[7.0] US Codebreakers In World War II

v2.4.0 / chapter 7 of 13 / 01 sep 16 / greg goebel

* With America at war, US codebreakers went into overdrive to work against Axis codes. The Americans also devised their own ingenious cryptographic schemes.

[7.1] CRACKING JN-25
[7.5] VENONA

[7.1] CRACKING JN-25

* After Pearl Harbor, the American codebreaking focus shifted from Japanese diplomatic codes to Japanese naval codes. The war in the Pacific was conducted over a huge ocean area, and the Japanese and American fleets were the most important players in that conflict. The US Navy needed to obtain intelligence on Japanese fleet strength, dispositions, and intentions.

US Navy codebreakers did not make real progress on JN-25 until January 1942. They were too late to defeat the attack on Pearl Harbor, but they would provide significant help to allow America put a stop to Japan's six-month rampage across the Pacific.

The most significant US Navy group in the effort to crack JN-25 was the "Combat Intelligence Unit" in the basement of the 14th Naval District Administration Building at Pearl Harbor, under the command of Commodore John Rochefort. Rochefort was a workaholic who had lived in Japan and was fluent in Japanese. His people worked 12-hour shifts, seven days a week, while Rochefort monitored and prodded their progress. He rarely emerged from the basement, falling onto a cot when he absolutely had to have some sleep.

The Rochefort group had managed to analyze the patterns in documents encoded in JN-25 through exhaustive mathematical analysis. They were able to perform some of the analysis with automatic punch-card tabulating machines, thanks to the work of Lieutenant Commander Thomas H. Dyer, one of the staff in Rochefort's group.

Cracking JN-25 required two steps, the first being to crack the cipher scheme, the second being to figure out the underlying code values. The fact that the Japanese couldn't replace their code books more often than once every several months meant that cipher sequences were often reused. Eventually, the Rochefort group was able to build up their own cipher table, and if one crib could be identified in a message, it could be used to index into the Americans' reverse-engineered cipher table, allowing decipherment of the rest of the message.

Once the cryptanalysts were able to strip away the cipher scheme that hid the code values, they then began to build up a dictionary of the code values from context and hints. For example, signals intercept combined with radio direction finding often allowed messages to be linked to the specific ships that sent them. Another hint was that different Japanese telegraphers often had distinct "keying" styles that allowed signals intercept technicians to identify them. It was said of one Japanese telegrapher on the carrier AKAGI that "he hits the key like he's kicking it with his foot."

The generally orderly nature of military communications was a natural source of cribs. Messages would generally begin with a code giving the name of the ship transmitting the message, and sometimes the name of the commander of the ship. The message would also include a time-date stamp and often the coordinates of the ship, which could be matched to radio direction finding data.

By April 1942, the Rochefort group could read about a third of JN-25's codewords. This might not have seemed like enough, but it was the most useful third, since it included those codewords that were most heavily used, making them the most easily targeted and most important.

* The first really useful information obtained by cracking JN-25 indicated the Japanese were preparing an amphibious assault on Port Moresby, the Australian base on the southern coast of New Guinea. In early April, the US Navy communications intercept and radio direction finding station in Hawaii, codenamed "HYPO", warned that the Japanese were assembling a naval strike force at their major base at Rabaul on the island of New Britain, north of New Guinea. Decrypts of Japanese messages indicated the fleet would move on Port Moresby early on 7 May 1942.

American Admiral Chester W. Nimitz moved his forces to respond. A US Navy fleet with two carriers, the LEXINGTON and the YORKTOWN, steamed to the Coral Sea, between New Guinea and Australia, while combat aircraft were sent to Port Moresby to reinforce the base. The Japanese and American fleets struck at each other by air for two days in the Battle of the Coral Sea. Neither side's ships ever got within gun range of each other.

The LEXINGTON was sunk and the YORKTOWN was badly damaged. The Japanese light carrier SHOHO was sunk, and two larger Japanese carriers had to return to Japan for repairs. The battle was tactically a draw, but strategically an Allied victory because the Japanese drive on Port Moresby had been turned back. The Americans and Australians were able to ramp up their efforts to dislodge the Japanese from the northern regions of New Guinea.

* Even before the Battle of the Coral Sea, US Navy intelligence was aware the Japanese were planning another naval operation. This one was intended to finally destroy the US fleet in the "decisive battle" that senior IJN officers dreamed of. The Japanese plan was to launch a diversionary attack on the Aleutian Islands in the north Pacific, and send out a small task force to raid an American outpost in the western Pacific. When the Americans attempted to intercept the raiding force, the full might of the IJN would fall on the American fleet and send it to the bottom of the sea.

