# Theory P2

```(*  Title:      HOL/Auth/Guard/P2.thy
Author:     Frederic Blanqui, University of Cambridge Computer Laboratory

From G. Karjoth, N. Asokan and C. Gulcu
"Protecting the computation results of free-roaming agents"
Mobiles Agents 1998, LNCS 1477.
*)

section‹Protocol P2›

theory P2 imports Guard_Public List_Msg begin

subsection‹Protocol Definition›

text‹Like P1 except the definitions of ‹chain›, ‹shop›,
‹next_shop› and ‹nonce››

subsubsection‹offer chaining:
B chains his offer for A with the head offer of L for sending it to C›

definition chain :: "agent => nat => agent => msg => agent => msg" where
"chain B ofr A L C ==
let m1= sign B (Nonce ofr) in
let m2= Hash ⦃head L, Agent C⦄ in
⦃Crypt (pubK A) m1, m2⦄"

declare Let_def [simp]

lemma chain_inj [iff]: "(chain B ofr A L C = chain B' ofr' A' L' C')
= (B=B' & ofr=ofr' & A=A' & head L = head L' & C=C')"
by (auto simp: chain_def Let_def)

lemma Nonce_in_chain [iff]: "Nonce ofr ∈ parts {chain B ofr A L C}"
by (auto simp: chain_def sign_def)

subsubsection‹agent whose key is used to sign an offer›

fun shop :: "msg => msg" where
"shop ⦃Crypt K ⦃B,ofr,Crypt K' H⦄,m2⦄ = Agent (agt K')"

lemma shop_chain [simp]: "shop (chain B ofr A L C) = Agent B"

subsubsection‹nonce used in an offer›

fun nonce :: "msg => msg" where
"nonce ⦃Crypt K ⦃B,ofr,CryptH⦄,m2⦄ = ofr"

lemma nonce_chain [simp]: "nonce (chain B ofr A L C) = Nonce ofr"

subsubsection‹next shop›

fun next_shop :: "msg => agent" where
"next_shop ⦃m1,Hash ⦃headL,Agent C⦄⦄ = C"

lemma "next_shop (chain B ofr A L C) = C"

subsubsection‹anchor of the offer list›

definition anchor :: "agent => nat => agent => msg" where
"anchor A n B == chain A n A (cons nil nil) B"

lemma anchor_inj [iff]:
"(anchor A n B = anchor A' n' B') = (A=A' ∧ n=n' ∧ B=B')"
by (auto simp: anchor_def)

lemma Nonce_in_anchor [iff]: "Nonce n ∈ parts {anchor A n B}"
by (auto simp: anchor_def)

lemma shop_anchor [simp]: "shop (anchor A n B) = Agent A"

subsubsection‹request event›

definition reqm :: "agent => nat => nat => msg => agent => msg" where
"reqm A r n I B == ⦃Agent A, Number r, cons (Agent A) (cons (Agent B) I),
cons (anchor A n B) nil⦄"

lemma reqm_inj [iff]: "(reqm A r n I B = reqm A' r' n' I' B')
= (A=A' & r=r' & n=n' & I=I' & B=B')"
by (auto simp: reqm_def)

lemma Nonce_in_reqm [iff]: "Nonce n ∈ parts {reqm A r n I B}"
by (auto simp: reqm_def)

definition req :: "agent => nat => nat => msg => agent => event" where
"req A r n I B == Says A B (reqm A r n I B)"

lemma req_inj [iff]: "(req A r n I B = req A' r' n' I' B')
= (A=A' & r=r' & n=n' & I=I' & B=B')"
by (auto simp: req_def)

subsubsection‹propose event›

definition prom :: "agent => nat => agent => nat => msg => msg =>
msg => agent => msg" where
"prom B ofr A r I L J C == ⦃Agent A, Number r,
app (J, del (Agent B, I)), cons (chain B ofr A L C) L⦄"

lemma prom_inj [dest]: "prom B ofr A r I L J C = prom B' ofr' A' r' I' L' J' C'
⟹ B=B' & ofr=ofr' & A=A' & r=r' & L=L' & C=C'"
by (auto simp: prom_def)

