Review of The SIGABA/ECM II Cipher Machine: “A Beautiful Idea” by Timothy J. Mucklow

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Notes

¹Friedman wrote a two-part report, “Analysis of a Mechanico-Electrical Cryptograph.” Part II is available online from the Friedman collection (https://www.nsa.gov/public_info/_files/friedmanDocuments/PatentandEquipmentRecords/FOLDER_102/41709409074875.pdf).

²The quote is from a 3 April 1934 letter from Friedman to the Patent Office, which was written when Friedman was attempting to patent his idea for using an externally generated key to step rotors.

³Teletype machines used the five-level Baudot code, each level being a hole or no hole.

⁴The quote is from Rowlett’s oral history interviews: #OH-1974-01 through OH-1974-12, Center for Cryptologic History.

⁵An endnote gives references that suggest that the Navy found plugboards inconvenient to use, that the Navy recognized that plugboards had not prevented solutions of other cipher machines, and that rotors offered more stepping combinations than plugboards.

⁶The quote is from Rowlett’s oral history interviews: #OH-1974-01 through OH-1974-12, Center for Cryptologic History.

⁷The appendix contains images of pp. 5–9 of “Crypto-Operating Instructions for Converter M-134-C.” (M-134-C was another Army designation for SIGABA.) Unfortunately, page 9 ends as the instructions just begin to describe the 26–30 check for the “correctness of the daily rotor arrangement and index alignment and the stepping of the stepping control and alphabet rotors.” That check was performed by zeroizing the machine and typing a string of 30 a’s. If the machine were set correctly, the last five encipherments of the letter a (encipherments 26 through 30) should be as listed in the key list.