Historical Document · 1992
Friedman's six 1963 lectures on cryptologic history, biographical sketch and bibliography, Callimahos's 'The Legendary William F. Friedman', Chiles's essay and the 1980 tribute to Elizebeth (226 pp, 33 MB, text layer)
UNITED STATES CRYPTOLOGIC HISTORY Sources in Cryptologic History Number 3 The Friedman Legacy: A Tribute to William and Elizebeth Friedman Third Printing CENTER FOR CRYPTOLOGIC HISTORY NATIONAL SECURITY AGENCY 2006 Table of Contents Page Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v by David Gaddy Biographical Sketch, William F. Friedman . . . . . . . . . . . . . . . . . . . . . . vii “Six Lectures on Cryptology” by William F. Friedman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 by Frank Rowlett Lecture I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Introduction Lecture II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 The earliest attempts at cryptography, from the invention of the art of writing to Bacon’s “Bi-literarie” cipher. Lecture III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 The cryptosystems used by the British Regulars and by the Colonials during the period of the American Revolution. This is followed by a brief explanation of the cryptanalytic nature of the initial breaks in the solution of the ancient Egyptian hieroglyphic writing. Lecture IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55 Cryptology in the Civil War. Lecture V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91 Cryptology from the end of the Civil War to the end of World War I. Lecture VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133 Cryptology from the end of World War I to the end of World War II. The emphasis has been placed upon communications security (COMSEC), not only because in five preceding lectures the emphasis was placed very largely upon communications intelligence (COMINT), but Page iii also because, in the final analysis, COMSEC, though not as spectacular as COMINT, is really more vital to national security. Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173 Appendix II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177 Bibliography [for Friedman lectures] . . . . . . . . . . . . . . . . . . . . . . . .183 “The Legendary William F. Friedman” by Lambros Callimahos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185 “Breaking Codes Was This Couple’s Lifetime Career” by James R. Chiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195 In Memoriam: Elizebeth Smith Friedman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .209 Page iv Foreword To term this modest collection The Friedman Legacy requires both explanation and apologia. Of Friedman, as of Wren, it might well be said, “If you seek his monument, look around you” at the giant and far-flung corporate entity that represents American cryptology today. But a most tangible and rewarding form of his legacy for many of us has long been his “Lectures.” First published within NSA in 1963, after serialization in a journal five years earlier, they were republished two years later by his first recruit into government service and the first commandant of the National Cryptologic School, the eminent cryptologist Frank Rowlett. In his Foreword to that edition, Mr. Rowlett described the lectures as “. . . the history of Cryptology [as] recorded by the most prominent pioneer in the application of scientific principles to the field – one who, without question, laid the foundation for our modern concepts. It is hoped that both new and old employees may be inspired with a feeling of belonging to a profession that abounds in drama and fascination and that has had a profound impact on history.” The sense of what one might term “the romance of cryptology” continues to adhere: Director Vice Admiral W.O. Studeman, introducing the 1990 Cryptologic History Symposium in NSA’s William F. Friedman Auditorium, referred affectionately and with a hint of awe to “this magical [MAGIC-al?] place.” That mystique, derived from an appreciation of the privilege of service to the nation in a largely anonymous but most rewarding profession, in company with a rare breed of men and women, must be rediscovered with each new generation. As tools and techniques become less personal, as individual accomplishment is more difficult to discern, it comes to depend increasingly on awareness of the past – the heritage, the traditions, the symbols, of the Friedman era, when a tiny unit of Army civilians and their uniformed Navy counterparts began a revolution – and the ability to find equally satisfactory modern equivalents, to become part of a continuum. In making The Friedman Lectures again available to the professional community, several related papers have been included to give the newcomer a fuller appreciation of Friedman and his fellow cryptanalyst and lifemate, Elizebeth: the recollections of