src/HOL/Auth/TLS.thy
author wenzelm
Thu Jul 22 18:08:39 2010 +0200 (2010-07-22)
changeset 37936 1e4c5015a72e
parent 35702 fb7a386a15cb
child 41413 64cd30d6b0b8
permissions -rw-r--r--
updated some headers;
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(*  Title:      HOL/Auth/TLS.thy
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    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
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    Copyright   1997  University of Cambridge
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Inductive relation "tls" for the TLS (Transport Layer Security) protocol.
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This protocol is essentially the same as SSL 3.0.
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Abstracted from "The TLS Protocol, Version 1.0" by Tim Dierks and Christopher
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Allen, Transport Layer Security Working Group, 21 May 1997,
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INTERNET-DRAFT draft-ietf-tls-protocol-03.txt.  Section numbers below refer
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to that memo.
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An RSA cryptosystem is assumed, and X.509v3 certificates are abstracted down
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to the trivial form {A, publicKey(A)}privateKey(Server), where Server is a
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global signing authority.
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A is the client and B is the server, not to be confused with the constant
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Server, who is in charge of all public keys.
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The model assumes that no fraudulent certificates are present, but it does
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assume that some private keys are to the spy.
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REMARK.  The event "Notes A {|Agent B, Nonce PMS|}" appears in ClientKeyExch,
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CertVerify, ClientFinished to record that A knows M.  It is a note from A to
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herself.  Nobody else can see it.  In ClientKeyExch, the Spy can substitute
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his own certificate for A's, but he cannot replace A's note by one for himself.
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The Note event avoids a weakness in the public-key model.  Each
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agent's state is recorded as the trace of messages.  When the true client (A)
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invents PMS, he encrypts PMS with B's public key before sending it.  The model
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does not distinguish the original occurrence of such a message from a replay.
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In the shared-key model, the ability to encrypt implies the ability to
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decrypt, so the problem does not arise.
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Proofs would be simpler if ClientKeyExch included A's name within
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Crypt KB (Nonce PMS).  As things stand, there is much overlap between proofs
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about that message (which B receives) and the stronger event
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Notes A {|Agent B, Nonce PMS|}.
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*)
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header{*The TLS Protocol: Transport Layer Security*}
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theory TLS imports Public Nat_Bijection begin
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definition certificate :: "[agent,key] => msg" where
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    "certificate A KA == Crypt (priSK Server) {|Agent A, Key KA|}"
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text{*TLS apparently does not require separate keypairs for encryption and
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signature.  Therefore, we formalize signature as encryption using the
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private encryption key.*}
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datatype role = ClientRole | ServerRole
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consts
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  (*Pseudo-random function of Section 5*)
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  PRF  :: "nat*nat*nat => nat"
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  (*Client, server write keys are generated uniformly by function sessionK
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    to avoid duplicating their properties.  They are distinguished by a
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    tag (not a bool, to avoid the peculiarities of if-and-only-if).
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    Session keys implicitly include MAC secrets.*)
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  sessionK :: "(nat*nat*nat) * role => key"
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abbreviation
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  clientK :: "nat*nat*nat => key" where
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  "clientK X == sessionK(X, ClientRole)"
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abbreviation
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  serverK :: "nat*nat*nat => key" where
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  "serverK X == sessionK(X, ServerRole)"
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specification (PRF)
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  inj_PRF: "inj PRF"
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  --{*the pseudo-random function is collision-free*}
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   apply (rule exI [of _ "%(x,y,z). prod_encode(x, prod_encode(y,z))"])
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   apply (simp add: inj_on_def prod_encode_eq)
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   done
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specification (sessionK)
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  inj_sessionK: "inj sessionK"
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  --{*sessionK is collision-free; also, no clientK clashes with any serverK.*}
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   apply (rule exI [of _ 
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         "%((x,y,z), r). prod_encode(role_case 0 1 r, 
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                           prod_encode(x, prod_encode(y,z)))"])
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   apply (simp add: inj_on_def prod_encode_eq split: role.split) 
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   done
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axioms
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  --{*sessionK makes symmetric keys*}
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  isSym_sessionK: "sessionK nonces \<in> symKeys"
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  --{*sessionK never clashes with a long-term symmetric key  
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     (they don't exist in TLS anyway)*}
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  sessionK_neq_shrK [iff]: "sessionK nonces \<noteq> shrK A"
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inductive_set tls :: "event list set"
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  where
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   Nil:  --{*The initial, empty trace*}
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         "[] \<in> tls"
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 | Fake: --{*The Spy may say anything he can say.  The sender field is correct,
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          but agents don't use that information.*}
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         "[| evsf \<in> tls;  X \<in> synth (analz (spies evsf)) |]
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          ==> Says Spy B X # evsf \<in> tls"
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 | SpyKeys: --{*The spy may apply @{term PRF} and @{term sessionK}
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                to available nonces*}
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         "[| evsSK \<in> tls;
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             {Nonce NA, Nonce NB, Nonce M} <= analz (spies evsSK) |]
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          ==> Notes Spy {| Nonce (PRF(M,NA,NB)),
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                           Key (sessionK((NA,NB,M),role)) |} # evsSK \<in> tls"
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 | ClientHello:
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         --{*(7.4.1.2)
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           PA represents @{text CLIENT_VERSION}, @{text CIPHER_SUITES} and @{text COMPRESSION_METHODS}.
