author | wenzelm |
Mon, 16 Mar 2009 18:24:30 +0100 | |
changeset 30549 | d2d7874648bd |
parent 30510 | 4120fc59dd85 |
child 32149 | ef59550a55d3 |
permissions | -rw-r--r-- |
18886 | 1 |
(* ID: $Id$ |
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Author: Giampaolo Bella, Catania University |
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*) |
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header{*Theory of smartcards*} |
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theory Smartcard imports EventSC begin |
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text{* |
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As smartcards handle long-term (symmetric) keys, this theoy extends and |
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supersedes theory Private.thy |
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An agent is bad if she reveals her PIN to the spy, not the shared key that |
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is embedded in her card. An agent's being bad implies nothing about her |
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smartcard, which independently may be stolen or cloned. |
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*} |
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consts |
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shrK :: "agent => key" (*long-term keys saved in smart cards*) |
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crdK :: "card => key" (*smart cards' symmetric keys*) |
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pin :: "agent => key" (*pin to activate the smart cards*) |
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(*Mostly for Shoup-Rubin*) |
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Pairkey :: "agent * agent => nat" |
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pairK :: "agent * agent => key" |
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axioms |
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inj_shrK: "inj shrK" --{*No two smartcards store the same key*} |
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inj_crdK: "inj crdK" --{*Nor do two cards*} |
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inj_pin : "inj pin" --{*Nor do two agents have the same pin*} |
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(*pairK is injective on each component, if we assume encryption to be a PRF |
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or at least collision free *) |
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inj_pairK [iff]: "(pairK(A,B) = pairK(A',B')) = (A = A' & B = B')" |
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comm_Pairkey [iff]: "Pairkey(A,B) = Pairkey(B,A)" |
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(*long-term keys differ from each other*) |
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pairK_disj_crdK [iff]: "pairK(A,B) \<noteq> crdK C" |
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pairK_disj_shrK [iff]: "pairK(A,B) \<noteq> shrK P" |
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pairK_disj_pin [iff]: "pairK(A,B) \<noteq> pin P" |
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shrK_disj_crdK [iff]: "shrK P \<noteq> crdK C" |
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shrK_disj_pin [iff]: "shrK P \<noteq> pin Q" |
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crdK_disj_pin [iff]: "crdK C \<noteq> pin P" |
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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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constdefs |
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legalUse :: "card => bool" ("legalUse (_)") |
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"legalUse C == C \<notin> stolen" |
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consts |
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illegalUse :: "card => bool" |
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primrec |
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illegalUse_def: |
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"illegalUse (Card A) = ( (Card A \<in> stolen \<and> A \<in> bad) \<or> Card A \<in> cloned )" |
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text{*initState must be defined with care*} |
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primrec |
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(*Server knows all long-term keys; adding cards' keys may be redundant but |
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helps prove crdK_in_initState and crdK_in_used to distinguish cards' keys |
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from fresh (session) keys*) |
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initState_Server: "initState Server = |
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(Key`(range shrK \<union> range crdK \<union> range pin \<union> range pairK)) \<union> |
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(Nonce`(range Pairkey))" |
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(*Other agents know only their own*) |
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initState_Friend: "initState (Friend i) = {Key (pin (Friend i))}" |
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(*Spy knows bad agents' pins, cloned cards' keys, pairKs, and Pairkeys *) |
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initState_Spy: "initState Spy = |
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(Key`((pin`bad) \<union> (pin `{A. Card A \<in> cloned}) \<union> |
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(shrK`{A. Card A \<in> cloned}) \<union> |
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(crdK`cloned) \<union> |
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(pairK`{(X,A). Card A \<in> cloned}))) |
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\<union> (Nonce`(Pairkey`{(A,B). Card A \<in> cloned & Card B \<in> cloned}))" |
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text{*Still relying on axioms*} |
