CryptographY/Hashfunctions

/Hashfunctions are used in Cryptography for many purposes, eg. verifying the validity of a public key (this is commonly known as the key's fingerprint). A hash function returns the bits of a string in the form of a hash value, which has a fixed size. This is done in such a manner that the probability of two different strings having the same hash value is infestimal. Changing just one bit (character) in string will result in a different hash value.

Practical example: The record companies came up with the idea of identifying MP3 files by using their hash value in order to able to trace the files on the net and in various filesharing communities. However, by changing or adding just one fit to the file will defeat this system completely.