today, all publicly
availably machines, such as this machine from the
Royal Dutch Signals Museum, are carefully
sanitized and stripped of any wiring, related to
the rotors and stepping unit.
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