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           It is uninterpreted but will be confirmed in the FINISHED messages.
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           NA is CLIENT RANDOM, while SID is @{text SESSION_ID}.
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           UNIX TIME is omitted because the protocol doesn't use it.
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           May assume @{term "NA \<notin> range PRF"} because CLIENT RANDOM is 
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           28 bytes while MASTER SECRET is 48 bytes*}
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         "[| evsCH \<in> tls;  Nonce NA \<notin> used evsCH;  NA \<notin> range PRF |]
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          ==> Says A B {|Agent A, Nonce NA, Number SID, Number PA|}
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                # evsCH  \<in>  tls"
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 | ServerHello:
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         --{*7.4.1.3 of the TLS Internet-Draft
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           PB represents @{text CLIENT_VERSION}, @{text CIPHER_SUITE} and @{text COMPRESSION_METHOD}.
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           SERVER CERTIFICATE (7.4.2) is always present.
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           @{text CERTIFICATE_REQUEST} (7.4.4) is implied.*}
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         "[| evsSH \<in> tls;  Nonce NB \<notin> used evsSH;  NB \<notin> range PRF;
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             Says A' B {|Agent A, Nonce NA, Number SID, Number PA|}
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               \<in> set evsSH |]
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          ==> Says B A {|Nonce NB, Number SID, Number PB|} # evsSH  \<in>  tls"
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 | Certificate:
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         --{*SERVER (7.4.2) or CLIENT (7.4.6) CERTIFICATE.*}
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         "evsC \<in> tls ==> Says B A (certificate B (pubK B)) # evsC  \<in>  tls"
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 | ClientKeyExch:
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         --{*CLIENT KEY EXCHANGE (7.4.7).
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           The client, A, chooses PMS, the PREMASTER SECRET.
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           She encrypts PMS using the supplied KB, which ought to be pubK B.
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           We assume @{term "PMS \<notin> range PRF"} because a clash betweem the PMS
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           and another MASTER SECRET is highly unlikely (even though
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           both items have the same length, 48 bytes).
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           The Note event records in the trace that she knows PMS
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               (see REMARK at top). *}
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         "[| evsCX \<in> tls;  Nonce PMS \<notin> used evsCX;  PMS \<notin> range PRF;
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             Says B' A (certificate B KB) \<in> set evsCX |]
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          ==> Says A B (Crypt KB (Nonce PMS))
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              # Notes A {|Agent B, Nonce PMS|}
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              # evsCX  \<in>  tls"
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 | CertVerify:
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        --{*The optional Certificate Verify (7.4.8) message contains the
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          specific components listed in the security analysis, F.1.1.2.
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          It adds the pre-master-secret, which is also essential!
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          Checking the signature, which is the only use of A's certificate,
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          assures B of A's presence*}
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         "[| evsCV \<in> tls;
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             Says B' A {|Nonce NB, Number SID, Number PB|} \<in> set evsCV;
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             Notes A {|Agent B, Nonce PMS|} \<in> set evsCV |]
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          ==> Says A B (Crypt (priK A) (Hash{|Nonce NB, Agent B, Nonce PMS|}))
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              # evsCV  \<in>  tls"
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        --{*Finally come the FINISHED messages (7.4.8), confirming PA and PB
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          among other things.  The master-secret is PRF(PMS,NA,NB).
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          Either party may send its message first.*}
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 | ClientFinished:
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        --{*The occurrence of Notes A {|Agent B, Nonce PMS|} stops the
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          rule's applying when the Spy has satisfied the "Says A B" by
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          repaying messages sent by the true client; in that case, the
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          Spy does not know PMS and could not send ClientFinished.  One
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          could simply put @{term "A\<noteq>Spy"} into the rule, but one should not
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          expect the spy to be well-behaved.*}
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         "[| evsCF \<in> tls;
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             Says A  B {|Agent A, Nonce NA, Number SID, Number PA|}
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               \<in> set evsCF;
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             Says B' A {|Nonce NB, Number SID, Number PB|} \<in> set evsCF;
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             Notes A {|Agent B, Nonce PMS|} \<in> set evsCF;
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             M = PRF(PMS,NA,NB) |]
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          ==> Says A B (Crypt (clientK(NA,NB,M))
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                        (Hash{|Number SID, Nonce M,
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                               Nonce NA, Number PA, Agent A,
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                               Nonce NB, Number PB, Agent B|}))
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              # evsCF  \<in>  tls"
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 | ServerFinished:
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        --{*Keeping A' and A'' distinct means B cannot even check that the
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          two messages originate from the same source. *}
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         "[| evsSF \<in> tls;
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             Says A' B  {|Agent A, Nonce NA, Number SID, Number PA|}
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               \<in> set evsSF;
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             Says B  A  {|Nonce NB, Number SID, Number PB|} \<in> set evsSF;
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             Says A'' B (Crypt (pubK B) (Nonce PMS)) \<in> set evsSF;
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             M = PRF(PMS,NA,NB) |]
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          ==> Says B A (Crypt (serverK(NA,NB,M))
