Quelle  Message_SET.thy

(*  Title:      HOL/SET_Protocol/Message_SET.thy
  Author: Giampaolo Bella
  Author: Fabio Massacci
  Author: Lawrence C Paulson
*)

section‹The Message Theory, Modified for SET›

theory Message_SET
imports Main "HOL-Library.Nat_Bijection"
begin

subsection‹General Lemmas›

text‹Needed occasionally with ‹spy_analz_tac›, e.g. in
  ‹analz_insert_Key_newK›\›

lemma Un_absorb3 [simp] : "A ∪ (B ∪ A) = B ∪ A"
by blast

text‹Collapses redundant cases in the huge protocol proofs›
lemmas disj_simps = disj_comms disj_left_absorb disj_assoc

text‹Effective with assumptions like 🍋‹K ∉ range pubK› and
  🍋‹K ∉ invKey`range pubK›\›
lemma notin_image_iff: "(y ∉ f`I) = (∀i∈I. f i ≠ y)"
by blast

text‹Effective with the assumption 🍋‹KK ⊆ - (range(invKey o pubK))›\›
lemma disjoint_image_iff: "(A ⊆ - (f`I)) = (∀i∈I. f i ∉ A)"
by blast



type_synonym key = nat

consts
  all_symmetric :: bool        🍋 ‹true if all keys are symmetric›
  invKey        :: "key==>key"  🍋 ‹inverse of a symmetric key›

specification (invKey)
  invKey [simp]: "invKey (invKey K) = K"
  invKey_symmetric: "all_symmetric ⟶ invKey = id"
    by (rule exI [of _ id], auto)


text‹The inverse of a symmetric key is itself; that of a public key
  is the private key and vice versa›

definition symKeys :: "key set" where
  "symKeys == {K. invKey K = K}"

text‹Agents. We allow any number of certification authorities, cardholders
  merchants, and payment gateways.›
datatype
  agent = CA nat | Cardholder nat | Merchant nat | PG nat | Spy

text‹Messages›
datatype
     msg = Agent  agent     🍋 ‹Agent names›
         | Number nat       🍋 ‹Ordinary integers, timestamps, ...›
         | Nonce  nat       🍋 ‹Unguessable nonces›
         | Pan    nat       🍋 ‹Unguessable Primary Account Numbers (??)›
         | Key    key       🍋 ‹Crypto keys›
         | Hash   msg       🍋 ‹Hashing›
         | MPair  msg msg   🍋 ‹Compound messages›
         | Crypt  key msg   🍋 ‹Encryption, public- or shared-key›


(*Concrete syntax: messages appear as \<open>\<lbrace>A,B,NA\<rbrace>\<close>, etc...*)
syntax
  "_MTuple" :: "['a, args] ==> 'a * 'b"  (‹(‹indent=2 notation=‹mixfix message tuple›\›\})›)
syntax_consts
  "_MTuple" ⇌ MPair
translations
  "{x, y, z}" ⇌ "{x, {y, z}}"
  "{x, y}" ⇌ "CONST MPair x y"


definition nat_of_agent :: "agent ==> nat" where
   "nat_of_agent == case_agent (curry prod_encode 0)
                               (curry prod_encode 1)
                               (curry prod_encode 2)
                               (curry prod_encode 3)
                               (prod_encode (4,0))"
    🍋 ‹maps each agent to a unique natural number, for specifications›

text‹The function is indeed injective›
lemma inj_nat_of_agent: "inj nat_of_agent"
by (simp add: nat_of_agent_def inj_on_def curry_def prod_encode_eq split: agent.split)


definition
  (*Keys useful to decrypt elements of a message set*)
  keysFor :: "msg set ==> key set"
  where "keysFor H = invKey ` {K. ∃X. Crypt K X ∈ H}"

subsubsection‹Inductive definition of all "parts" of a message.›

inductive_set
  parts :: "msg set ==> msg set"
  for H :: "msg set"
  where
    Inj [intro]:               "X ∈ H ==> X ∈ parts H"
  | Fst:         "{X,Y} ∈ parts H ==> X ∈ parts H"
  | Snd:         "{X,Y} ∈ parts H ==> Y ∈ parts H"
  | Body:        "Crypt K X ∈ parts H ==> X ∈ parts H"


