author | wenzelm |
Wed, 29 Nov 2006 15:44:51 +0100 | |
changeset 21588 | cd0dc678a205 |
parent 20048 | a7964311f1fb |
child 23894 | 1a4167d761ac |
permissions | -rw-r--r-- |
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(* Title: HOL/Auth/Shared |
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ID: $Id$ |
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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Copyright 1996 University of Cambridge |
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Theory of Shared Keys (common to all symmetric-key protocols) |
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Shared, long-term keys; initial states of agents |
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*) |
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theory Shared imports Event begin |
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consts |
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shrK :: "agent => key" (*symmetric keys*); |
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specification (shrK) |
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inj_shrK: "inj shrK" |
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--{*No two agents have the same long-term key*} |
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apply (rule exI [of _ "agent_case 0 (\<lambda>n. n + 2) 1"]) |
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apply (simp add: inj_on_def split: agent.split) |
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done |
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text{*All keys are symmetric*} |
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defs all_symmetric_def: "all_symmetric == True" |
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lemma isSym_keys: "K \<in> symKeys" |
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by (simp add: symKeys_def all_symmetric_def invKey_symmetric) |
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text{*Server knows all long-term keys; other agents know only their own*} |
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primrec |
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initState_Server: "initState Server = Key ` range shrK" |
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initState_Friend: "initState (Friend i) = {Key (shrK (Friend i))}" |
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initState_Spy: "initState Spy = Key`shrK`bad" |
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subsection{*Basic properties of shrK*} |
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(*Injectiveness: Agents' long-term keys are distinct.*) |
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lemmas shrK_injective = inj_shrK [THEN inj_eq] |
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declare shrK_injective [iff] |
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lemma invKey_K [simp]: "invKey K = K" |
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apply (insert isSym_keys) |
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apply (simp add: symKeys_def) |
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done |
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lemma analz_Decrypt' [dest]: |
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"[| Crypt K X \<in> analz H; Key K \<in> analz H |] ==> X \<in> analz H" |
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by auto |
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text{*Now cancel the @{text dest} attribute given to |
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@{text analz.Decrypt} in its declaration.*} |
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declare analz.Decrypt [rule del] |
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text{*Rewrites should not refer to @{term "initState(Friend i)"} because |
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that expression is not in normal form.*} |
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lemma keysFor_parts_initState [simp]: "keysFor (parts (initState C)) = {}" |
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apply (unfold keysFor_def) |
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apply (induct_tac "C", auto) |
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done |
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(*Specialized to shared-key model: no @{term invKey}*) |
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lemma keysFor_parts_insert: |
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"[| K \<in> keysFor (parts (insert X G)); X \<in> synth (analz H) |] |
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==> K \<in> keysFor (parts (G \<union> H)) | Key K \<in> parts H"; |
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by (force dest: Event.keysFor_parts_insert) |
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lemma Crypt_imp_keysFor: "Crypt K X \<in> H ==> K \<in> keysFor H" |
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by (drule Crypt_imp_invKey_keysFor, simp) |
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subsection{*Function "knows"*} |
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(*Spy sees shared keys of agents!*) |
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lemma Spy_knows_Spy_bad [intro!]: "A: bad ==> Key (shrK A) \<in> knows Spy evs" |
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apply (induct_tac "evs") |
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apply (simp_all (no_asm_simp) add: imageI knows_Cons split add: event.split) |
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done |
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(*For case analysis on whether or not an agent is compromised*) |
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lemma Crypt_Spy_analz_bad: "[| Crypt (shrK A) X \<in> analz (knows Spy evs); A: bad |] |
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==> X \<in> analz (knows Spy evs)" |
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apply (force dest!: analz.Decrypt) |
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done |
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(** Fresh keys never clash with long-term shared keys **) |
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(*Agents see their own shared keys!*) |
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lemma shrK_in_initState [iff]: "Key (shrK A) \<in> initState A" |
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by (induct_tac "A", auto) |
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lemma shrK_in_used [iff]: "Key (shrK A) \<in> used evs" |
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by (rule initState_into_used, blast) |
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(*Used in parts_induct_tac and analz_Fake_tac to distinguish session keys |
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from long-term shared keys*) |
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lemma Key_not_used [simp]: "Key K \<notin> used evs ==> K \<notin> range shrK" |
