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Preimage Resistance: The hash function must be a one-way function: For any given code h itis ‘computationally infeasible to find br Tenab Second Preimage Resistance: In this criterion, an adversary i provided withthe value of, reper ona, sor, 700 Cryptography and Network Security B.Tech(CSE) IV Year ISem x and is asked to compute the value of x1 # x, such that h(x) = h(x). {ft difficult for the attacker to perform this computation we claim thatthe hash function is second pre-image resistant. A function without preimage resistance is usually also not second preimage resistant: Given a message 2, calculate h := H(a1) and then get a preimage ap from h, then we usually have a £ 22 and H(2:) = H(22). Collision Resistance: Collision of a hash function is the event when two values x and xl such that x1 #x hash tothe same value, ie, h(x) = h(x!) M: Message Hash: Hash function (M): DigestHMAC (iashed MAC: HMAC algorithm stands for Hashed or Hash based Message Authentication Code + it uses the Hashing concept twice, so great resistant to attacker 1 HMAC consists of twin benfts of Hashing and MAC 7 The working of HMAG stars wih taking a messene it, M containing blocks of length b / Am input signature is padded tothe loft of the message and the whole is given as input to 2 hash function which gives us a intermediate HMAC. + Intermediate HMAC again is appended to an output signature and the whole is applied ‘a hach function again, the result is our final HMAC of n bits pied to aac By Ch Samsonu, r. 708 Cryptography and Network Security B.Tech(CSE) IV Year I Sem EMAC (Cipher based MAC) «+ This is similar to CBC{Cipher Block Chaining), ‘ereatos one block of MAG + It takes N blocks of message but “The message is divided into N blocks of it size. If ast block isnot m- size,then padded with start 1 then 0000... ke 100000. aie teks encrypted wih key K then its outputis XOR wih the next block for pe ‘encryption, $008, : Taeoat block is encrypted with some adational k value fr more seutity (CRIRC ston Tappan oe