To be considered secure, a MAC function must resist existential forgery under chosen-message attacks. While MAC functions are similar to cryptographic hash functions, they possess different security requirements. Clearly we require that any adversary cannot directly query the string x on S, since otherwise a valid tag can be easily obtained by that adversary. ), 1 n) denotes the set of the queries on S made by A, which knows n.) denotes that A has access to the oracle S( k,.
Ī MAC is unforgeable if for every efficient adversary A Pr [ k ← G(1 n), ( x, t) ← A S( k, V (verifying) outputs accepted or rejected on inputs: the key k, the string x and the tag t.S (signing) outputs a tag t on the key k and the input string x.G (key-generator) gives the key k on input 1 n, where n is the security parameter.
#Massage software for mac code#
įormally, a message authentication code ( MAC) system is a triple of efficient algorithms ( G, S, V) satisfying: It should be computationally infeasible to compute a valid tag of the given message without knowledge of the key, even if for the worst case, we assume the adversary knows the tag of any message but the one in question. That is, return accepted when the message and tag are not tampered with or forged, and otherwise return rejected.Ī secure message authentication code must resist attempts by an adversary to forge tags, for arbitrary, select, or all messages, including under conditions of known- or chosen-message.
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