Information Security. Mark Stamp

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СКАЧАТЬ 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.

Figure 2.5 Enigma wiring diagram

In the post–World War II era, cryptography made the move from a black art into the realm of a true science. The publication of Claude Shannonś seminal 1949 paper, “Information Theory of Secrecy Systems″ [109], marks the turning point. Shannon proved that the one‐time pad is secure and he also offered two fundamental cipher design principles, confusion and diffusion. These two principles have guided symmetric cipher design ever since.

      In Shannonś use, confusion consists of, roughly speaking, obscuring the relationship between the plaintext and ciphertext. On the other hand, diffusion is spreading of the plaintext statistics through the ciphertext. A simple substitution cipher and a one‐time pad employ only confusion, whereas a double transposition is a diffusion‐only cipher. Since the one‐time pad is provably secure, confusion alone is enough, while diffusion alone is apparently not.

      These two concepts—confusion and diffusion—are as relevant today as they were on the day that Shannonś paper was originally published. In subsequent chapters, it will become clear that these concepts remain crucial to modern block cipher design.

Until relatively recently, cryptography was almost exclusively the domain of governments and militaries. This changed dramatically in the 1970s, due in large part to the computer revolution which led to the need to protect large amounts of electronic data. By the mid‐1970s, even the U.S. government realized that there was a legitimate commercial need for secure cryptography. Furthermore, it was clear that the commercial products of the day were severely lacking. So, the National Bureau of Standards, or NBS,¹⁰ issued a request for cryptographic algorithms. The plan was that NBS would select an algorithm that would then become an official U.S. government standard. The ultimate result of this ill‐conceived process was a cipher known as the Data Encryption Standard, or DES.

      Itś difficult to overemphasize the role that DES has played in the modern crypto history. Weĺl have much more to say about DES in the next chapter.

      Post‐DES, academic interest in cryptography grew rapidly. Public key cryptography was discovered (or, more precisely, rediscovered) shortly after the arrival of DES. By the 1980s there were annual CRYPTO conferences, СКАЧАТЬ