his colleague and amanuensis, Lambros Callimahos, Guru and Caudillo of the Dundee Society (parochial humor that must be separately explained to the newcomer), a tribute to Elizebeth on the occasion of her death, and an appreciation of the two from a fellow laborer in the vineyard – these, with the Lectures, we have been bold to style The Friedman Legacy. David W. Gaddy Chief Center For Cryptologic History [1992] Page v Biographical Sketch WILLIAM FREDERICK FRIEDMAN (18911969), the dean of modern American cryptologists, was the most eminent pioneer in the application of scientific principles to cryptology and laid the foundation for present-day cryptologic concepts. Born in Kishinev, Russia, on 24 September 1891, he was brought to the United States in 1892; married Elizebeth Smith in May 1917; fathered a son, John, and a daughter, Barbara. He retired from the National Security Agency in 1955 after thirty-five years of service with U.S. cryptologic activities. Mr. Friedman died at his home in Washington, D.C., on 2 November 1969. B.S. (genetics), Cornell University, 1914; Research Fellow, New York State Experiment Station, Geneva, N.Y., 1914; Graduate Student and Instructor in Genetics, Cornell University, 19141915; Director, Department of Genetics, Riverbank Laboratories, Geneva, Ill., 1915-1916; Director, Departments of Ciphers and Genetics, Riverbank Laboratories, 1916-1918; 1st lieutenant, serving in Code and Cipher Solving Section, G-2, General Headquarters, American Expeditionary Forces (GHQ AEF), Chaumont, France, 1918-1919 (retired as lieutenant vcolonel, USAR, 1951); Director, Department of Ciphers, Riverbank Laboratories, 1919-1920; Cryptographer, Office of the Chief Signal Officer (OCSigO), Washington, D.C., 1921; Chief Cryptographer, U.S. Signal Corps, 1922-1929; Cryptanalyst, War Department, 1930-1942; Director, Communications Research, Signal Intelligence Service, later Army Security Agency, 1942-1947; Chief, Communications Research Section, Army Security Agency, 1947-1949; Cryptologic Consultant, Army Security Agency, 1949; Research Consultant, Armed Forces Security Agency, 1949-1951; Research Consultant, National Security Agency, 1951-1954; Special Assistant to the Director, NSA, 1954-1955 (retirement); Member, NSA Scientific Advisory Board, 1954-1969; Special Consultant, National Security Agency, 1955-1969. Page vii For his many contributions to the security of his country, he received the War Department Medal for Exceptional Civilian Service (1944), the Presidential Medal for Merit (1946), the Presidential National Security Medal (1955), and a special congressional award of $100,000 for inventions and patent in the field of cryptology (1956). For their contributions to literature, he and Mrs. Friedman received the Fifth Annual Shakespeare Award in 1958 from the American Shakespeare Festival Theater and Academy for their book The Shakespearean Ciphers Examined. Mr. Friedman was a member of Sigma Xi, the Cosmos Club, the U.S. Naval Institute, and the Shakespeare Association of America. He was listed in Who’s Who in America and American Men of Science. Author of many classified books and brochures, technical treatises and articles on cryptologic subjects; articles in the Signal Corps Bulletin (19251940); Riverbank Publications on Cryptology (1918-1922), the more important of which are “Several Machine Ciphers and their Solution,” “The Index of Coincidence and Its Applications to Cryptography,” and “Applications of the Science of Statistics to Cryptography,” Elements of Cryptanalysis (1923); technical papers and reports published by the Office of the Chief Signal Officer and by the Signal Intelligence Service (1935-1945), among which may be mentioned “The Principles of Indirect Symmetry of Position in Secondary Alphabets and their Application in the Solution of Polyalphabetic Substitution Ciphers,” “American Army Field Codes in the American Expeditionary Forces in the First World War” (1942); “Field Codes used by the German Army during the World War,” and “Analysis of a Mechanico-Electrical Cryptograph”; Encyclopedia Britannica article “Codes and Ciphers (Cryptology),” 1927 (revised 1954); Military Cryptanalytics, Parts I & II (with L. Callimahos); “The Cryptologist Looks at Shakespeare”; The Shakespearean Ciphers Examined, coauthor with his wife Elizebeth Smith Friedman (Folger Shakespeare Prize, 1955); Page viii “Acrostics, Anagrams, and Chaucer,” Philological Quarterly, 1959; “Jacques Casanova, Cryptologist,” in Casanova Gleanings, Nice, France, 1961. William & Elizebeth The Riverbank Years The Friedman home in Washington, DC William & Elizebeth The Later Years Six Lectures on Cryptology by William F. Friedman Foreword These six lectures by Mr. William F. Friedman, dean of American cryptologists, were prepared in order to have the history of cryptology recorded by the most eminent pioneer in the