References
- Bauer, C. 2021. Secret history: The story of cryptology, 2nd ed. Boca Raton: CRC Press.
- Boersma, S. 2022a. Complete examples of encryption systems broken by Elizebeth Smith Friedman: 1923-1934. Cryptologia 47 (5):397–418. doi: 10.1080/01611194.2021.2023235.
- Boersma, S. 2022b. Elizebeth Smith Friedman and one example of prohibition era encryption system. Cryptologia 47 (3):227–38. doi: 10.1080/01611194.2021.2003913.
- Christensen, C. 2021. Review of codebreaking: A practical guide by Elonka Dunin and Klaus Schmeh. Cryptologia 45 (6):571–2. doi: 10.1080/01611194.2021.1873207.
- Singh, S. 1999. The code book. New York: Anchor Books.