(*Monotonicity*)
lemma parts_mono: "G⊆H ==> parts(G) ⊆ parts(H)"
apply auto
apply (erule parts.induct)
apply (auto dest: Fst Snd Body)
done


subsubsection‹Inverse of keys›

(*Equations hold because constructors are injective; cannot prove for all f*)
lemma Key_image_eq [simp]: "(Key x ∈ Key`A) = (x∈A)"
by auto

lemma Nonce_Key_image_eq [simp]: "(Nonce x ∉ Key`A)"
by auto

lemma Cardholder_image_eq [simp]: "(Cardholder x ∈ Cardholder`A) = (x ∈ A)"
by auto

lemma CA_image_eq [simp]: "(CA x ∈ CA`A) = (x ∈ A)"
by auto

lemma Pan_image_eq [simp]: "(Pan x ∈ Pan`A) = (x ∈ A)"
by auto

lemma Pan_Key_image_eq [simp]: "(Pan x ∉ Key`A)"
by auto

lemma Nonce_Pan_image_eq [simp]: "(Nonce x ∉ Pan`A)"
by auto

lemma invKey_eq [simp]: "(invKey K = invKey K') = (K=K')"
apply safe
apply (drule_tac f = invKey in arg_cong, simp)
done


subsection‹keysFor operator›

lemma keysFor_empty [simp]: "keysFor {} = {}"
by (unfold keysFor_def, blast)

lemma keysFor_Un [simp]: "keysFor (H ∪ H') = keysFor H ∪ keysFor H'"
by (unfold keysFor_def, blast)

lemma keysFor_UN [simp]: "keysFor (∪i∈A. H i) = (∪i∈A. keysFor (H i))"
by (unfold keysFor_def, blast)

(*Monotonicity*)
lemma keysFor_mono: "G⊆H ==> keysFor(G) ⊆ keysFor(H)"
by (unfold keysFor_def, blast)

lemma keysFor_insert_Agent [simp]: "keysFor (insert (Agent A) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Nonce [simp]: "keysFor (insert (Nonce N) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Number [simp]: "keysFor (insert (Number N) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Key [simp]: "keysFor (insert (Key K) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Pan [simp]: "keysFor (insert (Pan A) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Hash [simp]: "keysFor (insert (Hash X) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_MPair [simp]: "keysFor (insert {X,Y} H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_Crypt [simp]:
    "keysFor (insert (Crypt K X) H) = insert (invKey K) (keysFor H)"
by (unfold keysFor_def, auto)

lemma keysFor_image_Key [simp]: "keysFor (Key`E) = {}"
by (unfold keysFor_def, auto)

lemma Crypt_imp_invKey_keysFor: "Crypt K X ∈ H ==> invKey K ∈ keysFor H"
by (unfold keysFor_def, blast)


subsection‹Inductive relation "parts"›

lemma MPair_parts:
     "[| {X,Y} ∈ parts H;
         [| X ∈ parts H; Y ∈ parts H |] ==> P |] ==> P"
by (blast dest: parts.Fst parts.Snd)

declare MPair_parts [elim!]  parts.Body [dest!]
text‹NB These two rules are UNSAFE in the formal sense, as they discard the
  compound message. They work well on THIS FILE.
  ‹MPair_parts› i
  The Crypt rule is normally kept UNSAFE to avoid breaking up certificates.›

lemma parts_increasing: "H ⊆ parts(H)"
by blast

lemmas parts_insertI = subset_insertI [THEN parts_mono, THEN subsetD]

lemma parts_empty [simp]: "parts{} = {}"
apply safe
apply (erule parts.induct, blast+)
done

lemma parts_emptyE [elim!]: "X∈ parts{} ==> P"
by simp

(*WARNING: loops if H = {Y}, therefore must not be repeated!*)
lemma parts_singleton: "X∈ parts H ==> ∃Y∈H. X∈ parts {Y}"
by (erule parts.induct, fast+)


subsubsection‹Unions›

lemma parts_Un_subset1: "parts(G) ∪ parts(H) ⊆ parts(G ∪ H)"
by (intro Un_least parts_mono Un_upper1 Un_upper2)

lemma parts_Un_subset2: "parts(G ∪ H) ⊆ parts(G) ∪ parts(H)"
apply (rule subsetI)
apply (erule parts.induct, blast+)
done

lemma parts_Un [simp]: "parts(G ∪ H) = parts(G) ∪ parts(H)"
by (intro equalityI parts_Un_subset1 parts_Un_subset2)

lemma parts_insert: "parts (insert X H) = parts {X} ∪ parts H"
apply (subst insert_is_Un [of _ H])
apply (simp only: parts_Un)
done