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                        (Hash{|Number SID, Nonce M,
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                               Nonce NA, Number PA, Agent A,
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                               Nonce NB, Number PB, Agent B|}))
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              # evsSF  \<in>  tls"
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 | ClientAccepts:
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        --{*Having transmitted ClientFinished and received an identical
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          message encrypted with serverK, the client stores the parameters
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          needed to resume this session.  The "Notes A ..." premise is
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          used to prove @{text Notes_master_imp_Crypt_PMS}.*}
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         "[| evsCA \<in> tls;
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             Notes A {|Agent B, Nonce PMS|} \<in> set evsCA;
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             M = PRF(PMS,NA,NB);
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             X = Hash{|Number SID, Nonce M,
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                       Nonce NA, Number PA, Agent A,
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                       Nonce NB, Number PB, Agent B|};
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             Says A  B (Crypt (clientK(NA,NB,M)) X) \<in> set evsCA;
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             Says B' A (Crypt (serverK(NA,NB,M)) X) \<in> set evsCA |]
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          ==>
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             Notes A {|Number SID, Agent A, Agent B, Nonce M|} # evsCA  \<in>  tls"
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 | ServerAccepts:
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        --{*Having transmitted ServerFinished and received an identical
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          message encrypted with clientK, the server stores the parameters
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          needed to resume this session.  The "Says A'' B ..." premise is
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          used to prove @{text Notes_master_imp_Crypt_PMS}.*}
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         "[| evsSA \<in> tls;
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             A \<noteq> B;
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             Says A'' B (Crypt (pubK B) (Nonce PMS)) \<in> set evsSA;
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             M = PRF(PMS,NA,NB);
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             X = Hash{|Number SID, Nonce M,
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                       Nonce NA, Number PA, Agent A,
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                       Nonce NB, Number PB, Agent B|};
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             Says B  A (Crypt (serverK(NA,NB,M)) X) \<in> set evsSA;
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             Says A' B (Crypt (clientK(NA,NB,M)) X) \<in> set evsSA |]
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          ==>
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             Notes B {|Number SID, Agent A, Agent B, Nonce M|} # evsSA  \<in>  tls"
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 | ClientResume:
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         --{*If A recalls the @{text SESSION_ID}, then she sends a FINISHED
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             message using the new nonces and stored MASTER SECRET.*}
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         "[| evsCR \<in> tls;
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             Says A  B {|Agent A, Nonce NA, Number SID, Number PA|}: set evsCR;
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             Says B' A {|Nonce NB, Number SID, Number PB|} \<in> set evsCR;
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             Notes A {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evsCR |]
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          ==> Says A B (Crypt (clientK(NA,NB,M))
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                        (Hash{|Number SID, Nonce M,
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                               Nonce NA, Number PA, Agent A,
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                               Nonce NB, Number PB, Agent B|}))
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              # evsCR  \<in>  tls"
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 | ServerResume:
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         --{*Resumption (7.3):  If B finds the @{text SESSION_ID} then he can 
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             send a FINISHED message using the recovered MASTER SECRET*}
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         "[| evsSR \<in> tls;
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             Says A' B {|Agent A, Nonce NA, Number SID, Number PA|}: set evsSR;
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             Says B  A {|Nonce NB, Number SID, Number PB|} \<in> set evsSR;
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             Notes B {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evsSR |]
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          ==> Says B A (Crypt (serverK(NA,NB,M))
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                        (Hash{|Number SID, Nonce M,
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                               Nonce NA, Number PA, Agent A,
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                               Nonce NB, Number PB, Agent B|})) # evsSR
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                \<in>  tls"
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 | Oops:
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         --{*The most plausible compromise is of an old session key.  Losing
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           the MASTER SECRET or PREMASTER SECRET is more serious but
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           rather unlikely.  The assumption @{term "A\<noteq>Spy"} is essential: 
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           otherwise the Spy could learn session keys merely by 
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           replaying messages!*}
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         "[| evso \<in> tls;  A \<noteq> Spy;
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             Says A B (Crypt (sessionK((NA,NB,M),role)) X) \<in> set evso |]
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          ==> Says A Spy (Key (sessionK((NA,NB,M),role))) # evso  \<in>  tls"
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(*
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Protocol goals:
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* M, serverK(NA,NB,M) and clientK(NA,NB,M) will be known only to the two
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     parties (though A is not necessarily authenticated).
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* B upon receiving CertVerify knows that A is present (But this
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    message is optional!)
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* A upon receiving ServerFinished knows that B is present
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* Each party who has received a FINISHED message can trust that the other
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  party agrees on all message components, including PA and PB (thus foiling
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  rollback attacks).
