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CRYPTOGRAPHIC HASH FUNCTIONS: A hash function H accepts a variable-length block of data M as input and produces a fixed-size hash value h=(M). Typically, the input is padded out to an integer multiple of some fixed length (e.g., 1024 bits), and the padding includes the value of the length of the original message in bits. The length field is a security measure to increase the difficulty for an attacker to produce an alternative message with the same hash value. APPLICATIONS OF CRYPTOGRAPHIC HASH FUNCTIONS: 1) Message Authentication Message authentication is a mechanism or service used to verify the integrity of a message. Message authentication assures that data received are exactly as sent (i.e., contain no modification, insertion, deletion, or replay). When a hash function is used to provide message authentication, the hash function value is often referred to as a message digest .
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