**You are counting letters in the ciphertext and drawing a histogram for cryptanalysis. Which of the following is least related to the cryptanalysis? (Wentz QOTD)**A. Transposition cipher

B. Frequency analysis

C. Ciphertext-only attack (COA)

D. Side-Channel Analysis

**Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.**

My suggested answer is D. Side-Channel Analysis.

Wentz’s book, *The Effective CISSP: Security and Risk Management*, helps CISSP and CISM aspirants build a solid conceptual security model. It is a tutorial for information security and a supplement to the official study guides for the CISSP and CISM exams and an informative reference for security professionals.

## Frequency analysis

Counting letters in the ciphertext and drawing a histogram for cryptanalysis is a paraphrase of frequency analysis.

## Transposition cipher

“A transposition cipher is one which rearranges the order of the letters in the ciphertext (encoded text), according to some predetermined method, without making any substitutions.” (NRICH)

## Ciphertext-only attack (COA)

“In cryptography, a ciphertext-only attack (COA) or known ciphertext attack is an attack model for cryptanalysis where the attacker is assumed to have access only to a set of ciphertexts.” (Wikipedia)

# Reference

**您正在計算密文中的字母並繪製直方圖以進行密碼分析(cryptanalysis)。 以下哪項與密碼分析的關係最小？ (Wentz QOTD)**

A. 轉置密碼 (Transposition cipher)

B. 頻率分析

C. 純密文攻擊 (COA)

D. 側通道分析