Cryptanalysis Types of Attacks Chosen-Plaintext Attack Attacker can choose the plaintext that gets encrypted thereby potentially getting more information about the key Given: P,C= Ek(PD, P2,C2=(P2P, Ci=Ek(PV, where the cryptanalyst gets to choose Ppo r 2 Deduce: Either k, or an algorithm to infer Pi+, from Ek(P It Adaptive chosen-Plaintext Attack Attacker can choose a series of plaintexts, basing choice on the result of previous encryption >differential cryptanalysis Chosen-ciphertext attack Given: Cl, PI=DK(C1, C2, P2=DK(C2),Ci, P=DKC educe kCryptanalysis - Types of Attacks • Chosen-Plaintext Attack – Attacker can choose the plaintext that gets encrypted thereby potentially getting more information about the key – Given: P1 , C1 = Ek (P1 ), P2 , C2 = Ek (P2 ),...Pi , Ci = Ek (Pi ), where the cryptanalyst gets to choose P1 , P2 ,...Pi Deduce: Either k, or an algorithm to infer Pi+1 from Ci+1 = Ek (Pi+1) • Adaptive Chosen-Plaintext Attack – Attacker can choose a series of plaintexts, basing choice on the result of previous encryption → differential cryptanalysis! • Chosen-ciphertext attack – Given: C1 , P1 = Dk (C1 ), C2 , P2 = Dk (C2 ),...Ci , Pi = Dk (Ci ) – Deduce: k