(*TWO inserts to avoid looping.  This rewrite is better than nothing.
  Not suitable for Addsimps: its behaviour can be strange.*)
lemma parts_insert2:
     "parts (insert X (insert Y H)) = parts {X} ∪ parts {Y} ∪ parts H"
apply (simp add: Un_assoc)
apply (simp add: parts_insert [symmetric])
done

(*Added to simplify arguments to parts, analz and synth.*)


text‹This allows ‹blast› to simplify occurrences of
  🍋‹parts(G∪H)› in the assumption.›
declare parts_Un [THEN equalityD1, THEN subsetD, THEN UnE, elim!]


lemma parts_insert_subset: "insert X (parts H) ⊆ parts(insert X H)"
by (blast intro: parts_mono [THEN [2] rev_subsetD])

subsubsection‹Idempotence and transitivity›

lemma parts_partsD [dest!]: "X∈ parts (parts H) ==> X∈ parts H"
by (erule parts.induct, blast+)

lemma parts_idem [simp]: "parts (parts H) = parts H"
by blast

lemma parts_trans: "[| X∈ parts G; G ⊆ parts H |] ==> X∈ parts H"
by (drule parts_mono, blast)

(*Cut*)
lemma parts_cut:
     "[| Y∈ parts (insert X G); X∈ parts H |] ==> Y∈ parts (G ∪ H)"
by (erule parts_trans, auto)

lemma parts_cut_eq [simp]: "X∈ parts H ==> parts (insert X H) = parts H"
by (force dest!: parts_cut intro: parts_insertI)


subsubsection‹Rewrite rules for pulling out atomic messages›

lemmas parts_insert_eq_I = equalityI [OF subsetI parts_insert_subset]


lemma parts_insert_Agent [simp]:
     "parts (insert (Agent agt) H) = insert (Agent agt) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Nonce [simp]:
     "parts (insert (Nonce N) H) = insert (Nonce N) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Number [simp]:
     "parts (insert (Number N) H) = insert (Number N) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Key [simp]:
     "parts (insert (Key K) H) = insert (Key K) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Pan [simp]:
     "parts (insert (Pan A) H) = insert (Pan A) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Hash [simp]:
     "parts (insert (Hash X) H) = insert (Hash X) (parts H)"
apply (rule parts_insert_eq_I)
apply (erule parts.induct, auto)
done

lemma parts_insert_Crypt [simp]:
     "parts (insert (Crypt K X) H) =
          insert (Crypt K X) (parts (insert X H))"
apply (rule equalityI)
apply (rule subsetI)
apply (erule parts.induct, auto)
apply (erule parts.induct)
apply (blast intro: parts.Body)+
done

lemma parts_insert_MPair [simp]:
     "parts (insert {X,Y} H) =
          insert {X,Y} (parts (insert X (insert Y H)))"
apply (rule equalityI)
apply (rule subsetI)
apply (erule parts.induct, auto)
apply (erule parts.induct)
apply (blast intro: parts.Fst parts.Snd)+
done

lemma parts_image_Key [simp]: "parts (Key`N) = Key`N"
apply auto
apply (erule parts.induct, auto)
done

lemma parts_image_Pan [simp]: "parts (Pan`A) = Pan`A"
apply auto
apply (erule parts.induct, auto)
done


(*In any message, there is an upper bound N on its greatest nonce.*)
lemma msg_Nonce_supply: "∃N. ∀n. N≤n ⟶ Nonce n ∉ parts {msg}"
apply (induct_tac "msg")
apply (simp_all (no_asm_simp) add: exI parts_insert2)
(*MPair case: blast_tac works out the necessary sum itself!*)
prefer 2 apply (blast elim!: add_leE)
(*Nonce case*)
apply (rename_tac nat)
apply (rule_tac x = "N + Suc nat" in exI)
apply (auto elim!: add_leE)
done

