The Zendian problem was an exercise in communication intelligence operations (mainly traffic analysis and cryptanalysis) devised by Lambros D. Callimahos as part of an advanced course, CA-400, that Callimahos taught to National Security Agency cryptanalysts starting in the 1950s.
The scenario involves 375 radio messages said to have been intercepted on December 23 by the US Army contingent of a United Nations force landed on the fictional island of Zendia in the Pacific Ocean.
A typical intercept looks like this:
XYR DE OWN 4235KCS 230620T USM-99/00091 9516 8123 0605 7932 8423 5095 8444 6831 JAAAJ EUEBD OETDN GXAWR SUTEU EIWEN YUENN ODEUH RROMM EELGE AEGID TESRR RASEB ENORS RNOMM EAYTU NEONT ESFRS NTCRO QCEET OCORE IITLP OHSRG SSELY TCCSV SOTIU GNTIV EVOMN TMPAA CIRCS ENREN OTSOI ENREI EKEIO PFRNT CDOGE NYFPE TESNI EACEA ISTEM SOFEA TROSE EQOAO OSCER HTTAA LUOUY LSAIE TSERR ESEPA PHVDN HNNTI IARTX LASLD URATT OPPLO AITMW OTIAS TNHIR DCOUT NMFCA SREEE USSDS DHOAH REEXI PROUT NTTHD JAAAJ EUEBD
For each message, the first line is provided by the intercept operator, giving call signs, frequency, time, and reference number. The rest of the message is a transcript of the Morse code transmission.
At the beginning of the intercepted message there is a header which consists of 8 four-digit groups. Initially, the meaning of the numeric header is not known; the meanings of various components of this header (such as a serial number assigned by the transmitting organization's message center) can be worked out through traffic analysis.
The rest of the message consists of "indicators" and ciphertext; the first group is evidently a "discriminant" indicating the cryptosystem used, and (depending on the cryptosystem) some or all of the second group may contain a message-specific keying element such as initial rotor settings. The first two groups are repeated at the end of the message, which allows correction of garbled indicators. The remaining characters are encrypted text. Since the transmissions always use complete groups, "nulls" may have been used to pad out the text.
Cryptosystems employed include transposition, dinome, and rotor-based ciphers and a one-part code. While these can be successfully tackled without use of a computer, solution is not easy. The practical exercise reinforces many basic principles, including ways to exploit having a collection of message traffic.
A certain amount of Plaintext inter-operator "chatter" is also provided, and may help with the analysis.
Headers and discriminants are also given for intercepts from the next three days; these may be used for traffic analysis and in determining daily operating procedures.
The Zendian problem has been declassified and is available either as part of Military Cryptanalytics [1] or as a book in itself. [2] Both were published as reprints by Aegean Park Press, Walnut Creek, CA, USA. There are a few small differences in the ciphertext between these sources, with neither being entirely error-free; indeed, some errors were intentional, and dealing with them is part of the learning process.
Karl Heinz-Everts' Web site provides a link to a downloadable archive [3] of the "intercepts." (The site also provides analysis and partial solutions, which should not be viewed by anyone wishing to learn from working on this exercise.)
Cryptanalists who successfully finished CA-400 became members of the Dundee Society. This society was founded by Lambros D. Callimahos [4] and was so named after the empty Dundee marmalade jar on his desk, as he couldn't disclose the society's real purpose.
A large print showing the fictional nation of Zendia hangs on the wall of the library at the National Cryptologic Museum, which is operated by the NSA. Copies of this map, shrunken to such a degree that most feature labels are illegible, appear in the previously cited books.
Cryptanalysis refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.
In the history of cryptography, the "System 97 Typewriter for European Characters" or "Type B Cipher Machine", codenamed Purple by the United States, was an encryption machine used by the Japanese Foreign Office from February 1939 to the end of World War II. The machine was an electromechanical device that used stepping-switches to encrypt the most sensitive diplomatic traffic. All messages were written in the 26-letter English alphabet, which was commonly used for telegraphy. Any Japanese text had to be transliterated or coded. The 26-letters were separated using a plug board into two groups, of six and twenty letters respectively. The letters in the sixes group were scrambled using a 6 × 25 substitution table, while letters in the twenties group were more thoroughly scrambled using three successive 20 × 25 substitution tables.
