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I love to read about Thomas Jefferson & Lewis & Clark- just found this, about a letter where TJ explains to ML what to do if they need to secretly communicate.

thought some might find this helpful. also think it shows just how smart (autist;) Thomas Jefferson was,

and how important secret codes were.

https://founders.archives.gov/documents/Jefferson/01-40-02-0220-0001

"The tableau-style cipher system that Jefferson drew up for Lewis dated from the sixteenth century (Weber, United States Diplomatic Codes, 10–12; David Kahn, The Codebreakers: The Story of Secret Writing, rev. ed. [New York, 1996], 133–7, 145–51).

The letters of the alphabet appear in order in each row, but the position of the letters shifts from row to row. (Jefferson included the ampersand as, in effect, a 27th letter of the alphabet.) In his first trial of the cipher, at the top of the grid he numbered the columns, leaving the one on the far left unnumbered (see Document i). The user would work through the intended message letter by letter, finding the first letter in the column on the left and reading across to the column numbered “1,” then finding the second letter in the left column and reading across to column 2, and so on. On reaching the 27th letter of the message, the user would begin again with column 1.

Jefferson experimentally encrypted a passage that was 27 letters long, “the man whose mind on virtue bent,” to get the result “ujh qft epxbp yvas dd maknpa zcmu.” He followed that exercise with a brief set of directions. He revised the instructions to incorporate the usage of a key word, a device that was, like the form of the cipher itself, well established (Kahn, Codebreakers, 148). Now instead of finding the numbered column to match the letter’s position in the message, he decided on a key word—“artichoke”—and aligned the letters of the message to be encoded with the letters of the key, repeating the key word as many times as necessary to complete the message."