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Belligerents: Choose Your Code Machines
Down through military and diplomatic history, where there has been an adversary there has been cryptology. It is a two-sided art. On one side are the methods used to prevent communications with colleagues and allies from being read by rivals. On the other are the technologies for penetrating shielded messages and extracting their meaning for information that can provide an advantage in acting against the opposition.
Historians of cryptology, such as David Kahn, can trace the beginnings of this art back to some of the earliest civilizations of recorded history, including the ancient Egyptians, Mesopotamians, Babylonians, Hebrews, Greeks, and Romans. The Greek Herodotus tells us, as a celebrated example, how a Spartan, Demaratus, scratched on a wooden tablet the letters warning the Greek nations that the Persians under Xerxes were about to invade and then covered the letters with wax in order to conceal them from guards along the way. So alerted, the Greeks beat off the Persians and ended the threat of conquest.
In those early days, the simplest encoding was enough to throw off would-be codebreakers. The most-used systems were ciphers, in which the original letters of a message—its plaintext—were transposed or replaced by other letters. One of Julius Caesar's ciphers, as an instance, consisted of substituting plaintext letters with those that were three places farther along in the Roman alphabetic sequence. Even that was too complicated for his great-nephew Augustus, the first emperor of Rome, who simply substituted the very next letter in the alphabet. Use of these single-alphabet—or monoalphabetic—ciphers could convert the plaintext order attack into the meaningless jumble taktac by the transposition of letters, or buubdl by applying Augustus's substitution method.
Over time, a second type of cryptographic system that came into widespread use was that of codes. For key words he wanted to communicate, the code-maker would create lists of unintelligible equivalents—letters, numbers or symbols—and assemble them in codebooks to be held both by senders and receivers. To signal attack the sender would look up the equivalent—1502, say—in his book. The receiver would, in turn, track down that number in his codebook, read its plaintext meaning and know what his commander was ordered to do.
Those primitive types of codes were easy prey for cryptanalysts who discovered the technique of frequency analysis. By counting the number of times a given letter appeared in a message, the analyst could take a good guess that the most frequently used code letter stood for the most common plaintext letter in a given language—e, in English for example—and thus gain a lever for opening up the remainder of the plaintext.
It was essential that codemakers come up with new ways to outwit the cryptanalysts. One way to foil frequency analysis was to treat the consonants of a code alphabet as usual, but to add several different variants for e and each of the other vowels. An even better system was invented by Leon Battista Alberti, a Florentine born in 1404. Alberti developed a cipher disk, with the plaintext alphabet on the outer ring and a cipher alphabet on the inner ring. By prearrangement between sender and receiver, the sender would set his cipher ring at, say, G under the plaintext A and encode several words. But then he would turn the cipher ring so that Y would fall under A. In effect he would bring a whole new cipher alphabet into play. With other shifts, he would employ additional alphabets. This was the start of the multi-alphabet, or polyalphabetic, substitution system that, in ever more advanced forms, remained a cryptographer's mainstay for centuries.
So it went, down through the ages. In medieval England, both Roger Bacon and Geoffrey Chaucer were ardent users of cryptography. During the Renaissance, the city-states of Italy raised the art to high levels of sophistication. Napoleon Bonaparte's neglect of more secure forms of code-making led to his first great defeat. In a preview of a much later cryptanalytic triumph, the Russians read Napoleon's dispatches and combined these disclosures with the rigors of the Russian winter to turn back the invaders at the gates of Moscow.
New technologies necessitated new security safeguards for communications. Invention of the telegraph, for example, led Union commanders in the American Civil War to seek better ways to prevent their messages from being betrayed to Confederate generals. For Union generals McClellan and Grant, cryptographers devised codebooks in which user-friendly ordinary words substituted for plaintext. Colonel became Venus, Neptune was Richmond, and Adam was President Lincoln.
Superior cryptography gave Union leaders an advantage over their Confederate opponents. The South relied on ciphers that included a version of the venerable Vigenère system that Kahn has described as "probably the most famous cipher system of all time." Its origination is attributed to Blaise de Vigenère, who lived in the sixteenth century. He used a square bounded on the left side by a vertical alphabet and across the top by a horizontal one. Within the square, each horizontal row is another alphabet, which begins with the letter of the left-hand column. To replace a plaintext letter with a cipher one, the cryptographer traced the column beneath the top horizontal letter down to its row on the vertical alphabet. In other words, this was a creative complication of Alberti's polyalphabetic ciphers. When combined with a key word or phrase and such complications as reversed alphabets, Vigenère confounded cryptanalysts for a long time. But as early as the 1840s, America's Charles Babbage demonstrated how to solve the Vigenère system, and Union analysts' unraveling of the Confederates' use of them contributed to the South's defeat.
