author paulson
Thu, 18 Sep 1997 13:24:04 +0200
changeset 3683 aafe719dff14
parent 3519 ab0a9fbed4c0
child 5183 89f162de39cf
permissions -rw-r--r--
Global change: lost->bad and sees Spy->spies First change just gives a more sensible name. Second change eliminates the agent parameter of "sees" to simplify definitions and theorems

(*  Title:      HOL/Auth/Shared
    ID:         $Id$
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1996  University of Cambridge

Theory of Shared Keys (common to all symmetric-key protocols)

Shared, long-term keys; initial states of agents

Shared = Event + Finite +

  shrK    :: agent => key  (*symmetric keys*)

  isSym_keys "isSymKey K"	(*All keys are symmetric*)
  inj_shrK   "inj shrK"		(*No two agents have the same long-term key*)

primrec initState agent
        (*Server knows all long-term keys; other agents know only their own*)
  initState_Server  "initState Server     = Key `` range shrK"
  initState_Friend  "initState (Friend i) = {Key (shrK (Friend i))}"
  initState_Spy     "initState Spy        = Key``shrK``bad"

  (*Unlike the corresponding property of nonces, this cannot be proved.
    We have infinitely many agents and there is nothing to stop their
    long-term keys from exhausting all the natural numbers.  The axiom
    assumes that their keys are dispersed so as to leave room for infinitely
    many fresh session keys.  We could, alternatively, restrict agents to
    an unspecified finite number.*)
  Key_supply_ax  "finite KK ==> EX K. K ~: KK & Key K ~: used evs"