A hash function usually means a function that compresses, meaning the output is shorter than the input A hash function takes a group of characters (called a key) and maps it to a value of a certain length (called a hash value or hash). The hash value is representative of the original string of characters, but is normally smaller than the original. This term is also known as a hashing algorithm or message digest function. Hash functions also called message digests or one-way encryption or hashing algorithm. http://phpexecutor.com

1. Hash Function

2. What is Hash Function
 A hash function usually means a function that compresses, meaning the
output is shorter than the input
 A hash function takes a group of characters (called a key) and maps it to a
value of a certain length (called a hash value or hash).
 The hash value is representative of the original string of characters, but is
normally smaller than the original.
 This term is also known as a hashing algorithm or message digest function.
 Hash functions also called message digests or one-way encryption or
hashing algorithm.

3. Advantages Of Hash Function
 Basically, a hash function for any file can be generated to create a digital
fingerprint. It’s almost impossible to alter the file in any way without
changing the hash function of that file, so this is a good way of checking if
a file has been changed or corrupted.
 It’s also widely used for checking that downloaded files are exactly the
same as the ones still on the server, which is why there’s sometimes an
MD5 number on the download page of a web site.
 Another application of hash functions is the encryption of passwords for
operating systems

4. Several Hash Functions In Use Today
 Hashed Message Authentication Code (HMAC): Combines authentication
via a shared secret with hashing.
 Message Digest 2 (MD2): Byte-oriented, produces a 128-bit hash value
from an arbitrary-length message, designed for smart cards.
 MD4: Similar to MD2, designed specifically for fast processing in software.
 MD5: Similar to MD4 but slower because the data is manipulated more.
Developed after potential weaknesses were reported in MD4
 Secure Hash Algorithm (SHA): Modeled after MD4 and proposed by NIST
for the Secure Hash Standard (SHS), produces a 160-bit hash value.