(* Ditto, for numbers.*)
lemma msg_Number_supply: "∃N. ∀n. N≤n ⟶ Number n ∉ parts {msg}"
apply (induct_tac "msg")
apply (simp_all (no_asm_simp) add: exI parts_insert2)
prefer 2 apply (blast elim!: add_leE)
apply (rename_tac nat)
apply (rule_tac x = "N + Suc nat" in exI, auto)
done

subsection‹Inductive relation "analz"›

text‹Inductive definition of "analz" -- what can be broken down from a set of
  messages, including keys. A form of downward closure. Pairs can
  be taken apart; messages decrypted with known keys.›

inductive_set
  analz :: "msg set => msg set"
  for H :: "msg set"
  where
    Inj [intro,simp] :    "X ∈ H ==> X ∈ analz H"
  | Fst:     "{X,Y} ∈ analz H ==> X ∈ analz H"
  | Snd:     "{X,Y} ∈ analz H ==> Y ∈ analz H"
  | Decrypt [dest]:
             "[|Crypt K X ∈ analz H; Key(invKey K) ∈ analz H|] ==> X ∈ analz H"


(*Monotonicity; Lemma 1 of Lowe's paper*)
lemma analz_mono: "G⊆H ==> analz(G) ⊆ analz(H)"
apply auto
apply (erule analz.induct)
apply (auto dest: Fst Snd)
done

text‹Making it safe speeds up proofs›
lemma MPair_analz [elim!]:
     "[| {X,Y} ∈ analz H;
             [| X ∈ analz H; Y ∈ analz H |] ==> P
          |] ==> P"
by (blast dest: analz.Fst analz.Snd)

lemma analz_increasing: "H ⊆ analz(H)"
by blast

lemma analz_subset_parts: "analz H ⊆ parts H"
apply (rule subsetI)
apply (erule analz.induct, blast+)
done

lemmas analz_into_parts = analz_subset_parts [THEN subsetD]

lemmas not_parts_not_analz = analz_subset_parts [THEN contra_subsetD]


lemma parts_analz [simp]: "parts (analz H) = parts H"
apply (rule equalityI)
apply (rule analz_subset_parts [THEN parts_mono, THEN subset_trans], simp)
apply (blast intro: analz_increasing [THEN parts_mono, THEN subsetD])
done

lemma analz_parts [simp]: "analz (parts H) = parts H"
apply auto
apply (erule analz.induct, auto)
done

lemmas analz_insertI = subset_insertI [THEN analz_mono, THEN [2] rev_subsetD]

subsubsection‹General equational properties›

lemma analz_empty [simp]: "analz{} = {}"
apply safe
apply (erule analz.induct, blast+)
done

(*Converse fails: we can analz more from the union than from the
  separate parts, as a key in one might decrypt a message in the other*)
lemma analz_Un: "analz(G) ∪ analz(H) ⊆ analz(G ∪ H)"
by (intro Un_least analz_mono Un_upper1 Un_upper2)

lemma analz_insert: "insert X (analz H) ⊆ analz(insert X H)"
by (blast intro: analz_mono [THEN [2] rev_subsetD])

subsubsection‹Rewrite rules for pulling out atomic messages›

lemmas analz_insert_eq_I = equalityI [OF subsetI analz_insert]

lemma analz_insert_Agent [simp]:
     "analz (insert (Agent agt) H) = insert (Agent agt) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma analz_insert_Nonce [simp]:
     "analz (insert (Nonce N) H) = insert (Nonce N) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma analz_insert_Number [simp]:
     "analz (insert (Number N) H) = insert (Number N) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma analz_insert_Hash [simp]:
     "analz (insert (Hash X) H) = insert (Hash X) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

(*Can only pull out Keys if they are not needed to decrypt the rest*)
lemma analz_insert_Key [simp]:
    "K ∉ keysFor (analz H) ==>
          analz (insert (Key K) H) = insert (Key K) (analz H)"
apply (unfold keysFor_def)
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma analz_insert_MPair [simp]:
     "analz (insert {X,Y} H) =
          insert {X,Y} (analz (insert X (insert Y H)))"
apply (rule equalityI)
apply (rule subsetI)
apply (erule analz.induct, auto)
apply (erule analz.induct)
apply (blast intro: analz.Fst analz.Snd)+
done