application of scientific principles to the field – one who, without question, laid the foundation for our modern concepts. It is hoped that both new and old employees may be inspired with a feeling of belonging to a profession that abounds in drama and fascination and that has had a profound impact on history. The lectures, published for the first time in 1963,* are now [1965] being reprinted to meet a continuing demand for an authoritative history of our craft. Frank B. Rowlett Commandant, National Cryptologic School * Editor’s Note: The Friedman lectures were also serialized in the NSA Technical Journal from 1959 to 1961. Page 2 Lecture I The objective of this series of lectures is to create an awareness of the background, development, and manner of employment of a science that is the basis of a vital military offensive and defensive weapon known as CRYPTOLOGY, a word that comes from the Greek kryptos, meaning secret or hidden, plus logos, meaning knowledge or learning. Cryptology will be specifically defined a little later; at the moment, however, I’m sure you know that it has to do with secret communications. Let me say at the outset of these lectures that I may from time to time touch upon matters that are perhaps essentially peripheral or even irrelevant to the main issues, and if a defense is needed for such occasional browsing along the byways of the subject, it will be that long preoccupation with any field of knowledge begets a curiosity, the satisfaction of which is what distinguishes the dedicated professional from the person who merely works just to gain a livelihood in whatever field he happens to find himself a job. That’s not much fun, I’m afraid. By the way, a British writer, James Agate, defines a professional as the man who can do his job even when he doesn’t feel like doing it; an amateur as a man who can’t do his job even when he does feel like doing it. This is pretty tough on the gifted amateur, and I for one won’t go all the way with Agate’s definition. There are plenty of instances where gifted amateurs have done and discovered things to the chagrin and red-facedness of the professionals. Coming back now to the main thoroughfare after the foregoing brief jaunt along a byway, I may well begin by telling you that the science of cryptology has not always been regarded as a vital military offensive and defensive weapon, or even as a weapon in the first place. Here I am reminded of a story in a very old book on cryptography. The story is probably apocryphal, but it’s a bit amusing, and I give it for what it’s worth. It seems that about two thousand years ago there lived a Persian queen named Semiramis, who took an active interest in cryptology. She was in some respects an extraordinarily unpleasant woman, and we learn without surprise that she met with an untimely death. She left behind her instructions that her earthly remains were to be placed in a golden sarcophagus within an imposing mausoleum, on the outside of which, on its front stone wall, there was to be graven a message, saying Stay, weary traveller! If thou art footsore, hungry, or in need of money Unlock the riddle of the cipher graven below, And thou wilt be led to riches beyond all dreams of avarice! Below this curious inscription was a cryptogram, a jumble of letters without meaning or even pronounceability. For several hundred years the possibility of sudden wealth served as allure to many experts who tried very hard to decipher the cryptogram. They were all without success, until one day there appeared on the scene a longhaired, bewhiskered, and bespectacled savant who after working at the project for a considerable length of time, solved the cipher, which gave him detailed instructions for finding a secret entry into the tomb. When he got inside, he found an instruction to open the sarcophagus, but he had to solve several more cryptograms, the last one of which may have involved finding the correct combination to a five-tumbler combination lock – who knows? Well, he solved that one too, after a lot of work, and this enabled him to open the sarcophagus, inside which he found a box. In Page 3 the box was a message, this time in plain language, and this is what it said: O, thou vile and insatiable monster! To disturb these poor bones! If thou hast learned something more useful than the art of deciphering, Thou wouldst not be footsore, hungry, or in need of money! I’m frank to confess that many times during my forty-year preoccupation with cryptology, and generally near the middle and the end of each month, I have felt that good old Queen Semiramis knew what she was talking about. However, earning money is only a part of the recompense for working in the cryptologic field, and I hope that most of you will find out sooner or later what some of these other recompenses are, and what they can mean to you. If Queen Semiramis thought there