src/HOL/Auth/Message.thy

contributors

(*  Title:      HOL/Auth/Message.thy
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1996  University of Cambridge

Datatypes of agents and messages;
Inductive relations "parts", "analz" and "synth"
*)

section\<open>Theory of Agents and Messages for Security Protocols\<close>

theory Message
imports Main
begin

(*Needed occasionally with spy_analz_tac, e.g. in analz_insert_Key_newK*)
lemma [simp] : "A \<union> (B \<union> A) = B \<union> A"
by blast

type_synonym
  key = nat

consts
  all_symmetric :: bool        \<comment> \<open>true if all keys are symmetric\<close>
  invKey        :: "key\<Rightarrow>key"  \<comment> \<open>inverse of a symmetric key\<close>

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


text\<open>The inverse of a symmetric key is itself; that of a public key
      is the private key and vice versa\<close>

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

datatype  \<comment> \<open>We allow any number of friendly agents\<close>
  agent = Server | Friend nat | Spy

datatype
     msg = Agent  agent     \<comment> \<open>Agent names\<close>
         | Number nat       \<comment> \<open>Ordinary integers, timestamps, ...\<close>
         | Nonce  nat       \<comment> \<open>Unguessable nonces\<close>
         | Key    key       \<comment> \<open>Crypto keys\<close>
         | Hash   msg       \<comment> \<open>Hashing\<close>
         | MPair  msg msg   \<comment> \<open>Compound messages\<close>
         | Crypt  key msg   \<comment> \<open>Encryption, public- or shared-key\<close>


text\<open>Concrete syntax: messages appear as \<open>\<lbrace>A,B,NA\<rbrace>\<close>, etc...\<close>
syntax
  "_MTuple" :: "['a, args] \<Rightarrow> 'a * 'b"  ("(2\<lbrace>_,/ _\<rbrace>)")
translations
  "\<lbrace>x, y, z\<rbrace>" \<rightleftharpoons> "\<lbrace>x, \<lbrace>y, z\<rbrace>\<rbrace>"
  "\<lbrace>x, y\<rbrace>" \<rightleftharpoons> "CONST MPair x y"


definition HPair :: "[msg,msg] \<Rightarrow> msg" ("(4Hash[_] /_)" [0, 1000]) where
    \<comment> \<open>Message Y paired with a MAC computed with the help of X\<close>
    "Hash[X] Y == \<lbrace>Hash\<lbrace>X,Y\<rbrace>, Y\<rbrace>"

definition keysFor :: "msg set \<Rightarrow> key set" where
    \<comment> \<open>Keys useful to decrypt elements of a message set\<close>
  "keysFor H == invKey ` {K. \<exists>X. Crypt K X \<in> H}"


subsubsection\<open>Inductive Definition of All Parts" of a Message\<close>

inductive_set
  parts :: "msg set \<Rightarrow> msg set"
  for H :: "msg set"
  where
    Inj [intro]: "X \<in> H ==> X \<in> parts H"
  | Fst:         "\<lbrace>X,Y\<rbrace> \<in> parts H ==> X \<in> parts H"
  | Snd:         "\<lbrace>X,Y\<rbrace> \<in> parts H ==> Y \<in> parts H"
  | Body:        "Crypt K X \<in> parts H ==> X \<in> parts H"


text\<open>Monotonicity\<close>
lemma parts_mono: "G \<subseteq> H ==> parts(G) \<subseteq> parts(H)"
apply auto
apply (erule parts.induct) 
apply (blast dest: parts.Fst parts.Snd parts.Body)+
done


text\<open>Equations hold because constructors are injective.\<close>
lemma Friend_image_eq [simp]: "(Friend x \<in> Friend`A) = (x\<in>A)"
by auto

lemma Key_image_eq [simp]: "(Key x \<in> Key`A) = (x\<in>A)"
by auto

lemma Nonce_Key_image_eq [simp]: "(Nonce x \<notin> Key`A)"
by auto


subsubsection\<open>Inverse of keys\<close>

lemma invKey_eq [simp]: "(invKey K = invKey K') = (K=K')"
by (metis invKey)


