a destructive function that throws away data from a string and outputs another string, and therefore cannot be decrypted.  examples: sha1, sha256
a destructive function that throws away data from a string and outputs another string, and therefore cannot be decrypted.  examples: sha1, sha256
takes a key, i.e. a string or integer, for a data record, scrambles it, and outputs an index to be used in a hash table