secure hash is aimed at preventing the modification of documents that would keep their hash unchanged
the secret may be a one time key shared by both the sender and the recipient
this guarentees the identity of the sender
encryption may be done by a one time key shared between the forwarder and the forwardee
using the hash encrypted by the original sender
as the neither the hashed document nor the hash that should be replicated is known .
as, the one time ley used for hash encyption can not be guessed , even with a quantum computer, by listning to transmitted messages.
will lead to an odd of 1/ 8 500 000 000 for a forged document not to be detected as such.
a 1Gbyte card can fit 8bn 33bit keys, enough to power transactions with 150 million devices
the process can be used to secure emails between the client and the mail server.
Files can be stored and their integrity checked .
Web pages integrity , including their embeded pictures, can be checked while being downloaded.