Frequency Analysis

Frequency Analysis leading to techniques for breaking monoalphabetic substitution ciphers: most likely motivated due to textual analysis of the Koran. It has been suggested that close textual study of the Qur'an first brought to light that Arabic has a characteristic letter frequency. Its use spread, and was so widely used by European states by the Renaissance that several schemes were invented by cryptographers to defeat it. These included homophones, polyalphabetic substitution and polygraphic substitution schemes. Frequency analysis is based on the fact that in any given stretch of a language, letters and combinations of letters occur with varying frequencies. In the English language for example, E is the most common letter, while X is rare.