Hagelin Cipher Machine C-446-RT One-Time Pad
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The one-time pad was also incorporated into traditional cipher machines by the Hagelin company. They had a "pin and lug" mechanical cipher
device called the C-446 which was similar to the M-209 cipher machine they sold to the US during WW2. The C-446 used the same cryptologic
technology as the M-209, including the use of pin and lugs with 6 rotor wheels and both were based on the prior C-38 cipher device. The M-209
was introduced in 1943 and the C-446 was introduced in 1944. The main difference between the two devices was the M-209
used one paper tape roll to print either the enciphered text or the deciphered text while the C-446 had two tape rolls and could print both
enciphered and deciphered texts simultaneously. The C-446 was compatible with the C-38, the M-209, the BC-38 and the later BC-543.
The C-446 was available in a commercial gray color or a military green color. It was known to be used by the Dutch and Norwegian militaries
into the 1960s when they were replaced with the later and more powerful CX-52s. These machines were then kept in storage for several decades
for possible backup use. Since they were entirely mechanical devices, they would continue to operate even after a nuclear blast may render
other electro-mechanical cipher devices inoperable.
The C-446-RT (Random Tape) was a special version of the C-446 which did not have rotor wheels but used a paper tape reader to automatically
encipher and decipher the message. This device was not compatible with the other Hagelin cipher machines. The tape reader replaced the
function of the rotor wheels, as you can see in the picture below. The random tape was a teletype paper tape using the 5 bit Baudot code
and would advance a character at a time as the lever is depressed to encipher or decipher each character of a message.
Hagelin Cipher Machine C-446-RT on left compared to standard C-446
Photo courtesy of Paul Reuvers and CryptoMuseum.com
The random tape used for the C-446-RT was the same as the tape used for the SIGTOT teletype cipher above but the SIGTOT converted the paper
tape into electrical impulses to be XOR'ed and then sent via wired or radio connections. The C-446-RT is entirely mechanical so the paper
tape is read a letter at a time to then be XOR'ed and printed on the roll of paper tape in the C-446. There are two print reels, one for
the plaintext and the other for the ciphertext.
Compared to the SIGTOT teletype system, this is a much more manual process and similar to the use of other manually operated cipher devices.
After enciphering each letter of a message, the message would normally be sent in morse code via radio. The receiver of the message would
have a duplicate random tape set to the same starting position and then decode the message a letter at a time. After the random tape was
used once, it would be destroyed.
Hagelin made other traditional pin and lug cipher machines into random tape machines, including the CX-52-RT and CD-57-RT. Hagelin also
manufactured a traditional teletype one-time tape machines, called the T-52 and the T-55. These machines had the option of incorporating the
pin and lug of the CX-52, so it could exchange messages with the CX-52 or use the psuedo number generator of the CX-52 instead of using
random tapes. Using the T-52 or T-55 in this fashion would not be unbreakable, since this would not be true random tapes.
While the one-time pad provides a secure cipher, it also requires the use of large volumes random paper tape reels. Producing and
transporting these random tapes was cumbersome and a security threat if captured, so the use of one-time pads was limited to the most
secure messages. Both the SIGTOT Teletype cipher and the Hagelin C-446-RT are rare cipher devices. They were sold exclusively
for military use and most were destroyed instead of being made surplus and available for resale.
The SIGTOT receiving TD is a US Air Force Model 14 Teletype device, which is the first device manufactured to the specifications of the
original Vernam one-time pad patent of 1919. The Hagelin C-446-RT was used by the Dutch Navy until it was made surplus in the late 1990s,
by mistake, and removed from the surplus market after only one day. Only a few were already sold and the rest were destroyed. Some of
these devices were also given to retiring Dutch Navy personnel as mementos. Only a small number of these remaining devices are of the
special Random Tape variety.
