Solving an Alchemical Cipher in a Shared Notebook of John and Arthur Dee


  • Richard Bean
  • Sarah Lang
  • Megan Piorko



cryptanalysis, Porta cipher, Latin, alchemy, Decknamen


This paper builds on a work in progress by Lang and Piorko published in HistoCrypt 2021, which presented a seventeenthcentury ciphertext and cipher table discovered in a shared notebook of John and Arthur Dee (Sloane MS 1902). Using Latin statistical models we have successfully deciphered the encrypted text. Our results found the plaintext to consist of 177 Latin words describing a practical experiment for the creation of the alchemical Philosophers’ Stone, presented as a chrysopoeic recipe. The encryption method is a variant of a Bellaso/Della Porta style-cipher, agreeing with the paper by Lang and Piorko. After correcting some errors in the seventeenth-century ciphertext and table it was noted that the cipherkey, 45 letters in length, forms part of the original plaintext and is also derived from an alchemical context. This article presents the transcription of the cipher table and ciphertext, the key, and the Latin plaintext, and discusses the decryption process as well as the historical context.