# Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

# Hash Functions

Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1482

## Synonyms

Cryptographic hash functions; One-way hash functions

## Definition

A hash function h is a well-defined deterministic algorithm that takes as input data of arbitrary length and produces a short fixed-length digital representation of the data, or a digest, as its output. The output of a hash function can serve the role of a digital “fingerprint” of the input data. A cryptographic hash function is often expected to have the following security properties:
1. 1.

One-way (or preimage resistance): given a hash value y, it is infeasible to find an input x that hashes to y, i.e., h(x) = y.

2. 2.

Weak collision resistance (or second preimage resistance): given an input x and the corresponding digest of that input h(x), it is infeasible to find another input x′; that matches the digest, i.e., h(x) = h(x′).

3. 3.

Strong collission resistance (or simply collision resistance): it is infeasible to find two different inputs x and x′; that hash to the same value, i.e., h(x) = h(x′).

The third...

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1. 1.
Bertoni G, Daemen J, Peeters M, Van Assche G. The Keccak sponge function family: specifications summary. http://keccak.noekeon.org/specs_summary.html
2. 2.
Eastlake D, Jones P. US secure hash algorithm 1 (SHA1). IETF RFC 3174 (2001). http://www.ietf.org/rfc/rfc3174.txt
3. 3.
National Institute of Standards and Technology (NIST). FIPS 180-4: Secure Hash Standard (SHS). 2012.Google Scholar
4. 4.
Rivest R. The MD5 message-digest algorithm. IETF RFC 1321. 1992. http://www.ietf.org/rfc/rfc1321.txt
5. 5.
Schneier B. Applied cryptography: protocols, algorithms, and source code. 2nd ed. New York: Wiley; 1996.