Theory P2

(*  Title:      HOL/Auth/Guard/P2.thy
    Author:     Frederic Blanqui, University of Cambridge Computer Laboratory
    Copyright   2002  University of Cambridge

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

sectionProtocol P2

theory P2 imports Guard_Public List_Msg begin

subsectionProtocol Definition


textLike P1 except the definitions of chain›, shop›,
  next_shop› and nonce›

subsubsectionoffer 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)

subsubsectionagent 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"
by (simp add: chain_def sign_def)

subsubsectionnonce 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"
by (simp add: chain_def sign_def)

subsubsectionnext 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"
by (simp add: chain_def sign_def)

subsubsectionanchor 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"
by (simp add: anchor_def)

subsubsectionrequest 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)

subsubsectionpropose 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)

subsubsectionprotocol

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"

subsubsectionvalid 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"

subsubsectionbasic 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)

subsubsectionlist of offers

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


subsectionProperties of Protocol P2

textsame as P1_Prop› except that publicly verifiable forward
integrity is replaced by forward privacy

subsectionstrong 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)
apply (simp add: chain_def)
(* 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)

subsectioninsertion resilience:
except at the beginning, no offer can be inserted

lemma chain_isnt_head [simp]: "L  valid A n B 
head L  chain (next_shop (head L)) ofr A L C"
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)

subsectiontruncation 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)

subsectiondeclarations for tactics

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

subsectionget 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

subsectiongeneral 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"
by (unfold one_step_def, 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)

subsectionprivate keys are safe

lemma priK_parts_Friend_imp_bad [rule_format,dest]:
     "[| 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
            simp add: no_Key_in_appdel)
done

lemma priK_analz_Friend_imp_bad [rule_format,dest]:
     "[| 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)

subsectiongeneral 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)

subsectionguardedness 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)

subsectionNonce 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)

subsectionrequests 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)

subsectionpropositions 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 (simp add: pro_def)
apply (blast dest: prom_inj Says_Nonce_not_used_guard Nonce_not_used_Guard)
(* 5 *)
apply simp
apply safe (* +1 subgoal *)
apply (simp add: pro_def)
apply (blast dest: prom_inj Says_Nonce_not_used_guard)
(* 6 *)
apply (simp add: pro_def)
apply (blast dest: Says_imp_knows_Spy)
(* Request *)
apply (simp add: pro_def)
apply (blast dest: prom_inj Says_Nonce_not_used_guard Nonce_not_used_Guard)
(* Propose *)
apply simp
apply safe (* +1 subgoal *)
(* 1 *)
apply (simp add: pro_def)
apply (blast dest: prom_inj Says_Nonce_not_used_guard)
(* 2 *)
apply (simp add: pro_def)
by (blast dest: Says_imp_knows_Spy)

lemma pro_imp_Guard_Friend: "[| evs  p2; B  bad; A  bad;
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)

subsectiondata 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)

lemma Nonce_pro_notin_spies: "[| evs  p2; B  bad; A  bad;
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+)

lemma Nonce_pro_notin_knows_max_Friend: "[| evs  p2; B  bad; A  bad;
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)

subsectionforward privacy:
only the originator can know the identity of the shops

lemma forward_privacy_Spy: "[| evs  p2; B  bad; A  bad;
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 )

subsectionnon 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 (simp add: req_def, clarify)
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 (simp add: pro_def, clarify)
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 (simp add: req_def, clarify)
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 (simp add: pro_def, clarify)
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 (simp add: chain_def sign_def)
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