(*Can pull out enCrypted message if the Key is not known*)
lemma analz_insert_Crypt:
     "Key (invKey K) ∉ analz H
      ==> analz (insert (Crypt K X) H) = insert (Crypt K X) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma analz_insert_Pan [simp]:
     "analz (insert (Pan A) H) = insert (Pan A) (analz H)"
apply (rule analz_insert_eq_I)
apply (erule analz.induct, auto)
done

lemma lemma1: "Key (invKey K) ∈ analz H ==>
               analz (insert (Crypt K X) H) ⊆
               insert (Crypt K X) (analz (insert X H))"
apply (rule subsetI)
apply (erule_tac x = x in analz.induct, auto)
done

lemma lemma2: "Key (invKey K) ∈ analz H ==>
               insert (Crypt K X) (analz (insert X H)) ⊆
               analz (insert (Crypt K X) H)"
apply auto
apply (erule_tac x = x in analz.induct, auto)
apply (blast intro: analz_insertI analz.Decrypt)
done

lemma analz_insert_Decrypt:
     "Key (invKey K) ∈ analz H ==>
               analz (insert (Crypt K X) H) =
               insert (Crypt K X) (analz (insert X H))"
by (intro equalityI lemma1 lemma2)

(*Case analysis: either the message is secure, or it is not!
  Effective, but can cause subgoals to blow up!
  Use with if_split; apparently split_tac does not cope with patterns
  such as "analz (insert (Crypt K X) H)" *)
lemma analz_Crypt_if [simp]:
     "analz (insert (Crypt K X) H) =
          (if (Key (invKey K) ∈ analz H)
           then insert (Crypt K X) (analz (insert X H))
           else insert (Crypt K X) (analz H))"
by (simp add: analz_insert_Crypt analz_insert_Decrypt)


(*This rule supposes "for the sake of argument" that we have the key.*)
lemma analz_insert_Crypt_subset:
     "analz (insert (Crypt K X) H) ⊆
           insert (Crypt K X) (analz (insert X H))"
apply (rule subsetI)
apply (erule analz.induct, auto)
done

lemma analz_image_Key [simp]: "analz (Key`N) = Key`N"
apply auto
apply (erule analz.induct, auto)
done

lemma analz_image_Pan [simp]: "analz (Pan`A) = Pan`A"
apply auto
apply (erule analz.induct, auto)
done


subsubsection‹Idempotence and transitivity›

lemma analz_analzD [dest!]: "X∈ analz (analz H) ==> X∈ analz H"
by (erule analz.induct, blast+)

lemma analz_idem [simp]: "analz (analz H) = analz H"
by blast

lemma analz_trans: "[| X∈ analz G; G ⊆ analz H |] ==> X∈ analz H"
by (drule analz_mono, blast)

(*Cut; Lemma 2 of Lowe*)
lemma analz_cut: "[| Y∈ analz (insert X H); X∈ analz H |] ==> Y∈ analz H"
by (erule analz_trans, blast)

(*Cut can be proved easily by induction on
  "Y: analz (insert X H) ==> X: analz H ⟶ Y: analz H"
*)

(*This rewrite rule helps in the simplification of messages that involve
  the forwarding of unknown components (X). Without it, removing occurrences
  of X can be very complicated. *)
lemma analz_insert_eq: "X∈ analz H ==> analz (insert X H) = analz H"
by (blast intro: analz_cut analz_insertI)


text‹A congruence rule for "analz"›

lemma analz_subset_cong:
     "[| analz G ⊆ analz G'; analz H ⊆ analz H'
               |] ==> analz (G ∪ H) ⊆ analz (G' ∪ H')"
apply clarify
apply (erule analz.induct)
apply (best intro: analz_mono [THEN subsetD])+
done

lemma analz_cong:
     "[| analz G = analz G'; analz H = analz H'
               |] ==> analz (G ∪ H) = analz (G' ∪ H')"
by (intro equalityI analz_subset_cong, simp_all)

lemma analz_insert_cong:
     "analz H = analz H' ==> analz(insert X H) = analz(insert X H')"
by (force simp only: insert_def intro!: analz_cong)

