| (I) A cryptographic hash (e.g., [R1828]) in which the mapping to a
hash result is varied by a second input parameter that is a
cryptographic key. (See: checksum.)
(C) If the input data object is changed, a new hash result cannot
be correctly computed without knowledge of the secret key. Thus,
the secret key protects the hash result so it can be used as a
checksum even when there is a threat of an active attack on the
data. There are least two forms of keyed hash:
- A function based on a keyed encryption algorithm. (E.g., see:
Data Authentication Code.)
- A function based on a keyless hash that is enhanced by
combining (e.g., by concatenating) the input data object
parameter with a key parameter before mapping to the hash
result. (E.g., see: HMAC.)
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