What is Hashing?

Hashing is an algorithm that calculates a fixed-size bit string value from a file. A file basically contains blocks of data. Hashing transforms this data into a far shorter fixed-length value or key which represents the original string. The hash value can be considered the distilled summary of everything within that file.

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.

A hash is usually a hexadecimal string of several characters. Hashing is also a unidirectional process so you can never work backwards to get back the original data.

Use of Hashing?

One main use of hashing is to compare two files for equality. Without opening two document files to compare them word-for-word, the calculated hash values of these files will allow the owner to know immediately if they are different.

Hashing is also used to verify the integrity of a file after it has been transferred from one place to another, typically in a file backup program. To ensure the transferred file is not corrupted, a user can compare the hash value of both files. If they are the same, then the transferred file is an identical copy.

External Links

• More information about MD5 (Wikipedia)
• More information about SHA (Wikipedia)
• More information about HAVAL (Wikipedia)
• Comparison of cryptographic hash functions Compression (Wikipedia)