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August 4, 2011

Who invented the one-time pad?

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It's long been believed to have been invented during World War I by AT&T engineer Gilbert Vernam and Joseph Mauborgne, later chief of the Army Signal Corps.

Now comes a chance discovery that takes the origin of the mighty cipher back 35 years into the late nineteenth century.

Below, excerpts from John Markoff's July 25, 2011 New York Times story about the serendipitous convergence of the right person in the right place at the right time that led to the remarkable unearthing of a metaphorically buried treasure.

If not for a computer scientist's hobby of collecting old telegraph codebooks, a crucial chapter in modern cryptography might have been lost to history.

The collector is Steven M. Bellovin, a professor of computer science at the Columbia University School of Engineering and a former computer security researcher at AT&T Bell Laboratories. On a recent trip to Washington he found himself with a free afternoon and decided to spend it at the Library of Congress, looking for codebooks that weren't in his collection.

But when Dr. Bellovin hunted though the card catalog, his interest was piqued by an 1882 codebook whose title included the word "secrecy."

"I thought, 'O.K., let me go see how they did it,' " he recalled. "When I read the two-page preface, my jaw dropped."

He could plainly see that the document described a technique called the one-time pad fully 35 years before its supposed invention during World War I by Gilbert Vernam, an AT&T engineer, and Joseph Mauborgne, later chief of the Army Signal Corps.

Although not widely used today because it is relatively difficult to work with, the one-time pad is still viewed as one of strongest ways to encrypt a communication. The technique is distinguished by the use of a random key, shared by both parties, to encode the message and decode it; the key must be used only once and then securely disposed of.

It was the Soviet Union’s misuse of the technique — code clerks were occasionally reusing the one-time pads instead of discarding them — that led to the Venona project, the collaboration between the United States and British intelligence services that yielded code-cracking coups during World War II and the cold war.

The 1882 monograph that Dr. Bellovin stumbled across in the Library of Congress was "Telegraphic Code to Insure Privacy and Secrecy in the Transmission of Telegrams," by Frank Miller, a successful banker in Sacramento who later became a trustee of Stanford University. In Miller's preface, the key points jumped off the page:

"A banker in the West should prepare a list of irregular numbers to be called 'shift numbers,' "he wrote. "The difference between such numbers must not be regular. When a shift-number has been applied, or used, it must be erased from the list and not be used again."

That sent the astonished Dr. Bellovin to the Internet to try to find out whether Mr. Miller’s innovation was known to the later inventors.

The results of his largely online detective work can be found in the July issue of the journal Cryptologia. Born in Milwaukee in 1842, Mr. Miller attended Yale and then joined the Union Army, where he fought at Antietam and was wounded at the Second Battle of Bull Run.

He was transferred to the Army inspector general's office, where he became a member of a squad of detectives investigating Lincoln’s assassination — perhaps his first contact with cryptanalysis, Dr. Bellovin speculates.

According to several independent specialists in cryptography, Mr. Miller was undoubtedly the first to propose the concept of the one-time pad.

Dr. Bellovin found no evidence that either Mr. Vernam or Mr. Mauborgne ever met Mr. Miller, but he did uncover one more tantalizing clue — in the society pages of The San Francisco Chronicle, of all places. At a military ball at the Presidio in 1907, Mr. Miller met Parker Hitt, a cryptographer who was a student and colleague of Mr. Mauborgne's.

"It is quite certain that if Hitt knew of Miller's system," Dr. Bellovin writes, "he would have shared that knowledge with Mauborgne when they were together at the Army Signal School in Fort Leavenworth." But as he acknowledges, that is still a big "if."

Read Bellovin's Cryptologia paper here.

Generate your own one-time pad here.

August 4, 2011 at 02:01 PM | Permalink


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