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Frequency Analysis

Tools for frequency analysis, a cryptanalysis method studying the frequency of letters or groups of characters in a ciphered message.

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Frequency Analysis -

Tag(s) : Cryptanalysis

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# Frequency Analysis

## Frequency Analysis (advanced)

### Items to Analyze

 (For ngrams) Blocks Analysis (ABCDEF => AB,CD,EF) Sliding Window/Overlapping (ABCDEF => AB,BC,CD,DE,EF)

### Analyse to perform

 Calculate Frequencies Count Appearances List missing letters/ngrams Count longest repeats of any n-grams Count n-grams with repeated characters Suggest an alphabetic transcription of n-grams (statistically)

### Mono-alphabetical substitution decryption

dCode offers a dedicated tool for decrypting an alphabetic substitution automatically:

## Answers to Questions (FAQ)

### What is frequency analysis? (Definition)

Frequency analysis is the study of the distribution (and count) of the letters in a text. Analysis of frequencies helps cryptanalysis and decrypting substitution-based ciphers using the fact that some letters apparitions are varying in a given language: in english, letters E, T or A are common while Z or Q are rare.

### How to use frequency analysis?

Frequency analysis generates an histogram that allows decrypting a text by comparing letters frequencies in a plain text message with letters frequences in a ciphered message.

For some ngrams analyzes, use the sliding window mode:

Example: ABCD has bigrams AB, CD '(blocks mode)

Example: ABCD has bigrams AB, BC, CD '(sliding window mode)

For simple substitution, it can be useful to try replacing the most common letter in the ciphertext by the letter E, the most common letter in English, and so on. This principle is applicable only if the message is relatively long for the frequencies to be statistically significant.

### When frequency analysis is useless?

Frequency analysis is less relevant when the message has been encrypted with polyalphabetic encryption (which tends to randomize the frequency of the letters), or when the encryption is homophonic (several different encrypted characters for the same plain letter) or polygrammic (groups of characters replace each letter). In these cases, the analysis does not allow a decoding but allows to filter or find the type of encryption used.

### What are letter appearance frequencies in English language?

Letters by frequency of appearance in English:

E T A 12.7 % 9.1 % 8.2 % 7.5 % 7.0 % 6.7 % 6.3 % 6.1 % 6.0 % 4.0 % 4.3 % 2.8 % 2.8 % 2.4 % 2.4 % 2.2 % 2.0 % 2.0 % 1.9 % 1.5 % 1.0 % 0.8 % 0.2 % 0.2 % 0.1 % 0.1 %

For comparison purposes, here are letters frequency in French:

E P A 17.3 % 3.0 % 8.4 % 1.3 % 8.1 % 1.3 % 7.3 % 1.1 % 7.1 % 1.1 % 7.1 % 1.0 % 6.6 % 0.9 % 6.0 % 0.4 % 5.7 % 0.3 % 5.3 % 0.3 % 4.2 % 0.1 % 3.0 % 0.1 % 3.0 % 0.1 %

## Source code

dCode retains ownership of the "Frequency Analysis" source code. Except explicit open source licence (indicated Creative Commons / free), the "Frequency Analysis" algorithm, the applet or snippet (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, translator), or the "Frequency Analysis" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) and all data download, script, or API access for "Frequency Analysis" are not public, same for offline use on PC, mobile, tablet, iPhone or Android app!
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## Cite dCode

The copy-paste of the page "Frequency Analysis" or any of its results, is allowed as long as you cite dCode!
Cite as source (bibliography):
Frequency Analysis on dCode.fr [online website], retrieved on 2022-11-28, https://www.dcode.fr/frequency-analysis

## Need Help ?

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NB: for encrypted messages, test our automatic cipher identifier!

## Questions / Comments

Feedback and suggestions are welcome so that dCode offers the best 'Frequency Analysis' tool for free! Thank you!

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