On May 24th, 1556, barely one year into power, Spanish Emperor Philip the Second wrote a letter to his uncle Ferdinand Ist (Emperor of the German Empire and King of Hungary) his decision to change his father Charles Vth´s ciphers, as they fell into obsolescence or were compromised. Six months later, the first Cifra General (General Cipher) of Philip the Second´s kingdom was in use.
The Cifra General was used for communications between the Emperor and his main government members abroad. We can see it as a diplomatic master cipher. The Cifra General of 1556 was addressed to:
the Princess of Portugal
the Duke of Saboya, governor of Flanders
the Viceroys of Naples, Sicily and Catalonia
the Cardinal of Trento
the Marquis of Pescara at Milan
the Cardinal of Burgos at Sena (¿Siena?)
Prince Andrea Doria
ambassadors in Rome, Venice, Genoa, France and England.
The Cifra General of 1556 is dated at Gent on November 8th, 1556 and, according to David Kahn, it was one of the finest encryption systems in its time. It is made up of three parts: a monoalphabetic (with homophones) substitution vocabulary, a list of digraphs and trigraphs, and a dictionary of common terms.
The original Cifra General is stored at the Simancas Archive, Spain. This copy comes from the book by J.P. Devos (Les chiffres de Philippe II (1555-1598) et du Despacho Universal durant le XVIIe Siecle, 1950).
Vocabulary Digraph/trigraph table Dúplices/double letters)
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