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(* Title: HOL/Auth/Event.thy
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1996 University of Cambridge
Datatype of events; function "spies"; freshness
"bad" agents have been broken by the Spy; their private keys and internal
stores are visible to him
*)
section\<open>Theory of Events for Security Protocols\<close>
theory Event imports Message begin
consts (*Initial states of agents -- parameter of the construction*)
initState :: "agent \ msg set"
datatype
event = Says agent agent msg
| Gets agent msg
| Notes agent msg
consts
bad :: "agent set" \<comment> \<open>compromised agents\<close>
text\<open>Spy has access to his own key for spoof messages, but Server is secure\<close>
specification (bad)
Spy_in_bad [iff]: "Spy \ bad"
Server_not_bad [iff]: "Server \ bad"
by (rule exI [of _ "{Spy}"], simp)
primrec knows :: "agent \ event list \ msg set"
where
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' \ 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))"
(*
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
*)
text\<open>The constant "spies" is retained for compatibility's sake\<close>
abbreviation (input)
spies :: "event list \ msg set" where
"spies == knows Spy"
(*Set of items that might be visible to somebody:
complement of the set of fresh items*)
primrec used :: "event list \ msg set"
where
used_Nil: "used [] = (UN B. parts (initState B))"
| used_Cons: "used (ev # evs) =
(case ev of
Says A B X \<Rightarrow> parts {X} \<union> used evs
| Gets A X \<Rightarrow> used evs
| Notes A X \<Rightarrow> parts {X} \<union> used evs)"
\<comment> \<open>The case for \<^term>\<open>Gets\<close> seems anomalous, but \<^term>\<open>Gets\<close> always
follows \<^term>\<open>Says\<close> in real protocols. Seems difficult to change.
See \<open>Gets_correct\<close> in theory \<open>Guard/Extensions.thy\<close>.\<close>
lemma Notes_imp_used [rule_format]: "Notes A X \ set evs \ X \ used evs"
apply (induct_tac evs)
apply (auto split: event.split)
done
lemma Says_imp_used [rule_format]: "Says A B X \ set evs \ X \ used evs"
apply (induct_tac evs)
apply (auto split: event.split)
done
subsection\<open>Function \<^term>\<open>knows\<close>\<close>
(*Simplifying
parts(insert X (knows Spy evs)) = parts{X} \<union> parts(knows Spy evs).
This version won't loop with the simplifier.*)
lemmas parts_insert_knows_A = parts_insert [of _ "knows A evs"] for A evs
lemma knows_Spy_Says [simp]:
"knows Spy (Says A B X # evs) = insert X (knows Spy evs)"
by simp
text\<open>Letting the Spy see "bad" agents' notes avoids redundant case-splits
on whether \<^term>\<open>A=Spy\<close> and whether \<^term>\<open>A\<in>bad\<close>\<close>
lemma knows_Spy_Notes [simp]:
"knows Spy (Notes A X # evs) =
(if A\<in>bad then insert X (knows Spy evs) else knows Spy evs)"
by simp
lemma knows_Spy_Gets [simp]: "knows Spy (Gets A X # evs) = knows Spy evs"
by simp
lemma knows_Spy_subset_knows_Spy_Says:
"knows Spy evs \ knows Spy (Says A B X # evs)"
by (simp add: subset_insertI)
lemma knows_Spy_subset_knows_Spy_Notes:
"knows Spy evs \ knows Spy (Notes A X # evs)"
by force
lemma knows_Spy_subset_knows_Spy_Gets:
"knows Spy evs \ knows Spy (Gets A X # evs)"
by (simp add: subset_insertI)
text\<open>Spy sees what is sent on the traffic\<close>
lemma Says_imp_knows_Spy [rule_format]:
"Says A B X \ set evs \ X \ knows Spy evs"
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
done
lemma Notes_imp_knows_Spy [rule_format]:
"Notes A X \ set evs \ A \ bad \ X \ knows Spy evs"
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
done
text\<open>Elimination rules: derive contradictions from old Says events containing
items known to be fresh\<close>
lemmas Says_imp_parts_knows_Spy =
Says_imp_knows_Spy [THEN parts.Inj, elim_format]
lemmas knows_Spy_partsEs =
Says_imp_parts_knows_Spy parts.Body [elim_format]
lemmas Says_imp_analz_Spy = Says_imp_knows_Spy [THEN analz.Inj]
text\<open>Compatibility for the old "spies" function\<close>
lemmas spies_partsEs = knows_Spy_partsEs
lemmas Says_imp_spies = Says_imp_knows_Spy
lemmas parts_insert_spies = parts_insert_knows_A [of _ Spy]
subsection\<open>Knowledge of Agents\<close>
lemma knows_subset_knows_Says: "knows A evs \ knows A (Says A' B X # evs)"
by (simp add: subset_insertI)
lemma knows_subset_knows_Notes: "knows A evs \ knows A (Notes A' X # evs)"
by (simp add: subset_insertI)
lemma knows_subset_knows_Gets: "knows A evs \ knows A (Gets A' X # evs)"
by (simp add: subset_insertI)
text\<open>Agents know what they say\<close>
lemma Says_imp_knows [rule_format]: "Says A B X \ set evs \ X \ knows A evs"
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
apply blast
done
text\<open>Agents know what they note\<close>
lemma Notes_imp_knows [rule_format]: "Notes A X \ set evs \ X \ knows A evs"
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
apply blast
done
text\<open>Agents know what they receive\<close>
lemma Gets_imp_knows_agents [rule_format]:
"A \ Spy \ Gets A X \ set evs \ X \ knows A evs"
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
done
text\<open>What agents DIFFERENT FROM Spy know
was either said, or noted, or got, or known initially\<close>
lemma knows_imp_Says_Gets_Notes_initState [rule_format]:
"[| X \ knows A evs; A \ Spy |] ==> \ B.