Another cipher invented to assure secrecy in telegraphic messages was named Playfair, after a British baron, although it was devised not by him but by his friend Charles Wheatstone. This cipher also uses a square, with a key word rather than an alphabet across the top. Instead of yielding just letter transpositions, though, it delivers "digraphs," in which two letters of a message are enciphered together. Since there are 26 letters but 676 digraphs, the use of digraphs overcame the limitations of alphabets and sharply complicated life for the cryptanalyst.
Great War Debacles Demand Cryptologic Change
As the Great War of 1914-18 began, military communications faced a formidable new technological challenge, that of radio. Marconi's not-yet-twenty-year-old invention put telegraphy on the air. With streams of Morse code sprayed out from their command center, deskbound admirals could direct warships far out at sea, and generals were able to better control highly mobile gasoline-driven armies.
Along with this positive came a negative. Skulduggery was no longer necessary to secure an enemy's messages; interceptors as well as intended recipients could pluck them out of the ether by monitoring message-transmitting frequencies. Cryptanalysts were given masses of enemy communications to work with.
The situation called for groundbreaking new codes. They weren't forthcoming. Military communicators were still relying on pen-and-paper ciphers left over from the previous century, often no more than variations of Vigenère or Playfair systems.
Cryptanalysts of warring nations were presented with opportunities they moved quickly to exploit. The French were best prepared, with a group of codebreakers who had been working together since well before the war began. They also had in place both a line of intercept stations and the beginnings of sites for the direction-finding of enemy transmitters. In London, the British organized the now famous Room 40, where some of the nation's best minds concentrated on messages fetched in by a new line of coastal intercept centers. Germany launched into the conflict without a single cryptanalyst on the western front, but then strove mightily to catch up.
With all this emphasis on codebreaking, the Great War soon became a codemaker's nightmare. Cryptanalysts held the upper hand. Everyone was breaking everyone else's codes.
The Germans were the first to reap a major victory from their opponent's cryptographic failures. They did this against the Russians pressing in on them from the east. The French tried to help their more primitively equipped allies by supplying them with codebooks, but the czarist government and military were so corrupt that the code was quickly betrayed, for a payoff, to the Germans. Efforts by the Russian commanders to introduce a new code came to nought. In August 1914, as they approached the Battle of Tannenberg, the decisive struggle on the eastern front, the Russian leaders ran short of the wire and wire-laying equipment to communicate by telephone. Trying to coordinate their huge two-pronged pincer movement, they had no choice but to use radio—and to send their messages unenciphered. The Germans intercepted them and translated them. They revealed the Russians' entire plan of attack.
Intercepted messages in hand, the Germans knew how to counter the offensive. Aware that the Russians' northern wing, after an initial victory against the Germans, was pausing to reorganize, Generals Hindenburg and Ludendorff held that front with a thin screen of cavalry and concentrated their main forces to fall on the southern wing. They enveloped the Russian armies, killed some thirty thousand troops and captured one hundred thousand others, setting Russia on the long downward slide that ended in 1917 with the Bolshevik revolution and the Russian withdrawal from the war.
Early on, Britain's Room 40 began breaking German naval codes. The decrypts led to two relatively inconsequential British forays, but then were used with great effect on May 31, 1916, when decrypted messages warned that German navy commanders were massing their ships for a major offensive in the North Sea. The result was the climactic Battle of Jutland. "Without the cryptographic department," Winston Churchill wrote, "there would have been no Battle of Jutland." Although both navies were badly battered, the surviving German ships retreated into their home ports and did not again take on the Royal Navy throughout the rest of the war. With Room 40's aid, the British navy also ended the threat of German U-boats in their attempt to choke off Britain's Atlantic supply line.
