Secure Hashes

A hash is a digital summary of a chunk of data of any size. Simple types of hashes include check digits; secure hashes produce longer results (often 128 bits or longer). Good secure hashes are extremely difficult for attackers to reverse-engineer or subvert in other ways. Secure hashes can be used with keys or without, but their purpose is to provide a digital summary of a message that can be used to verify whether some data that has been received is the same as the data sent. The sender calculates the hash and includes that value with the data; the recipient calculates the hash on the data received. If the results match the attached hash value, the recipient can be confident in the data's integrity.

Commonly used hashes include the MD2, MD4, and MD5 message digest functions published by Network Associates. The Secure Hash Algorithm ( SHA ) is a digest function developed as a standard by NIST. Hashes may be used on their own or as part of digital signatures.