The Combined Cipher Machine (CCM)

Introduction

The CCM files are documents from the US Naval cryptanalytical organisation OP-20-G's study of the combined British-US cipher machine Combined Cipher Machine (CCM). Many of the documents comes from the research done by Ralph Erskine (1933–2021) and I am deeply grateful to him for sharing them with me. An idea was to write a joint article about the CCM and the cycle studies of the machine, but the article never took shape. As a tribute to Ralph and with a fond memory of our friendship, I will let him introduce the CCM:

In June 1942, in order to ensure that the United States and the United Kingdom could afford high-level protection to their naval wireless traffic, it was therefore agreed that adaptors should be designed for both SIGABA and Typex by the United States Navy to transform them into a common machine, the Combined Cipher Machine (CCM). The extremely ingenious adaptor for Typex for this purpose was designed by Commander Don Seiler, who also devised the related adaptor for SIGABA. Although the design work was completed quickly, production delays prevented the CCM from entering service, except on a few minor circuits, until late 1943. The CCM was used in November 1943 for limited communications between the Royal Navy and the United States Navy and became operational with all five British and American services in April 1944. From then on, the Germans collected material on it and made counts on Hollerith punched card machines, but made no headway. The Allies had been lucky, because the CCM had a serious flaw.

The rest of Ralph's introduction and explanation you can read here.

CCM Documents

• Messages from GCCS to SSA about the CCM, March 1945, with an Introduction to CCM by Ralph Erskine, dated October 1996.
• Letter from Ralph Erskine about CCM, dated 2 October 1996.
• OP-20-G Report "Analysis of CCM keys", unknown author, unknown date
• OP-20-G Report "The Period of the CCM", unknown author, 17 April 1944
• OP-20-G Report "Termination of researches on CCM at Arlington Hall", by Lt. A.H. Clifford, 24 July 1944
• OP-20-G Report "Effect of Cross-Tie on Period of CCM", unknown author, 16 May 1944
• CSP 1100(C), Operating Instructions for ECM Mark 2 (CSP 888/889) and CCM Mark 1 (CSP 1600),"
  Navy Department, Washington, D.C., 16 May 1944

The wartime CCM carried on being used in the postwar era and ended up being distributed to most NATO countries as their high-level cryptographic system. CCM was physically, as explained above, two machines, the British Typex with a CCM adaptor and the SIGABA with a CCM rotor basket. The Typex version was CCM Mark III, carrying the British designation BID/08/3A. The SIGABA version was CCM Mark II, and the US designation was SIGROD or CSP 1700. SIGROD was the Army version of the Navy machine CSP 1700 and during the development phase it was called MX-783/U. Later, under a new procedure, the short titles, formerly beginning with SIG (e.g. SIGROD, SIGABA) then began with ASA (e.g. ASAM-5, ASAM-1) and SIGROD became ASAM 5. These CCM machines were known as the crypto system AJAX, a code name introduced in October 1950. On 1 October 1952, the machines were modified and became the crypto system HERMES, as explained here. After the HERMES modification, the CCM Mark III received the BID/08/3D designation. For the CCM Mark II, the Navy machine CSP 1700 changed to AFSAM 25 and the Army machine SIGROD changed to AFSAM 25B. Ultimately, in the modification for LUCIFER operation, the CCM Mark II machines became AFSAM 25B and AFSAM 25C, and the CCM Mark III became BID/08/6 and BID/08/3D. LUCIFER went into operation on 1 May 1953. From then on, the CCM machines could be used for both HERMES and LUCIFER operations.

The CCM machines were eventually replaced in NATO by the machine AFSAM 7 (codename ADONIS), later renamed to TSEC/KL-7, and AFSAM 47 (BRUTUS), which later, in the version AFSAM 47B, became KL-47. BRUTUS was a 7-rotor cipher machine with a complex stepping of the rotor maze where two of the rotors, rotors four and six, stepped backwards. The machine was known as BCM (Backward Combined Cipher Machine) during the development phase and carried the US Navy designation CSP 4800. The details are given here. Similar machines developed at the same were PCM (CSP 4700) and the 12-pinwheel type Hagelin machine MCM (CSP 3600). An overview of these machines can be found here. To get an idea of the development of cipher machines in the UK and USA during this period, the following document, "First Report of Subcommittee B to the BRUSA COMSEC Conference", is worth studying. Another report that it is worth reading is Donald W. Seiler's History of U.S. Naval Code and Signal Laboratory.

Post-War Documents

• Conference on CCM Modification at Arlington Hall on 12 February 1948
• History of U.S. Naval Code and Signal Laboratory, by Donald W. Seiler, 12 August 1950
• Replacement of the CCM by BRUTUS and Improvements to the Existing CCM, 11 July 1951
• Status of NATO Crypto Systems with CCM Dates, 28 April 1953
• Operating Instructions for CCM, Short Title: SIGDUBN-1, 13 March 1945
• SG-7-40, Provision of a General High-Grade Cypher System for NATO, 21 June 1951
• SGM-980-51, Provision of a General High-Grade Cypher System for NATO, 22 June 1951
• SGM-1922-51, CCM Systems for NATO, 10 November 1951
• SG-171-4, Plan for the Employment of the Combined Cipher Machine, 18 August 1952
• SGM-301-53, Status of CCM Cryptosystems, 2 March 1953
• SG-171-10, Distribution of the Combined Cipher Machine (CCM), 16 March 1953

Copyright:

This work is licensed under a
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
The material described on these pages is created, collected, edited and published
by Frode Weierud, © January 2025

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