In cryptography, coincidence counting is the technique of putting two texts side-by-side and counting the number of times that identical letters appear in the same position in both texts. This count, either as a ratio of the total or normalized by dividing by the expected count for a random source model, is known as the index of coincidence, or IC for short.
William Frederick Friedman was a US Army cryptographer who ran the research division of the Army's Signal Intelligence Service (SIS) in the 1930s, and parts of its follow-on services into the 1950s. In 1940, subordinates of his led by Frank Rowlett broke Japan's PURPLE cipher, thus disclosing Japanese diplomatic secrets before America's entrance into World War II.
Articles related to cryptography include:
Books on cryptography have been published sporadically and with highly variable quality for a long time. This is despite the tempting, though superficial, paradox that secrecy is of the essence in sending confidential messages — see Kerckhoffs' principle.
Elizebeth Smith Friedman was an American cryptanalyst and author who deciphered enemy codes in both World Wars and helped to solve international smuggling cases during Prohibition. Over the course of her career, she worked for the United States Treasury, Coast Guard, Navy and Army, and the International Monetary Fund. She has been called "America's first female cryptanalyst".
In cryptography, the ADFGVX cipher was a manually applied field cipher used by the Imperial German Army during World War I. It was used to transmit messages secretly using wireless telegraphy. ADFGVX was in fact an extension of an earlier cipher called ADFGX which was first used on 1 March 1918 on the German Western Front. ADFGVX was applied from 1 June 1918 on both the Western Front and Eastern Front.
The bombe was an electro-mechanical device used by British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II. The US Navy and US Army later produced their own machines to the same functional specification, albeit engineered differently both from each other and from Polish and British bombes.
The bomba, or bomba kryptologiczna, was a special-purpose machine designed around October 1938 by Polish Cipher Bureau cryptologist Marian Rejewski to break German Enigma-machine ciphers.
Cryptanalysis of the Enigma ciphering system enabled the western Allies in World War II to read substantial amounts of Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename Ultra.
The TSEC/KW-26, code named ROMULUS, was an encryption system used by the U.S. Government and, later, by NATO countries. It was developed in the 1950s by the National Security Agency (NSA) to secure fixed teleprinter circuits that operated 24 hours a day. It used vacuum tubes and magnetic core logic, replacing older systems, like SIGABA and the British 5-UCO, that used rotors and electromechanical relays.
The Two-square cipher, also called double Playfair, is a manual symmetric encryption technique. It was developed to ease the cumbersome nature of the large encryption/decryption matrix used in the four-square cipher while still being slightly stronger than the single-square Playfair cipher.
Military Cryptanalytics is a revision by Lambros D. Callimahos of the series of books written by William F. Friedman under the title Military Cryptanalysis. It may also contain contributions by other cryptanalysts. It was a training manual for National Security Agency and military cryptanalysts. It was published for government use between 1957 and 1977, though parts I and II were written in 1956 and 1959.
Lambros Demetrios Callimahos was a US Army cryptologist and a flute player.
The Dundee Society was a society of graduates of CA-400, a National Security Agency course in cryptology devised by Lambros D. Callimahos, which included the Zendian Problem. The class was held once a year, and new members were inducted into the Society upon completion of the class. The Society was founded in the mid-1950s and continued on after Callimahos' retirement from NSA in 1976. The last CA-400 class was held at NSA in 1979, formally closing the society's membership rolls.
Cryptography, or cryptology, is the practice and study of techniques for secure communication in the presence of adversarial behavior. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others. Core concepts related to information security are also central to cryptography. Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.
The Cipher Department of the High Command of the Wehrmacht was the Signal Intelligence Agency of the Supreme Command of the Armed Forces of the German Armed Forces before and during World War II. OKW/Chi, within the formal order of battle hierarchy OKW/WFsT/Ag WNV/Chi, dealt with the cryptanalysis and deciphering of enemy and neutral states' message traffic and security control of its own key processes and machinery, such as the rotor cipher ENIGMA machine. It was the successor to the former Chi bureau of the Reichswehr Ministry.
Laura Holmes (1932–2016) was a career cryptanalyst and a 2011 Inductee into the NSA Hall of Honor.
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