Friday, January 09, 2009


The SIGABA was probably the most secure rotor cipher machine during WW2. The SIGABA ECM Mark II (CSP 888/889) had three banks of five rotors each. One set of five rotors was used to encrypt the alphabet. The other two banks of rotors were used to scramble the signals that control the movement of the encryption rotors. The result is a very irregular and complex stepping of the encryption rotors. The SIGABA was a most secure machine and its message traffic has never been broken. It remained in service until the 1950's, when it was replaced by more modern systems such as the KL-7 and on-line ciphering machines.

During WW2 the US and Britain both developed a compatible cipher machine system, based on their own machines. On American side the special SIGABA CCM (Combined Cipher Machine), designated ASAM 5 by the Army and CSP-1700 by the Navy, was equipped with the CSP-1600 Typex compatible rotor cage. This machine was interoperable with the CCM version of the British Typex cipher machine. After the war, the CCM remained in service between The US, Britain and Canada, and later on within NATO.

The SIGABA was a wonderful machine that incorporated the newest developments in the field of cipher machines. Unfortunately all machines were systematically withdrawn and destructed for reasons of security. Only a hand-full most rare ECM Mark II's survived in museums and the special SIGABA CCM version is an even more endangered species. The story of the Famous German Enigma cipher machine is now widely known to the public, but regretfully the SIGABA with its far better cryptographic strength as the Enigma is only known within the world of cryptography.

More information is available on several good websites. On my Focus on Crypto Machines page you can see the rare SIGABA CCM in detail. The Crypto Museum has a fantastic page on the SIGABA. On the Pampanito website you can read all about the history of the ECM Mk II. They also published the complete SIGABA manual. More technical details are found on John Savard's website. Jerry proc provides more military information on both the SIGABA ECM Mk II and the CCM version. Finally, you can also read the Cryptologia article on SIGABA

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