subsection\<open>keysFor operator\<close>

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

lemma keysFor_Un [simp]: "keysFor (H \<union> H') = keysFor H \<union> keysFor H'"
by (unfold keysFor_def, blast)

lemma keysFor_UN [simp]: "keysFor (\<Union>i\<in>A. H i) = (\<Union>i\<in>A. keysFor (H i))"
by (unfold keysFor_def, blast)

text\<open>Monotonicity\<close>
lemma keysFor_mono: "G \<subseteq> H ==> keysFor(G) \<subseteq> 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_Hash [simp]: "keysFor (insert (Hash X) H) = keysFor H"
by (unfold keysFor_def, auto)

lemma keysFor_insert_MPair [simp]: "keysFor (insert \<lbrace>X,Y\<rbrace> 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 \<in> H ==> invKey K \<in> keysFor H"
by (unfold keysFor_def, blast)


subsection\<open>Inductive relation "parts"\<close>

lemma MPair_parts:
     "[| \<lbrace>X,Y\<rbrace> \<in> parts H;        
         [| X \<in> parts H; Y \<in> parts H |] ==> P |] ==> P"
by (blast dest: parts.Fst parts.Snd) 

declare MPair_parts [elim!]  parts.Body [dest!]
text\<open>NB These two rules are UNSAFE in the formal sense, as they discard the
     compound message.  They work well on THIS FILE.  
  \<open>MPair_parts\<close> is left as SAFE because it speeds up proofs.
  The Crypt rule is normally kept UNSAFE to avoid breaking up certificates.\<close>

lemma parts_increasing: "H \<subseteq> 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\<in> parts{} ==> P"
by simp

text\<open>WARNING: loops if H = {Y}, therefore must not be repeated!\<close>
lemma parts_singleton: "X\<in> parts H ==> \<exists>Y\<in>H. X\<in> parts {Y}"
by (erule parts.induct, fast+)


subsubsection\<open>Unions\<close>

lemma parts_Un_subset1: "parts(G) \<union> parts(H) \<subseteq> parts(G \<union> H)"
by (intro Un_least parts_mono Un_upper1 Un_upper2)

lemma parts_Un_subset2: "parts(G \<union> H) \<subseteq> parts(G) \<union> parts(H)"
apply (rule subsetI)
apply (erule parts.induct, blast+)
done

lemma parts_Un [simp]: "parts(G \<union> H) = parts(G) \<union> parts(H)"
by (intro equalityI parts_Un_subset1 parts_Un_subset2)

lemma parts_insert: "parts (insert X H) = parts {X} \<union> parts H"
by (metis insert_is_Un parts_Un)

text\<open>TWO inserts to avoid looping.  This rewrite is better than nothing.
  But its behaviour can be strange.\<close>
lemma parts_insert2:
     "parts (insert X (insert Y H)) = parts {X} \<union> parts {Y} \<union> parts H"
by (metis Un_commute Un_empty_right Un_insert_right insert_is_Un parts_Un)

lemma parts_UN_subset1: "(\<Union>x\<in>A. parts(H x)) \<subseteq> parts(\<Union>x\<in>A. H x)"
by (intro UN_least parts_mono UN_upper)

lemma parts_UN_subset2: "parts(\<Union>x\<in>A. H x) \<subseteq> (\<Union>x\<in>A. parts(H x))"
apply (rule subsetI)
apply (erule parts.induct, blast+)
done

lemma parts_UN [simp]:
  "parts (\<Union>x\<in>A. H x) = (\<Union>x\<in>A. parts (H x))"
  by (intro equalityI parts_UN_subset1 parts_UN_subset2)

lemma parts_image [simp]:
  "parts (f ` A) = (\<Union>x\<in>A. parts {f x})"
  apply auto
  apply (metis (mono_tags, hide_lams) image_iff parts_singleton)
  apply (metis empty_subsetI image_eqI insert_absorb insert_subset parts_mono)
  done

text\<open>Added to simplify arguments to parts, analz and synth.
  NOTE: the UN versions are no longer used!\<close>


text\<open>This allows \<open>blast\<close> to simplify occurrences of 
  \<^term>\<open>parts(G\<union>H)\<close> in the assumption.\<close>
lemmas in_parts_UnE = parts_Un [THEN equalityD1, THEN subsetD, THEN UnE] 
declare in_parts_UnE [elim!]


