formal/afp/Automated_Stateful_Protocol_Verification/Term_Abstraction.thy

(*
(C) Copyright Andreas Viktor Hess, DTU, 2020
(C) Copyright Sebastian A. Mödersheim, DTU, 2020
(C) Copyright Achim D. Brucker, University of Exeter, 2020
(C) Copyright Anders Schlichtkrull, DTU, 2020

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(*  Title:      Term_Abstraction.thy
    Author:     Andreas Viktor Hess, DTU
    Author:     Sebastian A. Mödersheim, DTU
    Author:     Achim D. Brucker, University of Exeter
    Author:     Anders Schlichtkrull, DTU
*)

section\<open>Term Abstraction\<close>
theory Term_Abstraction
  imports Transactions
begin

subsection \<open>Definitions\<close>
fun to_abs ("\<alpha>\<^sub>0") where
  "\<alpha>\<^sub>0 [] _ = {}"
| "\<alpha>\<^sub>0 ((Fun (Val m) [],Fun (Set s) S)#D) n =
    (if m = n then insert s (\<alpha>\<^sub>0 D n) else \<alpha>\<^sub>0 D n)"
| "\<alpha>\<^sub>0 (_#D) n = \<alpha>\<^sub>0 D n"

fun abs_apply_term (infixl "\<cdot>\<^sub>\<alpha>" 67) where
  "Var x \<cdot>\<^sub>\<alpha> \<alpha> = Var x"
| "Fun (Val n) T \<cdot>\<^sub>\<alpha> \<alpha> = Fun (Abs (\<alpha> n)) (map (\<lambda>t. t \<cdot>\<^sub>\<alpha> \<alpha>) T)"
| "Fun f T \<cdot>\<^sub>\<alpha> \<alpha> = Fun f (map (\<lambda>t. t \<cdot>\<^sub>\<alpha> \<alpha>) T)"

definition abs_apply_list (infixl "\<cdot>\<^sub>\<alpha>\<^sub>l\<^sub>i\<^sub>s\<^sub>t" 67) where
  "M \<cdot>\<^sub>\<alpha>\<^sub>l\<^sub>i\<^sub>s\<^sub>t \<alpha> \<equiv> map (\<lambda>t. t \<cdot>\<^sub>\<alpha> \<alpha>) M"

definition abs_apply_terms (infixl "\<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t" 67) where
  "M \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t \<alpha> \<equiv> (\<lambda>t. t \<cdot>\<^sub>\<alpha> \<alpha>) ` M"

definition abs_apply_pairs (infixl "\<cdot>\<^sub>\<alpha>\<^sub>p\<^sub>a\<^sub>i\<^sub>r\<^sub>s" 67) where
  "F \<cdot>\<^sub>\<alpha>\<^sub>p\<^sub>a\<^sub>i\<^sub>r\<^sub>s \<alpha> \<equiv> map (\<lambda>(s,t). (s \<cdot>\<^sub>\<alpha> \<alpha>, t \<cdot>\<^sub>\<alpha> \<alpha>)) F"

definition abs_apply_strand_step (infixl "\<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>t\<^sub>p" 67) where
  "s \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>t\<^sub>p \<alpha> \<equiv> (case s of
    (l,send\<langle>t\<rangle>) \<Rightarrow> (l,send\<langle>t \<cdot>\<^sub>\<alpha> \<alpha>\<rangle>)
  | (l,receive\<langle>t\<rangle>) \<Rightarrow> (l,receive\<langle>t \<cdot>\<^sub>\<alpha> \<alpha>\<rangle>)
  | (l,\<langle>ac: t \<doteq> t'\<rangle>) \<Rightarrow> (l,\<langle>ac: (t \<cdot>\<^sub>\<alpha> \<alpha>) \<doteq> (t' \<cdot>\<^sub>\<alpha> \<alpha>)\<rangle>)
  | (l,insert\<langle>t,t'\<rangle>) \<Rightarrow> (l,insert\<langle>t \<cdot>\<^sub>\<alpha> \<alpha>,t' \<cdot>\<^sub>\<alpha> \<alpha>\<rangle>)
  | (l,delete\<langle>t,t'\<rangle>) \<Rightarrow> (l,delete\<langle>t \<cdot>\<^sub>\<alpha> \<alpha>,t' \<cdot>\<^sub>\<alpha> \<alpha>\<rangle>)
  | (l,\<langle>ac: t \<in> t'\<rangle>) \<Rightarrow> (l,\<langle>ac: (t \<cdot>\<^sub>\<alpha> \<alpha>) \<in> (t' \<cdot>\<^sub>\<alpha> \<alpha>)\<rangle>)
  | (l,\<forall>X\<langle>\<or>\<noteq>: F \<or>\<notin>: F'\<rangle>) \<Rightarrow> (l,\<forall>X\<langle>\<or>\<noteq>: (F \<cdot>\<^sub>\<alpha>\<^sub>p\<^sub>a\<^sub>i\<^sub>r\<^sub>s \<alpha>) \<or>\<notin>: (F' \<cdot>\<^sub>\<alpha>\<^sub>p\<^sub>a\<^sub>i\<^sub>r\<^sub>s \<alpha>)\<rangle>))"

