computer science

Military Cryptanalytics

Military Cryptanalytics is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Military Cryptanalytics rather than just read about it. In short: Military Cryptanalytics (or MILCRYP as it is sometimes known) is a revision by Lambros D. Callimahos of the series of books written by William F.

Key takeaways

Military Cryptanalytics belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Military Cryptanalytics to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Military Cryptanalytics from memory before moving on to harder problems.

Reference excerpt

Military Cryptanalytics (or MILCRYP as it is sometimes known) 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.

Callimahos on the work From the Introduction in Part I, Volume I, by Callimahos: "This text represents an extensive expansion and revision, both in scope and content, of the earlier work entitled 'Military Cryptanalysis, Part I' by William F. Friedman. This expansion and revision was necessitated by the considerable advancement made in the art since the publication of the previous text." Callimahos referred to parts III–VI at the end of the first volume: "...Part III will deal with varieties of aperiodic substitution systems, elementary cipher devices and cryptomechanisms, and will embrace a detailed treatment of cryptomathematics and diagnostic tests in cryptanalysis; Part IV will treat transposition and fractioning systems, and combined substitution-transposition systems; Part V will treat the reconstruction of codes, and the solution of enciphered code systems, and Part VI will treat the solution of representative machine cipher systems." However, parts IV–VI were never completed.

Declassification Both Military Cryptanalytics and Military Cryptanalysis have been subjects of Mandatory Declassification Review (MDR) requests, including one by John Gilmore in 1992-1993 and two by Charles Varga in 2004 and 2016. All four parts of Military Cryptanalysis and the first two parts of the Military Cryptanalytics series have been declassified. The third part of Military Cryptanalytics was declassified in part in December 2020 and published by GovernmentAttic.org in 2021. In 1984 NSA released copies of Military Cryptanalytics parts I and II to the (US) National Archives and Records Administration, Record Group 457, as SRH-273 and SRH-274, respectively. ("SRH" stands for "Special Research History.")

Reprints All the declassified books except the third part of Military Cryptanalytics have been reprinted by Aegean Park Press. Each part of Military Cryptanalytics consists of two volumes: the first volume contains the tutorial text and the second volume contains appendices. Part I includes material on both uniliteral and multiliteral ciphers and polyalphabetic ciphers. Part II includes material on repeating-key and bipartite systems and periodic ciphers. Part II, volume II includes the Zendian Problem, a practical exercise in traffic analysis and cryptanalysis. For the Aegean Park Press edition, Wayne G. Barker added programs for the TRS-80.

Books Military Cryptanalytics, Part I, Volume 1, ISBN 0-89412-073-5 Military Cryptanalytics, Part I, Volume 2, ISBN 0-89412-074-3 Military Cryptanalytics, Part II, Volume 1, ISBN 0-89412-075-1 Military Cryptanalytics, Part II, Volume 2, ISBN 0-89412-076-X Military Cryptanalysis, Part I, ISBN 0-89412-044-1 Military Cryptanalysis, Part II, ISBN 0-89412-064-6 Military Cryptanalysis, Part III, Simpler Varieties of Aperiodic Substitution Systems, ISBN 0-89412-196-0 Military Cryptanalysis, Part IV, Transposition and Fractionating Systems, ISBN 0-89412-198-7

See also National Security Agency academic publications

External links Military Cryptanalysis at NSA.gov; this provides the text of the Friedman series (only) Friedman publications at NSA.gov Friedman collection at Archive.org Including Military Cryptanalysis I, II, III and IV and Military Cryptanalytics I and II EFF "Legal Cases - Privacy/FOIA - Gilmore v. NSA (Crypto Docs)" Archive 2004 FOIA Request for Military Cryptanalytics Vol III 2016 FOIA Request for Military Cryptanalytics Vol III Military Cryptanalytics, Part III, by Lambros D. Callimahos, 1977

Worked examples

Example 1 — a first encounter with Military Cryptanalytics

Start with the simplest possible case. Write down what Military Cryptanalytics claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Military Cryptanalytics before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Military Cryptanalytics ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Military Cryptanalytics

In research: Military Cryptanalytics appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Military Cryptanalytics in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Military Cryptanalytics is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cryptographic attacks, Cryptography books, Military communications, so understanding it makes those chapters shorter.
In everyday life: Look for Military Cryptanalytics outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Military Cryptanalytics in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Military Cryptanalytics means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Military Cryptanalytics out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Military Cryptanalytics in simple terms?

Military Cryptanalytics (or MILCRYP as it is sometimes known) is a revision by Lambros D. Callimahos of the series of books written by William F.

Why does Military Cryptanalytics matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Military Cryptanalytics?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Military Cryptanalytics.