lemma parts_insert_subset: "insert X (parts H) \<subseteq> parts(insert X H)"
by (blast intro: parts_mono [THEN [2] rev_subsetD])

subsubsection\<open>Idempotence and transitivity\<close>

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

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

lemma parts_subset_iff [simp]: "(parts G \<subseteq> parts H) = (G \<subseteq> parts H)"
by (metis parts_idem parts_increasing parts_mono subset_trans)

lemma parts_trans: "[| X\<in> parts G;  G \<subseteq> parts H |] ==> X\<in> parts H"
by (metis parts_subset_iff subsetD)

text\<open>Cut\<close>
lemma parts_cut:
     "[| Y\<in> parts (insert X G);  X\<in> parts H |] ==> Y\<in> parts (G \<union> H)" 
by (blast intro: parts_trans) 

lemma parts_cut_eq [simp]: "X\<in> parts H ==> parts (insert X H) = parts H"
by (metis insert_absorb parts_idem parts_insert)


subsubsection\<open>Rewrite rules for pulling out atomic messages\<close>

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_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 (blast intro: parts.Body)
done

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

lemma parts_image_Key [simp]: "parts (Key`N) = Key`N"
by auto

text\<open>In any message, there is an upper bound N on its greatest nonce.\<close>
lemma msg_Nonce_supply: "\<exists>N. \<forall>n. N\<le>n \<longrightarrow> Nonce n \<notin> parts {msg}"
proof (induct msg)
  case (Nonce n)
    show ?case
      by simp (metis Suc_n_not_le_n)
next
  case (MPair X Y)
    then show ?case \<comment> \<open>metis works out the necessary sum itself!\<close>
      by (simp add: parts_insert2) (metis le_trans nat_le_linear)
qed auto

subsection\<open>Inductive relation "analz"\<close>

text\<open>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.\<close>

inductive_set
  analz :: "msg set \<Rightarrow> msg set"
  for H :: "msg set"
  where
    Inj [intro,simp]: "X \<in> H ==> X \<in> analz H"
  | Fst:     "\<lbrace>X,Y\<rbrace> \<in> analz H ==> X \<in> analz H"
  | Snd:     "\<lbrace>X,Y\<rbrace> \<in> analz H ==> Y \<in> analz H"
  | Decrypt [dest]: 
             "\<lbrakk>Crypt K X \<in> analz H; Key(invKey K) \<in> analz H\<rbrakk> \<Longrightarrow> X \<in> analz H"


text\<open>Monotonicity; Lemma 1 of Lowe's paper\<close>
lemma analz_mono: "G\<subseteq>H ==> analz(G) \<subseteq> analz(H)"
apply auto
apply (erule analz.induct) 
apply (auto dest: analz.Fst analz.Snd) 
done

text\<open>Making it safe speeds up proofs\<close>
lemma MPair_analz [elim!]:
     "[| \<lbrace>X,Y\<rbrace> \<in> analz H;        
             [| X \<in> analz H; Y \<in> analz H |] ==> P   
          |] ==> P"
by (blast dest: analz.Fst analz.Snd)

lemma analz_increasing: "H \<subseteq> analz(H)"
by blast

lemma analz_subset_parts: "analz H \<subseteq> 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"
by (metis analz_increasing analz_subset_parts equalityI parts_mono parts_subset_iff)

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\<open>General equational properties\<close>

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

text\<open>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\<close>
lemma analz_Un: "analz(G) \<union> analz(H) \<subseteq> analz(G \<union> H)"
by (intro Un_least analz_mono Un_upper1 Un_upper2)

lemma analz_insert: "insert X (analz H) \<subseteq> analz(insert X H)"
by (blast intro: analz_mono [THEN [2] rev_subsetD])

subsubsection\<open>Rewrite rules for pulling out atomic messages\<close>

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

text\<open>Can only pull out Keys if they are not needed to decrypt the rest\<close>
lemma analz_insert_Key [simp]: 
    "K \<notin> 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 \<lbrace>X,Y\<rbrace> H) =  
          insert \<lbrace>X,Y\<rbrace> (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

