CRYPTOGRAPHIC  EQUIPMENT Some  of  the  systems  in  the  previous  figures contained   cryptographic   equipment.   Cryptographic equipment is only one of a number of the elements that make  up  a  secure  communications  system.  Though several different types of on-line cryptoequipments are in use throughout the naval communications system, they are all designed to perform the same basic function: to encipher and decipher teleprinter or digital data signals. Simply  stated,  the  transmitter  accepts  a  “plain  text” teleprinter or data signal containing classified material from the classified patch panel (red). It then adds a “key,” and relays the sum as “cipher text,” or an enciphered signal. A key is a sequence of random binary bits used to initially set and periodically change permutations  in  cryptoequipment  for  decrypting electronic signals. Following this encryption, the signal is fed to the unclassified  patch  panel  (black).  Here,  it  is  patched directly to the frequency-shift keyer or the multiplex equipment of the transmitter and converted into an audio signal. The audio signal, now in a form suitable for transmission, is routed to the transmitter via the transmitter transfer switchboard. On the receive side, the signal flow is quite similar to the send side in reverse order. The receiver accepts the enciphered signal from the black patch panel and generates a key to match the one generated by the transmitter. The receiver then subtracts the key from the cipher   text   input   (which   restores   the   plaintext teleprinter or data signal). Finally, it passes the signal on to the red patch panel for dissemination to the terminal equipment for printout. For further information and operator instructions on a specific type of cryptoequipment, refer to the applicable KAO publication. AN/UCC-1 TELEGRAPH MULTIPLEX TERMINAL Because of the traffic volume handled, many ships and shore stations require multiple teleprinter circuits on  one  sideband  circuit.  The  method  for  increasing circuits on a sideband is called  multiplexing.  The  Navy uses two multiplexing techniques in communications: time division and frequency division. The AN/UCC-1 Telegraph Multiplex Terminal uses the frequency- division   technique. The  AN/UCC-1  Telegraph  Multiplex  Terminal (figure  1-8)  is  a  frequency-division  multiplexed terminal equipment for use with single-sideband (SSB) or  double-sideband  (DSB)  radio  circuits,  audio- frequency  wire  lines,  or  microwave  circuits.  The AN/UCC-1 is normally used afloat on a multichannel ship-shore full-period termination (discussed later). The following is an overview of how the AN/ UCC-1 works: At the transmitting station, the signals from the individual circuits, known as  channels,  are multiplexed  into  one  composite  signal  for transmission.   The   transmission   with   the multiplexed  channels  is  known  as  a  tone package. At the receiving station, the composite signal (tone  package)  is  demultiplexed  (separated)  into individual  signals  and  distributed  to  separate teleprinters, as required. The terminal can operate in a nondiversity, audio- frequency  diversity,  space  diversity,  or  radio-frequency diversity  mode.  Because  of  this  versatility,  the  terminal is  installed  in  various  configurations  throughout  the Navy. Each electrical equipment cabinet houses one control attenuator (right side) and up to a maximum of eight frequency-shift keyers or eight frequency-shift converters. Since  the  control  attenuator,  keyers,  and  converters are solid-state, integrated-circuit, plug-in modules, the number of channels can be varied by increasing or decreasing  the  total  number  of  modules.  Depending upon  the  number  of  modules  and  the  configuration used, the terminal can provide up to 16 narrowband channels. For example, if the terminal has keyers in the top cabinet and converters in the bottom cabinet, the system could transmit different information on eight channels. Each keyer would represent a channel on the transmit side and each converter, a channel on the receive side. Each frequency-shift keyer accepts a dc telegraph signal input from an external loop and generates the appropriate   audio-frequency   mark   and   space frequency-shift  output.  The  individual  keyers  each contain two oscillators operating on opposite sides of a center  frequency.  For  example,  in  figure  1-9,  the  center frequency of keyer number one is 425 Hz, the mark frequency is 382.5 Hz, and the space frequency is 467.5 1-8