--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/SET_Protocol/Event_SET.thy Tue Oct 20 20:03:23 2009 +0200
@@ -0,0 +1,198 @@
+(* Title: HOL/SET_Protocol/Event_SET.thy
+ Author: Giampaolo Bella
+ Author: Fabio Massacci
+ Author: Lawrence C Paulson
+*)
+
+header{*Theory of Events for SET*}
+
+theory Event_SET
+imports Message_SET
+begin
+
+text{*The Root Certification Authority*}
+syntax RCA :: agent
+translations "RCA" == "CA 0"
+
+
+text{*Message events*}
+datatype
+ event = Says agent agent msg
+ | Gets agent msg
+ | Notes agent msg
+
+
+text{*compromised agents: keys known, Notes visible*}
+consts bad :: "agent set"
+
+text{*Spy has access to his own key for spoof messages, but RCA is secure*}
+specification (bad)
+ Spy_in_bad [iff]: "Spy \<in> bad"
+ RCA_not_bad [iff]: "RCA \<notin> bad"
+ by (rule exI [of _ "{Spy}"], simp)
+
+
+subsection{*Agents' Knowledge*}
+
+consts (*Initial states of agents -- parameter of the construction*)
+ initState :: "agent => msg set"
+ knows :: "[agent, event list] => msg set"
+
+(* Message reception does not extend spy's knowledge because of
+ reception invariant enforced by Reception rule in protocol definition*)
+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)
+ | Gets A' X => knows Spy evs
+ | Notes A' X =>
+ if A' \<in> bad then insert X (knows Spy evs) else knows Spy evs)
+ else
+ (case ev of
+ Says A' B 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
+ | Notes A' X =>
+ if A'=A then insert X (knows A evs) else knows A evs))"
+
+
+subsection{*Used Messages*}
+
+consts
+ (*Set of items that might be visible to somebody:
+ complement of the set of fresh items*)
+ used :: "event list => msg set"
+
+(* As above, message reception does extend used items *)
+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)
+ | Gets A X => used evs
+ | Notes A X => parts {X} Un (used evs))"
+
+
+
+(* Inserted by default but later removed. This declaration lets the file
+be re-loaded. Addsimps [knows_Cons, used_Nil, *)
+
+(** Simplifying parts (insert X (knows Spy evs))
+ = parts {X} Un parts (knows Spy evs) -- since general case loops*)
+
+lemmas parts_insert_knows_A = parts_insert [of _ "knows A evs", standard]
+
+lemma knows_Spy_Says [simp]:
+ "knows Spy (Says A B X # evs) = insert X (knows Spy evs)"
+by auto
+
+text{*Letting the Spy see "bad" agents' notes avoids redundant case-splits
+ on whether @{term "A=Spy"} and whether @{term "A\<in>bad"}*}
+lemma knows_Spy_Notes [simp]:
+ "knows Spy (Notes A X # evs) =
+ (if A:bad then insert X (knows Spy evs) else knows Spy evs)"
+apply auto
+done
+
+lemma knows_Spy_Gets [simp]: "knows Spy (Gets A X # evs) = knows Spy evs"
+by auto
+
+lemma initState_subset_knows: "initState A <= knows A evs"
+apply (induct_tac "evs")
+apply (auto split: event.split)
+done
+
+lemma knows_Spy_subset_knows_Spy_Says:
+ "knows Spy evs <= knows Spy (Says A B X # evs)"
+by auto
+
+lemma knows_Spy_subset_knows_Spy_Notes:
+ "knows Spy evs <= knows Spy (Notes A X # evs)"
+by auto
+
+lemma knows_Spy_subset_knows_Spy_Gets:
+ "knows Spy evs <= knows Spy (Gets A X # evs)"
+by auto
+
+(*Spy sees what is sent on the traffic*)
+lemma Says_imp_knows_Spy [rule_format]:
+ "Says A B X \<in> set evs --> X \<in> knows Spy evs"
+apply (induct_tac "evs")
+apply (auto split: event.split)
+done
+
+(*Use with addSEs to derive contradictions from old Says events containing
+ items known to be fresh*)
+lemmas knows_Spy_partsEs =
+ Says_imp_knows_Spy [THEN parts.Inj, THEN revcut_rl, standard]
+ parts.Body [THEN revcut_rl, standard]
+
+
+subsection{*The Function @{term used}*}
+
+lemma parts_knows_Spy_subset_used: "parts (knows Spy evs) <= used evs"
+apply (induct_tac "evs")
+apply (auto simp add: parts_insert_knows_A split: event.split)
+done
+
+lemmas usedI = parts_knows_Spy_subset_used [THEN subsetD, intro]
+
+lemma initState_subset_used: "parts (initState B) <= used evs"
+apply (induct_tac "evs")
+apply (auto split: event.split)
+done
+
+lemmas initState_into_used = initState_subset_used [THEN subsetD]
+
+lemma used_Says [simp]: "used (Says A B X # evs) = parts{X} Un used evs"
+by auto
+
+lemma used_Notes [simp]: "used (Notes A X # evs) = parts{X} Un used evs"
+by auto
+
+lemma used_Gets [simp]: "used (Gets A X # evs) = used evs"
+by auto
+
+
+lemma Notes_imp_parts_subset_used [rule_format]:
+ "Notes A X \<in> set evs --> parts {X} <= used evs"
+apply (induct_tac "evs")
+apply (induct_tac [2] "a", auto)
+done
+
+text{*NOTE REMOVAL--laws above are cleaner, as they don't involve "case"*}
+declare knows_Cons [simp del]
+ used_Nil [simp del] used_Cons [simp del]
+
+
+text{*For proving theorems of the form @{term "X \<notin> analz (knows Spy evs) --> P"}
+ New events added by induction to "evs" are discarded. Provided
+ this information isn't needed, the proof will be much shorter, since
+ it will omit complicated reasoning about @{term analz}.*}
+
+lemmas analz_mono_contra =
+ knows_Spy_subset_knows_Spy_Says [THEN analz_mono, THEN contra_subsetD]
+ knows_Spy_subset_knows_Spy_Notes [THEN analz_mono, THEN contra_subsetD]
+ knows_Spy_subset_knows_Spy_Gets [THEN analz_mono, THEN contra_subsetD]
+
+lemmas analz_impI = impI [where P = "Y \<notin> analz (knows Spy evs)", standard]
+
+ML
+{*
+val analz_mono_contra_tac =
+ rtac @{thm analz_impI} THEN'
+ REPEAT1 o (dresolve_tac @{thms analz_mono_contra})
+ THEN' mp_tac
+*}
+
+method_setup analz_mono_contra = {*
+ Scan.succeed (K (SIMPLE_METHOD (REPEAT_FIRST analz_mono_contra_tac))) *}
+ "for proving theorems of the form X \<notin> analz (knows Spy evs) --> P"
+
+end