 Ciphertext-only attack

An attack using observed ciphertexts without supplied corresponding plaintexts. Recognisable message redundancy or publicly testable relations can sometimes provide key-testing predicates.

A **ciphertext-only attack** is a type of cryptographic attack in which an attacker attempts to break a cipher and retrieve the original plaintext message by analyzing only the ciphertext—the encrypted message—without any access to the plaintext or the key used for encryption. In other words, the attacker only has the output of the encryption process and tries to deduce information about the input.