With the ability to read IJN messages encrypted in JN-25, US Navy commanders learned the outlines of the plan, the nature of the forces involved, and the timetable for the operation. The Navy sped up repairs on the carrier YORKTOWN and naval planners began to organize a counterstroke.

There was one thing that the JN-25 intercepts didn't spell out, however, and that was where the Japanese raiding force intended to strike. The target was only designated as "AF" in the messages. The cryptanalysts believed that these were Japanese map grid coordinates for Midway, but their superiors were skeptical. Rochefort arranged for Midway Island to send a message that could be intercepted by the Japanese stating that the island was short of fresh water. Not long afterward, a Japanese message was sent saying that AF was short of fresh water.

The Rochefort group managed to provide the information in the nick of time. On 1 June 1942, the Japanese changed their codes and cipher books according to their usual procedure, leaving the American codebreakers in the dark for the present. The Japanese attacked the Aleutians on 3 June. The next day, an American fleet engaged the superior Japanese fleet near Midway. In a battle lasting three days, the Americans sank all four carriers in the Japanese fleet, as well as several other vessels. The Americans lost the carrier YORKTOWN. The Battle of Midway was the most spectacular upset victory ever achieved by the US Navy, and was the turning point in the Pacific War.

Much to the shock of US naval intelligence, the newspaper THE CHICAGO TRIBUNE, which had been a vocal opponent of US involvement in the war before Pearl Harbor, published a story that said the Americans had known about the Japanese plans in advance, which was effectively saying in public that the US had broken JN-25. Fortunately, the Japanese never found out about the article. The leak was traced to the former captain of the YORKTOWN, who shared a cabin on ship with a reporter and talked too freely. He wasn't brought up on charges, but his career was quietly sidelined.

* The Japanese continued to use JN-25. On 14 April 1943, the US Navy signals intercept station in Hawaii picked up a message indicating that Admiral Isoroku Yamamoto, Japan's brilliant naval strategist, was to make an inspection tour of Japanese bases in the Solomon Islands. The message gave a schedule for the tour.

Killing specific enemy leaders wasn't normal American policy. It not only invited retaliation in kind, but it was perfectly possible that if one leader were killed, his replacement might be more effective. In the case of Admiral Yamamoto that possibility was quickly dismissed, since the IJN had no one else of comparable stature. A decision was made at the highest levels to assassinate Yamamoto, though such an action might tip off the Japanese to the fact that JN-25 had been cracked.

Yamamoto was to visit a Japanese base on the island of Bougainville, bringing his aircraft just barely within range of US Army Air Force P-38 Lightning fighters operating from Guadalcanal, at the other end of the Solomons chain. On the morning of 18 April 1943, 18 P-38s flew hundreds of miles above the wavetops, and arrived at exactly the right time to intercept Yamamoto's transport and its escorts as they were approaching Bougainville to land.

Yamamoto was killed. Although the Air Force flew other patrols in the area after the intercept to give the impression that the incident had happened by chance, the Japanese guessed that their codes had been broken -- but they guessed the wrong code and did not change JN-25.

* The Rochefort group made other significant contributions to the war in the Pacific. Japanese merchant vessels, or "maru" in Japanese usage, had their own code system, and they used it to radio daily position updates back to Japan. The "maru code" only used four-digit codewords, which should have made it easier to crack than JN-25, but the Rochefort group made little progress until it was realized that there were three separate maru codes. Once this was understood and the cryptanalysts managed to pick their way through the ciphers, they had an open window onto Japanese maru movements. The merchantmen became sitting ducks for US submarines and bombers.



* General Joseph Mauborgne, who had done much to build up the SIS, retired in 1941, but the organization continued its expansion with a vengeance as the war progressed. The different sections of the organization were relocated, with the cryptanalysts moving to a former girl's school in Arlington, Virginia, across the Potomac from Washington DC. The place was named "Arlington Hall". The entire organization went through a sequence of name changes, stabilizing as the "Signal Security Agency" in July 1943. After the war, it would be renamed the "Army Security Agency", the name by which the organization remains known today, though its charter and structure have changed.

The US Army codebreakers made significant further contributions to the war effort. Although the Japanese embassy in the US was closed when the war started and diplomatic relations were broken, the Americans intercepted communications from Japanese embassies in other countries, and the ability to read the PURPLE cipher still proved useful.

