CRYPTANALYSIS

(Part 1)

Hacking isn't new. Gentlemen have been reading other Gentlemen's mail for centuries.

By an agreement between the US Army and the US Navy, reached at a conference in Manila in May 1941, the Navy's own Sigint unit, Cast, was concentrating on breaking Japanese diplomatic traffic. For in the Navy Tunnel, Corregidor hid a secret copy of the Japanese Code Machine known as Purple - so ultra-secret and rare, even Pearl Harbour did not have one.

The breaking of the Purple cipher and the brilliant entry, before Midway, into the Japanese naval code were proof enough that the intellectual base of American cryptanalysis was strong. Yet once the nation was plunged into war several weaknesses were immediately apparent. Apparent, indeed, from the very day of the Pearl Harbor attack that in spite of pre-war recruitment and farsighted training there was still a critical shortage of personnel in all areas of signal intelligence.  

Indeed, a revolution was necessary, as may be gauged from the experience of a single lieutenant in the Signal Corps, Howard W. Brown. During the summer of 1941 Brown was Operations Officer in tie Army's little Sigint unit in the Philippines, which, headed by the able Major Joe Sherr, consisted of no more than six sergeants, three corporals and six privates. By an agreement between the Army and the Navy; reached at a conference in Manila in May 1941, the Navy's own Sigint unit, Cast, was concentrating (in its tunnel on Corregidor) on breaking Japanese diplomatic traffic, since it alone possessed a Purple machine. Sherr's team did the interception. What is astonishing is the slowness-and therefore the inefficiency-of the routine as Howard's own account (in his "Reminiscences of Lieutenant Colonel Howard W. Brown, prepared under the direction of the Chief Signal Officer) reveals. He is describing the method for passing over intercepted signals and their translations between his own unit and Cast.

• The normal procedure for handling exchange information was as follows.- Major Sherr or I would take the sealed bag into Manila in time to meet the harbor boat arriving from Corregidor at 1000; hand our bag to the code room at Fort Santiago, Manila ( a large vault built in one of the old Spanish dungeons); open the bag and extract the decoded messages; arrange decoded messages in a folder, by points of origin, attaching any message from previous days which had bearing on, or reference to, the current messages; take the folder to G-2 (or in his absence to his assistant), and let him read the file; return to the code room and file the translations by point of origin and date.

• When Headquarters, United States Armed Forces in the Far East, was established in July 1941, the above procedure was altered in that the file was first taken to General Sutherland, Chief of Staff to General MacArthur, and if it contained anything which he thought might be of interest to General MacArthur (which it frequently did) he would ask us to take it in to the General. Some of the General's off-the-record comments were classic.

• From a security standpoint this system was perfect . . . The serious drawback was the time delay. For instance, a message intercepted on the first day would be sent to Corregidor on the second day and the translation received from the Navy on the third day if in a readable system. Sundays and holidays usually delayed delivery another day because the Navy usually took these days off.

And so the system continued until the Japanese attacked. It may have been secure, but if it be considered as a means of operating wartime one might be forgiven for judging that they did things quicker in the days of the Pony Express.

During the weeks after the war began, Brown strove hectically to improvise, from bits and pieces of the sparse equipment available, means of interception which would enable him to listen in to radio traffic of the Japanese Air Force. Though he could not translate what he heard, by identifying individual call signs he could often calculate when a raid was imminent and warn a threatened airfield-only to discover, too often, that in these early days the U.S. Air Force had a blithe contempt for Sigint and disregarded his prophetic voice, with the result that precious planes were destroyed on the ground. It was war on a do-it-yourself basis. Still, he became so expert at predicting the appearance of the reconnaissance aircraft which regularly visited Corregidor, and so won the confidence of the anti-aircraft gunners, that "we were often able to tell them what 'Foto Joe' was up to, and at times could tell them at what time, and from where, he was likely to appear. The AA batteries would load and cock their guns, and pull the triggers as 'Foto Joe' came by trying to gain altitude. This information and action accounted for about six planes.' Before the end, a capture of Japanese code books on Bataan made it possible to set up a small radio intelligence office in Malinta Tunnel on Corregidor which, with four receivers and the occasional use or a naval direction finder, spent a profitable time monitoring the signal circuits of the enemy's army and air units in the Philippines, providing early warning about in coming raids, and even registering Japanese losses. "We were able to confirm 'probables,' or reports of safe arrival, and the extent of damage, by such messages as: 'Ikamura is landing in the water, looks like he won't be home,' or 'Taji landed at Nichols with one motor burning.'"

On the day that MacArthur departed, leaving General Wainwright to make the final stand, the general summoned Brown to his office shortly before midnight, shook his hand and said, "I want to congratulate you, Captain Hart tells me that you have discovered a system to solve Japanese messages. I am proud of you, and want to thank you." But, unlike Wainwright, Brown too left the Philippines. After an abortive attempt to establish an intercept station on Mindanao, on April 14 he was flown off to Darwin in Australia, a passenger in a moribund B-17, one of whose engines was dead while another was spouting oil, "When we landed, more than one big strong man kissed the ground.

The USN's Cryptanalysis was distributed amongst units in Washington, Hawaii and the Philippines. Only Washington attacked foreign diplomatic systems and naval codes used in the Atlantic (primarily German). Hawaii had primary responsibility for the Japanese naval systems. The Philippines chipped away at the Japanese fleet cryptographic system, and did some limited diplomatic deciphering, with keys provided by Washington. The unit, which was attached for administrative reasons to the Cavite local naval district (the 16th) was installed in a tunnel in Corregidor. The unit comprised 7 officers and 19 men, and had a liason man with its British equivalent in Singapore. It was equipped with 26 radio receivers, apparatus for intercepting both high and low-speed transmissions, a direction finder, and tabulating machinery. Lieutenant Rudolph J. Fabian, then 33, an Annapolis graduate who had three years of radio intelligence experience in Washington, commanded.

Even prior to the opening of hostilities, the Corregidor unit had, together with the Singapore unit, commenced the attack and breakdown of JN25. This most widely distributed and extensively used of Japan's cryptosystems, in which about half of her naval messages were transmitted, comprised a code with five digit code numbers to which were added a key of other numbers to complicate the system. The Navy called it the "five numeral system, " or more formally, JN25b - the JN for "Japanese Navy," the 25 an identifying number, the b for the second (and current) edition. It had made the difficult initial entries, and was in the best position to make new assumptions or confirm or disprove old ones, intercepting messages that the others might not have picked up. Positive or tentative code groups were flashed from unit to unit via the intercept channel for MAGIC, but the unit's work was interrupted when Fabian, with seventeen other code breakers, were evacuated by the submarine Seadragon on 4 February 1942, several weeks before MacArthur. The other code breakers followed later as other submarines made critical evacuations. In all, seventy-five members of the CAST unit were evacuated, the largest single contingent and the only complete outfit to leave the Rock.