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*)
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declare Says_imp_knows_Spy [THEN analz.Inj, dest]
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declare parts.Body  [dest]
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declare analz_into_parts [dest]
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declare Fake_parts_insert_in_Un  [dest]
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text{*Automatically unfold the definition of "certificate"*}
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declare certificate_def [simp]
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text{*Injectiveness of key-generating functions*}
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declare inj_PRF [THEN inj_eq, iff]
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declare inj_sessionK [THEN inj_eq, iff]
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declare isSym_sessionK [simp]
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   303
paulson@11287
   304
paulson@11287
   305
(*** clientK and serverK make symmetric keys; no clashes with pubK or priK ***)
paulson@11287
   306
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   307
lemma pubK_neq_sessionK [iff]: "publicKey b A \<noteq> sessionK arg"
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   308
by (simp add: symKeys_neq_imp_neq)
paulson@11287
   309
paulson@11287
   310
declare pubK_neq_sessionK [THEN not_sym, iff]
paulson@11287
   311
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   312
lemma priK_neq_sessionK [iff]: "invKey (publicKey b A) \<noteq> sessionK arg"
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   313
by (simp add: symKeys_neq_imp_neq)
paulson@11287
   314
paulson@11287
   315
declare priK_neq_sessionK [THEN not_sym, iff]
paulson@11287
   316
paulson@11287
   317
lemmas keys_distinct = pubK_neq_sessionK priK_neq_sessionK
paulson@11287
   318
paulson@11287
   319
paulson@13922
   320
subsection{*Protocol Proofs*}
paulson@11287
   321
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   322
text{*Possibility properties state that some traces run the protocol to the
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   323
end.  Four paths and 12 rules are considered.*}
paulson@11287
   324
paulson@11287
   325
paulson@11287
   326
(** These proofs assume that the Nonce_supply nonces
wenzelm@32960
   327
        (which have the form  @ N. Nonce N \<notin> used evs)
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   328
    lie outside the range of PRF.  It seems reasonable, but as it is needed
paulson@11287
   329
    only for the possibility theorems, it is not taken as an axiom.
paulson@11287
   330
**)
paulson@11287
   331
paulson@11287
   332
paulson@13922
   333
text{*Possibility property ending with ClientAccepts.*}
paulson@11287
   334
lemma "[| \<forall>evs. (@ N. Nonce N \<notin> used evs) \<notin> range PRF;  A \<noteq> B |]
paulson@11287
   335
      ==> \<exists>SID M. \<exists>evs \<in> tls.
paulson@11287
   336
            Notes A {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evs"
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   337
apply (intro exI bexI)
paulson@11287
   338
apply (rule_tac [2] tls.Nil
paulson@11287
   339
                    [THEN tls.ClientHello, THEN tls.ServerHello,
paulson@11287
   340
                     THEN tls.Certificate, THEN tls.ClientKeyExch,
paulson@11287
   341
                     THEN tls.ClientFinished, THEN tls.ServerFinished,
paulson@13507
   342
                     THEN tls.ClientAccepts], possibility, blast+)
paulson@11287
   343
done
paulson@11287
   344
paulson@11287
   345
paulson@13922
   346
text{*And one for ServerAccepts.  Either FINISHED message may come first.*}
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   347
lemma "[| \<forall>evs. (@ N. Nonce N \<notin> used evs) \<notin> range PRF; A \<noteq> B |]
paulson@11287
   348
      ==> \<exists>SID NA PA NB PB M. \<exists>evs \<in> tls.
paulson@11287
   349
           Notes B {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evs"
paulson@11287
   350
apply (intro exI bexI)
paulson@11287
   351
apply (rule_tac [2] tls.Nil
paulson@11287
   352
                    [THEN tls.ClientHello, THEN tls.ServerHello,
paulson@11287
   353
                     THEN tls.Certificate, THEN tls.ClientKeyExch,
paulson@11287
   354
                     THEN tls.ServerFinished, THEN tls.ClientFinished, 
paulson@13507
   355
                     THEN tls.ServerAccepts], possibility, blast+)
paulson@11287
   356
done
paulson@11287
   357
paulson@11287
   358
paulson@13922
   359
text{*Another one, for CertVerify (which is optional)*}
paulson@11287
   360
lemma "[| \<forall>evs. (@ N. Nonce N \<notin> used evs) \<notin> range PRF;  A \<noteq> B |]
paulson@11287
   361
       ==> \<exists>NB PMS. \<exists>evs \<in> tls.
paulson@11287
   362
              Says A B (Crypt (priK A) (Hash{|Nonce NB, Agent B, Nonce PMS|})) 
paulson@11287
   363
                \<in> set evs"
paulson@11287
   364
apply (intro exI bexI)
paulson@11287
   365
apply (rule_tac [2] tls.Nil
paulson@11287
   366
                    [THEN tls.ClientHello, THEN tls.ServerHello,
paulson@11287
   367
                     THEN tls.Certificate, THEN tls.ClientKeyExch,
paulson@13507
   368
                     THEN tls.CertVerify], possibility, blast+)
paulson@11287
   369
done
paulson@11287
   370
paulson@11287
   371
paulson@13922
   372
text{*Another one, for session resumption (both ServerResume and ClientResume).
paulson@13922
   373
  NO tls.Nil here: we refer to a previous session, not the empty trace.*}
paulson@11287
   374
lemma "[| evs0 \<in> tls;
paulson@11287
   375
          Notes A {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evs0;
paulson@11287
   376
          Notes B {|Number SID, Agent A, Agent B, Nonce M|} \<in> set evs0;
paulson@11287
   377
          \<forall>evs. (@ N. Nonce N \<notin> used evs) \<notin> range PRF;
paulson@11287
   378
          A \<noteq> B |]
paulson@11287
   379
      ==> \<exists>NA PA NB PB X. \<exists>evs \<in> tls.