Baron Hiroshi Oshima, the Japanese ambassador to Germany, was very sympathetic to Nazi ideology. Hitler, whose deep racial chauvinisms had odd inconsistencies, admired the militaristic Japanese and made Oshima a personal confidante. Baron Oshima had a remarkable level of access to Nazi top secrets. Oshima was a meticulous military officer by training and wrote detailed reports of the information provided to him by the Nazis. The reports were radioed back to Tokyo in the PURPLE code, and were promptly read by British signals intercept stations. The British had been provided with their own PURPLE analog machines by the Americans and so could decrypt the messages.

For example, Oshima's reports provided details on the effect of Allied bomb raids on specific German targets, and provided valuable "post-strike intelligence", in modern terms, to the British and Americans on the results of their attacks. In November 1943, Oshima was taken on a long tour of the Atlantic Wall fortifications on the coast of France. Oshima wrote a 20 page report, which provided valuable information to Allied D-Day planners. Even General George C. Marshall, head of the US Joint Chiefs of Staff, is said to have identified Oshima as a "key source of information" on Hitler's intentions.

As the war drew to a close, PURPLE intercepts also helped gauge the will of the Japanese to continue resistance, decoding instructions sent to the Japanese ambassador in Moscow on how to send peace feelers to the Americans through the Soviets.

* In June 1941, the Canadians set up a codebreaking operation, and on the recommendation of General Joseph Mauborgne they hired none other than Herbert O. Yardley. It is hard to understand what Mauborgne was thinking. No doubt he respected Yardley's abilities, but the publication of THE AMERICAN BLACK CHAMBER had made Yardley "persona non grata" to US intelligence organizations. Although the Canadians provided useful decrypts of communications by the Vichy French government, Yardley's presence made cooperation with the Americans very difficult. He was finally dismissed in January 1942. He died of a stroke in 1958.



* During World War II, the US Navy developed a cipher machine, the "Electronic Code Machine (ECM) Mark II", that even by modern standards is regarded as impossible to crack except by a time-consuming brute-force attack.

The ECM Mark II, sometimes known as the "SIGABA" machine, had its roots in the "M-134", a cipher machine designed by William Friedman before the war, and in fact the SIGABA was also known as the "M-134C". The original M-134 was conceptually similar to the Enigma machine in that it used a rotor system to scramble letters, but it differed in that it had five rotors, not three, and in that the rotors advanced in an irregular fashion, not in a nice neat progression with each character entered.

The movement of the rotors was controlled by a "paper tape", which was a long strip of paper with holes punched across its width. In this case, the paper tape would accommodate five holes across its width, with a hole punched to, say, tell a corresponding rotor to advance. If no hole was punched, the rotor would not advance. Actually, it is unclear if a hole caused an advance or no hole caused an advance, but the principle is the same in either case.

For example, suppose the pattern of holes in a section of paper tape looked like this:


        + + + + + + + + + + +  
        o     o   o   o   o  
            o           o   o
   ...          o   o     o    ...
        o o o     o     o   o
                o o   o   o  
        + + + + + + + + + + +  

Then if the tape is read from left to right and from top to bottom, with rotor 1 corresponding to the top and rotor 2 to the bottom, the rotors would advance in the following sequence:


    1 . . 4 . 
    . . . 4 .
    . 2 . 4 .
    1 . . . .
    . . 3 . 5
    1 . . 4 5
    . . 3 . . 
    . . 3 . .
    1 . . . 5
    . 2 . 4 .
    1 . 3 . 5
    . 2 . 4 .

In reality, which hole controlled which rotor was determined by a plugboard with five plugs, adding another layer of obscuration to the cipher system. Given a long and properly devised paper tape, the sequence of rotor movements could be difficult to reverse-engineer. However, the paper tape was clumsy, and Frank Rowlett came up with a better idea: use a separate set of rotors to generate the unpredictable sequence of rotor movements. Friedman and Rowlett implemented this idea with a device called the "M-229", which was connected to the M-134 in place of the paper-tape system. The M-229 had three rotors of its own and a switch to vary its operation, and its output controlled the movement of the five rotors of the M-134.

Although the US Army and Navy codebreaker teams often worked at cross purposes, sometimes cooperation prevailed. Laurence Safford and another OP-20-G cryptologist, Donald Seiler, were informed of the Army research on code machines, and came up with their own implementation, the ECM Mark II. By the way, the "ECM Mark I" had been one of the very first rotor-based cipher machines, developed during the First World War by Edward Hebern.

