19.6 Attacks on encryption schemes
If Eve attacks an encryption scheme utilizing available ciphertext, she can try to recover either the plaintext of the encrypted messages or the secret key itself used by the encryption scheme.
Recovery of the secret key is typically considered a stronger attack (or, equivalently, a more severe security compromise) than deducing plaintext from the ciphertext. As an example, if Alice and Bob use some standard, pre-defined messages that significantly vary in size – that is, to an extent that is not compensated by padding – Eve can easily guess the plaintext for a given ciphertext even if the encryption scheme is perfectly secret.
On the other hand, to determine the secret key, Eve must find statistical relations between the plaintext and the ciphertext. As far as we know, this is practically impossible for standardized ciphers, let alone for perfectly secret encryption schemes.
19.6.1 Brute-force attack
A brute-force attack is simply an...
