Prey to a Privateer. Two Portuguese Ciphertexts from 1649


  • Jörgen Dinnissen
  • Hugo Araújo



Dutch Brazil, Portuguese Brazil, short-distance communication, long-distance communication, Dutch privateers, letterbooks, ciphers in Portuguese history, monoalphabetic substitution cipher, homophonic substitution cipher, Jewish cryptology specialists


The deciphered ciphertexts from the former governor-general of Brazil, António Teles da Silva, reveal two letters from him to the king of Portugal from 1649, while he was a prisoner. The letters were written in Portuguese and found on a Luso-Brazilian ship captured by a Dutch privateer, from the Brasilse Directie Middelburg, before the coast of Brazil. These letters were already known as plaintext letters in the National Archives, The Hague. We were able to relate the ciphertexts to the plaintexts and translations. This paper shows that the revealed strategic military information and state secrets made no impact on the superiors of the Dutch company, the Gentlemen XIX, in The Netherlands. It also shows that ciphers were provided from 1638 onwards in Portuguese Brazil. Based on the surviving sources, ciphertexts were used by the Portuguese mainly after the Dutch structurally threatened their communication. They became frequent in short-distance communication (on land) after the revolt of the sugar planters in 1645. In long-distance communication, over the seas, after the Dutch privateers compromised the Portuguese shipping between 1647 and 1648.