are other things to learn that are more useful than the art of deciphering, I suppose we’d have to agree, but we are warranted in saying, at least, that there isn’t any question about the importance of the role that cryptology plays in modern times: all of us are influenced and affected by it, as I hope to show you in a few minutes. I shall begin by reading from a source you’ll all recognize – Time, the issue of 17 December 1945. I will preface the reading by reminding you that by that date World War II was all over – or at least V-E and V-J days had been celebrated some months before. Some of you may be old enough to remember very clearly the loud clamor on the part of certain vociferous members of Congress, who had for years been insisting upon learning the reasons why we had been caught by surprise in such a disastrous defeat as the Japanese had inflicted upon us at Pearl Harbor. This clamor had to be met, for these congressmen contended that the truth could no longer be hushed up or held back because of an alleged continuing need for military secrecy, as claimed by the adminis- Page 4 tration and by many Democratic senators and representatives. The war was over – wasn’t it? – Republican senators and representatives insisted. There had been investigations – a half dozen of them – but all except one were TOP SECRET. The Republicans wanted – and at last they got what they desired – a grand finale joint congressional investigation that would all be completely open to the public. No more secrets! It was spectacular. Not only did the congressional inquiry bring into the open every detail and exhibit uncovered by its own lengthy hearings, but it also disclosed to America and to the whole world everything that had been said and shown at all the previous Army and Navy investigations. Most of the information that was thus disclosed had been, and much of it still was, TOP SECRET; yet all of these precious secrets became matters of public information as a result of the congressional investigation. There came a day in the congressional hearings when the Chief of Staff of the United States Army at the time of the Pearl Harbor attack, fivestar general George C. Marshall, was called to the witness stand. He testified for several long, long days, eight of them in all. Toward the end of the second day of his ordeal, he was questioned about a letter it had been rumored he’d written to Governor Dewey in the autumn of 1944 during the presidential campaign. The letter was about codes. With frozen face, General Marshall balked at disclosing the whole letter. He pleaded most earnestly with the committee not to force him to disclose certain of its contents, but to no avail. He had to bow to the will of the majority of the committee. I shall now read from Time a bit of information that may be new to many of my listeners, especially to those who were too young in December 1945 to be delving into periodical literature or to be reading any pages of the daily newspaper other than those on which the comics appear. Said Time: U.S. citizens discovered last week that perhaps their most potent secret weapon of World War II was not radar, not the VT fuse, not the atom bomb, but a harmless little machine which cryptographers had painstakingly constructed in a hidden room in Washington. With this machine, built after years of trial and error, of inference and deduction, cryptographers had duplicated the decoding devices used in Tokyo. Testimony before the Pearl Harbor Committee had already shown that the machine, known as ‘Magic’, was in use long before December 7,1941, and had given ample warning of the Jap’s sneak attack, if only U.S. brass hats had been smart enough to realize it. Now, General Marshall continued the story of “Magic’s” magic: 1. It had enabled a relatively small U.S. Force to intercept a Jap invasion fleet, win a decisive victory in the Battle of the Coral Sea, thus saving Australia and New Zealand. 2. It had directed U.S. submarines unerringly to the sea lanes where Japanese convoys would be passing. winning of World War II without telling you that the account given by Time of the achievements of Magic makes it appear that all the secret intelligence gained from our reading Japanese messages was obtained by using that “harmless little machine” that Time said was used in Tokyo by the Japanese Foreign Office. I must correct that error by explaining first that Magic was not the name of the machine but a term used to describe the intelligence material to which the machine, among other sources, contributes and then by telling you that the secret information we obtained that way had little to do with those portions of the Magic material that enabled our navy to win such spectacular battles as those of the Coral Sea and Midway, and to waylay Japanese convoys. The naval parts of Magic were nearly all obtained from Japanese naval messages by our own very ingenious U.S. Navy cryptanalysts. At that time, I may tell those of you who are new, the army and navy had separate but cooperating cryptologic agencies and activities; the United States Air Force was not yet in existence as an autonomous and separate component of the armed forces; and work on Japanese, German, and Italian air force communications was done by army cryptanalysts, admirably assisted by personnel of what was then known as the Army Air Corps. 