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Combined Cipher Machine (CCM)
Allied communication during WWII

During WWII, the Amerians and the British each used their own cipher machines for high-level communication. Whilst the Americans knew their M-209 could be broken by the Germans within a few hours, they used the highly secret SIGABA for messages at the highest level (TOP SECRET). As far as we know, SIGABA was never broken in operational context. For messages at this level, the British Government used Typex, which was in fact inspired by the German Enigma machine.

In 1943, the need for secure communication between the US and the UK began to emerge, but it appeared difficult to decide which machine had to be selected for inter-Allied communication. Although the Americans knew every aspect of the British Typex, details of their SIGABA machine were kept secret. At the initiative of the NSA it was then decided to modify both machines, in order to make them interoperable. As a result, there are now two different CCM models:

  • CCM/SIGABA
    This version is based on a modified version of the American SIGABA (ECM II) cipher machine, in which the rotor basket was swapped for an alternative one. Known as ASAM 5, CSP-1600, CSP-1700, CCM Mark I and CCM Mark II.

  • CCM/Typex
    This version, which is also known as Typex Mark 23 was basically a modified Typex Mark 22, to which an NSA-supplied rotor basket could be attached. Also known as BID/08/3 and CCM Mark III.
The conversion kits for both machines were developed and supplied by the NSA. Once converted, the machines each had five SIGABA cipher wheels, and were fully interoperable. The modified machines were used from November 1943 onwards. As far as we known CCM was never broken.

CCM/SIGABA
The SIGABA machine (ECM Mark II) was modified by removing the standard rotor basket (with 15 cipher wheels) and fitting a drop-in replacement with five cipher wheels in its place. The modified machine was known as CCM Mark I or CSP-1600, and could still be reverted to a standard SIGABA.

A later variant was CCM-only, and could not be reverted to SIGABA functionality. It was known as CCM Mark II (CSP-1700) and was used by NATO. The machine shown on the right is of this type.

 More information
  
SIGABA CCM CSP-1700

CCM/Typex
In the UK, several versions of the Typex cipher machine were used, but the most common one was the Typex Mark 22, which features two large cylindrical printers and two plug-boards. This machine is also known as BID/08/2 and was also used to emulate the Enigma cipher machine.

The Typex Mark 22 was modified in such a way that an external NSA-supplied rotor basket with five SIGABA cipher wheels could be fitted on top. In CCM mode, the standard Typex cipher wheels were bypassed and the NSA basket was actuated directly by Typex' main shaft.

The modified machine was designated BID/08/3 or Typex Mark 23 or CCM Mark III, and could still be used as a standard Typex machine.

 More information
  
Typex Mark 23

Versions
  1. CCM Mark I
    Standard SIGABA (ECM Mark II) with alternative rotor basket ASAM 5.
    Also known as CSP-1600.

  2. CCM Mark II
    Later variant with fixed 5-rotor basket. Could not be converted back to SIGABA.
    Also known as CSP-1700 and as SIGROD.

  3. CCM Mark III
    British Typex Mark 23 (BID/08/3) with NSA-supplied BID/08/3A rotor basket.
Nato and CCM
In the years following WWII, the alliance of West-European states, known as the Western Union (WU), used the remaining Typex and CCM machines for communication between the member states. The WU was dissolved into the North Atlantic Treaty Organisation (NATO) in 1949.

In the early years of the NATO, the links between NATO headquarters and the UK mainly consisted of Typex machines, whilst CCM machines were used for communication between the other member states and NATO. The following types of CCM were recognised by NATO [5]:

  • CCM Mark III - Typex
    This version is a modified British Typex BID/08/3 1 with CCM adapter BID/08/3A. These machines were distributed to the Navies of the NATO member states.

  • CCM Mark II - CSP 1700
    This is the CCM/SIGABA shown above, but unlike the CCM Mark I (which was basically a SIGABA (ECM-Mark II) with an adapter, the CSP-1700 could not be converted back to a SIGABA as the contacts and wiring for the additional wheels had been removed. These machines were distributed to the Navies of the NATO members.

  • CCM Mark II - SIGROD
    This is basically the same machine as the one above (CSP 1700) 2 , albeit with an Army designator (SIGROD) rather than a naval one (CSP 1700). These machines were distributed to the Armies and Air Forces of the NATO member states.
Although all CCM types were used by NATO until at least 1955, it was known by US and British cryptanalists as early as 1948 that the security of the CCM was rapidly declining [6]. Several improvements were suggested, such as the addition of conditional reverse wheel stepping and the development of a BRUTUS rotor basket [7], but eventually the events were overtaken by the adoption of the AFSAM-7 (later renamed KL-7 or TSEC/KL-7) by NATO and its member states.

  1. The original document [5] identifies the CCM/Typex as BID/08/6, but we believe this to be an error. BID/08/6 referes to the British Rockex machine. The Typex variant that was modified for use with the BID/08/3A adapter, was designated BID/08/3.
  2. In some literature, it is suggested that SIGROD was a different machine that was considered as a possible replacement for the SIGABA ECM-II. However, we have found no evidence to support this claim and the NATO designation CCM Mark II clearly confirms that it is basically the same machine as the CSP 1700.

References
  1. Crypto Museum, CCM/SIGABA
    Detailed information about CCM version of SIGABA. November 2012.

  2. Crypto Museum, CCM/Typex
    Detailed information about CCM version of Typex. November 2012.

  3. Wikipedia, Combined Cipher Machine
    Retrieved November 2012.

  4. Jerry Proc's crypto pages, CCM Mk II (Combined Cipher Machine)
    Retrieved November 2012.

  5. NATO, CCM Systems for NATO
    SGM-1922-51. 10 November 1951. NATO SECRET.
    Declassified by NATO on 12 October 1994 (IMSM-431-99).

  6. US Navy, Comments on Army Proposals Regarding the CCM
    10 January 1948. SECRET.
    Declassified by NSA on 20 September 2013 (EO 13526).

  7. Richard James Aldrich, Espionage, Security and Intelligence in Britain, 1945-1970
    ISBN 0-7190-4955-5 (hardback) 0-7190-4956-3 (paperback). 1998. pp. 51-53.
Further information
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Crypto Museum. Created: Saturday 12 November 2016. Last changed: Sunday, 13 November 2016 - 14:29 CET.
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