src/HOL/Auth/Shared.thy
author paulson
Mon Jul 14 12:47:21 1997 +0200 (1997-07-14)
changeset 3519 ab0a9fbed4c0
parent 3512 9dcb4daa15e8
child 3683 aafe719dff14
permissions -rw-r--r--
Changing "lost" from a parameter of protocol definitions to a constant.

Advantages: no "lost" argument everywhere; fewer Vars in subgoals;
less need for specially instantiated rules
Disadvantage: can no longer prove "Agent_not_see_encrypted_key", but this
theorem was never used, and its original proof was also broken
the introduction of the "Notes" constructor.
     1 (*  Title:      HOL/Auth/Shared
     2     ID:         $Id$
     3     Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
     4     Copyright   1996  University of Cambridge
     5 
     6 Theory of Shared Keys (common to all symmetric-key protocols)
     7 
     8 Shared, long-term keys; initial states of agents
     9 *)
    10 
    11 Shared = Event + Finite +
    12 
    13 consts
    14   shrK    :: agent => key  (*symmetric keys*)
    15 
    16 rules
    17   isSym_keys "isSymKey K"	(*All keys are symmetric*)
    18   inj_shrK   "inj shrK"		(*No two agents have the same long-term key*)
    19 
    20 primrec initState agent
    21         (*Server knows all long-term keys; other agents know only their own*)
    22   initState_Server  "initState Server     = Key `` range shrK"
    23   initState_Friend  "initState (Friend i) = {Key (shrK (Friend i))}"
    24   initState_Spy     "initState Spy        = Key``shrK``lost"
    25 
    26 
    27 rules
    28   (*Unlike the corresponding property of nonces, this cannot be proved.
    29     We have infinitely many agents and there is nothing to stop their
    30     long-term keys from exhausting all the natural numbers.  The axiom
    31     assumes that their keys are dispersed so as to leave room for infinitely
    32     many fresh session keys.  We could, alternatively, restrict agents to
    33     an unspecified finite number.*)
    34   Key_supply_ax  "finite KK ==> EX K. K ~: KK & Key K ~: used evs"
    35 
    36 end