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axioms |
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Key_supply_ax: "finite KK \<Longrightarrow> \<exists> K. K \<notin> KK & Key K \<notin> used evs" |
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(*Needed because of Spy's knowledge of Pairkeys*) |
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Nonce_supply_ax: "finite NN \<Longrightarrow> \<exists> N. N \<notin> NN & Nonce N \<notin> used evs" |
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subsection{*Basic properties of shrK*} |
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(*Injectiveness: Agents' long-term keys are distinct.*) |
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declare inj_shrK [THEN inj_eq, iff] |
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declare inj_crdK [THEN inj_eq, iff] |
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declare inj_pin [THEN inj_eq, 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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"\<lbrakk> Crypt K X \<in> analz H; Key K \<in> analz H \<rbrakk> \<Longrightarrow> 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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text{*Added to extend initstate with set of nonces*} |
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lemma parts_image_Nonce [simp]: "parts (Nonce`N) = Nonce`N" |
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apply auto |
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apply (erule parts.induct) |
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apply auto |
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done |
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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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"\<lbrakk> K \<in> keysFor (parts (insert X G)); X \<in> synth (analz H) \<rbrakk> |
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\<Longrightarrow> K \<in> keysFor (parts (G \<union> H)) | Key K \<in> parts H"; |
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by (force dest: EventSC.keysFor_parts_insert) |
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lemma Crypt_imp_keysFor: "Crypt K X \<in> H \<Longrightarrow> 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 knows the pins of bad agents!*) |
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lemma Spy_knows_bad [intro!]: "A \<in> bad \<Longrightarrow> Key (pin 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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(*Spy knows the long-term keys of cloned cards!*) |
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lemma Spy_knows_cloned [intro!]: |
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"Card A \<in> cloned \<Longrightarrow> Key (crdK (Card A)) \<in> knows Spy evs & |
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Key (shrK A) \<in> knows Spy evs & |
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Key (pin A) \<in> knows Spy evs & |
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(\<forall> B. Key (pairK(B,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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lemma Spy_knows_cloned1 [intro!]: "C \<in> cloned \<Longrightarrow> Key (crdK C) \<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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lemma Spy_knows_cloned2 [intro!]: "\<lbrakk> Card A \<in> cloned; Card B \<in> cloned \<rbrakk> |
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\<Longrightarrow> Nonce (Pairkey(A,B))\<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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(*Spy only knows pins of bad agents!*) |
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lemma Spy_knows_Spy_bad [intro!]: "A\<in> bad \<Longrightarrow> Key (pin 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: |
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"\<lbrakk> Crypt (pin A) X \<in> analz (knows Spy evs); A\<in>bad \<rbrakk> |
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\<Longrightarrow> 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 other keys **) |
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lemma shrK_in_initState [iff]: "Key (shrK A) \<in> initState Server" |
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apply (induct_tac "A") |
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apply auto |
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done |
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lemma shrK_in_used [iff]: "Key (shrK A) \<in> used evs" |
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apply (rule initState_into_used) |
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apply blast |
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done |
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lemma crdK_in_initState [iff]: "Key (crdK A) \<in> initState Server" |
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apply (induct_tac "A") |
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apply auto |
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done |
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lemma crdK_in_used [iff]: "Key (crdK A) \<in> used evs" |
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apply (rule initState_into_used) |
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apply blast |
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done |
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lemma pin_in_initState [iff]: "Key (pin A) \<in> initState A" |
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apply (induct_tac "A") |
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apply auto |
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done |
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lemma pin_in_used [iff]: "Key (pin A) \<in> used evs" |
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apply (rule initState_into_used) |
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apply blast |
