The secret code of Antonio Pimentel de Prado, the Spanish ambassador in Sweden in the first half of the 17th century
During the Thirty Years’ War (1618–1648) Sweden became a European power. With the use of political, diplomatic and military means Sweden arrived to take control over the coast of the Baltic Sea. Since it was a Lutheran country, Sweden controlled the actions of Protestant countries which, at that time, were fighting Catholic countries. Due to the mentioned reasons Sweden aroused the interest of Spain ruled by the Habsburgs. During the 1650s Antonio Pimentel de Prado was the ambassador of Spain in Stockholm. In his encrypted correspondence with Madrid he used the key, which has not been preserved until today. The reconstruction of that key was possible thanks to the comparison of the encoded and decoded letters. This text discusses the methods of reconstructing the encoding matrices of Spanish diplomacy from the 17th century, in particular Antonio Pimentel de Prado’s key.