The Combined Cipher Machine (CCM) (or Combined Cypher Machine) was a common cipher

Cipher

In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...

 machine system for securing Allied communications during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 and for a few years after amongst NATO. The British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 Typex

Typex

In the history of cryptography, Typex machines were British cipher machines used from 1937. It was an adaptation of the commercial German Enigma with a number of enhancements that greatly increased its security....

 machine and the US

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 ECM Mark II were both modified so that they were interoperable.

The British had shown their main cipher machine — Typex — to the US on their entry into the war, but the Americans were reluctant to share their machine, the 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. 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.

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 23 was a later model of Typex adapted for use with the Combined Cipher Machine.

Security

While Allied codebreakers had much success reading the equivalent German machine, the Enigma, their German counterparts, although performing some initial analysis, had no success with the CCM.

However, there were security problems with the CCM. In one case, it was discovered that certain rotor combinations produced a dangerously short period of 338, and that the rotor wiring could have been recovered from an actual 1,000-group message that had been sent using the machine.

In 1952, a later version of CCM, "Ajax", was also found to have security problems.