Despite the various rivalries between the Army and Navy groups, the Army group recognized that the ECM Mark II was a superior device, and with minor changes it went into operation with both services. There were a number of variations, some used for high-level communications, such as the "POTUS-PRIME" link between the White House in the US and Number 10 Downing Street in Britain.

* The ECM Mark II included a total of fifteen rotors. Five of these rotors were normal cipher rotors with 26 connections, in essence just as in the original M-134. Also as with the M-134, they stepped in an irregular fashion -- but were not controlled by a paper tape. Five of the rotors were known as "control rotors", and had 26 contacts like the cipher rotors, while the remaining five rotors, the "index rotors", had 10 contacts each. These two sets of rotors controlled the stepping sequence of the cipher rotors.

The index rotors were only moved by hand, and were used to provide a setting that was fed into the control rotors as an initial value, providing 500 different possible initial "index" values. The control rotors stepped sequentially with each character moving the first control rotor one step, the next control rotor moving one step when the first control rotor completed a full revolution, and so on, driving the cipher rotors in an unpredictable sequence some 26^5 = 11,881,376 steps long.

SIGABA / ECM Mark II telecipher machine

* The SIGABA was at the center of one of the more comic-movie stories of World War II. On 3 February 1945, in Colmar, France, two sergeants who were in charge of security for the SIGABA machines for their division decided to spend a little quality time with some local Frenchwomen. The sergeants were carrying the SIGABA machine in a truck, with the machine stored in pieces in three 135-kilogram (300-pound) safes.

When they came back out again, the truck was gone along with the safes. This led to a frantic six-week exercise in which American security officers tracked down what had happened to the safes. As it turned out, a French driver had lost his truck, and when he saw the American truck just sitting there, decided it would be a good replacement. When he found the three safes in the back, he came to the conclusion that he had just bought himself a great deal of trouble of some sort; he rolled the safes off the truck into a local stream, where they had been discovered unopened. The security officers who managed the investigation were decorated; what happened to the two sergeants is unclear.



* The US Marines wrote an interesting footnote in the history of codes and ciphers in World War II when they adopted one of the most unusual and impenetrable ciphers ever used in warfare: the language of the Navaho American native tribe of the US Southwest.

While the US military made effective use of cipher machines, they were often too slow for combat use. Trying to encrypt and decrypt messages during a running battle was just too difficult to be practical, and when things got hot enough, messages just had to be shouted over the radio or field phone "in the clear", allowing the enemy to intercept them.

In early 1942, Philip Johnston, a World War I veteran then working as an engineer in Los Angeles, California, came to the US Marine Corps with a proposal. Johnston was the son of a missionary who had grown up on the Navaho tribal reservation. He was one of the few outsiders who could speak the language, which has no close relationship to any European or Asian tongue. Johnston suggested that Navaho would make a good "real time" code.

The idea was not new. Several US Army regiments, on the front in World War I, had as an ad-hoc measure pooled a total of 19 Choctaw tribesmen into an "telephone squad" to conduct secret communications; it worked very well, and it is said the idea was copied by other US Army frontline units using other tribes, such as the Comanche. There were worries that the Germans had acquired expertise in American native languages in the years between the wars, but the Marines were intrigued, and after conducting a few simple trials decided to set a program to train and deploy Navaho tribesmen as radio operators for Marine units in the field. Navaho tribal leaders patriotically cooperated with the effort.

There was some consideration of using other tribes since one tribal language was about as incomprehensible as the other, but the Navahos are one of the biggest tribes and provided the biggest pool of candidates. It was also known that no Japanese or German scholars had worked on the Navaho reservation, making it unlikely that the Axis had anyone who knew the language.

The first Navaho "code-talkers", as they were known, went ashore with the Marines at Guadalcanal in August 1942. At first there were some problems in getting the scheme to work, but after the bugs were worked out, the code-talkers proved remarkably effective -- though there were a few cases where jumpy Marines took Navahos prisoner, thinking they were Japanese in American uniforms. No code-talker transmission was ever cracked, and in fact, during the evaluations Marine cryptologists said they couldn't even transcribe the language, much less figure out what was being said.

