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TURN Spycraft Handbook — Codebooks

The codebook Ben Tallmadge has delivered to Abe Woodhull in Episode 107, “Mercy Moment Murder Measure” represents an important chapter in the history of cryptography. Inventing a workable code to encipher correspondence and transmit secret messages was a very tall order for Ben as a neophyte intelligence chief. One of the disadvantages of being so new to his job was that there were no instruction manuals or rulebooks for Tallmadge to follow — instead, he had to create on the fly. Smartly, he opted for a simple code key that would be easy for an agent to use and decode.

Tallmadge’s codebook had roots in the earliest incarnations of cryptography dating back to the 16th century. The Ave Maria cipher was created by Johannes Trithemius, a young priest and the author of the 1518 book Polygraphiae, the first book on the subject of cryptography. The cipher had its roots in the masking of information in Latin phrases and prayers. Trithemius, like many men of the cloth at the time, had superb abilities to translate Hebrew, Greek and Latin, which proved useful in creating the cipher. A sender would substitute a corresponding word for each letter of the text to form a coherent prayer, thus hiding the secret message. While Trithemius’ cipher was clever, it was laborious to use an entire word to replace a single letter.

New ground in coding would be broken in the 17th and 18th centuries. French cryptographer Antoine Rossignol mastered a system of coding that used a two-part nomenclator with one basic principle: turning words into numbers. Years later, this would become the springboard for what is known as a “stream cipher,” where the encrypter and the decrypter share the same text for their correspondence. Using the stream cipher as a foundation, Tallmadge decided to make some changes to the codebook he was creating for his young, inexperienced agent. He opted for the simpler one-part nomenclator and decided to use a readily available tome as the sourcebook. The 1777 London edition of Entick’s Spelling Dictionary became the touchstone for enciphering all secret correspondence. The Culper Cipher was born.

Tallmadge selected 710 words, as he zeroed in on the terms he thought would be most useful. Works like “county,” “artillery,” “troops” and so forth were written alphabetically in the left hand column of the dictionary and numbered consecutively. The title of Episode 107, “Mercy Moment Murder Measure,” was derived directly form the the codebook, with those words given the numbers 385 to 388, respectively.

Tallmadge also added 53 numbers running from 711 to 763 to represent proper names, including the names of his agents, important figures, and places they encountered. Long Island was 728, New York was 727, General Washington was 711 and the key agent operative, Samuel Culper, was 722. The correspondence looked like a string of words and numbers jumbled together, making it very difficult to decode. While not the most complex code, it did the most important job, which was to keep hidden messages hidden.

The codebook Ben Tallmadge created was simple, elegant, and essential to the work of the Culper Ring. In the espionage world of the time, it was cutting-edge spycraft. The cryptography that the ring pioneered would later become a pillar of numerical coding, which is still used in the spycraft trade today.

Read TURN: Washington’s Spies Spycraft Handbook — Ghost Messages >>

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