text\<open>Can pull out enCrypted message if the Key is not known\<close>
lemma analz_insert_Crypt:
     "Key (invKey K) \<notin> 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 lemma1: "Key (invKey K) \<in> analz H ==>   
               analz (insert (Crypt K X) H) \<subseteq>  
               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) \<in> analz H ==>   
               insert (Crypt K X) (analz (insert X H)) \<subseteq>  
               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) \<in> analz H ==>   
               analz (insert (Crypt K X) H) =  
               insert (Crypt K X) (analz (insert X H))"
by (intro equalityI lemma1 lemma2)

text\<open>Case analysis: either the message is secure, or it is not! Effective,
but can cause subgoals to blow up! Use with \<open>if_split\<close>; apparently
\<open>split_tac\<close> does not cope with patterns such as \<^term>\<open>analz (insert
(Crypt K X) H)\<close>\<close> 
lemma analz_Crypt_if [simp]:
     "analz (insert (Crypt K X) H) =                 
          (if (Key (invKey K) \<in> 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)


text\<open>This rule supposes "for the sake of argument" that we have the key.\<close>
lemma analz_insert_Crypt_subset:
     "analz (insert (Crypt K X) H) \<subseteq>   
           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


subsubsection\<open>Idempotence and transitivity\<close>

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

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

lemma analz_subset_iff [simp]: "(analz G \<subseteq> analz H) = (G \<subseteq> analz H)"
by (metis analz_idem analz_increasing analz_mono subset_trans)

lemma analz_trans: "[| X\<in> analz G;  G \<subseteq> analz H |] ==> X\<in> analz H"
by (drule analz_mono, blast)

text\<open>Cut; Lemma 2 of Lowe\<close>
lemma analz_cut: "[| Y\<in> analz (insert X H);  X\<in> analz H |] ==> Y\<in> analz H"
by (erule analz_trans, blast)

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

text\<open>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.\<close>
lemma analz_insert_eq: "X\<in> analz H ==> analz (insert X H) = analz H"
by (metis analz_cut analz_insert_eq_I insert_absorb)


text\<open>A congruence rule for "analz"\<close>

lemma analz_subset_cong:
     "[| analz G \<subseteq> analz G'; analz H \<subseteq> analz H' |] 
      ==> analz (G \<union> H) \<subseteq> analz (G' \<union> H')"
by (metis Un_mono analz_Un analz_subset_iff subset_trans)

lemma analz_cong:
     "[| analz G = analz G'; analz H = analz H' |] 
      ==> analz (G \<union> H) = analz (G' \<union> 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)

text\<open>If there are no pairs or encryptions then analz does nothing\<close>
lemma analz_trivial:
     "[| \<forall>X Y. \<lbrace>X,Y\<rbrace> \<notin> H;  \<forall>X K. Crypt K X \<notin> H |] ==> analz H = H"
apply safe
apply (erule analz.induct, blast+)
done

text\<open>These two are obsolete (with a single Spy) but cost little to prove...\<close>
lemma analz_UN_analz_lemma:
     "X\<in> analz (\<Union>i\<in>A. analz (H i)) ==> X\<in> analz (\<Union>i\<in>A. H i)"
apply (erule analz.induct)
apply (blast intro: analz_mono [THEN [2] rev_subsetD])+
done

lemma analz_UN_analz [simp]: "analz (\<Union>i\<in>A. analz (H i)) = analz (\<Union>i\<in>A. H i)"
by (blast intro: analz_UN_analz_lemma analz_mono [THEN [2] rev_subsetD])


subsection\<open>Inductive relation "synth"\<close>

text\<open>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.\<close>

inductive_set
  synth :: "msg set => msg set"
  for H :: "msg set"
  where
    Inj    [intro]:   "X \<in> H ==> X \<in> synth H"
  | Agent  [intro]:   "Agent agt \<in> synth H"
  | Number [intro]:   "Number n  \<in> synth H"
  | Hash   [intro]:   "X \<in> synth H ==> Hash X \<in> synth H"
  | MPair  [intro]:   "[|X \<in> synth H;  Y \<in> synth H|] ==> \<lbrace>X,Y\<rbrace> \<in> synth H"
  | Crypt  [intro]:   "[|X \<in> synth H;  Key(K) \<in> H|] ==> Crypt K X \<in> synth H"

