Hash

Acronym: IT

A hash is a number given by a hash function from a message. This is a one way function; it means that it is impossible to get the original message knowing the hash. However, the hash will drastically change even for the slightest modification in the message. It is therefore extremely difficult to modify a message while keeping its original hash. It is also called a message digest. Hash functions are used in password mechanisms, in certifying that applications are original (MD5 sum), and in general in ensuring that any message has not been tampered with. It seems that the Internet Engineering Task Force (IETF) prefers SHA1 over MD5 for a number of technical reasons (Cf RFC2459 7.1.2 and 7.1.3).