Symmetric Key: Confidentialit Block Ciphers(ex: AES) Block 1 Block 2 Block 3 Block 4 (fixed block size, e.g. 128 bits) Round 1 round #2 Round #n Alice A-B Block 1 Block 2 Block 3 Block 4 Bob breaks the ciphertext into blocks, feeds it through decryption engine using Ka-b to recover the message
Symmetric Key: Confidentiality Block 1 Block 2 Block 3 Block 4 Round #1 Round #2 Round #n Block 1 ◼ Block Ciphers (ex: AES) K A-B Alice: Bob breaks the ciphertext into blocks, feeds it through decryption engine using KA-B to recover the message. Block 2 Block 3 Block 4 (fixed block size, e.g. 128 bits)
Cryptographic Hash Functions Consistent hash(X)always yields same result One-way given Y, can't findX s t hash (X=Y Collision resistant given hash ( W)=Z, can't find X such that hash(X)=Z Fixed Size Message of arbitrary length Hash Fn Hash
Cryptographic Hash Functions ◼ Consistent hash(X) always yields same result ◼ One-way given Y, can’t find X s.t. hash(X) = Y ◼ Collision resistant given hash(W) = Z, can’t find X such that hash(X) = Z Message of arbitrary length Hash Fn Fixed Size Hash