definition abs_apply_strand (infixl "\<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>t" 67) where
  "S \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>t \<alpha> \<equiv> map (\<lambda>x. x \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>t\<^sub>p \<alpha>) S"


subsection \<open>Lemmata\<close>
lemma to_abs_alt_def:
  "\<alpha>\<^sub>0 D n = {s. \<exists>S. (Fun (Val n) [], Fun (Set s) S) \<in> set D}"
by (induct D n rule: to_abs.induct) auto

lemma abs_term_apply_const[simp]:
  "is_Val f \<Longrightarrow> Fun f [] \<cdot>\<^sub>\<alpha> a = Fun (Abs (a (the_Val f))) []"
  "\<not>is_Val f \<Longrightarrow> Fun f [] \<cdot>\<^sub>\<alpha> a = Fun f []"
by (cases f; auto)+

lemma abs_fv: "fv (t \<cdot>\<^sub>\<alpha> a) = fv t"
by (induct t a rule: abs_apply_term.induct) auto

lemma abs_eq_if_no_Val:
  assumes "\<forall>f \<in> funs_term t. \<not>is_Val f"
  shows "t \<cdot>\<^sub>\<alpha> a = t \<cdot>\<^sub>\<alpha> b"
using assms
proof (induction t)
  case (Fun f T) thus ?case by (cases f) simp_all
qed simp

lemma abs_list_set_is_set_abs_set: "set (M \<cdot>\<^sub>\<alpha>\<^sub>l\<^sub>i\<^sub>s\<^sub>t \<alpha>) = (set M) \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t \<alpha>"
unfolding abs_apply_list_def abs_apply_terms_def by simp

lemma abs_set_empty[simp]: "{} \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t \<alpha> = {}"
unfolding abs_apply_terms_def by simp

lemma abs_in:
  assumes "t \<in> M"
  shows "t \<cdot>\<^sub>\<alpha> \<alpha> \<in> M \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t \<alpha>"
using assms unfolding abs_apply_terms_def
by (induct t \<alpha> rule: abs_apply_term.induct) blast+

lemma abs_set_union: "(A \<union> B) \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a = (A \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a) \<union> (B \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a)"
unfolding abs_apply_terms_def
by auto

lemma abs_subterms: "subterms (t \<cdot>\<^sub>\<alpha> \<alpha>) = subterms t \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t \<alpha>"
proof (induction t)
  case (Fun f T) thus ?case by (cases f) (auto simp add: abs_apply_terms_def)
qed (simp add: abs_apply_terms_def)

lemma abs_subterms_in: "s \<in> subterms t \<Longrightarrow> s \<cdot>\<^sub>\<alpha> a \<in> subterms (t \<cdot>\<^sub>\<alpha> a)"
proof (induction t)
  case (Fun f T) thus ?case by (cases f) auto
qed simp

lemma abs_ik_append: "(ik\<^sub>s\<^sub>s\<^sub>t (A@B) \<cdot>\<^sub>s\<^sub>e\<^sub>t I) \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a = (ik\<^sub>s\<^sub>s\<^sub>t A \<cdot>\<^sub>s\<^sub>e\<^sub>t I) \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a \<union> (ik\<^sub>s\<^sub>s\<^sub>t B \<cdot>\<^sub>s\<^sub>e\<^sub>t I) \<cdot>\<^sub>\<alpha>\<^sub>s\<^sub>e\<^sub>t a"
unfolding abs_apply_terms_def ik\<^sub>s\<^sub>s\<^sub>t_def
by auto

