Renaissance Ciphers: Encryption and Eggshells - Queens' Old Library
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In this book on ciphers Porta, a popular Italian writer, describes Cardano’s most enduring invention, the Cardan grille. By placing the grille over paper and writing through the holes, then filling the spaces with meaningless or misleading text, the writer could hide the fact that a secret message even existed, a method called steganography.
These leaves also contain the materials to construct the most famous piece of espionage equipment from the Renaissance – the cipher wheel. The cryptographer turned the inner disc at intervals to generate an unpredictable cipher, and the recipient, provided they knew the encoder’s 'key', used their identical cipher wheel to decipher the message. That both key and wheel were required to crack the code made it an extremely secure form of cryptography. On the innermost disc, shown here, the hand of God points to the truth.
[One of two pages shown]

Author: Giambattista della Porta 
Title: De occultis literarum
  [On the concealment of letters]  (Montbeliard, 1593)
Shelfmark: S.3.26  (catalogue record)

In this book on ciphers Porta, a popular Italian writer, describes Cardano’s most enduring invention, the Cardan grille. By placing the grille over paper and writing through the holes, then filling the spaces with meaningless or misleading text, the writer could hide the fact that a secret message even existed, a method called steganography.

These leaves also contain the materials to construct the most famous piece of espionage equipment from the Renaissance – the cipher wheel. The cryptographer turned the inner disc at intervals to generate an unpredictable cipher, and the recipient, provided they knew the encoder’s 'key', used their identical cipher wheel to decipher the message. That both key and wheel were required to crack the code made it an extremely secure form of cryptography. On the innermost disc, shown here, the hand of God points to the truth.

[One of two pages shown]

Author: Giambattista della Porta
Title: De occultis literarum [On the concealment of letters] (Montbeliard, 1593)
Shelfmark: S.3.26 (catalogue record)

16th centuryS.3.26cipherswoodcuts