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{{Short description|An exercise in communication intelligence}}
'''The Zendian Problem''' was a series of problems in ] and ] devised by ] as part of a course taught to ] ], whose graduates became members of the ]. The '''Zendian problem''' was an exercise in communication intelligence operations (mainly ] and ]) devised by ] as part of an advanced course, CA-400, that Callimahos taught to ] ] starting in the 1950s.


==Content==
The scenario involves 375 radio messages intercepted on December 23 by the ] contingent of a ] force landed on the fictional island of Zendia in the ]. A typical intercept looks like this: The scenario involves 375 radio messages said to have been intercepted on December 23 by the ] contingent of a ] force landed on the fictional island of Zendia in the ].

A typical intercept looks like this:
<pre><nowiki> <pre><nowiki>
XYR DE OWN 4235KCS 230620T USM-99/00091 XYR DE OWN 4235KCS 230620T USM-99/00091
Line 15: Line 19:
SREEE USSDS DHOAH REEXI PROUT NTTHD JAAAJ EUEBD SREEE USSDS DHOAH REEXI PROUT NTTHD JAAAJ EUEBD
</nowiki></pre> </nowiki></pre>
where the first line is provided by the ] operator, giving ]s, ], time, and reference number. The rest of the message is a transcript of the ] transmission. The numeric "]" originally has unknown meaning; the meanings of various components of this header (such as a serial number assigned by the transmitting organization's message center) can be puzzled out through traffic analysis. The rest of the message is ]; the first group indicates the cryptosystem used, and often the second group contains a message-specific ] element such as initial ] settings.


For each message, the first line is provided by the ] operator, giving ]s, ], time, and reference number. The rest of the message is a transcript of the ] transmission.
⚫ Cryptosystems employed include a one-part ] and ], dinome, and rotor-based machine ciphers; these can be solved without use of a computer. However, solution is not easy, and the practical exercise reinforces many basic principles.

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 ] assigned by the transmitting organization's message center) can be worked out through traffic analysis.

The rest of the message consists of "indicators" and ]; 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 ] element such as initial ] 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 ] the text.

⚫ Cryptosystems employed include ], dinome, and ]-based ]s and a ]. 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 ] 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.

==Availability==
The Zendian problem has been ] and is available either as part of '']''<ref>{{cite book |author1=Callimahos, Lambros D. |author2=Friedman, William F |name-list-style=amp | title=Military Cryptanalytics, Part II, Volume II |publisher=Aegean Park Press | isbn=0-89412-076-X | location=Walnut Creek, CA}}</ref> or as a book in itself.<ref>{{cite book | author=Callimahos, Lambros D. | title=Traffic Analysis and the Zendian Problem |publisher=Aegean Park Press | isbn=0-89412-161-8 | year=1989 | location=Walnut Creek, CA}}</ref> Both were published as reprints by ], 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<ref>{{cite web | url=http://www.karlheinz-everts.de/messages.zip
| title=Problem of Zendia – Messages
| publisher=Karl Heinz-Everts
| year=2009
| access-date=2015-08-07 }}</ref> 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.)

==The Dundee Society==
{{Main|Dundee Society}}
Cryptanalists who successfully finished CA-400 became members of the ]. This society was founded by Lambros D. Callimahos<ref>{{cite web
| url=http://www.nsa.gov/about/cryptologic-heritage/historical-figures-publications/hall-of-honor/2003/lcallimahos.shtml
| title=Lambros D. Callimahos, 1910–1977 (NSA Hall of Honor)
| publisher=National Security Agency
| year=2003
| access-date=2009-11-03 }}</ref> and was so named after the empty Dundee marmalade jar on his desk, as he couldn't disclose the society's real purpose.

==Map of Zendia==
]

A large print showing the fictional nation of Zendia hangs on the wall of the library at the ], 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.


==See also==
⚫ A certain amount of ] inter-] "chatter" is provided, and may help with the analysis.
* ]
* ]
* ]


==References==
⚫ Headers and initial ciphertext groups are also given for intercepts from the next three days; these may be helpful in traffic analysis and in determining certain daily operating procedures.
{{reflist}}


==External links==
The problem has been ] and is available either as part of ] or as a book in itself. Both are published by ].
* — Reprinted books containing the Zendian problem, and other training material.
⚫ * for the Zendian problem. Anyone intending to learn from working on this exercise should ''not'' look at these solutions.
* from Geographicus Rare Antique Maps.


{{cryptography navbox}}
{{spoiler-blank|(partial solutions)}}
{{National Security Agency}}
⚫ There is also a which posts partial solutions for the Zendian Problem. It is ''highly recommended'' that anyone intending to learn from working on this exercise ''not'' look at these solutions.


]
] ]
]
] ]
]

Latest revision as of 15:05, 26 January 2024

An exercise in communication intelligence

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.

Content

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.

Availability

The Zendian problem has been declassified and is available either as part of Military Cryptanalytics or as a book in itself. 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 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.)

The Dundee Society

Main article: Dundee Society

Cryptanalists who successfully finished CA-400 became members of the Dundee Society. This society was founded by Lambros D. Callimahos and was so named after the empty Dundee marmalade jar on his desk, as he couldn't disclose the society's real purpose.

Map of Zendia

High-resolution color map of Zendia

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.

See also

References

  1. Callimahos, Lambros D. & Friedman, William F. Military Cryptanalytics, Part II, Volume II. Walnut Creek, CA: Aegean Park Press. ISBN 0-89412-076-X.
  2. Callimahos, Lambros D. (1989). Traffic Analysis and the Zendian Problem. Walnut Creek, CA: Aegean Park Press. ISBN 0-89412-161-8.
  3. "Problem of Zendia – Messages". Karl Heinz-Everts. 2009. Retrieved 2015-08-07.
  4. "Lambros D. Callimahos, 1910–1977 (NSA Hall of Honor)". National Security Agency. 2003. Retrieved 2009-11-03.

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