lemma Nonce_in_prom [iff]: "Nonce ofr ∈ parts {prom B ofr A r I L J C}"
by (auto simp: prom_def)

definition pro :: "agent => nat => agent => nat => msg => msg =>
msg => agent => event" where
"pro B ofr A r I L J C == Says B C (prom B ofr A r I L J C)"

lemma pro_inj [dest]: "pro B ofr A r I L J C = pro B' ofr' A' r' I' L' J' C'
⟹ B=B' & ofr=ofr' & A=A' & r=r' & L=L' & C=C'"
by (auto simp: pro_def dest: prom_inj)

subsubsection‹protocol›

inductive_set p2 :: "event list set"
where

Nil: "[] ∈ p2"

| Fake: "⟦evsf ∈ p2; X ∈ synth (analz (spies evsf))⟧ ⟹ Says Spy B X # evsf ∈ p2"

| Request: "⟦evsr ∈ p2; Nonce n ∉ used evsr; I ∈ agl⟧ ⟹ req A r n I B # evsr ∈ p2"

| Propose: "⟦evsp ∈ p2; Says A' B ⦃Agent A,Number r,I,cons M L⦄ ∈ set evsp;
I ∈ agl; J ∈ agl; isin (Agent C, app (J, del (Agent B, I)));
Nonce ofr ∉ used evsp⟧ ⟹ pro B ofr A r I (cons M L) J C # evsp ∈ p2"

subsubsection‹valid offer lists›

inductive_set
valid :: "agent ⇒ nat ⇒ agent ⇒ msg set"
for A :: agent and  n :: nat and B :: agent
where
Request [intro]: "cons (anchor A n B) nil ∈ valid A n B"

| Propose [intro]: "L ∈ valid A n B
⟹ cons (chain (next_shop (head L)) ofr A L C) L ∈ valid A n B"

subsubsection‹basic properties of valid›

lemma valid_not_empty: "L ∈ valid A n B ⟹ ∃M L'. L = cons M L'"
by (erule valid.cases, auto)

lemma valid_pos_len: "L ∈ valid A n B ⟹ 0 < len L"
by (erule valid.induct, auto)

subsubsection‹list of offers›

fun offers :: "msg ⇒ msg"
where
"offers (cons M L) = cons ⦃shop M, nonce M⦄ (offers L)"
| "offers other = nil"

subsection‹Properties of Protocol P2›

text‹same as ‹P1_Prop› except that publicly verifiable forward
integrity is replaced by forward privacy›

subsection‹strong forward integrity:
except the last one, no offer can be modified›

lemma strong_forward_integrity: "∀L. Suc i < len L
⟶ L ∈ valid A n B ⟶ repl (L,Suc i,M) ∈ valid A n B ⟶ M = ith (L,Suc i)"
apply (induct i)
(* i = 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,xa,l'a⦄ ∈ valid A n B" for x xa l'a)
apply (ind_cases "⦃x,M,l'a⦄ ∈ valid A n B" for x l'a)
(* i > 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,repl(l',Suc na,M)⦄ ∈ valid A n B" for x l' na)
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,l'⦄ ∈ valid A n B" for x l')
by (drule_tac x=l' in spec, simp, blast)

subsection‹insertion resilience:
except at the beginning, no offer can be inserted›

lemma chain_isnt_head [simp]: "L ∈ valid A n B ⟹
by (erule valid.induct, auto simp: chain_def sign_def anchor_def)

lemma insertion_resilience: "∀L. L ∈ valid A n B ⟶ Suc i < len L
⟶ ins (L,Suc i,M) ∉ valid A n B"
supply [[simproc del: defined_all]]
apply (induct i)
(* i = 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,l'⦄ ∈ valid A n B" for x l', simp)
apply (ind_cases "⦃x,M,l'⦄ ∈ valid A n B" for x l', clarsimp)
apply (ind_cases "⦃head l',l'⦄ ∈ valid A n B" for l', simp, simp)
(* i > 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,l'⦄ ∈ valid A n B" for x l')
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,ins(l',Suc na,M)⦄ ∈ valid A n B" for x l' na)