(*If there are no pairs or encryptions then analz does nothing*)
lemma analz_trivial:
     "[| ∀X Y. {X,Y} ∉ H; ∀X K. Crypt K X ∉ H |] ==> analz H = H"
apply safe
apply (erule analz.induct, blast+)
done


subsection‹Inductive relation "synth"›

text‹Inductive definition of "synth" -- what can be built up from a set of
  messages. A form of upward closure. Pairs can be built, messages
  encrypted with known keys. Agent names are public domain.
  Numbers can be guessed, but Nonces cannot be.›

inductive_set
  synth :: "msg set ==> msg set"
  for H :: "msg set"
  where
    Inj    [intro]:   "X ∈ H ==> X ∈ synth H"
  | Agent  [intro]:   "Agent agt ∈ synth H"
  | Number [intro]:   "Number n ∈ synth H"
  | Hash   [intro]:   "X ∈ synth H ==> Hash X ∈ synth H"
  | MPair  [intro]:   "[|X ∈ synth H; Y ∈ synth H|] ==> {X,Y} ∈ synth H"
  | Crypt  [intro]:   "[|X ∈ synth H; Key(K) ∈ H|] ==> Crypt K X ∈ synth H"

(*Monotonicity*)
lemma synth_mono: "G⊆H ==> synth(G) ⊆ synth(H)"
apply auto
apply (erule synth.induct)
apply (auto dest: Fst Snd Body)
done

(*NO Agent_synth, as any Agent name can be synthesized.  Ditto for Number*)
inductive_cases Nonce_synth [elim!]: "Nonce n ∈ synth H"
inductive_cases Key_synth   [elim!]: "Key K ∈ synth H"
inductive_cases Hash_synth  [elim!]: "Hash X ∈ synth H"
inductive_cases MPair_synth [elim!]: "{X,Y} ∈ synth H"
inductive_cases Crypt_synth [elim!]: "Crypt K X ∈ synth H"
inductive_cases Pan_synth   [elim!]: "Pan A ∈ synth H"


lemma synth_increasing: "H ⊆ synth(H)"
by blast

subsubsection‹Unions›

(*Converse fails: we can synth more from the union than from the
  separate parts, building a compound message using elements of each.*)
lemma synth_Un: "synth(G) ∪ synth(H) ⊆ synth(G ∪ H)"
by (intro Un_least synth_mono Un_upper1 Un_upper2)

lemma synth_insert: "insert X (synth H) ⊆ synth(insert X H)"
by (blast intro: synth_mono [THEN [2] rev_subsetD])

subsubsection‹Idempotence and transitivity›

lemma synth_synthD [dest!]: "X∈ synth (synth H) ==> X∈ synth H"
by (erule synth.induct, blast+)

lemma synth_idem: "synth (synth H) = synth H"
by blast

lemma synth_trans: "[| X∈ synth G; G ⊆ synth H |] ==> X∈ synth H"
by (drule synth_mono, blast)

(*Cut; Lemma 2 of Lowe*)
lemma synth_cut: "[| Y∈ synth (insert X H); X∈ synth H |] ==> Y∈ synth H"
by (erule synth_trans, blast)

lemma Agent_synth [simp]: "Agent A ∈ synth H"
by blast

lemma Number_synth [simp]: "Number n ∈ synth H"
by blast

lemma Nonce_synth_eq [simp]: "(Nonce N ∈ synth H) = (Nonce N ∈ H)"
by blast

lemma Key_synth_eq [simp]: "(Key K ∈ synth H) = (Key K ∈ H)"
by blast

lemma Crypt_synth_eq [simp]: "Key K ∉ H ==> (Crypt K X ∈ synth H) = (Crypt K X ∈ H)"
by blast

lemma Pan_synth_eq [simp]: "(Pan A ∈ synth H) = (Pan A ∈ H)"
by blast

lemma keysFor_synth [simp]:
    "keysFor (synth H) = keysFor H ∪ invKey`{K. Key K ∈ H}"
by (unfold keysFor_def, blast)


subsubsection‹Combinations of parts, analz and synth›

lemma parts_synth [simp]: "parts (synth H) = parts H ∪ synth H"
apply (rule equalityI)
apply (rule subsetI)
apply (erule parts.induct)
apply (blast intro: synth_increasing [THEN parts_mono, THEN subsetD]
                    parts.Fst parts.Snd parts.Body)+
done

lemma analz_analz_Un [simp]: "analz (analz G ∪ H) = analz (G ∪ H)"
apply (intro equalityI analz_subset_cong)+
apply simp_all
done

lemma analz_synth_Un [simp]: "analz (synth G ∪ H) = analz (G ∪ H) ∪ synth G"
apply (rule equalityI)
apply (rule subsetI)
apply (erule analz.induct)
prefer 5 apply (blast intro: analz_mono [THEN [2] rev_subsetD])
apply (blast intro: analz.Fst analz.Snd analz.Decrypt)+
done

lemma analz_synth [simp]: "analz (synth H) = analz H ∪ synth H"
apply (cut_tac H = "{}" in analz_synth_Un)
apply (simp (no_asm_use))
done


subsubsection‹For reasoning about the Fake rule in traces›

lemma parts_insert_subset_Un: "X∈ G ==> parts(insert X H) ⊆ parts G ∪ parts H"
by (rule subset_trans [OF parts_mono parts_Un_subset2], blast)

