Frequency analysis is primarily used against which type of cryptographic method?

Frequency analysis is a technique used to break ciphers by studying the frequency of letters or groups of letters in a given text. This method is particularly effective against monoalphabetic ciphers, where each letter of the plaintext is consistently replaced by the same letter in the ciphertext.

In a monoalphabetic cipher, each letter maintains its frequency of appearance from the original text. For instance, in the English language, the letter 'E' is the most frequently used letter. By analyzing the frequency of letters in the ciphertext, an attacker can identify which letter corresponds to 'E' and proceed to decode other letters based on their frequency.

This method becomes less effective against polyalphabetic ciphers, which use multiple substitution alphabets, making letter frequencies change throughout the coded message. As a result, frequency analysis would not yield as reliable results due to the variability in substitutions. Similarly, secure hash algorithms are not susceptible to frequency analysis since they transform data into a fixed-size hash that does not retain letter frequencies, and transposition ciphers rearrange the letters rather than substituting them, complicating frequency analysis further.