(* Title: HOL/Auth/Event
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1996 University of Cambridge
Theory of events for security protocols
Datatype of events; function "spies"; freshness
"bad" agents have been broken by the Spy; their private keys and internal
stores are visible to him
*)
Event = Message + List +
consts (*Initial states of agents -- parameter of the construction*)
initState :: agent => msg set
datatype (*Messages--could add another constructor for agent knowledge*)
event = Says agent agent msg
| Notes agent msg
| Gets agent msg
consts
bad :: agent set (*compromised agents*)
knows :: agent => event list => msg set
(*"spies" is retained for compability's sake*)
syntax
spies :: event list => msg set
translations
"spies" => "knows Spy"
rules
(*Spy has access to his own key for spoof messages, but Server is secure*)
Spy_in_bad "Spy: bad"
Server_not_bad "Server ~: bad"
primrec
knows_Nil "knows A [] = initState A"
knows_Cons "knows A (ev # evs) =
(if A = Spy then
(case ev of
Says A' B X => insert X (knows Spy evs)
| Notes A' X =>
if A' : bad then insert X (knows Spy evs) else knows Spy evs
| Gets A' X => knows Spy evs)
else
(case ev of
Says A' B X =>
if A'=A then insert X (knows A evs) else knows A evs
| Notes A' X =>
if A'=A then insert X (knows A evs) else knows A evs
| Gets A' X =>
if A'=A then insert X (knows A evs) else knows A evs))"
(*
Case A=Spy on the Gets event
enforces the fact that if a message is received then it must have been sent,
therefore the oops case must use Notes
*)
consts
(*Set of items that might be visible to somebody:
complement of the set of fresh items*)
used :: event list => msg set
primrec
used_Nil "used [] = (UN B. parts (initState B))"
used_Cons "used (ev # evs) =
(case ev of
Says A B X => parts {X} Un (used evs)
| Notes A X => parts {X} Un (used evs)
| Gets A X => used evs)"
end