3. It had given the U.S. full advance information on the size of the Jap forces advancing on Midway, enabled our Navy to concentrate ships which otherwise might have been 3,000 miles away, thus set up an ambush which proved to the the turning-point victory of the Pacific war. 4. By decoding messages from Japan’s Ambassador Oshima in Berlin, often reporting interviews with Hitler, it had given our forces invaluable information on German war plans. Time goes on to give more details of that story, to which I may later return, but I can’t leave this citation of what cryptology did toward our It is hardly necessary to tell you how carefully the Magic of World War II was guarded before, during, and after the war until the congressional inquiry brought most of it out in the open. Some remaining parts of it are still very carefully guarded. Even the fact of the existence of Magic was known to only a very few persons at the time of Pearl Harbor – and that is an important element in any attempt to explain why we were caught by surprise by the Japanese at Pearl Harbor in a devastating attack that crippled our navy for many months. Let me read a bit from page 261 of the Report of the Majority of the Joint Congressional Investigation of the attack: Page 5 The Magic intelligence was pre-eminently important and the necessity for keeping it confidential cannot be overesti- appears that $1.00 spent for that sort of intelligence was worth $1,000 spent for other military activities and materials. mated. However, so closely held and top secret was this intelligence that it appears that the fact that the Japanese codes had been broken was regarded as of more importance than the information obtained from decoded traffic. Time says, in connection with this phase of the story of Magic during World War II: So priceless a possession was Magic that the U.S. high command lived in constant fear that the Japs would discover the secret, change their code machinery, force U.S. cryptographers to start all over again. Now I don’t want to overemphasize the importance of communications intelligence in World War II, but I think it warranted to read a bit more of what is said about its importance in the Report of the Majority. The following is from p. 232: . . . all witnesses familiar with Magic material throughout the war have testified that it contributed enormously to the defeat of the enemy, greatly shortened the war, and saved many thousands of lives. General Chamberlin, who was General MacArthur’s operations officer, or G-3, throughout the war in the Pacific, has written: “The information G-2, that is, the intelligence staff, gave me in the Pacific Theater alone saved us many thousands of lives and shortened the war by no less than two years.” We can’t put a dollars-and-cents value on what our possession of COMINT meant in the way of saving lives; but we can make a dollars-and-cents estimate of what communications intelligence meant by shortening the war by two years, and the result of that estimate is that it Page 6 In short, when our commanders had that kind of intelligence in World War II, they were able to put what small forces they had at the right place, at the right time. But when they didn’t have it – and this happened, too – their forces often took a beating. Later on we’ll note instances of each type. I hope I’ve not tried your patience by such a lengthy preface to the real substance of this series of lectures; let’s get down to brass tacks. For those of you who come to the subject of cryptology for the first time, a few definitions will be useful, in order that what I shall be talking about may be understood without question. Agreement on basic terminology is always desirable in tackling any new subject. In giving you the definitions, there may be a bit of repetition because we shall be looking at the same terms from somewhat different angles. First, then, what is cryptology? Briefly, we may define it as the doctrine, theory, or branch of knowledge that treats of hidden, disguised, or secret communications. You won’t find the word in a small dictionary. Even Webster’s Unabridged defines it merely as “secret or enigmatical language”; and in its “Addenda Section,” which presumably contains new or recently coined words, it is defined merely as “the study of cryptography.” Neither of these definitions is broad or specific enough for those who are going to delve