text\<open>Monotonicity\<close>
lemma synth_mono: "G\<subseteq>H ==> synth(G) \<subseteq> synth(H)"
  by (auto, erule synth.induct, auto)  

text\<open>NO \<open>Agent_synth\<close>, as any Agent name can be synthesized.  
  The same holds for \<^term>\<open>Number\<close>\<close>

inductive_simps synth_simps [iff]:
 "Nonce n \<in> synth H"
 "Key K \<in> synth H"
 "Hash X \<in> synth H"
 "\<lbrace>X,Y\<rbrace> \<in> synth H"
 "Crypt K X \<in> synth H"

lemma synth_increasing: "H \<subseteq> synth(H)"
by blast

subsubsection\<open>Unions\<close>

text\<open>Converse fails: we can synth more from the union than from the 
  separate parts, building a compound message using elements of each.\<close>
lemma synth_Un: "synth(G) \<union> synth(H) \<subseteq> synth(G \<union> H)"
by (intro Un_least synth_mono Un_upper1 Un_upper2)

lemma synth_insert: "insert X (synth H) \<subseteq> synth(insert X H)"
by (blast intro: synth_mono [THEN [2] rev_subsetD])

subsubsection\<open>Idempotence and transitivity\<close>

lemma synth_synthD [dest!]: "X\<in> synth (synth H) ==> X\<in> synth H"
by (erule synth.induct, auto)

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

lemma synth_subset_iff [simp]: "(synth G \<subseteq> synth H) = (G \<subseteq> synth H)"
by (metis subset_trans synth_idem synth_increasing synth_mono)

lemma synth_trans: "[| X\<in> synth G;  G \<subseteq> synth H |] ==> X\<in> synth H"
by (drule synth_mono, blast)

text\<open>Cut; Lemma 2 of Lowe\<close>
lemma synth_cut: "[| Y\<in> synth (insert X H);  X\<in> synth H |] ==> Y\<in> synth H"
by (erule synth_trans, blast)

lemma Crypt_synth_eq [simp]:
     "Key K \<notin> H ==> (Crypt K X \<in> synth H) = (Crypt K X \<in> H)"
by blast


lemma keysFor_synth [simp]: 
    "keysFor (synth H) = keysFor H \<union> invKey`{K. Key K \<in> H}"
by (unfold keysFor_def, blast)


subsubsection\<open>Combinations of parts, analz and synth\<close>

lemma parts_synth [simp]: "parts (synth H) = parts H \<union> 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 \<union> H) = analz (G \<union> H)"
apply (intro equalityI analz_subset_cong)+
apply simp_all
done

lemma analz_synth_Un [simp]: "analz (synth G \<union> H) = analz (G \<union> H) \<union> 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 \<union> synth H"
by (metis Un_empty_right analz_synth_Un)


subsubsection\<open>For reasoning about the Fake rule in traces\<close>

lemma parts_insert_subset_Un: "X\<in> G ==> parts(insert X H) \<subseteq> parts G \<union> parts H"
by (metis UnCI Un_upper2 insert_subset parts_Un parts_mono)

text\<open>More specifically for Fake. See also \<open>Fake_parts_sing\<close> below\<close>
lemma Fake_parts_insert:
     "X \<in> synth (analz H) ==>  
      parts (insert X H) \<subseteq> synth (analz H) \<union> parts H"
by (metis Un_commute analz_increasing insert_subset parts_analz parts_mono 
          parts_synth synth_mono synth_subset_iff)

lemma Fake_parts_insert_in_Un:
     "\<lbrakk>Z \<in> parts (insert X H);  X \<in> synth (analz H)\<rbrakk> 
      \<Longrightarrow> Z \<in> synth (analz H) \<union> parts H"
by (metis Fake_parts_insert subsetD)

text\<open>\<^term>\<open>H\<close> is sometimes \<^term>\<open>Key ` KK \<union> spies evs\<close>, so can't put 
  \<^term>\<open>G=H\<close>.\<close>
lemma Fake_analz_insert:
     "X\<in> synth (analz G) ==>  
      analz (insert X H) \<subseteq> synth (analz G) \<union> analz (G \<union> H)"
apply (rule subsetI)
apply (subgoal_tac "x \<in> analz (synth (analz G) \<union> H)", force)
apply (blast intro: analz_mono [THEN [2] rev_subsetD] analz_mono [THEN synth_mono, THEN [2] rev_subsetD])
done

lemma analz_conj_parts [simp]:
     "(X \<in> analz H \<and> X \<in> parts H) = (X \<in> analz H)"
by (blast intro: analz_subset_parts [THEN subsetD])

