A mathematical procedure that takes information contained in files and scrambles it to create a fixed-length string of numbers and characters called a hash.
A good hashing algorithm has the following characteristic: if you apply a hashing algorithm to some data and then change only a few bits in the data and apply the algorithm again, the two resulting hashes will differ in almost every bit.
Hashing algorithms are used extensively in cryptography for encrypting keys or messages. Examples of popular cryptographic hashing algorithms include MD2, MD4, MD5, and SHA-1. Message Digest 5 (MD5) uses a 128-bit hash, and Secure Hash Algorithm (SHA) uses a 60-bit hash. The more bits in a hash, the greater the security of the encryption process.
Hashing is also used in some database technology for creating indexes of items in a database. Hashes of database objects are generally smaller than the objects themselves, so they can be indexed and searched more quickly. You can generate unique hashes of fixed length for each database record, creating a hash table that you can use for quick searches for records.