(*More specifically for Fake.  Very occasionally we could do with a version
  of the form  parts{X} \<subseteq> synth (analz H) \<union> parts H *)
lemma Fake_parts_insert: "X ∈ synth (analz H) ==>
      parts (insert X H) ⊆ synth (analz H) ∪ parts H"
apply (drule parts_insert_subset_Un)
apply (simp (no_asm_use))
apply blast
done

lemma Fake_parts_insert_in_Un:
     "[|Z ∈ parts (insert X H); X ∈ synth (analz H)|]
      ==> Z ∈ synth (analz H) ∪ parts H"
by (blast dest: Fake_parts_insert [THEN subsetD, dest])

(*H is sometimes (Key ` KK \<union> spies evs), so can't put G=H*)
lemma Fake_analz_insert:
     "X∈ synth (analz G) ==>
      analz (insert X H) ⊆ synth (analz G) ∪ analz (G ∪ H)"
apply (rule subsetI)
apply (subgoal_tac "x ∈ analz (synth (analz G) ∪ H) ")
prefer 2 apply (blast intro: analz_mono [THEN [2] rev_subsetD] analz_mono [THEN synth_mono, THEN [2] rev_subsetD])
apply (simp (no_asm_use))
apply blast
done

lemma analz_conj_parts [simp]:
     "(X ∈ analz H ∧ X ∈ parts H) = (X ∈ analz H)"
by (blast intro: analz_subset_parts [THEN subsetD])

lemma analz_disj_parts [simp]:
     "(X ∈ analz H | X ∈ parts H) = (X ∈ parts H)"
by (blast intro: analz_subset_parts [THEN subsetD])

(*Without this equation, other rules for synth and analz would yield
  redundant cases*)
lemma MPair_synth_analz [iff]:
     "({X,Y} ∈ synth (analz H)) =
      (X ∈ synth (analz H) ∧ Y ∈ synth (analz H))"
by blast

lemma Crypt_synth_analz:
     "[| Key K ∈ analz H; Key (invKey K) ∈ analz H |]
       ==> (Crypt K X ∈ synth (analz H)) = (X ∈ synth (analz H))"
by blast


lemma Hash_synth_analz [simp]:
     "X ∉ synth (analz H)
      ==> (Hash{X,Y} ∈ synth (analz H)) = (Hash{X,Y} ∈ analz H)"
by blast


(*We do NOT want Crypt... messages broken up in protocols!!*)
declare parts.Body [rule del]


text‹Rewrites to push in Key and Crypt messages, so that other messages can
  be pulled out using the ‹analz_insert› r

lemmas pushKeys =
  insert_commute [of "Key K" "Agent C"]
  insert_commute [of "Key K" "Nonce N"]
  insert_commute [of "Key K" "Number N"]
  insert_commute [of "Key K" "Pan PAN"]
  insert_commute [of "Key K" "Hash X"]
  insert_commute [of "Key K" "MPair X Y"]
  insert_commute [of "Key K" "Crypt X K'"]
  for K C N PAN X Y K'

lemmas pushCrypts =
  insert_commute [of "Crypt X K" "Agent C"]
  insert_commute [of "Crypt X K" "Nonce N"]
  insert_commute [of "Crypt X K" "Number N"]
  insert_commute [of "Crypt X K" "Pan PAN"]
  insert_commute [of "Crypt X K" "Hash X'"]
  insert_commute [of "Crypt X K" "MPair X' Y"]
  for X K C N PAN X' Y

text‹Cannot be added with ‹[simp]› -- messages should not always be
  re-ordered.›
lemmas pushes = pushKeys pushCrypts


subsection‹Tactics useful for many protocol proofs›
(*<*)
ML
‹
 (*Analysis of Fake cases. Also works for messages that forward unknown parts,
  but this application is no longer necessary if analz_insert_eq is used.
  DEPENDS UPON "X" REFERRING TO THE FRADULENT MESSAGE *)

fun impOfSubs th = th RSN (2, @{thm rev_subsetD})

