University Times

A cryptographic device conceived by Gottfried Leibniz in the 1670s but never built, has been constructed based on the philosopher/ mathematician’s writings.

Nicholas Rescher

Pitt faculty member Nicholas Rescher, Distinguished University Professor of Philosophy, oversaw the production of a working model of Leibniz’s machina deciphratoria, or cipher machine, built with the help of retired Pittsburgh engineer Richard Kotler, Leibniz machine expert Klaus Badur and Wolfgang Rottstedt, a German machinist who specializes in historical recreations.

The machine was unveiled last month in Hillman Library. It will be on display Feb. 1-May 1 in the library’s 3rd floor special collections room.

In conjunction with the display, the University Library System is publishing Rescher’s 2012 book, “Leibniz and Cryptography,” which will be available free online or by print-on-demand later this spring, according to a library spokesperson.

ULS director and Hillman University Librarian Rush G. Miller said, “Libraries these days are involved in many more things than collecting books — all sorts of things to expand knowledge —and this is just one more example. We are very excited to have this exhibited in the library.”

Miller said his meetings with Rescher, a Leibniz scholar who in 2010 donated his collection of philosophy materials to the University’s Archives of Scientific Philosophy and in 2011 donated to ULS a letter handwritten by Leibniz, “always have resulted in enlightening conversation, stimulating discussion and concrete results that always expand the library’s ability to meet the needs of scholars.”

Miller said, “The most interesting meeting I’ve had with him was over a year ago when he came to me to talk about this machine he had discovered in the published archive of Leibniz that he wanted to build.”

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The cipher machine was the offspring of a more complex four-function calculating machine Leibniz devised in the early 1670s.

The calculating machine “served Leibniz as an introduction card to various and sundry important agents and agencies,” Rescher said, adding that Leibniz’s demonstration before the Royal Society in London led to his election to the society. A calculating machine sent to Czar Peter the Great earned Leibniz the position of privy counselor and a request for a copy that the czar could present to the emperor of China.

Leibniz considered the cryptographic machine very topical at a time when other European nations were attempting to curtail superpower France’s expansion, but it was mentioned only in simple terms in Leibniz’s writings. “Unlike the calculating machine, which he sent forth and used as an introduction card … this cryptographic machine was to be secret,” Rescher said.

Leibniz described it twice: Once in a memorandum to John Frederick, the Duke of Hanover-Calenberg, then to Leopold I, neither of whom pursued its construction. Leibniz “would have loved to see this device,” Rescher said. “He contrived this machine mentally as a plan and never actually had it built.”

Leibniz’s cryptographic machine bore sophistication unmatched until the World War I era. “It marks an unknown but remarkable transit point in the history of cryptography because earlier on people encoded things by very simple devices, decoder-ring kinds of things: disks that could be turned against each other with letters, or slides like a slide rule that had different banks of letters up against each other,” Rescher explained.

“These were devices. These were not machines. Only the era immediately after World War I led to the creation of the cryptographic machines — and it was not until that era some 250 years later that machines of the complexity and sophistication and cryptographic security of his machine were finally realized.”

The key mechanism underlying the calculator and the cipher machine was a stepped drum, which came to be known as the Leibniz wheel.

“Unlike ordinary gears which engage each other so that one turns the other at different speeds, this one has skips. It will turn for a while and then suddenly it will skip. These skips can be programmed and it’s very useful for introducing an element of irregularity that’s very important in a cryptographic device,” Rescher explained.

The machine is operated by typing on keys marked with the letters of the alphabet. Inside are two drums: A hexagonal alphabet drum containing six slats (each with a scrambled alphabet) and a stepped drum that determines how many keystrokes it takes to make the output drum rotate and change the substitution alphabet.

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Busso von Alvensleben, Germany’s consul general in New York, who was an invited speaker at last month’s unveiling of the device, said, “Leibniz is known to the world as one of the last great scholars who commanded the entire knowledge base of that era. This extraordinarily talented man is remembered much less for his role in diplomacy, which nonetheless was a major part of his lifelong bread-and-butter job.”

Von Alvensleben comes from a family that has been involved in public service in Germany since the 12th century. His ancestors held positions in the courts of Hanover, Wolffenguettel and Berlin and, in that capacity, interacted with Leibniz himself, von Alvensleben said, noting that Leibniz used their libraries in his research and shared their interest in mediating among the diverging interests of the courts.

Leibniz’s court connections and the fact that his extensive writings were preserved helped make the reconstruction of the cipher machine possible.

Rescher said, “One thing that was known about court was that Leibniz was this sort of scriptomaniac type. He did indeed have everything recorded on paper. The other aspect of it was he knew everything that happened in or around the court,” including court scandals, Rescher said. “When Leibniz died, one of the first things that George I [who had been an elector of Hanover prior to ascending to the British throne] did was to instruct the people in Hanover to impound his archive.

“It was as a result of that that this enormous mass of paper has been preserved for posterity,” Rescher said.

In the late 19th century, scholarly academies to which Leibniz belonged began plans to publish his writings — which total more than 200,000 pieces — only to be delayed by World Wars I and II. “In the best tradition of German scholarship, one does things thoroughly, that is to say chronologically,” Rescher said. “So, year by year, as time goes on, the Leibniz edition grows.”

Rescher discovered memoranda detailing the cipher machine in notes Leibniz prepared for an audience with Holy Roman Emperor Leopold I in 1688. Virtually all that’s known about the cipher machine comes from those notes, which were published in 2001 as part of the ongoing systematic publication of Leibniz’s voluminous writings, Rescher said.

“I was interested in Leibniz’s work on cryptography and I was blown away with the fact that here suddenly was the description of this machine — I was able to get it organized, to have it reconstructed or resurrected.”

—Kimberly K. Barlow