Steps Toward Unraveling a Vatican Cipher of the 1930s

Abstract

A handful of letters sent in the 1930s by the Berlin Nunciature to the Vatican Secretariat of State contain encrypted portions along with their clear-text versions. These Rosetta-stone-like documents enable a partial unraveling of the adopted cipher system, which has the structure of a substitution-type nomenclator.

Apparently, no cipher is used more than once and different ciphers are related through an indicator. The findings are offered as a stepping stone for the benefit of future investigators.

Keywords:

• nomenclator ciphers
• Rosetta-stone documents
• Vatican ciphers

Acknowledgments

This note could not have been written without the invaluable findings of David Kertzer and Alessandro Visani, who, with great foresight, promptly assessed their great potential. Gratefully acknowledged are also remarks of David Kertzer on the historical documentation, and insightful suggestions of David Alvarez, which significantly improved the quality of this note.

Notes

¹Department of Anthropology, Brown University, Providence, RI 02912, USA.

²Universita'di Roma, La Sapienza, Rome, Italy.

³It was only in 2006 that the full Vatican archives for the period of the papacy of Pius XI (1922–1939) were opened to scholars, although some of the German materials had been made available in 2003. Materials for the period after the death of Pius XI (February 1939) are not currently available to scholars.

⁴The hypothesis of careless practice is supported by the historical account by D. Alvarez [1, p. 124–125], according to which during WWI both plain- and cipher-text were archived, possibly for further verification, but certainly to the detriment of security.

⁵See reference [1, pp. 99–100].

Additional information

Notes on contributors

Franco P. Preparata

Franco P. Preparata is the An Wang Professor of Computer Science at Brown University. His research interests in theoretical computer science have evolved over the years from coding theory to design of algorithms, parallel computation, and computational biology. He is a student of history and the arts, and his interest in cryptography has been stimulated by the discovery of encrypted letters by historians D. Kertzer and A. Visani.