Objetivo 1 Determinar el perfil de resistencia a los antibióticos en Salmonella spp, Campylobacter spp, Listeria monocytogenes, Escherichia coli, Enterococcus spp.

Don’t let yesterday take up too much of today. —Abraham Lincoln

Throughout the 20th century, cryptography played an important role in major world events. Late in the 20th century, cryptography became a critical technology for com- mercial and business communications as well. The Zimmermann telegram is one of the first examples from the last century of the role that cryptanalysis has had in political and military affairs. In this section, we mention a few other historical highlights from the past century. For more on the history of cryptography, the best source is Kahn’s fascinating book [119].

In 1929, Secretary of State Henry L. Stimson ended the U.S. government’s official cryptanalytic activity, justifying his actions with the immortal line, “Gentlemen do not read each other’s mail” [224]. This would prove to be a costly mistake in the run up to the Japanese attack on Pearl Harbor.

Shortly after the attack of December 7, 1941, the United States restarted its crypt- analytic program in earnest. 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 and the value of the intelligence obtained from these systems is difficult to overestimate.

In the Pacific theatre, 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 [61]. The Japanese 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 halt the advance of the Japanese in the Pacific for the first time. The Japanese Navy was never able to recover from the losses inflicted during this battle.

In Europe, the breaking of the Enigma cipher (code named ULTRA) was also a crucial aid to the allies during the war [59, 87]. It is often claimed that the ULTRAintelligence was so valuable that in November of 1940, 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 [229]. Churchill was supposedly concerned that a warning might tip off the Germans that their cipher had been broken.

The Enigma was initially broken by the Poles. After the fall of Poland, the Polish cryptanalysts escaped to France. Shortly thereafter, France fell to the Nazis and the Polish cryptanalysts escaped to England, where they provided their knowledge to British cryptanalysts. Remarkably, the Polish cryptanalysts were not allowed to continue their work on the Enigma. However, the British team—including the computing pioneer,

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Alan Turing—developed an improved attack [59]. A picture of the Enigma appears in Figure 2.5, and the inner workings of the guts of the Enigma are presented in Problem 12 of Chapter 6.

In the post World War II era, cryptography finally moved from a “black art” into the realm of science. The publication of Claude Shannon’s seminal 1949 paperInformation Theory of Secrecy Systems[207] marks the turning point. Shannon’s paper proved that the one-time pad is secure and also offered two fundamental cipher design principles: confusionanddiffusion.

Confusion is designed to obscure the relationship between the plaintext and cipher- text, while diffusion is supposed to spread 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, evidently confusion alone is “enough,” while, apparently, diffusion alone is not.

These two concepts—confusion and diffusion—are still the guiding principles in cipher design today. In subsequent chapters, it will become clear how crucial these concepts are to modern block cipher design.

Until recently, cryptography remained primarily the domain of governments. That changed dramatically in the 1970s, primarily due 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, and it was clear that the commercial products of the day were lacking. The National Bureau of Standards, or NBS4_{, issued a request for cryptographic algorithms.}

The ultimate result of this process was a cipher known as the Data Encryption Standard, or DES, which became an official U.S. government standard.

It’s impossible to overemphasize the role that DES has played in the modern history of cryptography. We’ll have much more to say about DES in the next chapter.

After DES, academic interest in cryptography grew rapidly. Public key cryptog- raphy was discovered (or, more precisely, rediscovered) shortly after the arrival of DES. By the 1980s, there were annual CRYPTO conferences, which have consis- tently displayed high-quality work in the field. In the 1990s, the Clipper Chip and the development of a replacement for the aging DES were two of the many crypto highlights.

Governments continue to fund major organizations that work in crypto and related fields. However, it’s clear that the crypto genie has escaped from its government bottle, never to be put back.