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done |
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lemma pairK_in_initState [iff]: "Key (pairK X) \<in> initState Server" |
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apply (induct_tac "X") |
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apply auto |
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done |
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lemma pairK_in_used [iff]: "Key (pairK X) \<in> used evs" |
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apply (rule initState_into_used) |
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apply blast |
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done |
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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 \<Longrightarrow> K \<notin> range shrK" |
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by blast |
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lemma shrK_neq [simp]: "Key K \<notin> used evs \<Longrightarrow> shrK B \<noteq> K" |
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by blast |
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lemma crdK_not_used [simp]: "Key K \<notin> used evs \<Longrightarrow> K \<notin> range crdK" |
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apply clarify |
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done |
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lemma crdK_neq [simp]: "Key K \<notin> used evs \<Longrightarrow> crdK C \<noteq> K" |
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apply clarify |
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done |
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lemma pin_not_used [simp]: "Key K \<notin> used evs \<Longrightarrow> K \<notin> range pin" |
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apply clarify |
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done |
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lemma pin_neq [simp]: "Key K \<notin> used evs \<Longrightarrow> pin A \<noteq> K" |
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apply clarify |
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done |
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lemma pairK_not_used [simp]: "Key K \<notin> used evs \<Longrightarrow> K \<notin> range pairK" |
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apply clarify |
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done |
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lemma pairK_neq [simp]: "Key K \<notin> used evs \<Longrightarrow> pairK(A,B) \<noteq> K" |
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apply clarify |
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done |
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declare shrK_neq [THEN not_sym, simp] |
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declare crdK_neq [THEN not_sym, simp] |
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declare pin_neq [THEN not_sym, simp] |
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declare pairK_neq [THEN not_sym, simp] |
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subsection{*Fresh nonces*} |
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lemma Nonce_notin_initState [iff]: "Nonce N \<notin> parts (initState (Friend i))" |
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by auto |
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(*This lemma no longer holds of smartcard protocols, where the cards can store |
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nonces. |
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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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So, we must use old-style supply fresh nonce theorems relying on the appropriate axiom*) |
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subsection{*Supply fresh nonces for possibility theorems.*} |
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lemma Nonce_supply1: "\<exists>N. Nonce N \<notin> used evs" |
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apply (rule finite.emptyI [THEN Nonce_supply_ax, THEN exE], blast) |
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done |
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lemma Nonce_supply2: |
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"\<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 finite.emptyI [THEN Nonce_supply_ax]) |
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apply (erule exE) |
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apply (cut_tac evs = evs' in finite.emptyI [THEN finite.insertI, THEN Nonce_supply_ax]) |
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apply auto |
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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 finite.emptyI [THEN Nonce_supply_ax]) |
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apply (erule exE) |
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apply (cut_tac evs = evs' and a1 = N in finite.emptyI [THEN finite.insertI, THEN Nonce_supply_ax]) |
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apply (erule exE) |
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apply (cut_tac evs = evs'' and a1 = Na and a2 = N in finite.emptyI [THEN finite.insertI, THEN finite.insertI, THEN Nonce_supply_ax]) |
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apply blast |
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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 finite.emptyI [THEN Nonce_supply_ax, 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 \<Longrightarrow> \<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{*Specialized Rewriting for Theorems About @{term analz} and Image*} |
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lemma subset_Compl_range_shrK: "A \<subseteq> - (range shrK) \<Longrightarrow> shrK x \<notin> A" |
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by blast |