apply (frule len_not_empty, clarsimp)
by (drule_tac x=l' in spec, clarsimp)

subsection‹truncation resilience:
only shop i can truncate at offer i›

lemma truncation_resilience: "∀L. L ∈ valid A n B ⟶ Suc i < len L
⟶ cons M (trunc (L,Suc i)) ∈ valid A n B ⟶ shop M = shop (ith (L,i))"
apply (induct i)
(* i = 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,l'⦄ ∈ valid A n B" for x l')
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃M,l'⦄ ∈ valid A n B" for l')
apply (frule len_not_empty, clarsimp, simp)
(* i > 0 *)
apply clarify
apply (frule len_not_empty, clarsimp)
apply (ind_cases "⦃x,l'⦄ ∈ valid A n B" for x l')
apply (frule len_not_empty, clarsimp)
by (drule_tac x=l' in spec, clarsimp)

subsection‹declarations for tactics›

declare knows_Spy_partsEs [elim]
declare Fake_parts_insert [THEN subsetD, dest]
declare initState.simps [simp del]

subsection‹get components of a message›

lemma get_ML [dest]: "Says A' B ⦃A,R,I,M,L⦄ ∈ set evs ⟹
M ∈ parts (spies evs) ∧ L ∈ parts (spies evs)"
by blast

subsection‹general properties of p2›

lemma reqm_neq_prom [iff]:
"reqm A r n I B ≠ prom B' ofr A' r' I' (cons M L) J C"
by (auto simp: reqm_def prom_def)

lemma prom_neq_reqm [iff]:
"prom B' ofr A' r' I' (cons M L) J C ≠ reqm A r n I B"
by (auto simp: reqm_def prom_def)

lemma req_neq_pro [iff]: "req A r n I B ≠ pro B' ofr A' r' I' (cons M L) J C"
by (auto simp: req_def pro_def)

lemma pro_neq_req [iff]: "pro B' ofr A' r' I' (cons M L) J C ≠ req A r n I B"
by (auto simp: req_def pro_def)

lemma p2_has_no_Gets: "evs ∈ p2 ⟹ ∀A X. Gets A X ∉ set evs"
by (erule p2.induct, auto simp: req_def pro_def)

lemma p2_is_Gets_correct [iff]: "Gets_correct p2"
by (auto simp: Gets_correct_def dest: p2_has_no_Gets)

lemma p2_is_one_step [iff]: "one_step p2"
unfolding one_step_def by (clarify, ind_cases "ev#evs ∈ p2" for ev evs, auto)

lemma p2_has_only_Says' [rule_format]: "evs ∈ p2 ⟹
ev ∈ set evs ⟶ (∃A B X. ev=Says A B X)"
by (erule p2.induct, auto simp: req_def pro_def)

lemma p2_has_only_Says [iff]: "has_only_Says p2"
by (auto simp: has_only_Says_def dest: p2_has_only_Says')

lemma p2_is_regular [iff]: "regular p2"
apply (simp only: regular_def, clarify)
apply (erule_tac p2.induct)
apply (simp_all add: initState.simps knows.simps pro_def prom_def
req_def reqm_def anchor_def chain_def sign_def)
by (auto dest: no_Key_in_agl no_Key_in_appdel parts_trans)

subsection‹private keys are safe›

"⟦evs ∈ p2; Friend B ≠ A⟧
⟹ (Key (priK A) ∈ parts (knows (Friend B) evs)) ⟶ (A ∈ bad)"
apply (erule p2.induct)
apply (simp_all add: initState.simps knows.simps pro_def prom_def
req_def reqm_def anchor_def chain_def sign_def)
apply (blast dest: no_Key_in_agl)
apply (auto del: parts_invKey disjE  dest: parts_trans
done

"⟦evs ∈ p2; Friend B ≠ A⟧
⟹ (Key (priK A) ∈ analz (knows (Friend B) evs)) ⟶ (A ∈ bad)"
by auto

lemma priK_notin_knows_max_Friend:
"⟦evs ∈ p2; A ∉ bad; A ≠ Friend C⟧
⟹ Key (priK A) ∉ analz (knows_max (Friend C) evs)"
