Theory Guard_Public

(*  Title:      HOL/Auth/Guard/Guard_Public.thy
    Author:     Frederic Blanqui, University of Cambridge Computer Laboratory
    Copyright   2002  University of Cambridge

Lemmas on guarded messages for public protocols.

theory Guard_Public imports Guard "../Public" Extensions begin

subsection‹Extensions to Theory Public›

declare initState.simps [simp del]


definition sign :: "agent => msg => msg" where
"sign A X == Agent A, X, Crypt (priK A) (Hash X)"

lemma sign_inj [iff]: "(sign A X = sign A' X') = (A=A' & X=X')"
by (auto simp: sign_def)

subsubsection‹agent associated to a key›

definition agt :: "key => agent" where
"agt K == SOME A. K = priK A | K = pubK A"

lemma agt_priK [simp]: "agt (priK A) = A"
by (simp add: agt_def)

lemma agt_pubK [simp]: "agt (pubK A) = A"
by (simp add: agt_def)

subsubsection‹basic facts about terminitState

lemma no_Crypt_in_parts_init [simp]: "Crypt K X  parts (initState A)"
by (cases A, auto simp: initState.simps)

lemma no_Crypt_in_analz_init [simp]: "Crypt K X  analz (initState A)"
by auto

lemma no_priK_in_analz_init [simp]: "A  bad
 Key (priK A)  analz (initState Spy)"
by (auto simp: initState.simps)

lemma priK_notin_initState_Friend [simp]: "A  Friend C
 Key (priK A)  parts (initState (Friend C))"
by (auto simp: initState.simps)

lemma keyset_init [iff]: "keyset (initState A)"
by (cases A, auto simp: keyset_def initState.simps)

subsubsection‹sets of private keys›

definition priK_set :: "key set => bool" where
"priK_set Ks  K. K  Ks  (A. K = priK A)"

lemma in_priK_set: "priK_set Ks; K  Ks  A. K = priK A"
by (simp add: priK_set_def)

lemma priK_set1 [iff]: "priK_set {priK A}"
by (simp add: priK_set_def)

lemma priK_set2 [iff]: "priK_set {priK A, priK B}"
by (simp add: priK_set_def)

subsubsection‹sets of good keys›

definition good :: "key set => bool" where
"good Ks == K. K  Ks  agt K  bad"

lemma in_good: "good Ks; K  Ks  agt K  bad"
by (simp add: good_def)

lemma good1 [simp]: "A  bad  good {priK A}"
by (simp add: good_def)

lemma good2 [simp]: "A  bad; B  bad  good {priK A, priK B}"
by (simp add: good_def)

subsubsection‹greatest nonce used in a trace, 0 if there is no nonce›

primrec greatest :: "event list => nat"
  "greatest [] = 0"
| "greatest (ev # evs) = max (greatest_msg (msg ev)) (greatest evs)"

lemma greatest_is_greatest: "Nonce n  used evs  n  greatest evs"
apply (induct evs, auto simp: initState.simps)
apply (drule used_sub_parts_used, safe)
apply (drule greatest_msg_is_greatest, arith)
by simp

subsubsection‹function giving a new nonce›

definition new :: "event list  nat" where
"new evs  Suc (greatest evs)"

lemma new_isnt_used [iff]: "Nonce (new evs)  used evs"
by (clarify, drule greatest_is_greatest, auto simp: new_def)

subsection‹Proofs About Guarded Messages›

subsubsection‹small hack necessary because priK is defined as the inverse of pubK›

lemma pubK_is_invKey_priK: "pubK A = invKey (priK A)"
by simp

lemmas pubK_is_invKey_priK_substI = pubK_is_invKey_priK [THEN ssubst]

lemmas invKey_invKey_substI = invKey [THEN ssubst]

lemma "Nonce n  parts {X}  Crypt (pubK A) X  guard n {priK A}"
apply (rule pubK_is_invKey_priK_substI, rule invKey_invKey_substI)
by (rule Guard_Nonce, simp+)

subsubsection‹guardedness results›

lemma sign_guard [intro]: "X  guard n Ks  sign A X  guard n Ks"
by (auto simp: sign_def)

lemma Guard_init [iff]: "Guard n Ks (initState B)"
by (induct B, auto simp: Guard_def initState.simps)

lemma Guard_knows_max': "Guard n Ks (knows_max' C evs)
 Guard n Ks (knows_max C evs)"
by (simp add: knows_max_def)

lemma Nonce_not_used_Guard_spies [dest]: "Nonce n  used evs
 Guard n Ks (spies evs)"
by (auto simp: Guard_def dest: not_used_not_known parts_sub)

lemma Nonce_not_used_Guard [dest]: "evs  p; Nonce n  used evs;
Gets_correct p; one_step p  Guard n Ks (knows (Friend C) evs)"
by (auto simp: Guard_def dest: known_used parts_trans)

lemma Nonce_not_used_Guard_max [dest]: "evs  p; Nonce n  used evs;
Gets_correct p; one_step p  Guard n Ks (knows_max (Friend C) evs)"
by (auto simp: Guard_def dest: known_max_used parts_trans)

lemma Nonce_not_used_Guard_max' [dest]: "evs  p; Nonce n  used evs;
Gets_correct p; one_step p  Guard n Ks (knows_max' (Friend C) evs)"
apply (rule_tac H="knows_max (Friend C) evs" in Guard_mono)
by (auto simp: knows_max_def)

subsubsection‹regular protocols›

definition regular :: "event list set  bool" where
"regular p  evs A. evs  p  (Key (priK A)  parts (spies evs)) = (A  bad)"

lemma priK_parts_iff_bad [simp]: "evs  p; regular p 
(Key (priK A)  parts (spies evs)) = (A  bad)"
by (auto simp: regular_def)

lemma priK_analz_iff_bad [simp]: "evs  p; regular p 
(Key (priK A)  analz (spies evs)) = (A  bad)"
by auto

lemma Guard_Nonce_analz: "Guard n Ks (spies evs); evs  p;
priK_set Ks; good Ks; regular p  Nonce n  analz (spies evs)"
apply (clarify, simp only: knows_decomp)
apply (drule Guard_invKey_keyset, simp+, safe)
apply (drule in_good, simp)
apply (drule in_priK_set, simp+, clarify)
apply (frule_tac A=A in priK_analz_iff_bad)
by (simp add: knows_decomp)+