lemma to_abs_in:
  assumes "(Fun (Val n) [], Fun (Set s) []) \<in> set D"
  shows "s \<in> \<alpha>\<^sub>0 D n"
using assms by (induct rule: to_abs.induct) auto

lemma to_abs_empty_iff_notin_db:
  "Fun (Val n) [] \<cdot>\<^sub>\<alpha> \<alpha>\<^sub>0 D = Fun (Abs {}) [] \<longleftrightarrow> (\<nexists>s S. (Fun (Val n) [], Fun (Set s) S) \<in> set D)"
by (simp add: to_abs_alt_def)

lemma to_abs_list_insert:
  assumes "Fun (Val n) [] \<noteq> t"
  shows "\<alpha>\<^sub>0 D n = \<alpha>\<^sub>0 (List.insert (t,s) D) n"
using assms to_abs_alt_def[of D n] to_abs_alt_def[of "List.insert (t,s) D" n]
by auto

lemma to_abs_list_insert':
  "insert s (\<alpha>\<^sub>0 D n) = \<alpha>\<^sub>0 (List.insert (Fun (Val n) [], Fun (Set s) S) D) n"
using to_abs_alt_def[of D n]
      to_abs_alt_def[of "List.insert (Fun (Val n) [], Fun (Set s) S) D" n]
by auto

lemma to_abs_list_remove_all:
  assumes "Fun (Val n) [] \<noteq> t"
  shows "\<alpha>\<^sub>0 D n = \<alpha>\<^sub>0 (List.removeAll (t,s) D) n"
using assms to_abs_alt_def[of D n] to_abs_alt_def[of "List.removeAll (t,s) D" n]
by auto

lemma to_abs_list_remove_all':
  "\<alpha>\<^sub>0 D n - {s} = \<alpha>\<^sub>0 (filter (\<lambda>d. \<nexists>S. d = (Fun (Val n) [], Fun (Set s) S)) D) n"
using to_abs_alt_def[of D n]
      to_abs_alt_def[of "filter (\<lambda>d. \<nexists>S. d = (Fun (Val n) [], Fun (Set s) S)) D" n]
by auto

lemma to_abs_db\<^sub>s\<^sub>s\<^sub>t_append:
  assumes "\<forall>u s. insert\<langle>u, s\<rangle> \<in> set B \<longrightarrow> Fun (Val n) [] \<noteq> u \<cdot> \<I>"
    and "\<forall>u s. delete\<langle>u, s\<rangle> \<in> set B \<longrightarrow> Fun (Val n) [] \<noteq> u \<cdot> \<I>"
  shows "\<alpha>\<^sub>0 (db'\<^sub>s\<^sub>s\<^sub>t A \<I> D) n = \<alpha>\<^sub>0 (db'\<^sub>s\<^sub>s\<^sub>t (A@B) \<I> D) n"
using assms
proof (induction B rule: List.rev_induct)
  case (snoc b B)
  hence IH: "\<alpha>\<^sub>0 (db'\<^sub>s\<^sub>s\<^sub>t A \<I> D) n = \<alpha>\<^sub>0 (db'\<^sub>s\<^sub>s\<^sub>t (A@B) \<I> D) n" by auto
  have *: "\<forall>u s. b = insert\<langle>u,s\<rangle> \<longrightarrow> Fun (Val n) [] \<noteq> u \<cdot> \<I>"
          "\<forall>u s. b = delete\<langle>u,s\<rangle> \<longrightarrow> Fun (Val n) [] \<noteq> u \<cdot> \<I>"
    using snoc.prems by simp_all
  show ?case
  proof (cases b)
    case (Insert u s)
    hence **: "db'\<^sub>s\<^sub>s\<^sub>t (A@B@[b]) \<I> D = List.insert (u \<cdot> \<I>,s \<cdot> \<I>) (db'\<^sub>s\<^sub>s\<^sub>t (A@B) \<I> D)"
      using db\<^sub>s\<^sub>s\<^sub>t_append[of "A@B" "[b]"] by simp
    have "Fun (Val n) [] \<noteq> u \<cdot> \<I>" using *(1) Insert by auto
    thus ?thesis using IH ** to_abs_list_insert by metis
  next
    case (Delete u s)
    hence **: "db'\<^sub>s\<^sub>s\<^sub>t (A@B@[b]) \<I> D = List.removeAll (u \<cdot> \<I>,s \<cdot> \<I>) (db'\<^sub>s\<^sub>s\<^sub>t (A@B) \<I> D)"
      using db\<^sub>s\<^sub>s\<^sub>t_append[of "A@B" "[b]"] by simp
    have "Fun (Val n) [] \<noteq> u \<cdot> \<I>" using *(2) Delete by auto
    thus ?thesis using IH ** to_abs_list_remove_all by metis
  qed (simp_all add: db\<^sub>s\<^sub>s\<^sub>t_no_upd_append[of "[b]" "A@B"] IH)
qed simp