(*Apply rules to break down assumptions of the form
  Y ∈ parts(insert X H) and Y ∈ analz(insert X H)
*)
fun Fake_insert_tac ctxt =
    dresolve_tac ctxt [impOfSubs @{thm Fake_analz_insert},
                  impOfSubs @{thm Fake_parts_insert}] THEN'
    eresolve_tac ctxt [asm_rl, @{thm synth.Inj}];

fun Fake_insert_simp_tac ctxt i =
  REPEAT (Fake_insert_tac ctxt i) THEN asm_full_simp_tac ctxt i;

fun atomic_spy_analz_tac ctxt =
  SELECT_GOAL
    (Fake_insert_simp_tac ctxt 1 THEN
      IF_UNSOLVED
        (Blast.depth_tac (ctxt addIs [@{thm analz_insertI},
            impOfSubs @{thm analz_subset_parts}]) 4 1));

fun spy_analz_tac ctxt i =
  DETERM
   (SELECT_GOAL
     (EVERY
      [  (*push in occurrences of X...*)
       (REPEAT o CHANGED)
         (Rule_Insts.res_inst_tac ctxt [((("x", 1), Position.none), "X")] []
          (@{thm insert_commute} RS ssubst) 1),
       (*...allowing further simplifications*)
       simp_tac ctxt 1,
       REPEAT (FIRSTGOAL (resolve_tac ctxt [allI,impI,notI,conjI,iffI])),
       DEPTH_SOLVE (atomic_spy_analz_tac ctxt 1)]) i);
›
(*>*)


(*By default only o_apply is built-in.  But in the presence of eta-expansion
  this means that some terms displayed as (f o g) will be rewritten, and others
  will not!*)
declare o_def [simp]


lemma Crypt_notin_image_Key [simp]: "Crypt K X ∉ Key ` A"
by auto

lemma Hash_notin_image_Key [simp] :"Hash X ∉ Key ` A"
by auto

lemma synth_analz_mono: "G⊆H ==> synth (analz(G)) ⊆ synth (analz(H))"
by (simp add: synth_mono analz_mono)

lemma Fake_analz_eq [simp]:
     "X ∈ synth(analz H) ==> synth (analz (insert X H)) = synth (analz H)"
apply (drule Fake_analz_insert[of _ _ "H"])
apply (simp add: synth_increasing[THEN Un_absorb2])
apply (drule synth_mono)
apply (simp add: synth_idem)
apply (blast intro: synth_analz_mono [THEN [2] rev_subsetD])
done

text‹Two generalizations of ‹analz_insert_eq›\›
lemma gen_analz_insert_eq [rule_format]:
     "X ∈ analz H ==> ∀G. H ⊆ G ⟶ analz (insert X G) = analz G"
by (blast intro: analz_cut analz_insertI analz_mono [THEN [2] rev_subsetD])

lemma synth_analz_insert_eq [rule_format]:
     "X ∈ synth (analz H)
      ==> ∀G. H ⊆ G ⟶ (Key K ∈ analz (insert X G)) = (Key K ∈ analz G)"
apply (erule synth.induct)
apply (simp_all add: gen_analz_insert_eq subset_trans [OF _ subset_insertI])
done

lemma Fake_parts_sing:
     "X ∈ synth (analz H) ==> parts{X} ⊆ synth (analz H) ∪ parts H"
apply (rule subset_trans)
 apply (erule_tac [2] Fake_parts_insert)
apply (simp add: parts_mono)
done

lemmas Fake_parts_sing_imp_Un = Fake_parts_sing [THEN [2] rev_subsetD]

method_setup spy_analz = ‹
  Scan.succeed (SIMPLE_METHOD' o spy_analz_tac)›
    "for proving the Fake case when analz is involved"

method_setup atomic_spy_analz = ‹
  Scan.succeed (SIMPLE_METHOD' o atomic_spy_analz_tac)›
    "for debugging spy_analz"

method_setup Fake_insert_simp = ‹
  Scan.succeed (SIMPLE_METHOD' o Fake_insert_simp_tac)›
    "for debugging spy_analz"

end