Antonio Elio “Cipher” and his Polyphonic-Syllabic Cipher

Abstract

Antonio Elio (Helius) (1506–1576) was a Roman Catholic prelate who served as Bishop of Capodistria and Pola and Titular Patriarch of Jerusalem. Also a prolific cryptographer in the service of Pope Paul III, he is credited for the invention of polyphonic ciphers. In this article, we provide an overview of his career and work in cryptography and describe an ingenious polyphonic-syllabic cipher he designed. Although several matching plaintext-ciphertext segments were available, reconstructing the cipher key required a significant and unusual amount of time, underscoring the cipher’s high level of security. Ciphertext-only cryptanalysis for such a cipher would be extremely difficult and nearly impossible, even with modern computing, without prior knowledge of the principles of its complex design.