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-Ek(P2,- Ek(P), where the cryptanalyst gets to choose P,, P,, .P Deduce: Either k, or an algorithm to infer Pi from Ci+I=Ek(P 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, PI= DK (C1, C2, P2=Dk( C2). Ci P=DK(C Deduce: 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