Communication Is Key Brenda Cunliffe
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Communication Is Key In Business
Contents • • • • • • • • • • • Definitions [ ] Informally, a message authentication code consists of three algorithms: • A key generation algorithm selects a key from the key space uniformly at random. • A signing algorithm efficiently returns a tag given the key and the message. • A verifying algorithm efficiently verifies the authenticity of the message given the key and the tag.
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That is, return accepted when the message and tag are not tampered with or forged, and otherwise return rejected. For a secure unforgeable message authentication code, 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 can forge the tag of any message except the given one. Formally, a message authentication code ( MAC) is a triple of efficient algorithms ( G, S, V) satisfying: • G (key-generator) gives the key k on input 1 n, where n is the security parameter. • S (signing) outputs a tag t on the key k and the input string x. • V (verifying) outputs accepted or rejected on inputs: the key k, the string x and the tag t.
S and V must satisfy the following: Pr [ k ← G(1 n), V( k, x, S( k, x) ) = accepted ] = 1. A MAC is unforgeable if for every efficient adversary A Pr [ k ← G(1 n), ( x, t) ← A S( k, )(1 n), x ∉ Query( A S( k, ), 1 n), V( k, x, t) = accepted]. In this example, the sender of a message runs it through a MAC algorithm to produce a MAC data tag. The message and the MAC tag are then sent to the receiver. The receiver in turn runs the message portion of the transmission through the same MAC algorithm using the same key, producing a second MAC data tag. Best medical billing software for mac. The receiver then compares the first MAC tag received in the transmission to the second generated MAC tag. Commercial i2pdf alternatives for mac. If they are identical, the receiver can safely assume that the message was not altered or tampered with during transmission ().
However, to allow the receiver to be able to detect, the message itself must contain data that assures that this same message can only be sent once (e.g. Time stamp, sequence number or use of a one-time MAC). Otherwise an attacker could – without even understanding its content – record this message and play it back at a later time, producing the same result as the original sender.
Communication Is Key
One-time MAC [ ] and in particular hash functions provide a secure message authentication code as long as the key is used at most once. This can be seen as the for authentication. The simplest such pairwise independent hash function is defined by the random key key = ( a, b), and the MAC tag for a message m is computed as tag = ( am + b) mod p, where p is prime. More generally, functions provide a secure message authentication code as long as the key is used less than k times for k-ways independent hashing functions. See also [ ] • • • (HMAC) • • • • • • • Notes [ ]. • The strongest adversary is assumed to have access to the signing algorithm without knowing the key.