wenzelm@32960
   380
                X = Hash{|Number SID, Nonce M,
wenzelm@32960
   381
                          Nonce NA, Number PA, Agent A,
wenzelm@32960
   382
                          Nonce NB, Number PB, Agent B|}  &
wenzelm@32960
   383
                Says A B (Crypt (clientK(NA,NB,M)) X) \<in> set evs  &
wenzelm@32960
   384
                Says B A (Crypt (serverK(NA,NB,M)) X) \<in> set evs"
paulson@11287
   385
apply (intro exI bexI)
paulson@11287
   386
apply (rule_tac [2] tls.ClientHello
paulson@11287
   387
                    [THEN tls.ServerHello,
paulson@13507
   388
                     THEN tls.ServerResume, THEN tls.ClientResume], possibility, blast+)
paulson@11287
   389
done
paulson@11287
   390
paulson@11287
   391
paulson@13922
   392
subsection{*Inductive proofs about tls*}
paulson@11287
   393
paulson@11287
   394
paulson@11287
   395
(** Theorems of the form X \<notin> parts (spies evs) imply that NOBODY
paulson@11287
   396
    sends messages containing X! **)
paulson@11287
   397
paulson@13922
   398
text{*Spy never sees a good agent's private key!*}
paulson@11287
   399
lemma Spy_see_priK [simp]:
paulson@13922
   400
     "evs \<in> tls ==> (Key (privateKey b A) \<in> parts (spies evs)) = (A \<in> bad)"
paulson@13922
   401
by (erule tls.induct, force, simp_all, blast)
paulson@11287
   402
paulson@11287
   403
lemma Spy_analz_priK [simp]:
paulson@13922
   404
     "evs \<in> tls ==> (Key (privateKey b A) \<in> analz (spies evs)) = (A \<in> bad)"
paulson@11287
   405
by auto
paulson@11287
   406
paulson@11287
   407
lemma Spy_see_priK_D [dest!]:
paulson@13922
   408
    "[|Key (privateKey b A) \<in> parts (knows Spy evs);  evs \<in> tls|] ==> A \<in> bad"
paulson@11287
   409
by (blast dest: Spy_see_priK)
paulson@11287
   410
paulson@11287
   411
paulson@13922
   412
text{*This lemma says that no false certificates exist.  One might extend the
paulson@11287
   413
  model to include bogus certificates for the agents, but there seems
paulson@11287
   414
  little point in doing so: the loss of their private keys is a worse
paulson@13922
   415
  breach of security.*}
paulson@11287
   416
lemma certificate_valid:
paulson@11287
   417
    "[| certificate B KB \<in> parts (spies evs);  evs \<in> tls |] ==> KB = pubK B"
paulson@11287
   418
apply (erule rev_mp)
paulson@13507
   419
apply (erule tls.induct, force, simp_all, blast) 
paulson@11287
   420
done
paulson@11287
   421
paulson@11287
   422
lemmas CX_KB_is_pubKB = Says_imp_spies [THEN parts.Inj, THEN certificate_valid]
paulson@11287
   423
paulson@11287
   424
paulson@13922
   425
subsubsection{*Properties of items found in Notes*}
paulson@11287
   426
paulson@11287
   427
lemma Notes_Crypt_parts_spies:
paulson@11287
   428
     "[| Notes A {|Agent B, X|} \<in> set evs;  evs \<in> tls |]
paulson@11287
   429
      ==> Crypt (pubK B) X \<in> parts (spies evs)"
paulson@11287
   430
apply (erule rev_mp)
paulson@11287
   431
apply (erule tls.induct, 
paulson@11287
   432
       frule_tac [7] CX_KB_is_pubKB, force, simp_all)
paulson@11287
   433
apply (blast intro: parts_insertI)
paulson@11287
   434
done
paulson@11287
   435
paulson@13922
   436
text{*C may be either A or B*}
paulson@11287
   437
lemma Notes_master_imp_Crypt_PMS:
paulson@11287
   438
     "[| Notes C {|s, Agent A, Agent B, Nonce(PRF(PMS,NA,NB))|} \<in> set evs;
paulson@11287
   439
         evs \<in> tls |]
paulson@11287
   440
      ==> Crypt (pubK B) (Nonce PMS) \<in> parts (spies evs)"
paulson@11287
   441
apply (erule rev_mp)
paulson@11287
   442
apply (erule tls.induct, force, simp_all)
paulson@13922
   443
txt{*Fake*}
paulson@11287
   444
apply (blast intro: parts_insertI)
paulson@13922
   445
txt{*Client, Server Accept*}
paulson@11287
   446
apply (blast dest!: Notes_Crypt_parts_spies)+
paulson@11287
   447
done
paulson@11287
   448
paulson@13922
   449
text{*Compared with the theorem above, both premise and conclusion are stronger*}
paulson@11287
   450
lemma Notes_master_imp_Notes_PMS:
paulson@11287
   451
     "[| Notes A {|s, Agent A, Agent B, Nonce(PRF(PMS,NA,NB))|} \<in> set evs;
paulson@11287
   452
         evs \<in> tls |]
paulson@11287
   453
      ==> Notes A {|Agent B, Nonce PMS|} \<in> set evs"
paulson@11287
   454
apply (erule rev_mp)
paulson@11287
   455
apply (erule tls.induct, force, simp_all)
paulson@13922
   456
txt{*ServerAccepts*}
paulson@11287
   457
apply blast
paulson@11287
