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# What are the requirement of hash function in Information Security?

A cryptographic hash function is a transformation that creates an input (or message) and restore a fixed-size string, which is known as the hash value. A hash value h is produced by a function H of the form −

h = H(M)

where M is the variable length message and H (M) is the fixed length hash value.

Hash functions are generally used mathematical functions in cryptography for executing security. A hash function transform an input value of any arbitrary size to a fixed-size value. Therefore, the input can be of any length but the output produced is always of a fixed length. The output generated is known as hash values or hashes.

The general use of hashing is password checking. When the user enters the password, the hash of the password is produced and compared with the hash in the database. If both the hashes are the equal thus the user is enabled to login else the user required to enter the password again.

The hash value is added to the message at the source at a time when message is considered or known to be correct. The receiver verify the message by recomputing the hash value.

A hash functions creates a string of any length as input and creates a fixed length string which facilitate as a type of signature for the information supported. In this approach, a person understanding the hash value is unable to work out the original message, but someone understanding the original message can prove the hash is generated from that message.

A cryptographic hash function should act like a random function while still being deterministic and effectively calculable. Cryptographic Hash functions are the essential tool in the field of cryptography and are used to carry out a number of security objectives like authenticity, digital signatures, pseudo number generation, digital steganography, digital time stamping etc.

There are some requirements of hash function are as follows −

The hash function makes a fingerprint of a file, a message or some other block of information. The hash function, H should have the following properties which are as follows −

Hash function can be used to a block of information of any size.

H (x) is relatively simply to calculate for any given x, creating both hardware and software implementation practical.

For any given value, h, it is computationally impossible to find x such that H (x) = h. This is defined as one-way property.

For any given block x, it is computationally impossible to find y ≠ x with H (y) = H (x). This property is defined as weak collision resistance.

It is computationally impossible to find some pair (x, y) such that H (x) = H (y). This property is called a strong collision resistance.