What type of cipher is more secure against frequency analysis?

A polyalphabetic cipher is more secure against frequency analysis because it uses multiple substitution alphabets. In this type of cipher, letters are substituted with different letters at different points in the text, making it harder for an attacker to identify patterns. Frequency analysis relies on the common occurrence and predictable patterns of letters in a given language; by changing the substitution method throughout the message, a polyalphabetic cipher disrupts these patterns significantly.

For example, in a monoalphabetic cipher, each letter is consistently replaced by the same letter throughout the text, making it relatively straightforward for an analyst to compile frequency counts and decode the message. Similarly, the Caesar cipher, a specific type of monoalphabetic cipher that shifts letters by a fixed number, also presents a consistent pattern. A substitution cipher may refer generally to these simpler forms where one character consistently substitutes for another, thereby being vulnerable to frequency analysis.

In contrast, the polyalphabetic cipher’s complexity and variability create multiple ways each letter can be encoded, thereby enhancing its security against these analytical strategies, as the same letter can appear as different characters in different contexts within the message.