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by blast |
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lemma shrK_neq [simp]: "Key K \<notin> used evs ==> shrK B \<noteq> K" |
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by blast |
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lemmas shrK_sym_neq = shrK_neq [THEN not_sym] |
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declare shrK_sym_neq [simp] |
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subsection{*Fresh nonces*} |
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lemma Nonce_notin_initState [iff]: "Nonce N \<notin> parts (initState B)" |
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by (induct_tac "B", auto) |
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lemma Nonce_notin_used_empty [simp]: "Nonce N \<notin> used []" |
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apply (simp (no_asm) add: used_Nil) |
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done |
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subsection{*Supply fresh nonces for possibility theorems.*} |
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(*In any trace, there is an upper bound N on the greatest nonce in use.*) |
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lemma Nonce_supply_lemma: "\<exists>N. ALL n. N<=n --> Nonce n \<notin> used evs" |
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apply (induct_tac "evs") |
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apply (rule_tac x = 0 in exI) |
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apply (simp_all (no_asm_simp) add: used_Cons split add: event.split) |
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apply safe |
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apply (rule msg_Nonce_supply [THEN exE], blast elim!: add_leE)+ |
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done |
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lemma Nonce_supply1: "\<exists>N. Nonce N \<notin> used evs" |
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by (rule Nonce_supply_lemma [THEN exE], blast) |
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lemma Nonce_supply2: "\<exists>N N'. Nonce N \<notin> used evs & Nonce N' \<notin> used evs' & N \<noteq> N'" |
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apply (cut_tac evs = evs in Nonce_supply_lemma) |
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apply (cut_tac evs = "evs'" in Nonce_supply_lemma, clarify) |
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apply (rule_tac x = N in exI) |
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apply (rule_tac x = "Suc (N+Na)" in exI) |
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apply (simp (no_asm_simp) add: less_not_refl3 le_add1 le_add2 less_Suc_eq_le) |
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done |
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lemma Nonce_supply3: "\<exists>N N' N''. Nonce N \<notin> used evs & Nonce N' \<notin> used evs' & |
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Nonce N'' \<notin> used evs'' & N \<noteq> N' & N' \<noteq> N'' & N \<noteq> N''" |
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apply (cut_tac evs = evs in Nonce_supply_lemma) |
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apply (cut_tac evs = "evs'" in Nonce_supply_lemma) |
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apply (cut_tac evs = "evs''" in Nonce_supply_lemma, clarify) |
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apply (rule_tac x = N in exI) |
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apply (rule_tac x = "Suc (N+Na)" in exI) |
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apply (rule_tac x = "Suc (Suc (N+Na+Nb))" in exI) |
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apply (simp (no_asm_simp) add: less_not_refl3 le_add1 le_add2 less_Suc_eq_le) |
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done |
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lemma Nonce_supply: "Nonce (@ N. Nonce N \<notin> used evs) \<notin> used evs" |
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apply (rule Nonce_supply_lemma [THEN exE]) |
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apply (rule someI, blast) |
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done |
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text{*Unlike the corresponding property of nonces, we cannot prove |
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@{term "finite KK ==> \<exists>K. K \<notin> KK & Key K \<notin> used evs"}. |
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We have infinitely many agents and there is nothing to stop their |
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long-term keys from exhausting all the natural numbers. Instead, |
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possibility theorems must assume the existence of a few keys.*} |
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subsection{*Tactics for possibility theorems*} |
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ML |
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{* |
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val inj_shrK = thm "inj_shrK"; |
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val isSym_keys = thm "isSym_keys"; |
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val Nonce_supply = thm "Nonce_supply"; |
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val invKey_K = thm "invKey_K"; |
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val analz_Decrypt' = thm "analz_Decrypt'"; |
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val keysFor_parts_initState = thm "keysFor_parts_initState"; |
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val keysFor_parts_insert = thm "keysFor_parts_insert"; |
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val Crypt_imp_keysFor = thm "Crypt_imp_keysFor"; |
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val Spy_knows_Spy_bad = thm "Spy_knows_Spy_bad"; |
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val Crypt_Spy_analz_bad = thm "Crypt_Spy_analz_bad"; |
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val shrK_in_initState = thm "shrK_in_initState"; |
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val shrK_in_used = thm "shrK_in_used"; |
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val Key_not_used = thm "Key_not_used"; |
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val shrK_neq = thm "shrK_neq"; |
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val Nonce_notin_initState = thm "Nonce_notin_initState"; |
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val Nonce_notin_used_empty = thm "Nonce_notin_used_empty"; |
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val Nonce_supply_lemma = thm "Nonce_supply_lemma"; |
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val Nonce_supply1 = thm "Nonce_supply1"; |