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

text\<open>Without this equation, other rules for synth and analz would yield
  redundant cases\<close>
lemma MPair_synth_analz [iff]:
     "(\<lbrace>X,Y\<rbrace> \<in> synth (analz H)) =  
      (X \<in> synth (analz H) \<and> Y \<in> synth (analz H))"
by blast

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


lemma Hash_synth_analz [simp]:
     "X \<notin> synth (analz H)  
      ==> (Hash\<lbrace>X,Y\<rbrace> \<in> synth (analz H)) = (Hash\<lbrace>X,Y\<rbrace> \<in> analz H)"
by blast


subsection\<open>HPair: a combination of Hash and MPair\<close>

subsubsection\<open>Freeness\<close>

lemma Agent_neq_HPair: "Agent A \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemma Nonce_neq_HPair: "Nonce N \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemma Number_neq_HPair: "Number N \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemma Key_neq_HPair: "Key K \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemma Hash_neq_HPair: "Hash Z \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemma Crypt_neq_HPair: "Crypt K X' \<noteq> Hash[X] Y"
  unfolding HPair_def by simp

lemmas HPair_neqs = Agent_neq_HPair Nonce_neq_HPair Number_neq_HPair 
                    Key_neq_HPair Hash_neq_HPair Crypt_neq_HPair

declare HPair_neqs [iff]
declare HPair_neqs [symmetric, iff]

lemma HPair_eq [iff]: "(Hash[X'] Y' = Hash[X] Y) = (X' = X \<and> Y'=Y)"
by (simp add: HPair_def)

lemma MPair_eq_HPair [iff]:
     "(\<lbrace>X',Y'\<rbrace> = Hash[X] Y) = (X' = Hash\<lbrace>X,Y\<rbrace> \<and> Y'=Y)"
by (simp add: HPair_def)

lemma HPair_eq_MPair [iff]:
     "(Hash[X] Y = \<lbrace>X',Y'\<rbrace>) = (X' = Hash\<lbrace>X,Y\<rbrace> \<and> Y'=Y)"
by (auto simp add: HPair_def)


subsubsection\<open>Specialized laws, proved in terms of those for Hash and MPair\<close>

lemma keysFor_insert_HPair [simp]: "keysFor (insert (Hash[X] Y) H) = keysFor H"
by (simp add: HPair_def)

lemma parts_insert_HPair [simp]: 
    "parts (insert (Hash[X] Y) H) =  
     insert (Hash[X] Y) (insert (Hash\<lbrace>X,Y\<rbrace>) (parts (insert Y H)))"
by (simp add: HPair_def)

lemma analz_insert_HPair [simp]: 
    "analz (insert (Hash[X] Y) H) =  
     insert (Hash[X] Y) (insert (Hash\<lbrace>X,Y\<rbrace>) (analz (insert Y H)))"
by (simp add: HPair_def)

lemma HPair_synth_analz [simp]:
     "X \<notin> synth (analz H)  
    ==> (Hash[X] Y \<in> synth (analz H)) =  
        (Hash \<lbrace>X, Y\<rbrace> \<in> analz H \<and> Y \<in> synth (analz H))"
by (auto simp add: HPair_def)


text\<open>We do NOT want Crypt... messages broken up in protocols!!\<close>
declare parts.Body [rule del]


text\<open>Rewrites to push in Key and Crypt messages, so that other messages can
    be pulled out using the \<open>analz_insert\<close> rules\<close>

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" "Hash X"]
  insert_commute [of "Key K" "MPair X Y"]
  insert_commute [of "Key K" "Crypt X K'"]
  for K C N X Y K'

