- A hash function H accepts a variable-length block of data M as input and produces a fixed-size hash value as output
- h = H(M)
- Principal objective of hash function is data integrity - A change to any bit or bits in M results, in a change to the hash code.
- Cryptographic hash function
- The kind of hash function needed for security applications is referred to as a cryptographic hash function
- The algorithm for this should be computationally infeasible to find either:
(a) a data object that maps to a pre-specified hash result (the one-way property)
(b) two data objects that map to the same hash result (the collision-free property)
Applications of Cryptographic Hash Functions
- Main Applications are in
- Message authentication and
- Digital signatures
- Other applications are:
- to create a one-way password file
- intrusion detection and virus detection
- to construct a pseudorandom number generator (PRNG).
Security Requirements for a Cryptographic Hash Function H