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val Nonce_supply2 = thm "Nonce_supply2"; |
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val Nonce_supply3 = thm "Nonce_supply3"; |
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val Nonce_supply = thm "Nonce_supply"; |
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*} |
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ML |
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{* |
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(*Omitting used_Says makes the tactic much faster: it leaves expressions |
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such as Nonce ?N \<notin> used evs that match Nonce_supply*) |
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fun gen_possibility_tac ss state = state |> |
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(REPEAT |
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(ALLGOALS (simp_tac (ss delsimps [used_Says, used_Notes, used_Gets] |
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setSolver safe_solver)) |
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THEN |
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REPEAT_FIRST (eq_assume_tac ORELSE' |
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resolve_tac [refl, conjI, Nonce_supply]))) |
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(*Tactic for possibility theorems (ML script version)*) |
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fun possibility_tac state = gen_possibility_tac (simpset()) state |
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(*For harder protocols (such as Recur) where we have to set up some |
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nonces and keys initially*) |
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fun basic_possibility_tac st = st |> |
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REPEAT |
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(ALLGOALS (asm_simp_tac (simpset() setSolver safe_solver)) |
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THEN |
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REPEAT_FIRST (resolve_tac [refl, conjI])) |
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*} |
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subsection{*Specialized Rewriting for Theorems About @{term analz} and Image*} |
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lemma subset_Compl_range: "A <= - (range shrK) ==> shrK x \<notin> A" |
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by blast |
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lemma insert_Key_singleton: "insert (Key K) H = Key ` {K} \<union> H" |
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by blast |
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lemma insert_Key_image: "insert (Key K) (Key`KK \<union> C) = Key`(insert K KK) \<union> C" |
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by blast |
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(** Reverse the normal simplification of "image" to build up (not break down) |
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the set of keys. Use analz_insert_eq with (Un_upper2 RS analz_mono) to |
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erase occurrences of forwarded message components (X). **) |
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lemmas analz_image_freshK_simps = |
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simp_thms mem_simps --{*these two allow its use with @{text "only:"}*} |
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disj_comms |
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image_insert [THEN sym] image_Un [THEN sym] empty_subsetI insert_subset |
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analz_insert_eq Un_upper2 [THEN analz_mono, THEN [2] rev_subsetD] |
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insert_Key_singleton subset_Compl_range |
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Key_not_used insert_Key_image Un_assoc [THEN sym] |
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(*Lemma for the trivial direction of the if-and-only-if*) |
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lemma analz_image_freshK_lemma: |
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"(Key K \<in> analz (Key`nE \<union> H)) --> (K \<in> nE | Key K \<in> analz H) ==> |
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(Key K \<in> analz (Key`nE \<union> H)) = (K \<in> nE | Key K \<in> analz H)" |
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by (blast intro: analz_mono [THEN [2] rev_subsetD]) |
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ML |
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{* |
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val analz_image_freshK_lemma = thm "analz_image_freshK_lemma"; |
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val analz_image_freshK_ss = |
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simpset() delsimps [image_insert, image_Un] |
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delsimps [imp_disjL] (*reduces blow-up*) |
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addsimps thms "analz_image_freshK_simps" |
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*} |
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(*Lets blast_tac perform this step without needing the simplifier*) |
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lemma invKey_shrK_iff [iff]: |
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"(Key (invKey K) \<in> X) = (Key K \<in> X)" |
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by auto |
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(*Specialized methods*) |
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method_setup analz_freshK = {* |
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Method.ctxt_args (fn ctxt => |
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(Method.SIMPLE_METHOD |
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(EVERY [REPEAT_FIRST (resolve_tac [allI, ballI, impI]), |
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REPEAT_FIRST (rtac analz_image_freshK_lemma), |
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ALLGOALS (asm_simp_tac (Simplifier.context ctxt analz_image_freshK_ss))]))) *} |
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"for proving the Session Key Compromise theorem" |
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method_setup possibility = {* |
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Method.ctxt_args (fn ctxt => |
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Method.SIMPLE_METHOD (gen_possibility_tac (local_simpset_of ctxt))) *} |
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"for proving possibility theorems" |
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lemma knows_subset_knows_Cons: "knows A evs <= knows A (e # evs)" |
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by (induct e, auto simp: knows_Cons) |
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end |