Good cryptography is built to last.

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Dr. Smithline apparently lost some sleep over this cipher, but he cracked it.

The overall calculations necessary to solve the puzzle were fewer than 100,000, which Dr. Smithline says would be "tedious in the 19th century, but doable."
Two Centuries On, a Cryptologist Cracks a Presidential Code - WSJ.com

Interesting technique.

Good job!