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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]
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