algorithm for computing a
function which maps strings of bits and a secret key to fixed-length strings of
bits, satisfying the following two properties:
·
for any
key and any input string the function can be computed efficiently;
·
for any
fixed key, and given no prior knowledge of the key, it is computationally
infeasible to compute the function value on any new input string, even given
knowledge of the set of input strings and corresponding function values, where
the value of the ith input string may have been chosen after observing the
value of the first i - 1 function values.
NOTE 1. A MAC algorithm is
sometimes called a cryptographic check function (see for example ISO-7498-2).
NOTE 2. Computational
feasibility depends on the users specific security requirements and
environment.
[ISO-9797-1:1999]