The University of SydneyPage 28Symmetric key cryptography
symmetric key crypto: Bob and Alice share same (symmetric) key: Ks–e.g., key is knowing substitution pattern in mono alphabetic substitution cipherQ:how do Bob and Alice agree on key value?plaintextciphertextKS
encryptionalgorithmdecryption algorithm
KSplaintextmessage, mK (m)Sm = KS(KS(m))