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lemma subset_Compl_range_crdK: "A \<subseteq> - (range crdK) \<Longrightarrow> crdK x \<notin> A" |
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apply blast |
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done |
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lemma subset_Compl_range_pin: "A \<subseteq> - (range pin) \<Longrightarrow> pin x \<notin> A" |
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apply blast |
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done |
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lemma subset_Compl_range_pairK: "A \<subseteq> - (range pairK) \<Longrightarrow> pairK x \<notin> A" |
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apply blast |
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done |
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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_shrK subset_Compl_range_crdK |
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subset_Compl_range_pin subset_Compl_range_pairK |
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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)) \<longrightarrow> (K \<in> nE | Key K \<in> analz H) \<Longrightarrow> |
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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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subsection{*Tactics for possibility theorems*} |
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ML |
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{* |
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structure Smartcard = |
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struct |
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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 possibility_tac ctxt = |
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(REPEAT |
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(ALLGOALS (simp_tac (local_simpset_of ctxt |
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delsimps [@{thm used_Says}, @{thm used_Notes}, @{thm used_Gets}, |
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@{thm used_Inputs}, @{thm used_C_Gets}, @{thm used_Outpts}, @{thm used_A_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, @{thm Nonce_supply}]))) |
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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 ctxt = |
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REPEAT |
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(ALLGOALS (asm_simp_tac (local_simpset_of ctxt setSolver safe_solver)) |
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THEN |
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REPEAT_FIRST (resolve_tac [refl, conjI])) |
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val analz_image_freshK_ss = |
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1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
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parents:
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@{simpset} delsimps [image_insert, image_Un] |
1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
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parents:
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delsimps [@{thm imp_disjL}] (*reduces blow-up*) |
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addsimps @{thms analz_image_freshK_simps} |
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end |
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*} |
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||
402 |
(*Lets blast_tac perform this step without needing the simplifier*) |
|
403 |
lemma invKey_shrK_iff [iff]: |
|
404 |
"(Key (invKey K) \<in> X) = (Key K \<in> X)" |
|
405 |
by auto |
|
406 |
||
407 |
(*Specialized methods*) |
|
408 |
||
409 |
method_setup analz_freshK = {* |
|
30549 | 410 |
Scan.succeed (fn ctxt => |
30510
4120fc59dd85
unified type Proof.method and pervasive METHOD combinators;
wenzelm
parents:
24122
diff
changeset
|
411 |
(SIMPLE_METHOD |
21588 | 412 |
(EVERY [REPEAT_FIRST (resolve_tac [allI, ballI, impI]), |
24122 | 413 |
REPEAT_FIRST (rtac @{thm analz_image_freshK_lemma}), |
414 |
ALLGOALS (asm_simp_tac (Simplifier.context ctxt Smartcard.analz_image_freshK_ss))]))) *} |
|
18886 | 415 |
"for proving the Session Key Compromise theorem" |
416 |
||
417 |
method_setup possibility = {* |
|
30549 | 418 |
Scan.succeed (fn ctxt => |
30510
4120fc59dd85
unified type Proof.method and pervasive METHOD combinators;
wenzelm
parents:
24122
diff
changeset
|
419 |
SIMPLE_METHOD (Smartcard.possibility_tac ctxt)) *} |
23894
1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
wenzelm
parents:
22265
diff
changeset
|
420 |
"for proving possibility theorems" |
1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
wenzelm
parents:
22265
diff
changeset
|
421 |
|
1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
wenzelm
parents:
22265
diff
changeset
|
422 |
method_setup basic_possibility = {* |
30549 | 423 |
Scan.succeed (fn ctxt => |
30510
4120fc59dd85
unified type Proof.method and pervasive METHOD combinators;
wenzelm
parents:
24122
diff
changeset
|
424 |
SIMPLE_METHOD (Smartcard.basic_possibility_tac ctxt)) *} |
18886 | 425 |
"for proving possibility theorems" |
426 |
||
427 |
lemma knows_subset_knows_Cons: "knows A evs \<subseteq> knows A (e # evs)" |
|
23894
1a4167d761ac
tactics: avoid dynamic reference to accidental theory context (via ML_Context.the_context etc.);
wenzelm
parents:
22265
diff
changeset
|
428 |
by (induct e) (auto simp: knows_Cons) |
18886 | 429 |
|
430 |
(*Needed for actual protocols that will follow*) |
|
431 |
declare shrK_disj_crdK[THEN not_sym, iff] |
|
432 |
declare shrK_disj_pin[THEN not_sym, iff] |
|
433 |
declare pairK_disj_shrK[THEN not_sym, iff] |
|
434 |
declare pairK_disj_crdK[THEN not_sym, iff] |
|
435 |
declare pairK_disj_pin[THEN not_sym, iff] |
|
436 |
declare crdK_disj_pin[THEN not_sym, iff] |
|
437 |
||
438 |
declare legalUse_def [iff] illegalUse_def [iff] |
|
439 |
||
440 |
end |