Coral is a machine used by various Naval Attaches. The traf-
nc is known as JNA20. It is a three bank 26 circuit tele-
phone selector machine. The stepping is strictly metric and
only 3 or the 6 possible orders or motion are used. The
pluggable sequence is the same at both ends.
The machine is stronger than the Purple cryptanalytically
because there is no six-bank, but fortunately the usage is
weak. A small setting list (15 settings per originator ex-
cept Tokyo which has 30) is in effect for a year at a time,
so that the problem of simultaneous stecker and setting re-
covery arises only rarely. This problem, which is very dif-
ficult has been handled by hand, using symmetric sequences or
other ravorable breaks.
Mike has been used to assist in sequence recovery when the
setting is known. I.C. machinery has been successful in find-
ing settings when the sequence is known. Rattler has been
equipped to handle short cribs when the sequence is known.
Jade is a machine used on a rleet operational system. The
traffic is known as JN157. It is a 5-bank 25-circuit tele-
phone selector machine. Only the first three banks step
(counting from the plain text side), and they have a strictly
metric motion using only three of the six orders of motion.
The 4th and 5th banks are only hand set.
The circuits are used doubly. There are 50 kana used, two
for each circuit, an upper and a lower case. Upper case
characters encipher as upper case; lower case encipher as
lower case. The plug board is on the cipher side only.
The system uses a small setting list, but there are a great
number of channels. Plug sequences remain in effect for 10-
The use or upper and lower case makes cribbing fairly easy.
Sequence recovery with known setting can be handled by means
similar to those for Coral. Rattler is a grenade for this
system which determines the setting for a message when the
sequence and a six-letter crib are given.