apply (rule not_parts_not_analz, simp add: knows_max_def, safe)
apply (drule_tac H="spies' evs" in parts_sub)
apply (rule_tac p=p2 in knows_max'_sub_spies', simp+)
apply (drule_tac H="spies evs" in parts_sub)
by (auto dest: knows'_sub_knows [THEN subsetD] priK_notin_initState_Friend)

subsection‹general guardedness properties›

lemma agl_guard [intro]: "I ∈ agl ⟹ I ∈ guard n Ks"
by (erule agl.induct, auto)

lemma Says_to_knows_max'_guard: "⟦Says A' C ⦃A'',r,I,L⦄ ∈ set evs;
Guard n Ks (knows_max' C evs)⟧ ⟹ L ∈ guard n Ks"
by (auto dest: Says_to_knows_max')

lemma Says_from_knows_max'_guard: "⟦Says C A' ⦃A'',r,I,L⦄ ∈ set evs;
Guard n Ks (knows_max' C evs)⟧ ⟹ L ∈ guard n Ks"
by (auto dest: Says_from_knows_max')

lemma Says_Nonce_not_used_guard: "⟦Says A' B ⦃A'',r,I,L⦄ ∈ set evs;
Nonce n ∉ used evs⟧ ⟹ L ∈ guard n Ks"
by (drule not_used_not_parts, auto)

subsection‹guardedness of messages›

lemma chain_guard [iff]: "chain B ofr A L C ∈ guard n {priK A}"
by (case_tac "ofr=n", auto simp: chain_def sign_def)

lemma chain_guard_Nonce_neq [intro]: "n ≠ ofr
⟹ chain B ofr A' L C ∈ guard n {priK A}"
by (auto simp: chain_def sign_def)

lemma anchor_guard [iff]: "anchor A n' B ∈ guard n {priK A}"
by (case_tac "n'=n", auto simp: anchor_def)

lemma anchor_guard_Nonce_neq [intro]: "n ≠ n'
⟹ anchor A' n' B ∈ guard n {priK A}"
by (auto simp: anchor_def)

lemma reqm_guard [intro]: "I ∈ agl ⟹ reqm A r n' I B ∈ guard n {priK A}"
by (case_tac "n'=n", auto simp: reqm_def)

lemma reqm_guard_Nonce_neq [intro]: "⟦n ≠ n'; I ∈ agl⟧
⟹ reqm A' r n' I B ∈ guard n {priK A}"
by (auto simp: reqm_def)

lemma prom_guard [intro]: "⟦I ∈ agl; J ∈ agl; L ∈ guard n {priK A}⟧
⟹ prom B ofr A r I L J C ∈ guard n {priK A}"
by (auto simp: prom_def)

lemma prom_guard_Nonce_neq [intro]: "⟦n ≠ ofr; I ∈ agl; J ∈ agl;
L ∈ guard n {priK A}⟧ ⟹ prom B ofr A' r I L J C ∈ guard n {priK A}"
by (auto simp: prom_def)

subsection‹Nonce uniqueness›

lemma uniq_Nonce_in_chain [dest]: "Nonce k ∈ parts {chain B ofr A L C} ⟹ k=ofr"
by (auto simp: chain_def sign_def)

lemma uniq_Nonce_in_anchor [dest]: "Nonce k ∈ parts {anchor A n B} ⟹ k=n"
by (auto simp: anchor_def chain_def sign_def)

lemma uniq_Nonce_in_reqm [dest]: "⟦Nonce k ∈ parts {reqm A r n I B};
I ∈ agl⟧ ⟹ k=n"
by (auto simp: reqm_def dest: no_Nonce_in_agl)

lemma uniq_Nonce_in_prom [dest]: "⟦Nonce k ∈ parts {prom B ofr A r I L J C};
I ∈ agl; J ∈ agl; Nonce k ∉ parts {L}⟧ ⟹ k=ofr"
by (auto simp: prom_def dest: no_Nonce_in_agl no_Nonce_in_appdel)

subsection‹requests are guarded›

lemma req_imp_Guard [rule_format]: "⟦evs ∈ p2; A ∉ bad⟧ ⟹
req A r n I B ∈ set evs ⟶ Guard n {priK A} (spies evs)"
apply (erule p2.induct, simp)
apply (simp add: req_def knows.simps, safe)
apply (erule in_synth_Guard, erule Guard_analz, simp)
by (auto simp: req_def pro_def dest: Says_imp_knows_Spy)

lemma req_imp_Guard_Friend: "⟦evs ∈ p2; A ∉ bad; req A r n I B ∈ set evs⟧
⟹ Guard n {priK A} (knows_max (Friend C) evs)"
apply (rule Guard_knows_max')
apply (rule_tac H="spies evs" in Guard_mono)
