Dictionary Attack (I)

Related Concepts

Block Ciphers; Password

Definition

Dictionary attack is an exhaustive cryptanalysis approach in which the attacker computes and stores a table of plaintext–ciphertext pairs $(P,{C}_{i} = {E}_{{K}_{i}}(P),{K}_{i})$ sorted by the ciphertexts C _i .

Theory

Here the plaintext P is chosen in advance among the most often encrypted texts like “login:,” “Hello John,” etc., and the key runs through all the possible keys K _i . If P is encrypted later by the user and the attacker observes its resulting ciphertext C _j , the attacker may search his or her table for the corresponding ciphertext and retrieve the secret key K _j . The term dictionary attack is also used in the area of password guessing, but with a different meaning.