Cryptographic Practices within Jacobite Diplomatic Networks (1715–1745): A Typology of Ciphers and Keys in Wartime

Abstract

This paper examines cryptographic practices within Jacobite diplomatic networks between 1715 and 1745 through the systematic analysis of a corpus of 57 cipher keys among the 318 ones preserved in the Stuart Papers. While Jacobite correspondence has been studied from political perspectives, the cipher keys themselves have rarely been considered as historical objects deserving systematic analysis. Focusing on periods of intense military and diplomatic activity, this study investigates the structure, typology, and circulation of cipher keys used by James Francis Edward Stuart and his agents across Europe. This article proposes a typology based on the combination of cryptographic features observed in the corpus and hybrid systems. A frequency-based analysis highlights recurrent patterns in key design and reveals a strong preference for hybrid systems combining jargon with monoalphabetic or homophonic substitution. The results show no clear correlation between the complexity of a cipher key and the status of the correspondents involved, suggesting that pragmatic constraints, such as usability, availability, and key reuse, played a decisive role in cryptographic choices. By foregrounding cipher keys as artefacts of communication, this study contributes to a better understanding of early modern cryptographic practices and sheds new light on the operational dynamics of Jacobite diplomatic networks during wartime.