What is a key characteristic of ciphertext-only attacks?

A ciphertext-only attack is a method where an attacker analyzes only the ciphertext (the encrypted data) without any knowledge of the corresponding plaintext (the original data). One key characteristic of this type of attack is that it often relies on frequency analysis, which involves studying the frequency of letters or groups of letters within the ciphertext. This is based on the idea that certain patterns, such as the frequency of certain characters, can reveal information about the plaintext.

In many encryption schemes, particularly those that are relatively weak or use simple substitution ciphers, the statistical properties of the plaintext will be reflected in the ciphertext. By analyzing these frequencies, an attacker can make educated guesses about the possible contents of the ciphertext. This technique is particularly useful against monoalphabetic ciphers, where each letter is consistently substituted for one other letter throughout the message, allowing for predictable patterns.

Therefore, the reliance on frequency analysis is a defining feature of ciphertext-only attacks, enabling attackers to potentially decipher the encrypted messages without access to the original data or the decryption key.