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Clive Robinson • September 3, 2021 6:14 PM
@ ALL,
“In fact, it was arguably the most secure rotor machine ever built.”Probably not the most secure rotor machine ever built, but probably the most secure rotor machine ever put into production even if for a very very small number (The British / Canadian Rockex was after TEMPEST issues were sorted out more secure than any rotor cipher machine ever envisaged and would still be secure today).
Some have heard of the US SIGABA / ECM II Cipher Machine[1] it had some interesting features including the way stepping was done. Because of this it was considered unbreakable at the time (but is breakable today).
One feature that the US thought was unknown to others was the ability to make wheels step not just forwards but backwards as well as not rotate at all etc.
The British had a problem the stalwart Typex was long over due for a full replacment. Unfortunately the British did not have the mechanical manufacturing capability at the time[2]. It was hoped that under the BRUSA arangment, the British could use either the US SIGABA or get parts manufactured secretly in the US.
As normal the “Special Relationship” rapidly hit the rocks. The US did not want the secret of the rotor wheel steping to be known to the British so the use of SIGABA was vetoed. The resulting cludge to enable a Typex and SIGABA to inter opperate evolved and became the CCM.
So one of the greatest brains at Bletchly Gordon Welchman was called upon to design an unbreakable and future proof rotor system which he went ahead and did.
The US did not want it built, they would not be able to eves drop on it and much backwards and forwards happened. As part of it the Brirish revealed their secret of independent rotor steping that would not just do all the US had tried to keep hidden but a few tricks more (lets be honest folks such rotor behaviour is kind of obvious and it turned up in other places).
What killed Welchman’s machine in the end was the US Navy that adamantly refused under any circumstances to have it aboard their ships… Thus as a more secure replacment for the CCM it was not to be, thus it was as far as British Civil Servants were concerned pointless continuing with it’s development.
It was without doubt a beast and yes it is doubtful that it’s reliability would have been good enough.
[2] Lack of mechanical manufacturing was one of the reasons the British designed the Rockex system that used Post Office relays valve/tube electronics using standard parts and standard teleprinter readers and punches. Another issue was that the US were pushing a voice scrambler X-Ray at the British on the notion it was easy to use. However those “in the know” were not just deeply suspicious they were fairly certain that the US would be able to evesdrop on the system. So bad was the situation that Churchill who was Prime Minister had to personally authorise which system should be used abd Rockex got the nod of approval because Churchill did not trust the US in the slightest at that time.