somewhat deeply into this science. Cryptology has two main branches: the first is cryptography or, very briefly, the science of preparing secret communications and the second is cryptanalysis or the science of solving secret communications. Let’s take up cryptography first, because as a procedure it logically precedes cryptanalysis: before solving anything, there must be something to solve. Cryptography is that branch of cryptology that deals with the various means, methods, devices, and machines for converting messages in ordinary, or what we call plain language, into secret language, or what we call cryptograms. Here’s a picture of one of the most famous cryptograms in history. (See fig. 1.) It was the solution of this cryptogram that resulted in bringing America into World War I on the side of the Allies on 6 April 1917 ,just about six weeks after it was solved. I’ll tell you about it later in this series. Cryptography also includes the business of reconverting the cryptograms into their original plain-language form, by a direct reversal of the steps followed in the original transformation. This implies that the persons involved in both of these bits of business, those at the enciphering and sending end, and those at the receiving and deciphering end, have an understanding of what procedures, devices, and so on, will be used and exactly how – down to the very last detail. The what and the how of the business constitutes what is generally referred to as the key. The key may consist of a set of rules, alphabets, procedures, and so on; it may also consist of an ordinary book that is used as a source of keys; or it may be a specialized book, called a codebook. That cryptogram I just showed you was made by using a book – a German codebook. To encrypt is to convert or transform a plaintext message into a cryptogram by following certain rules, steps, or processes constituting the key or keys and agreed upon in advance by the correspondents, or furnished them by higher authority. To decrypt is to reconvert or to transform a cryptogram into the original equivalent plaintext message by a direct reversal of the encrypting process, that is, by applying to the cryptogram the key or keys, usually in a reverse order, employed in producing it. A person who encrypts and decrypts messages by having in his possession the necessary keys is called a cryptographer or a cryptographic clerk. Fig. 1 The Zimmermann Telegram Encrypting and decrypting are accomplished by means collectively designated as codes and ciphers. Such means are used for either or both of two purposes: (1) secrecy and (2) economy. Secrecy usually is far more important in diplomatic and military cryptography than economy, but it is possible to combine secrecy and economy in a single system. Persons technically unacquainted with cryptology often talk about "cipher codes,” a term that I suppose came into use to differentiate the term "code" as used in cryptology from the connotations, for example, the Napoleonic Code, a traffic code, a building code, a code of ethics, and so on. Now, in cryptology, there is no such thing as a “cipher code.” There are codes and there are ciphers, and we might as well learn right off the differences between them, so that we get them straightened out in our minds before proceeding further. Page 7 In ciphers, or in cipher systems, cryptograms are produced by applying the cryptographic treatment to individual letters of the plaintext messages, whereas in codes or in code systems, cryptograms are produced by applying the cryptographic treatment generally to entire words, phrases, and sentences of the plaintext messages. More specialized meanings of the terms will be explained in detail later, but in a moment I'll show you an example of a cryptogram in cipher and one in code. ble. Here’s an authentic example of a transposition cipher; I call it authentic because it was sent to President Roosevelt, and the Secret Service asked me to decipher it (fig. 2). Imagine my chagrin when I had to report that it says “Did you ever bite a lemon?” In the second, called substitution, the letters of the plain text retain their original relative positions but are replaced by other letters with different sound values, or by symbols of some sort, so that the original text becomes unintelligible. A cryptogram produced by means of a cipher system is said to be in cipher and is called a cipher message, or sometimes simply a cipher. The act or operation of encrypting a cipher message is called enciphering, and the enciphered version of the plain text, as well as the act or process itself, is often referred to as the encipherment. A cryptographic clerk who performs the process serves as an encipherer. The corresponding terms applicable to the decrypting cipher messages are deciphering, decipherment, decipherer. Nobody will quarrel with you very hard if you wish to