Description
string 
mhash ( int hash, string data [, string key])
     mhash() applies a hash function specified by
     hash to the data and
     returns the resulting hash (also called digest). If the  key
     is specified it will return the resulting HMAC. HMAC is keyed hashing
     for message authentication, or simply a message digest that depends on 
     the specified key. Not all algorithms supported in mhash can be used in 
     HMAC mode. In case of an error returns FALSE.