   458
done
paulson@11287
   459
paulson@11287
   460
paulson@13922
   461
subsubsection{*Protocol goal: if B receives CertVerify, then A sent it*}
paulson@11287
   462
paulson@13922
   463
text{*B can check A's signature if he has received A's certificate.*}
paulson@11287
   464
lemma TrustCertVerify_lemma:
paulson@11287
   465
     "[| X \<in> parts (spies evs);
paulson@11287
   466
         X = Crypt (priK A) (Hash{|nb, Agent B, pms|});
paulson@11287
   467
         evs \<in> tls;  A \<notin> bad |]
paulson@11287
   468
      ==> Says A B X \<in> set evs"
paulson@11287
   469
apply (erule rev_mp, erule ssubst)
paulson@13507
   470
apply (erule tls.induct, force, simp_all, blast)
paulson@11287
   471
done
paulson@11287
   472
paulson@13922
   473
text{*Final version: B checks X using the distributed KA instead of priK A*}
paulson@11287
   474
lemma TrustCertVerify:
paulson@11287
   475
     "[| X \<in> parts (spies evs);
paulson@11287
   476
         X = Crypt (invKey KA) (Hash{|nb, Agent B, pms|});
paulson@11287
   477
         certificate A KA \<in> parts (spies evs);
paulson@11287
   478
         evs \<in> tls;  A \<notin> bad |]
paulson@11287
   479
      ==> Says A B X \<in> set evs"
paulson@11287
   480
by (blast dest!: certificate_valid intro!: TrustCertVerify_lemma)
paulson@11287
   481
paulson@11287
   482
paulson@13922
   483
text{*If CertVerify is present then A has chosen PMS.*}
paulson@11287
   484
lemma UseCertVerify_lemma:
paulson@11287
   485
     "[| Crypt (priK A) (Hash{|nb, Agent B, Nonce PMS|}) \<in> parts (spies evs);
paulson@11287
   486
         evs \<in> tls;  A \<notin> bad |]
paulson@11287
   487
      ==> Notes A {|Agent B, Nonce PMS|} \<in> set evs"
paulson@11287
   488
apply (erule rev_mp)
paulson@13507
   489
apply (erule tls.induct, force, simp_all, blast)
paulson@11287
   490
done
paulson@11287
   491
paulson@13922
   492
text{*Final version using the distributed KA instead of priK A*}
paulson@11287
   493
lemma UseCertVerify:
paulson@11287
   494
     "[| Crypt (invKey KA) (Hash{|nb, Agent B, Nonce PMS|})
paulson@11287
   495
           \<in> parts (spies evs);
paulson@11287
   496
         certificate A KA \<in> parts (spies evs);
paulson@11287
   497
         evs \<in> tls;  A \<notin> bad |]
paulson@11287
   498
      ==> Notes A {|Agent B, Nonce PMS|} \<in> set evs"
paulson@11287
   499
by (blast dest!: certificate_valid intro!: UseCertVerify_lemma)
paulson@11287
   500
paulson@11287
   501
paulson@11287
   502
lemma no_Notes_A_PRF [simp]:
paulson@11287
   503
     "evs \<in> tls ==> Notes A {|Agent B, Nonce (PRF x)|} \<notin> set evs"
paulson@11287
   504
apply (erule tls.induct, force, simp_all)
paulson@13922
   505
txt{*ClientKeyExch: PMS is assumed to differ from any PRF.*}
paulson@11287
   506
apply blast
paulson@11287
   507
done
paulson@11287
   508
paulson@11287
   509
paulson@11287
   510
lemma MS_imp_PMS [dest!]:
paulson@11287
   511
     "[| Nonce (PRF (PMS,NA,NB)) \<in> parts (spies evs);  evs \<in> tls |]
paulson@11287
   512
      ==> Nonce PMS \<in> parts (spies evs)"
paulson@11287
   513
apply (erule rev_mp)
paulson@11287
   514
apply (erule tls.induct, force, simp_all)
paulson@13922
   515
txt{*Fake*}
paulson@11287
   516
apply (blast intro: parts_insertI)
paulson@13922
   517
txt{*Easy, e.g. by freshness*}
paulson@11287
   518
apply (blast dest: Notes_Crypt_parts_spies)+
paulson@11287
   519
done
paulson@11287
   520
paulson@11287
   521
paulson@11287
   522
paulson@11287
   523
paulson@13922
   524
subsubsection{*Unicity results for PMS, the pre-master-secret*}
paulson@11287
   525
paulson@13922
   526
text{*PMS determines B.*}
paulson@11287
   527
lemma Crypt_unique_PMS:
paulson@11287
   528
     "[| Crypt(pubK B)  (Nonce PMS) \<in> parts (spies evs);
paulson@11287
   529
         Crypt(pubK B') (Nonce PMS) \<in> parts (spies evs);
paulson@11287
   530
         Nonce PMS \<notin> analz (spies evs);
paulson@11287
   531
         evs \<in> tls |]
paulson@11287
   532
      ==> B=B'"
paulson@11287
   533
apply (erule rev_mp, erule rev_mp, erule rev_mp)
paulson@11287
   534
apply (erule tls.induct, analz_mono_contra, force, simp_all (no_asm_simp))
paulson@13922
   535
txt{*Fake, ClientKeyExch*}
paulson@11287
   536
apply blast+
paulson@11287
   537
done
paulson@11287
   538
paulson@11287
   539
paulson@11287
   540
(** It is frustrating that we need two versions of the unicity results.