apply (rule req_imp_Guard, simp+)
apply (rule_tac B="spies' evs" in subset_trans)
apply (rule_tac p=p2 in knows_max'_sub_spies', simp+)
by (rule knows'_sub_knows)

subsection‹propositions are guarded›

lemma pro_imp_Guard [rule_format]: "⟦evs ∈ p2; B ∉ bad; A ∉ bad⟧ ⟹
pro B ofr A r I (cons M L) J C ∈ set evs ⟶ Guard ofr {priK A} (spies evs)"
supply [[simproc del: defined_all]]
apply (erule p2.induct) (* +3 subgoals *)
(* Nil *)
apply simp
(* Fake *)
apply (simp add: pro_def, safe) (* +4 subgoals *)
(* 1 *)
apply (erule in_synth_Guard, drule Guard_analz, simp, simp)
(* 2 *)
apply simp
(* 3 *)
apply (simp, simp add: req_def pro_def, blast)
(* 4 *)
apply (blast dest: prom_inj Says_Nonce_not_used_guard Nonce_not_used_Guard)
(* 5 *)
apply simp
apply safe (* +1 subgoal *)
apply (blast dest: prom_inj Says_Nonce_not_used_guard)
(* 6 *)
apply (blast dest: Says_imp_knows_Spy)
(* Request *)
apply (blast dest: prom_inj Says_Nonce_not_used_guard Nonce_not_used_Guard)
(* Propose *)
apply simp
apply safe (* +1 subgoal *)
(* 1 *)
apply (blast dest: prom_inj Says_Nonce_not_used_guard)
(* 2 *)
by (blast dest: Says_imp_knows_Spy)

pro B ofr A r I (cons M L) J C ∈ set evs⟧
⟹ Guard ofr {priK A} (knows_max (Friend D) evs)"
apply (rule Guard_knows_max')
apply (rule_tac H="spies evs" in Guard_mono)
apply (rule pro_imp_Guard, simp+)
apply (rule_tac B="spies' evs" in subset_trans)
apply (rule_tac p=p2 in knows_max'_sub_spies', simp+)
by (rule knows'_sub_knows)

subsection‹data confidentiality:
no one other than the originator can decrypt the offers›

lemma Nonce_req_notin_spies: "⟦evs ∈ p2; req A r n I B ∈ set evs; A ∉ bad⟧
⟹ Nonce n ∉ analz (spies evs)"
by (frule req_imp_Guard, simp+, erule Guard_Nonce_analz, simp+)

lemma Nonce_req_notin_knows_max_Friend: "⟦evs ∈ p2; req A r n I B ∈ set evs;
A ∉ bad; A ≠ Friend C⟧ ⟹ Nonce n ∉ analz (knows_max (Friend C) evs)"
apply (clarify, frule_tac C=C in req_imp_Guard_Friend, simp+)
apply (simp add: knows_max_def, drule Guard_invKey_keyset, simp+)
by (drule priK_notin_knows_max_Friend, auto simp: knows_max_def)

pro B ofr A r I (cons M L) J C ∈ set evs⟧ ⟹ Nonce ofr ∉ analz (spies evs)"
by (frule pro_imp_Guard, simp+, erule Guard_Nonce_analz, simp+)

A ≠ Friend D; pro B ofr A r I (cons M L) J C ∈ set evs⟧
⟹ Nonce ofr ∉ analz (knows_max (Friend D) evs)"
apply (clarify, frule_tac A=A in pro_imp_Guard_Friend, simp+)
apply (simp add: knows_max_def, drule Guard_invKey_keyset, simp+)
by (drule priK_notin_knows_max_Friend, auto simp: knows_max_def)

subsection‹forward privacy:
only the originator can know the identity of the shops›

pro B ofr A r I (cons M L) J C ∈ set evs⟧
⟹ sign B (Nonce ofr) ∉ analz (spies evs)"
by (auto simp:sign_def dest: Nonce_pro_notin_spies)

lemma forward_privacy_Friend: "⟦evs ∈ p2; B ∉ bad; A ∉ bad; A ≠ Friend D;
pro B ofr A r I (cons M L) J C ∈ set evs⟧
⟹ sign B (Nonce ofr) ∉ analz (knows_max (Friend D) evs)"
by (auto simp:sign_def dest:Nonce_pro_notin_knows_max_Friend )

subsection‹non repudiability: an offer signed by B has been sent by B›