lemma to_abs_neq_imp_db_update:
  assumes "\<alpha>\<^sub>0 (db\<^sub>s\<^sub>s\<^sub>t A I) n \<noteq> \<alpha>\<^sub>0 (db\<^sub>s\<^sub>s\<^sub>t (A@B) I) n"
  shows "\<exists>u s. u \<cdot> I = Fun (Val n) [] \<and> (insert\<langle>u,s\<rangle> \<in> set B \<or> delete\<langle>u,s\<rangle> \<in> set B)"
proof -
  { fix D have ?thesis when "\<alpha>\<^sub>0 D n \<noteq> \<alpha>\<^sub>0 (db'\<^sub>s\<^sub>s\<^sub>t B I D) n" using that
    proof (induction B I D rule: db'\<^sub>s\<^sub>s\<^sub>t.induct)
      case 2 thus ?case
        by (metis db'\<^sub>s\<^sub>s\<^sub>t.simps(2) list.set_intros(1,2) subst_apply_pair_pair to_abs_list_insert)
    next
      case 3 thus ?case
        by (metis db'\<^sub>s\<^sub>s\<^sub>t.simps(3) list.set_intros(1,2) subst_apply_pair_pair to_abs_list_remove_all)
    qed simp_all
  } thus ?thesis using assms by (metis db\<^sub>s\<^sub>s\<^sub>t_append db\<^sub>s\<^sub>s\<^sub>t_def)
qed

lemma abs_term_subst_eq:
  fixes \<delta> \<theta>::"(('a,'b,'c) prot_fun, ('d,'e prot_atom) term \<times> nat) subst"
  assumes "\<forall>x \<in> fv t. \<delta> x \<cdot>\<^sub>\<alpha> a = \<theta> x \<cdot>\<^sub>\<alpha> b"
    and "\<nexists>n T. Fun (Val n) T \<in> subterms t"
  shows "t \<cdot> \<delta> \<cdot>\<^sub>\<alpha> a = t \<cdot> \<theta> \<cdot>\<^sub>\<alpha> b"
using assms
proof (induction t)
  case (Fun f T) thus ?case
  proof (cases f)
    case (Val n)
    hence False using Fun.prems(2) by blast
    thus ?thesis by metis
  qed auto
qed simp

lemma abs_term_subst_eq':
  fixes \<delta> \<theta>::"(('a,'b,'c) prot_fun, ('d,'e prot_atom) term \<times> nat) subst"
  assumes "\<forall>x \<in> fv t. \<delta> x \<cdot>\<^sub>\<alpha> a = \<theta> x"
    and "\<nexists>n T. Fun (Val n) T \<in> subterms t"
  shows "t \<cdot> \<delta> \<cdot>\<^sub>\<alpha> a = t \<cdot> \<theta>"
using assms
proof (induction t)
  case (Fun f T) thus ?case
  proof (cases f)
    case (Val n)
    hence False using Fun.prems(2) by blast
    thus ?thesis by metis
  qed auto
qed simp

lemma abs_val_in_funs_term:
  assumes "f \<in> funs_term t" "is_Val f"
  shows "Abs (\<alpha> (the_Val f)) \<in> funs_term (t \<cdot>\<^sub>\<alpha> \<alpha>)"
using assms by (induct t \<alpha> rule: abs_apply_term.induct) auto

end