Frequency Analysis

In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.

Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and combinations of letters occur with varying frequencies. Moreover, there is a characteristic distribution of letters that is roughly the same for almost all samples of that language. For instance, given a section of English language, E, T, A and O are the most common, while Z, Q and X are rare. Likewise, TH, ER, ON, and AN are the most common pairs of letters (termed bigrams or digraphs), and SS, EE, TT, and FF are the most common repeats. The nonsense phrase "ETAOIN SHRDLU" represents the 12 most frequent letters in typical English language text.

In some ciphers, such properties of the natural language plaintext are preserved in the ciphertext, and these patterns have the potential to be exploited in a ciphertext-only attack.

Read more about Frequency AnalysisFrequency Analysis For Simple Substitution Ciphers, History and Usage, Frequency Analysis in Fiction

Other articles related to "analysis, frequency, frequency analysis":

Contact Analysis (cryptanalysis)
... In cryptanalysis, contact analysis is the study of the frequency with which certain symbols precede or follow other symbols ... Contact analysis is based on the fact that, in any sample of any written language, certain symbols appear adjacent to other symbols with varying frequencies ... Although in a sense contact analysis can be considered a type of frequency analysis, most discussions of frequency analysis concern themselves with the simple probabilities of the symbols in the ...
Frequency Analysis in Fiction
... Frequency analysis has been described in fiction ... of the Dancing Men" are examples of stories which describe the use of frequency analysis to attack simple substitution ciphers ...
Timeline Of Computing Hardware 2400 BC–1949 - 2400 BC–1641
... In particular, he is credited with developing the frequency analysis method whereby variations in the frequency of the occurrence of letters could be ... crypanalysis by frequency analysis) ... encipherments, cryptanalysis of certain encipherments, and statistical analysis of letters and letter combinations in Arabic ...
History Of Cryptography - Medieval Cryptography
... Manuscript It was probably religiously motivated textual analysis of the Qur'an which led to the invention of the frequency analysis technique for ... phonetics and syntax, and, most importantly, gave the first descriptions on frequency analysis ... encipherments, cryptanalysis of certain encipherments, and statistical analysis of letters and letter combinations in Arabic ...
Cryptographic Engineering - Major Issues - Active Opposition
... of which there were fewer than their users would have wanted) attempted to find ways to prevent frequency analysis success, starting, it must be assumed, almost immediately after that cryptanalytic ... The most effective way to defeat frequency analysis attacks was the polyalphabetic substitution cipher, invented by Alberti about 1465 ... For the next several hundred years, other designers also tried to evade frequency analysis, usually poorly, demonstrating that few had a clear understanding of the problem ...

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