Britain's breaking of another German message, the infamous Zimmermann telegram, brought the U.S. into the war. Wanting the U.S. to be a mediator for peace rather than a belligerent in the war, President Woodrow Wilson maintained American neutrality even after the Germans lifted their embargo on submarine attacks against neutral ships and sank the Cunard liner Lusitania, with the loss of 128 American lives. The U.S. public reacted with such fury that the Germans reconsidered and, for four months, suspended their U-boat campaign. But then Arthur Zimmermann, the German foreign minister, hatched what he considered an inspired scheme, one that would keep the U.S. so occupied with troubles close to home that American leaders would be unable to think about involvement in Europe. His idea was to induce Mexico to join with Germany in an alliance that would provide German financial backing for the Mexican army to cross its northern borders and reclaim its lost territories in Texas, New Mexico and Arizona. Moreover, he proposed that the Mexican president persuade the Japanese to attack the American West Coast. He sent encrypted instructions via a cablegram to the German ambassador in Washington, who was to forward them to the German ambassador in Mexico City and thence to the Mexican president.
The British, however, were tapping Atlantic cable communications. They intercepted the telegram and deciphered it. But they weren't sure what to do next. To reveal its contents to the Americans would give away the fact that they were breaking the German codes, which was an unacceptable disclosure. Yet they knew that Zimmermann's plan would infuriate the Americans and would likely draw them into the war. They came up with a bright solution. The German's Washington ambassador would have to strip off the instructions meant just for him before the relay to Mexico. Consequently, the version arriving in Mexico City would vary from the intercept as well as have a different transmission date. Germany's ambassador to Mexico would deliver a deciphered version of the message to the Mexican president. The British scheme was to have one of their agents in Mexico City obtain a copy of this second message and then have that turned over to the Americans. It was all done so skillfully that the Germans blamed treachery in Mexico rather than suspecting the British.
Once the telegram was leaked to the press, headlines across the U.S. blared the incredible news. Any doubts about the message's authenticity were dispelled when Zimmermann admitted that he had sent it. With that, Wilson could no longer withstand the storm of rage the telegram stirred up; the U.S. declared war on Germany.
In March 1918, came the foremost cryptanalytic victory of the war. The German armies were closing in on Paris, preparing for the push that would seize the capital and drive France to make peace. German generals had been launching devastating surprise attacks because their cryptographers had devised a new cipher the French were unable to break. Known as the ADFGVX, it used only these letters of the alphabet because their Morse code equivalents were distinct from one another and less liable to be garbled in transmission. With German salients only thirty miles from Paris, close enough that the city was being bombarded by long-range Big Bertha artillery, French commanders were desperate to know where the next assault would fall. The task of breaking ADFGVX was left to France's most able cryptanalyst, young Lieutenant Georges Painvin. In an incredible feat of sleepless concentration, he broke the cipher and revealed when and where the Germans would strike. This time the French were ready for the German advance. The assault was beaten back and France was saved from defeat.
When the U.S. sent the American Expeditionary Force to France, Herbert O. Yardley, organizer of the first serious U.S. cryptographic program, went along to help with code work at the headquarters of the AEF commander, General John Pershing. Yardley was horrified to find the American forces relying on "schoolboy codes and ciphers" that, he was sure, the Germans were decoding as quickly as American operators. Nonetheless, the doughboys turned the course of the war toward triumph by their fresh vitality and overwhelming numbers, despite having their leaders' orders almost instantly known to the enemy.
The Great War was, indeed, a cryptographer's nightmare.
Well before the war's end, it was evident that a new order of military communications was required. The gasoline-powered mobility of modern armed forces needed radio to coordinate and direct their movements, which, in turn, called for faster and more secure methods of encryption and decryption than were possible with manual systems out of the past. It was time for machines to take on the tasks of cryptology.
Inventors Concentrate on Rotor Machines
Late in the war, the British put forth a code machine, the work of J. St. Vincent Pletts, that they recommended for immediate use by Allied commands. To convince their U.S. allies, they sent over a sample to be tested. The machine was delivered to American cryptanalyst William Friedman, along with five encoded messages the British were sure would prove undecipherable. Friedman broke them in three hours, ending this early try at machine encoding.
The need for mechanical systems was so evident, however, that almost simultaneously inventors in four different countries began work on machines, each of which relied on the same idea. This was the application of the electric-powered rotor, a revolvable code wheel.
Excerpted from Codebreakers' Victory by Hervie Haufler. Copyright © 2003 Hervie Haufler. Excerpted by permission of OPEN ROAD INTEGRATED MEDIA.
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