Says A B X \<in> set evs \<or> Gets A X \<in> set evs \<or> Notes A X \<in> set evs \<or> X \<in> initState A"
apply (erule rev_mp)
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
apply blast
done
text\<open>What the Spy knows -- for the time being --
was either said or noted, or known initially\<close>
lemma knows_Spy_imp_Says_Notes_initState [rule_format]:
"X \ knows Spy evs \ \A B.
Says A B X \<in> set evs \<or> Notes A X \<in> set evs \<or> X \<in> initState Spy"
apply (erule rev_mp)
apply (induct_tac "evs")
apply (simp_all (no_asm_simp) split: event.split)
apply blast
done
lemma parts_knows_Spy_subset_used: "parts (knows Spy evs) \ used evs"
apply (induct_tac "evs", force)
apply (simp add: parts_insert_knows_A knows_Cons add: event.split, blast)
done
lemmas usedI = parts_knows_Spy_subset_used [THEN subsetD, intro]
lemma initState_into_used: "X \ parts (initState B) \ X \ used evs"
apply (induct_tac "evs")
apply (simp_all add: parts_insert_knows_A split: event.split, blast)
done
lemma used_Says [simp]: "used (Says A B X # evs) = parts{X} \ used evs"
by simp
lemma used_Notes [simp]: "used (Notes A X # evs) = parts{X} \ used evs"
by simp
lemma used_Gets [simp]: "used (Gets A X # evs) = used evs"
by simp
lemma used_nil_subset: "used [] \ used evs"
apply simp
apply (blast intro: initState_into_used)
done
text\<open>NOTE REMOVAL--laws above are cleaner, as they don't involve "case"\<close>
declare knows_Cons [simp del]
used_Nil [simp del] used_Cons [simp del]
text\<open>For proving theorems of the form \<^term>\<open>X \<notin> analz (knows Spy evs) \<longrightarrow> P\<close>
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>\<open>analz\<close>.\<close>
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]
lemma knows_subset_knows_Cons: "knows A evs \ knows A (e # evs)"
by (cases e, auto simp: knows_Cons)
lemma initState_subset_knows: "initState A \ knows A evs"
apply (induct_tac evs, simp)
apply (blast intro: knows_subset_knows_Cons [THEN subsetD])
done
text\<open>For proving \<open>new_keys_not_used\<close>\<close>
lemma keysFor_parts_insert:
"[| K \ keysFor (parts (insert X G)); X \ synth (analz H) |]
==> K \<in> keysFor (parts (G \<union> H)) | Key (invKey K) \<in> parts H"
by (force
dest!: parts_insert_subset_Un [THEN keysFor_mono, THEN [2] rev_subsetD]
analz_subset_parts [THEN keysFor_mono, THEN [2] rev_subsetD]
intro: analz_subset_parts [THEN subsetD] parts_mono [THEN [2] rev_subsetD])
lemmas analz_impI = impI [where P = "Y \ analz (knows Spy evs)"] for Y evs
ML
\<open>
fun analz_mono_contra_tac ctxt =
resolve_tac ctxt @{thms analz_impI} THEN'
REPEAT1 o (dresolve_tac ctxt @{thms analz_mono_contra})
THEN' (mp_tac ctxt)
\<close>
method_setup analz_mono_contra = \<open>
Scan.succeed (fn ctxt => SIMPLE_METHOD (REPEAT_FIRST (analz_mono_contra_tac ctxt)))\<close>
"for proving theorems of the form X \ analz (knows Spy evs) \ P"
subsubsection\<open>Useful for case analysis on whether a hash is a spoof or not\<close>
lemmas syan_impI = impI [where P = "Y \ synth (analz (knows Spy evs))"] for Y evs
ML
\<open>
fun synth_analz_mono_contra_tac ctxt =
resolve_tac ctxt @{thms syan_impI} THEN'
REPEAT1 o
(dresolve_tac ctxt
[@{thm knows_Spy_subset_knows_Spy_Says} RS @{thm synth_analz_mono} RS @{thm contra_subsetD},
@{thm knows_Spy_subset_knows_Spy_Notes} RS @{thm synth_analz_mono} RS @{thm contra_subsetD},
@{thm knows_Spy_subset_knows_Spy_Gets} RS @{thm synth_analz_mono} RS @{thm contra_subsetD}])
THEN'
mp_tac ctxt
\<close>
method_setup synth_analz_mono_contra = \<open>
Scan.succeed (fn ctxt => SIMPLE_METHOD (REPEAT_FIRST (synth_analz_mono_contra_tac ctxt)))\<close>
"for proving theorems of the form X \ synth (analz (knows Spy evs)) \ P"
end
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