Integrity Through Hashing

Integrity can be provided with a cryptographic hash. There are several well-known hash types, including MD2, MD4, MD5, SHA1, and RIPEMD160. These hash types have the following properties in common:

• They're one-way.

  You cannot reverse the operation and get back the text that produced the hash. Indeed, this is obvious since most hashes have values that are 128-256 bits long. The size of a typical message will far exceed this, so it's extremely unlikely that the hash could contain all of the original information.

• They're collision resistant.

  There's almost no possibility of finding two meaningful messages that produce the same hash. Each hash algorithm has a different degree of collision resistance.

To use hashing, you generate a hash value from your data and include it when you transmit the data. The recipient uses the same hash algorithm to generate a hash value from the received data. If the result matches the transmitted hash, the data wasn't altered in transit.