Frequency analysis

from Wikipedia, the free encyclopedia

The frequency analysis is a method of cryptanalysis . Here are statistical characteristics of the encrypted to draw conclusions on the unencrypted message text exploited. Frequency analysis has been used since the 7th century to decipher texts that have been encrypted using monoalphabetic encryption without transposition .

The letter frequency distribution of a longer German text

The frequency analysis was discovered by the Arab scholar al-Kindī , and this knowledge came to Europe much later.


The frequency analysis is the deciphering of secret texts with unknown keys . The individual letters are counted and their frequency is noted, usually in percent, i.e. relative to the total number of letters ( letter frequency ).

Based on the specific frequency of special letters in a language, which Eis by far the most common in the German language at around 17%, conclusions can be drawn about the alphabet used. If, for example, the otherwise very rare letter appears in a message Qwith around 17%, the conclusion that Qthis encoding Estands for. If there are several options for assignment, the same procedure can also be used for bigrams, i.e. letter pairings.

Since the accuracy of the frequency increases with the length of a message, a long message is much easier to decipher than a short one. Incidentally, this applies to most cryptanalysis processes.

Use in other contexts

Frequency analysis or frequency analysis also denotes a method of quantitative content analysis in empirical social research .

See also

Individual evidence

  1. Friedrich Bauer: Deciphered Secrets. Codes and ciphers and how to break them. Springer, Berlin / Heidelberg 1995. Chapter: Anatomy of language: frequency , page 213ff.