One of the issues with code-talking was that the tribal languages didn't have their own words for modern concepts such as "tanks", "machine guns", "battleships", "radar", and so on. Instead of using the English terms, which would have rendered the "code" almost useless, the code-talkers invented their own terms for such things, for example using the Navaho words for "iron fish" for a submarine, "hummingbird" for a fighter plane, "eggs" for bombs, and so on. Apparently the Choctaw code-talkers had come up with a similar scheme during WWI. At first, the list of Navaho codewords had 274 entries, though this was later expanded to 508. For terms with no Navaho equivalent that weren't covered in the list, a "phonetic alphabet" was devised, using the Navaho equivalents of English words whose first letters spelled out the phrase: "Ant" for "A", "Bear" for "B", "Cat" for "C", and so on.

Some sources claim the Japanese had captured a Navaho soldier during the seizure of the Philippines and forced the prisoner to try to interpret code-talker transmissions, but he was unable to figure out what they were saying. The Japanese never cracked the Navaho code, though in fact the Japanese demonstrated little skill at cracking any Allied codes and ciphers. After the war, the chief of Imperial Japanese Army intelligence, Lieutenant General Seizo Arisue, told American interrogators: "We couldn't break your codes at all."

That was something of an exaggeration, since they did penetrate some low-level codes, but the code talkers were certainly far beyond their abilities. A total of 420 Navaho code-talkers served with the Marines in World War II. The US Army also used 50 Choctaw and about 17 Comanche code-talkers in the invasion of Europe, and a number of other tribes contributed small numbers of code-talkers to the war effort as well. In each case, the code-talkers used their own tribal language.

The code-talkers remained unpublicized and unknown for decades, partly because the military wanted to keep the idea secret so it could be used again in the future, but with the increased emphasis on diversity in the US in the late 20th century, the story of the code-talkers became widely known, and now it is one of the most famous episodes in the history of cryptology.


[7.5] VENONA

* One of the biggest American cryptological secrets of World War II were the decrypts of Soviet communications intercepted during the war years, known as VENONA and mentioned in a previous chapter.

The effort was formally initiated by the SIS on 1 February 1943, with the goal of examining and hopefully cracking Soviet diplomatic communications. It was called JADE at first, with the name changing to BRIDE and DRUG and finally VENONA. These were all simple codenames, not acronyms. The effort was initially run by Ms. Gene Grabeel, who would stay with the effort through nearly all its long history, though within months uniformed military officers took over direction of the effort. The work quickly demonstrated that these messages fell into five separate categories, each representing a different class of user with their own encryption system. The five classes included, in decreasing order of traffic volume:

The first break took place in October 1943, when Richard Hallock, an Army Signal Corps lieutenant who had been an archaeologist in his peacetime life, managed to get a fingerhold into the cryptographic system used by Soviet trade officials. This gave leads into the other four cryptosystems, which were exploited by other cryptanalysts as they joined the effort.

In 1944, Cecil Phillips managed to get a fingerhold into the NKVD messages, which were protected with double encryption and were very strong. It would take two more years, however, before any of the NKVD messages could be read. In the summer of 1946, Meredith Garner began to decrypt portions of these messages, and by 1947 the decrypts had shown that Red agents had achieved significant penetrations of US organizations. In 1948, the British joined the effort, sending two personnel to Arlington Hall, and as concerns over Red spies in America grew, the VENONA group established contact with a Federal Bureau of Investigation agent named Robert J. Lamphere, who was given access to the decrypts.

By 1952, most of the messages that would be decrypted had been decrypted. The decryption was done though hard-working analysis. A partly-burned NKVD codebook had been seized by the Finns from the Soviet embassy in Helsinki on 22 June 1941, the day Hitler invaded the Soviet Union, and then passed on to the Nazis, with US military intelligence obtaining a copy of it in turn at the end of the war. However, due to compartmentalization in intelligence activities the VENONA office didn't get their hands on it until 1953, when the vast bulk of the work was done.

A total of 3,000 messages was decrypted in all or part. The NKVD and GRU messages were the most interesting, with insights into Soviet intelligence activities in America. The trade and diplomatic messages were of little interest in themselves, since they focused on mundane matters or issues that were no longer of any importance by the time the decrypts were performed, but they did help provide crosschecks on the NKVD / GRU messages. The Naval GRU was not a major organization, and the messages were relatively few and of lesser value.

Even though the number of messages decrypted was only a small fraction of the total, they gave a fascinating look at the Red spy organization in the US. A highly-placed agent at the Los Alamos atomic development project at Los Alamos, New Mexico, was known by codename CHARLZ; he turned out to be Klaus Fuchs, who gave the plans for the Bomb to the USSR. He was backed up by a machinist David Greenglass, codenamed WALTER LIPPMAN, and a teenaged summer hire named Ted Hall, codenamed MLAD. American intelligence got suspicious of Hall and questioned him, but he denied everything and didn't come clean until the end of his life. The decrypts didn't actually prove his guilt, and they were too secret to be used in court anyway.

