Cipher block chaining
Következo blokk kódolása az elozoét használja
Inicializáló vektor (IV): pl. elozo üzenet utolsó blokkja
IV elore ismerheto: támadás
“SSL … estimated ... on average, an attacker would need tens or hundreds of millions of opportunities to inject chosen plaintexts to be encrypted with a known IV to confirm guesses on the value of a few unknown plaintexts”.