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Technology

#68: Computer Program Cracks Cipher That Stumped Thomas Jefferson

A twist and some dummy letters camouflaged words that Jefferson would have easily recognized: the Preamble to the Declaration.

By Stephen OrnesDecember 26, 2009 6:00 AM

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In 1801 American mathematician Robert Patterson sent a letter containing an encrypted message to Thomas Jefferson. The president never figured it out, but this past March, mathematician Lawren Smithline of the Center for Communications Research in Princeton, New Jersey, finally cracked the code.

Patterson and Jefferson shared an interest in cryptography. In his letter, Patterson wrote that he had devised the perfect cipher: simple, yet impossible to break without the key. It entailed writing a message in vertical columns on a grid, scrambling the grid’s horizontal rows, and then inserting nonsense letters at the start of each row. The key consisted of numbers listing the proper order of the rows and the number of nonsense letters in each. Patterson claimed that his message would stump humanity “to the end of time.”

Smithline took on the challenge, writing a computer program to test different arrangements of rows and various quantities of nonsense letters, and zeroing in on options that produced the most promising two-letter pairs. Pairs like “qu” and “nt” suggested he was on the right track, while combinations that produced impossible neighbors like “vj” and “dx” were rejected. After a week, he exposed the mystery message as words that Jefferson would have easily recognized: the Preamble to the Declaration of Independence.

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