paulson@11287
   541
    But Notes A {|Agent B, Nonce PMS|} determines both A and B.  Sometimes
paulson@11287
   542
    we have only the weaker assertion Crypt(pubK B) (Nonce PMS), which
paulson@11287
   543
    determines B alone, and only if PMS is secret.
paulson@11287
   544
**)
paulson@11287
   545
paulson@13922
   546
text{*In A's internal Note, PMS determines A and B.*}
paulson@11287
   547
lemma Notes_unique_PMS:
paulson@11287
   548
     "[| Notes A  {|Agent B,  Nonce PMS|} \<in> set evs;
paulson@11287
   549
         Notes A' {|Agent B', Nonce PMS|} \<in> set evs;
paulson@11287
   550
         evs \<in> tls |]
paulson@11287
   551
      ==> A=A' & B=B'"
paulson@11287
   552
apply (erule rev_mp, erule rev_mp)
paulson@11287
   553
apply (erule tls.induct, force, simp_all)
paulson@13922
   554
txt{*ClientKeyExch*}
paulson@11287
   555
apply (blast dest!: Notes_Crypt_parts_spies)
paulson@11287
   556
done
paulson@11287
   557
paulson@11287
   558
paulson@13922
   559
subsection{*Secrecy Theorems*}
paulson@11287
   560
paulson@13956
   561
text{*Key compromise lemma needed to prove @{term analz_image_keys}.
paulson@13922
   562
  No collection of keys can help the spy get new private keys.*}
paulson@11287
   563
lemma analz_image_priK [rule_format]:
paulson@11287
   564
     "evs \<in> tls
paulson@11287
   565
      ==> \<forall>KK. (Key(priK B) \<in> analz (Key`KK Un (spies evs))) =
paulson@11287
   566
          (priK B \<in> KK | B \<in> bad)"
paulson@11287
   567
apply (erule tls.induct)
paulson@11287
   568
apply (simp_all (no_asm_simp)
wenzelm@32960
   569
                del: image_insert
paulson@11287
   570
                add: image_Un [THEN sym]
paulson@11287
   571
                     insert_Key_image Un_assoc [THEN sym])
paulson@13922
   572
txt{*Fake*}
paulson@11287
   573
apply spy_analz
paulson@11287
   574
done
paulson@11287
   575
paulson@11287
   576
paulson@13922
   577
text{*slightly speeds up the big simplification below*}
paulson@11287
   578
lemma range_sessionkeys_not_priK:
paulson@11287
   579
     "KK <= range sessionK ==> priK B \<notin> KK"
paulson@11287
   580
by blast
paulson@11287
   581
paulson@11287
   582
paulson@13922
   583
text{*Lemma for the trivial direction of the if-and-only-if*}
paulson@11287
   584
lemma analz_image_keys_lemma:
paulson@11287
   585
     "(X \<in> analz (G Un H)) --> (X \<in> analz H)  ==>
paulson@11287
   586
      (X \<in> analz (G Un H))  =  (X \<in> analz H)"
paulson@11287
   587
by (blast intro: analz_mono [THEN subsetD])
paulson@11287
   588
paulson@11287
   589
(** Strangely, the following version doesn't work:
paulson@11287
   590
\<forall>Z. (Nonce N \<in> analz (Key`(sessionK`Z) Un (spies evs))) =
paulson@11287
   591
    (Nonce N \<in> analz (spies evs))"
paulson@11287
   592
**)
paulson@11287
   593
paulson@11287
   594
lemma analz_image_keys [rule_format]:
paulson@11287
   595
     "evs \<in> tls ==>
paulson@11287
   596
      \<forall>KK. KK <= range sessionK -->
wenzelm@32960
   597
              (Nonce N \<in> analz (Key`KK Un (spies evs))) =
wenzelm@32960
   598
              (Nonce N \<in> analz (spies evs))"
paulson@11287
   599
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   600
apply (safe del: iffI)
paulson@11287
   601
apply (safe del: impI iffI intro!: analz_image_keys_lemma)
paulson@11287
   602
apply (simp_all (no_asm_simp)               (*faster*)
paulson@11287
   603
                del: image_insert imp_disjL (*reduces blow-up*)
wenzelm@32960
   604
                add: image_Un [THEN sym]  Un_assoc [THEN sym]
wenzelm@32960
   605
                     insert_Key_singleton
wenzelm@32960
   606
                     range_sessionkeys_not_priK analz_image_priK)
paulson@11287
   607
apply (simp_all add: insert_absorb)
paulson@13922
   608
txt{*Fake*}
paulson@11287
   609
apply spy_analz
paulson@11287
   610
done
paulson@11287
   611
paulson@13922
   612
text{*Knowing some session keys is no help in getting new nonces*}
paulson@11287
   613
lemma analz_insert_key [simp]:
paulson@11287
   614
     "evs \<in> tls ==>
wenzelm@11655
   615
      (Nonce N \<in> analz (insert (Key (sessionK z)) (spies evs))) =
paulson@11287
   616
      (Nonce N \<in> analz (spies evs))"
paulson@11287
   617
by (simp del: image_insert
paulson@11287
   618
         add: insert_Key_singleton analz_image_keys)
paulson@11287
   619
paulson@11287
   620
paulson@13922
   621
subsubsection{*Protocol goal: serverK(Na,Nb,M) and clientK(Na,Nb,M) remain secure*}
paulson@11287
   622
paulson@11287
   623
(** Some lemmas about session keys, comprising clientK and serverK **)
paulson@11287
   624
paulson@11287
   625
paulson@13922
   626
text{*Lemma: session keys are never used if PMS is fresh.
