References
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- Hamer, D. H. 1997. Enigma: Actions involved in the “double stepping” of the middle rotor. Cryptologia 21(1):47–50. doi:10.1080/0161-119791885779.
- Herslow, C. 1946. Moskva–Berlin–Warszawa (in Swedish). Stockholm: Fritzes.
- Quirantes, A. 2004. Model Z: A numbers-only Enigma version. Cryptologia 28(2):153–56. doi:10.1080/0161-110491892845.
- TICOM. 1945. Enigma document from Heimsoeth & Rinke. Bestand Rückgabe TICOM, Politisches Archiv des Auswärtigen Amts. Berlin. Archive Signature: T1717.
- TICOM. 1946. European axis signal intelligence in World War II as revealed by “TICOM” investigations. Vol. 1. www.nsa.gov (accessed May 2015).