Information Security. Mark Stamp

hoped, the Germans concluded that their codebook had not been compromised and continued to use it for sensitive messages throughout the war.

      2.4.3 Project VENONA

      The so‐called VENONA project [130] provides an interesting example of a real‐world use of the one‐time pad. In the 1930s and 1940s, spies from the Soviet Union who entered the United States brought with them one‐time pad keys. When it was time to report back to their handlers in Moscow, these spies used the one‐time pads to encrypt their messages, which were then sent. These spies were extremely successful, and their messages dealt with the most sensitive U.S. government secrets of the time. In particular, the development of the first atomic bomb was a focus of much of the espionage. The Rosenbergs, Alger Hiss, and many other well‐known traitors—and many who were never identified—figure prominently in VENONA messages.

      The Soviet spies were well trained and never reused the key, yet many of the intercepted ciphertext messages were eventually decrypted by American cryptanalysts. How can that be, given that the one‐time pad is provably secure? In fact, there was a flaw in the method used to generate the pads, so that, in effect, long stretches of the keys were repeated. As a result, many messages were in depth, which allowed for successful cryptanalysis of about 3000 VENONA messages.

Part of one interesting VENONA decrypt is given in Table 2.4. This message refers to David Greenglass and his wife Ruth. LIBERAL is Julius Rosenberg who (along with his wife Ethyl) was eventually executed for his role in nuclear espionage.⁸ The Soviet codename for the atomic bomb was, appropriately, ENORMOUS. For any World War II‐era history buff, the VENONA decrypts at [130] make for fascinating reading.

Table 2.4 VENONA decrypt of message of 21 September 1944

[C% Ruth] learned that her husband [v] was called up by the army
but he was not sent to the front. He is a mechanical engineer
and is now working at the ENORMOUS [ENORMOZ] [vi] plant in
SANTA FE, New Mexico.
45 groups unrecoverable]
detain VOLOK [vii] who is working in a plant on ENORMOUS. He is a
FELLOWCOUNTRYMAN [ZEMLYaK] [viii]. Yesterday he learned that
they had dismissed him from his work. His active work in
progressive organizations in the past was cause of his dismissal.
In the FELLOWCOUNTRYMAN line LIBERAL is in touch with CHESTER [ix].
They meet once a month for the payment of dues. CHESTER is
interested in whether we are satisfied with the collaboration and
whether there are not any misunderstandings. He does not inquire
about specific items of work [KONKRETNAYa RABOTA]. In as much
as CHESTER knows about the role of LIBERALś group we beg consent
to ask C. through LIBERAL about leads from among people who are
working on ENOURMOUS and in other technical fields.

      

2.5 Modern Crypto History

      Throughout the 20th century, cryptography played an important role in major world events. Late in the 20th century, cryptography became a critical technology for commercial and business communications as well, and it remains so today.

      The Zimmermann Telegram is one of the first examples from the last century of the role that cryptanalysis can play in political and military affairs. In this section, we mention a few other historical highlights from the past century, with an eye towards the modern development of cryptography as a scientific discipline. For more on the history of cryptography, the indispensable source is Kahnś book [61].

In 1929, Secretary of State Henry L. Stimson ended the U.S. governmentś official cryptanalytic activity, justifying his actions with the immortal line, “Gentlemen do not read each otherś mail″ [115]. This would prove to be a costly mistake in the run‐up to the attack on Pearl Harbor.

      Prior to the Japanese attack of 7 December 1941, the United States had restarted its cryptanalytic programs. The successes of allied cryptanalysts during the World War II era were remarkable, and this period is often seen as the golden age of cryptanalysis. Virtually all significant Axis cryptosystems were broken by the Allies and the value of the intelligence obtained from these systems is difficult to overestimate.

      In the Pacific theater, the so‐called “Purple cipher″ was used for high level Japanese government communication. This cipher was broken by American cryptanalysts before the attack on Pearl Harbor, but the intelligence gained (code named Magic) provided no clear indication of the impending attack. Japanś Imperial Navy used a cipher known as JN‐25, which was also broken by the Americans. The intelligence from JN‐25 was almost certainly decisive in the extended battle of Coral Sea and Midway, where an inferior American force was able to to halt the advance of the Japanese in the Pacific for the first time. The Japanese Imperial Navy was never able to recover from the losses inflicted during this crucial battle.

      In Europe, the German Enigma cipher (code named Ultra) was a major source of intelligence for the Allies during the war. It is often claimed that the Ultra intelligence was so valuable that Churchill decided not to inform the British city of Coventry of an impending attack by the German Luftwaffe, since the primary source of information on the attack came from Enigma decrypts [44]. Churchill was supposedly concerned that a warning might tip off the Germans that their cipher had been broken. That this did not occur has been well documented. Nevertheless, it was a challenge to utilize valuable Ultra intelligence without giving away the fact that the Enigma had been broken [12].

The Enigma was initially broken by Polish cryptanalysts. After the fall of Poland, these cryptanalysts escaped to France, but shortly thereafter France fell to the Nazis. The Polish cryptanalysts eventually made their way to England, where they provided their knowledge to British cryptanalysts.⁹ A British team that included computing pioneer Alan Turing developed improved attacks on the Enigma.

An illustration of the “wiring diagram″ for the Enigma cipher appears in Figure 2.5. Additional details on the inner workings of the Enigma are given in the problems at the end of this chapter and a cryptanalytic attack is presented in the cryptanalysis material available on the textbook website.