lemma Crypt_reqm: "⟦Crypt (priK A) X ∈ parts {reqm A' r n I B}; I ∈ agl⟧ ⟹ A=A'"
by (auto simp: reqm_def anchor_def chain_def sign_def dest: no_Crypt_in_agl)

lemma Crypt_prom: "⟦Crypt (priK A) X ∈ parts {prom B ofr A' r I L J C};
I ∈ agl; J ∈ agl⟧ ⟹ A=B | Crypt (priK A) X ∈ parts {L}"
apply (simp add: prom_def anchor_def chain_def sign_def)
by (blast dest: no_Crypt_in_agl no_Crypt_in_appdel)

lemma Crypt_safeness: "⟦evs ∈ p2; A ∉ bad⟧ ⟹ Crypt (priK A) X ∈ parts (spies evs)
⟶ (∃B Y. Says A B Y ∈ set evs & Crypt (priK A) X ∈ parts {Y})"
apply (erule p2.induct)
(* Nil *)
apply simp
(* Fake *)
apply clarsimp
apply (drule_tac P="λG. Crypt (priK A) X ∈ G" in parts_insert_substD, simp)
apply (erule disjE)
apply (drule_tac K="priK A" in Crypt_synth, simp+, blast, blast)
(* Request *)
apply (drule_tac P="λG. Crypt (priK A) X ∈ G" in parts_insert_substD, simp)
apply (erule disjE)
apply (frule Crypt_reqm, simp, clarify)
apply (rule_tac x=B in exI, rule_tac x="reqm A r n I B" in exI, simp, blast)
(* Propose *)
apply (drule_tac P="λG. Crypt (priK A) X ∈ G" in parts_insert_substD, simp)
apply (rotate_tac -1, erule disjE)
apply (frule Crypt_prom, simp, simp)
apply (rotate_tac -1, erule disjE)
apply (rule_tac x=C in exI)
apply (rule_tac x="prom B ofr Aa r I (cons M L) J C" in exI, blast)
apply (subgoal_tac "cons M L ∈ parts (spies evsp)")
apply (drule_tac G="{cons M L}" and H="spies evsp" in parts_trans, blast, blast)
apply (drule Says_imp_spies, rotate_tac -1, drule parts.Inj)
apply (drule parts.Snd, drule parts.Snd, drule parts.Snd)
by auto

lemma Crypt_Hash_imp_sign: "⟦evs ∈ p2; A ∉ bad⟧ ⟹
Crypt (priK A) (Hash X) ∈ parts (spies evs)
⟶ (∃B Y. Says A B Y ∈ set evs ∧ sign A X ∈ parts {Y})"
apply (erule p2.induct)
(* Nil *)
apply simp
(* Fake *)
apply clarsimp
apply (drule_tac P="λG. Crypt (priK A) (Hash X) ∈ G" in parts_insert_substD)
apply simp
apply (erule disjE)
apply (drule_tac K="priK A" in Crypt_synth, simp+, blast, blast)
(* Request *)
apply (drule_tac P="λG. Crypt (priK A) (Hash X) ∈ G" in parts_insert_substD)
apply simp
apply (erule disjE)
apply (frule Crypt_reqm, simp+)
apply (rule_tac x=B in exI, rule_tac x="reqm Aa r n I B" in exI)
apply (simp add: reqm_def sign_def anchor_def no_Crypt_in_agl)
apply (simp add: chain_def sign_def, blast)
(* Propose *)
apply (drule_tac P="λG. Crypt (priK A) (Hash X) ∈ G" in parts_insert_substD)
apply simp
apply (rotate_tac -1, erule disjE)
apply (simp add: prom_def sign_def no_Crypt_in_agl no_Crypt_in_appdel)
apply (rotate_tac -1, erule disjE)
apply (rule_tac x=C in exI)
apply (rule_tac x="prom B ofr Aa r I (cons M L) J C" in exI)
apply (simp add: prom_def chain_def sign_def)
apply (erule impE)
apply (blast dest: get_ML parts_sub)
apply (blast del: MPair_parts)+
done

lemma sign_safeness: "⟦evs ∈ p2; A ∉ bad⟧ ⟹ sign A X ∈ parts (spies evs)
⟶ (∃B Y. Says A B Y ∈ set evs ∧ sign A X ∈ parts {Y})"
apply (clarify, simp add: sign_def, frule parts.Snd)
apply (blast dest: Crypt_Hash_imp_sign [unfolded sign_def])
done

end
```