View source for Combined Cipher Machine

{{Short description|WWII-era Allied cipher system}}
[[Image:CCM-rotor-unit.jpg|thumbnail|upright=1.2|CSP 1600, the replacement stepping unit to adapt the ECM Mark II to CCM]]
The '''Combined Cipher Machine''' ('''CCM''') (or '''Combined Cypher Machine''') was a common [[cipher]] machine system for securing [[Allies of World War II|Allied]] communications during [[World War II]] and, for a few years after, by [[NATO]]. The [[United Kingdom|British]] [[Typex]] machine and the [[United States|US]] [[ECM Mark II]] were both modified so that they were interoperable.

[[Image:CCM-stepping-mechanism.jpg|thumb|upright=1.2|Stepping mechanism in the CSP 1600]]

== History ==
The British had shown their main cipher machine &mdash; Typex &mdash; to the US on their entry into the war, but the Americans were reluctant to share their machine, the [[SIGABA|ECM Mark II]]. There was a need for secure inter-Allied communications, and so a joint cipher machine adapted from both countries' systems was developed by the [[US Navy]].

== Use ==
The "Combined Cipher Machine" was approved in October 1942, and production began two months later. The requisite adapters, designed by Don Seiler, were all manufactured in the US, as Britain did not have sufficient manufacturing resources at the time. The CCM was initially used on a small scale for naval use from 1 November 1943, becoming operational on all US and UK armed services in April 1944.

The adapter to convert the ECM into the CCM was denoted the '''ASAM 5''' by the US Army (in 1949) and '''CSP 1600''' by the US Navy (the Navy referred to the entire ECM machine with CCM adapter as the '''CSP 1700'''). The adapter was a replacement rotor basket, so the ECM could be easily converted for CCM use in the field. A specially converted ECM, termed the '''CCM Mark II''', was also made available to Britain and Canada.

[[Image:Typex nocase.jpg|thumbnail|Typex Mark 23, pictured, was similar to the Mark 22, but modified for use with the Combined Cypher Machine (CCM).]]

The CCM programme cost US$6 million.

'''SIGROD''' was an implementation of the CCM which, at one point, was proposed as a replacement for the ECM Mark II (Savard and Pekelney, 1999).

[[TypeX]] Mark 23 was a later model of the [[Typex|Typex cipher machine family]] that was adapted for use with the Combined Cipher Machine.

==Security==
While Allied codebreakers had much success reading the equivalent German machine, the [[Lorenz cipher]], their German counterparts, although performing some initial analysis, had no success with the CCM.

However, there were security problems with the CCM. It was discovered that certain rotor combinations produced a dangerously short [[periodic function|period]] of 338;{{fact|date=August 2022}} a three-rotor [[Enigma machine]] had a period of 16,900.<ref name="enigma_period">{{cite journal |first=David |last=Hamer |title=Enigma: Actions Involved in the 'Double-Stepping' of the Middle Rotor |journal=Cryptologia |volume=21 |issue=1 |date=January 1997 |pages=47–50 |url=http://www.eclipse.net/~dhamer/downloads/rotorpdf.zip |archive-date=19 July 2011 |archive-url=https://web.archive.org/web/20110719081659/http://www.eclipse.net/~dhamer/downloads/rotorpdf.zip |format=zip |doi=10.1080/0161-119791885779}}</ref>  In addition, the rotor wiring could be recovered from a 1,000-group message that had been sent using the machine.{{fact|date=August 2022}}

In 1952, a later version of CCM, "Ajax", was also found to have security problems.{{fact|date=August 2022}}

==See also==
* [[KL-7]]  –  a rotor-based cipher machine used by the US in the 1950s and 1960s

==References==
{{reflist}}
* Ralph Erskine, "The Admiralty and Cipher Machines During the Second World War: Not So Stupid after All", ''Journal of Intelligence History'', 2(2) (Winter 2002).
* Ralph Erskine, "The Development of Typex", The Enigma Bulletin 2 (1997): pp69&ndash;86.
* John J. G. Savard and Richard S. Pekelney, "The ECM Mark II: Design, History and Cryptology", ''Cryptologia'', Vol 23(3), July 1999, pp211&ndash;228.
* CSP 1100(C), Operating Instructions for ECM Mark 2 (CSP 888/889) and CCM Mark 1 (CSP 1600), May 1944, [http://www.maritime.org/doc/crypto/ecm/index.htm].
* Crypto-Operating Instructions for ASAM 1, 1949, [http://www.maritime.org/ecminst.htm] {{Webarchive|url=https://web.archive.org/web/20101203152642/http://www.maritime.org/ecminst.htm |date=2010-12-03 }}.

== External links ==
* [http://www.cryptomuseum.com/crypto/usa/sigaba#ccm Combined Cipher Machine on the Crypto Museum website]  with many photographs

{{Cryptography navbox | machines}}

[[Category:Rotor machines]]
[[Category:Cryptographic hardware]]
[[Category:Encryption devices]]