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

text\<open>Cannot be added with \<open>[simp]\<close> -- messages should not always be
  re-ordered.\<close>
lemmas pushes = pushKeys pushCrypts


subsection\<open>The set of key-free messages\<close>

(*Note that even the encryption of a key-free message remains key-free.
  This concept is valuable because of the theorem analz_keyfree_into_Un, proved below. *)

inductive_set
  keyfree :: "msg set"
  where
    Agent:  "Agent A \<in> keyfree"
  | Number: "Number N \<in> keyfree"
  | Nonce:  "Nonce N \<in> keyfree"
  | Hash:   "Hash X \<in> keyfree"
  | MPair:  "[|X \<in> keyfree;  Y \<in> keyfree|] ==> \<lbrace>X,Y\<rbrace> \<in> keyfree"
  | Crypt:  "[|X \<in> keyfree|] ==> Crypt K X \<in> keyfree"


declare keyfree.intros [intro] 

inductive_cases keyfree_KeyE: "Key K \<in> keyfree"
inductive_cases keyfree_MPairE: "\<lbrace>X,Y\<rbrace> \<in> keyfree"
inductive_cases keyfree_CryptE: "Crypt K X \<in> keyfree"

lemma parts_keyfree: "parts (keyfree) \<subseteq> keyfree"
  by (clarify, erule parts.induct, auto elim!: keyfree_KeyE keyfree_MPairE keyfree_CryptE)

(*The key-free part of a set of messages can be removed from the scope of the analz operator.*)
lemma analz_keyfree_into_Un: "\<lbrakk>X \<in> analz (G \<union> H); G \<subseteq> keyfree\<rbrakk> \<Longrightarrow> X \<in> parts G \<union> analz H"
apply (erule analz.induct, auto dest: parts.Body)
apply (metis Un_absorb2 keyfree_KeyE parts_Un parts_keyfree UnI2)
done

subsection\<open>Tactics useful for many protocol proofs\<close>
ML
\<open>
(*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 \<in> parts(insert X H)  and  Y \<in> 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")] []
           (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);
\<close>

text\<open>By default only \<open>o_apply\<close> is built-in.  But in the presence of
eta-expansion this means that some terms displayed as \<^term>\<open>f o g\<close> will be
rewritten, and others will not!\<close>
declare o_def [simp]


lemma Crypt_notin_image_Key [simp]: "Crypt K X \<notin> Key ` A"
by auto

lemma Hash_notin_image_Key [simp] :"Hash X \<notin> Key ` A"
by auto

lemma synth_analz_mono: "G\<subseteq>H ==> synth (analz(G)) \<subseteq> synth (analz(H))"
by (iprover intro: synth_mono analz_mono) 

lemma Fake_analz_eq [simp]:
     "X \<in> synth(analz H) ==> synth (analz (insert X H)) = synth (analz H)"
by (metis Fake_analz_insert Un_absorb Un_absorb1 Un_commute 
          subset_insertI synth_analz_mono synth_increasing synth_subset_iff)

text\<open>Two generalizations of \<open>analz_insert_eq\<close>\<close>
lemma gen_analz_insert_eq [rule_format]:
     "X \<in> analz H \<Longrightarrow> \<forall>G. H \<subseteq> G \<longrightarrow> 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 \<in> synth (analz H) 
      \<Longrightarrow> \<forall>G. H \<subseteq> G \<longrightarrow> (Key K \<in> analz (insert X G)) = (Key K \<in> 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 \<in> synth (analz H) ==> parts{X} \<subseteq> synth (analz H) \<union> parts H"
by (metis Fake_parts_insert empty_subsetI insert_mono parts_mono subset_trans)

lemmas Fake_parts_sing_imp_Un = Fake_parts_sing [THEN [2] rev_subsetD]

method_setup spy_analz = \<open>
    Scan.succeed (SIMPLE_METHOD' o spy_analz_tac)\<close>
    "for proving the Fake case when analz is involved"

method_setup atomic_spy_analz = \<open>
    Scan.succeed (SIMPLE_METHOD' o atomic_spy_analz_tac)\<close>
    "for debugging spy_analz"

method_setup Fake_insert_simp = \<open>
    Scan.succeed (SIMPLE_METHOD' o Fake_insert_simp_tac)\<close>
    "for debugging spy_analz"

end