say that a code system is nothing but a specialized form of substitution; but it’s best to use the word “code” when a codebook is involved, and to use “substitution cipher” when a literal system of substitution is used. It is possible to encrypt a message by a substitution method and then to apply a transposition method to the substitution text, or vice versa. Combined transposition-substitution ciphers do not form a third class of ciphers; they are only A cryptogram produced by means of a code system is said to be in code and is called a code message. The text of the cryptogram is referred to as code text. This act or operation of encrypting is called encoding, and the encoded version of the plain text, as well as the act or process itself, is referred to as the encodement. The clerk who performs the process serves as an encoder. The corresponding terms applicable to the decrypting of code messages are decoding, decodement, and decoder. A clerk who encodes and decodes messages by having in his possession the pertinent codebooks is called a code clerk. Technically, there are only two distinctly different types of treatment that may be applied to written plain text to convert it into a cipher, yielding two different classes of ciphers. In the first, called transposition, the letters of the plain text retain their original identities and merely undergo some change in the relative positions, with the result that the original text becomes unintelligi- Page 8 Fig. 2 occasionally encountered in military cryptography. Applying a cipher to code groups is a very frequently used procedure, and we’ll see cases of that too. Fig. 4 Fig. 5 Fig. 3 Now for an example of a cryptogram in code. In figure 3 is a plaintext message in the handwriting of President Wilson to his special emissary in London, Colonel House. Contained in figure 4 is the cryptogram after the plain text was encoded by Mrs. Wilson. The president himself then typed out the final message on his own typewriter, for transmission by the Department of State. It would appear that President Wilson lacked confidence in the security of the Department of State’s methods – and maybe with good reason, as may be seen in the following extract from a letter dated 14 September 1914 from the president to Ambassador Page in London: “We have for some time been trying to trace the leaks, for they have occurred frequently, and we are now convinced that our code is in possession of persons at intermediary points. We are going to take thoroughgoing measures.” Perhaps one of the measures was that the president got himself a code of his own. I must follow this up some day. A cipher device is a relatively simple mechanical contrivance for encipherment and decipherment, usually hand-operated or manipulated by the fingers, for example, a device with concentric rings of alphabets, manually powered. In figure 5 is an example – a cipher device with such rings. I’ll tell you about it later. A cipher machine is a relatively complex apparatus or mechanism for encipherment and decipherment, usually equipped with a typewriter keyboard and generally requiring an external power source. Modern cryptology, following the trend in mechanization and automation in other fields, now deals largely with cipher machines, some highly complicated. Figure 6 shows an example of a modern cipher machine with keyboard and printing mechanism. One of the expressions that uninformed laymen use, but that you must never use, is “the German code,” or “the Japanese code,” or “the Navy cipher,” and the like. When you hear this sort of expression, you may put the speaker down at once as a novice. There are literally hundreds of different codes and ciphers in simultaneous use by every large and important government or service, each suited to a special purpose; or where there is a multiplicity of systems of the same general nature, the object is to prevent a great deal of traffic being encrypted in the same key, thus overloading the system and making it vulnerable to attack by methods and procedures to be mentioned in broad terms in a few moments. The need for secrecy in the conduct of important affairs has been recognized from time immemorial. In the case of diplomacy and organized warfare, this need is especially important in regard to communications. However, when such Page 9 That branch of cryptology that deals with the principles, methods, and means employed in the solution or analysis of cryptosystems is called cryptanalytics. The steps and operations performed in applying the principles of cryptanalytics constitute cryptanalysis. To cryptanalyze a cryptogram is to solve it by cryptanalysis. A person skilled in the art of cryptanalysis is called a cryptanalyst, and a clerk who assists in such work is called a cryptanalytic clerk. Fig.6. TSEC/KL-7 Cipher Machine (U.S.) communications are transmitted by electrical means, they