A Red agent named Elizabeth Bentley was codenamed MYRNA and GOOD GIRL, the second proving to be an ironic designation when she became disillusioned with Communism and went to the FBI; she sang like a canary, giving a detailed picture of Soviet intelligence activities in the US that did much to break up the spy network. Spy ring head Julius Rosenberg was designated ANTENNA and then LIBERAL; he and his wife Ethel would go to the electric chair in 1953 for treason.

The Soviets were aware of VENONA from early on. Bill Weisband, a native Russian speaker who worked at Arlington Hall from 1944, passed back considerable information on US intelligence and counterintelligence efforts under the codename ZVENO, until he was arrested in 1950. British Red agent Kim Philby was assigned to Washington DC in 1949 and 1950, to be was briefed on VENONA reports. However, all Weisband and Philby could do was tell the Soviets that the damage had been done; there was no way of undoing it.

The VENONA office remained in operation until 1980. Although the messages were very old by that time, examination had continued in hopes of finding clues in the past to current Soviet intelligence efforts in the US. The VENONA papers were finally released to the public in 1995.



* During the war, the American government established various committees in attempts to coordinate the various signal-intercept and codebreaking operations run by different government organizations, leading eventually to the establishment of the comprehensive "US Communications Intelligence Board (USCIB)" in 1947. Although the USCIB had oversight of all the involved parties, they still squabbled among themselves as they always had, and resisted attempts to bring them closer together.

The "Armed Forces Security Agency (AFSA)" was established in May 1949 to help reduce the chaos, initially under the leadership of Rear Admiral Earl E. Stone and reporting indirectly to the Joint Chiefs of Staff. Stone was replaced in 1951 by Army Major General Ralph J. Canine. Canine might well have wondered what kind of a prize he had been handed, because the AFSA had spent much of its time spinning its wheels. The agency had no real facilities of its own, being operationally dependent on the armed services, and ended up being not much more than another faction in the multi-way quarrel over the coordination of signals intelligence.

When North Korea invaded South Korea in June 1950, American intelligence was caught completely off-guard; the system was clearly not working. In late 1951, US President Harry Truman initiated a comprehensive review of the issue. The conclusions of the review were released in October 1952 and stated that a new national signals intelligence organization was required, with its own assets and reporting directly to the office of the Secretary of Defense.

The result was the National Security Agency (NSA), which was a powerful organization with direct control over a worldwide signals intelligence and codebreaking network. The different American armed services retained their own signals-intelligence organizations, but were generally limited to intelligence-gathering for tactical operations, while the NSA retained control over the strategic domain. Ralph Canine was appointed the first director of the NSA on 4 November 1952.

In 1957, NSA headquarters was consolidated at Fort Meade, Maryland, in between Washington DC and Baltimore, and it still resides there today. The agency, known as "No Such Agency" and "Never Say Anything" for its secretiveness, operates out of a nearly featureless twin glass box structure known as the "Puzzle Palace". The agency operates the small but impressive "National Cryptologic Museum" outside of its gates for the benefit of the public. The road into the facility is named "Canine Road" after the first director.

NSA HQ at Fort Meade VA

* William F. Friedman became the chief technical consultant to the NSA, and later became a special assistant to the director of the agency. When Friedman retired in 1955, he was replaced by Frank Rowlett.

In 1956, Friedman was given an award of $100,000 USD by the US Congress for his contributions. This award remains somewhat controversial, since the formal basis for it included a number of inventions for which Friedman's contributions were minor, such as derivatives of the Bazeries cylinder or Hebern's rotor machines. However, Friedman's true contributions were so substantial that the fact that he received the award mostly for the wrong reasons seems irrelevant. Elizebeth Friedman also returned to cryptological work during the war. She set up the cryptological bureau of the US Office of Strategic Services (OSS), which was revived after the war into the US Central Intelligence Agency (CIA).

After their retirement, the Friedmans went back to their roots and wrote a monograph titled THE CRYPTOLOGIST LOOKS AT SHAKESPEARE, which was a debunking of the Baconian myth that argued there was no cipher in Shakespeare's plays. The meticulous Friedmans were annoyed when Cambridge University Press published the document under the title THE SHAKESPEARIAN CIPHERS EXAMINED, which implied a cipher actually existed. The whole subject of such dubious codes, known as "pseudocryptology", is discussed at the end of this document.