can be heard or, as we say, intercepted, and copied by unauthorized persons, usually referred to collectively as the enemy. The protection resulting from all measures designed to deny to the enemy information of value that may be derived from the interception and study of such communications is called communications security or, for short, COMSEC. In theory, any cryptosystem except one, to be discussed in due time, can be attacked and “broken,” i.e., solved, if enough time, labor, and skill are devoted to it, and if the volume of traffic in that system is large enough. This can be done even if the general system and the specific key are unknown at the start. You will remember that I prefaced my statement any cryptosystem can be solved by saying “in theory,” because in military operations theoretical rules usually give way to practical considerations. Page 10 Information derived from the organized interception, study, and analysis of the enemy’s communications is called communications intelligence or, for short, COMINT. Let us take careful note that COMINT and COMSEC deal with communications. Although no phenomenon is more familiar to us than that of communication, the fact of the matter is that this magic word means many things to many people. A definition of communication that is broad enough for our purposes would be that communication deals with intelligent messages exchanged between intelligent beings. This implies that human beings and human operators are involved in the preparation, encryption, transmission, reception, decryption, and recording of messages that at some stage or stages are in written form and in some stage or stages are in electrical form as signals of one sort or another. But in recent years there have come into prominence and importance electrical signals that are not of the sort I’ve just indicated. They do not carry “messages” in the usual sense of the word; they do not convey from one human being to another an intelligible sequence of words and an intelligible sense. I refer here to electrical or electronic signals such as are employed in homing or directional beacons, in radar, in telemetering or recording data of an electrical or electronic nature at a distance, and so on. Information obtained from a study of enemy electronic emissions of these sorts is called electronic intelligence or, for short, ELINT. COMINT and ELINT comprise SIGINT, that is, signals intelligence. Cryptology is the science that is concerned with all these branches of secret signaling. In this series of lectures we shall be concerned only with COMSEC and COMINT, leaving for others and for other times the subject of ELINT. This means that we shall deal with communications or messages. Communication may be conducted by any means susceptible of ultimate interpretation by one of the five senses, but those most commonly used are seeing and hearing. Aside from the use of simple visual and auditory signals for communication over relatively short distances, the usual method of communication between or among individuals separated from another by relatively long distances involves, at one stage or another, the act of writing or of speaking over a telephone. Privacy or secrecy in communication by telephone can be obtained by using equipment that affects the electrical currents involved in telephony, so that the conversations can be understood only by persons provided with suitable equipment properly arranged for the purpose. The same thing is true in the case of facsimile transmission (i.e., the electrical transmission of ordinary writing, pictures, drawings, maps). Even today there are already simple forms of enciphered television transmissions. Enciphered facsimile is called cifax; enciphered telephony, ciphony; and enciphered television, civision. However, these lectures will not deal with these electrically and cryptanalytically more complex forms of cryptology. We shall stick to enciphered or encrypted writing – which will be hard enough for most of us. Writing may be either visible or invisible. In the former, the characters are inscribed with ordinary writing materials and can be seen with the naked eye; in the latter, the characters are inscribed by means or methods that make the writing invisible to the naked eye. Invisible writing can be prepared with certain chemicals called sympathetic or secret inks, and in order to “develop” such writing, that is, make it visible, special processes must usually be applied. Shown in fig- ure 7 is an interesting example – the developed secret-ink message that figured in an $80,000,000 suit won by two American firms against the German government after World War I sabotage was proved, There are also methods of producing writing that is invisible to the naked eye because the characters are of microscopic size, thus requiring special microscopic and photographic apparatus to enlarg