paulson@11287
   627
  Nonces don't have to agree, allowing session resumption.
paulson@11287
   628
  Converse doesn't hold; revealing PMS doesn't force the keys to be sent.
paulson@13922
   629
  THEY ARE NOT SUITABLE AS SAFE ELIM RULES.*}
paulson@11287
   630
lemma PMS_lemma:
paulson@11287
   631
     "[| Nonce PMS \<notin> parts (spies evs);
paulson@11287
   632
         K = sessionK((Na, Nb, PRF(PMS,NA,NB)), role);
paulson@11287
   633
         evs \<in> tls |]
paulson@11287
   634
   ==> Key K \<notin> parts (spies evs) & (\<forall>Y. Crypt K Y \<notin> parts (spies evs))"
paulson@11287
   635
apply (erule rev_mp, erule ssubst)
paulson@13922
   636
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB) 
paulson@11287
   637
apply (force, simp_all (no_asm_simp))
paulson@13922
   638
txt{*Fake*}
paulson@11287
   639
apply (blast intro: parts_insertI)
paulson@13922
   640
txt{*SpyKeys*}
paulson@11287
   641
apply blast
paulson@13922
   642
txt{*Many others*}
paulson@11287
   643
apply (force dest!: Notes_Crypt_parts_spies Notes_master_imp_Crypt_PMS)+
paulson@11287
   644
done
paulson@11287
   645
paulson@11287
   646
lemma PMS_sessionK_not_spied:
paulson@11287
   647
     "[| Key (sessionK((Na, Nb, PRF(PMS,NA,NB)), role)) \<in> parts (spies evs);
paulson@11287
   648
         evs \<in> tls |]
paulson@11287
   649
      ==> Nonce PMS \<in> parts (spies evs)"
paulson@11287
   650
by (blast dest: PMS_lemma)
paulson@11287
   651
paulson@11287
   652
lemma PMS_Crypt_sessionK_not_spied:
paulson@11287
   653
     "[| Crypt (sessionK((Na, Nb, PRF(PMS,NA,NB)), role)) Y
paulson@11287
   654
           \<in> parts (spies evs);  evs \<in> tls |]
paulson@11287
   655
      ==> Nonce PMS \<in> parts (spies evs)"
paulson@11287
   656
by (blast dest: PMS_lemma)
paulson@11287
   657
paulson@13922
   658
text{*Write keys are never sent if M (MASTER SECRET) is secure.
paulson@11287
   659
  Converse fails; betraying M doesn't force the keys to be sent!
paulson@11287
   660
  The strong Oops condition can be weakened later by unicity reasoning,
paulson@11287
   661
  with some effort.
paulson@13956
   662
  NO LONGER USED: see @{text clientK_not_spied} and @{text serverK_not_spied}*}
paulson@11287
   663
lemma sessionK_not_spied:
paulson@11287
   664
     "[| \<forall>A. Says A Spy (Key (sessionK((NA,NB,M),role))) \<notin> set evs;
paulson@11287
   665
         Nonce M \<notin> analz (spies evs);  evs \<in> tls |]
paulson@11287
   666
      ==> Key (sessionK((NA,NB,M),role)) \<notin> parts (spies evs)"
paulson@11287
   667
apply (erule rev_mp, erule rev_mp)
paulson@11287
   668
apply (erule tls.induct, analz_mono_contra)
paulson@11287
   669
apply (force, simp_all (no_asm_simp))
paulson@13922
   670
txt{*Fake, SpyKeys*}
paulson@11287
   671
apply blast+
paulson@11287
   672
done
paulson@11287
   673
paulson@11287
   674
paulson@13922
   675
text{*If A sends ClientKeyExch to an honest B, then the PMS will stay secret.*}
paulson@11287
   676
lemma Spy_not_see_PMS:
paulson@11287
   677
     "[| Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   678
         evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   679
      ==> Nonce PMS \<notin> analz (spies evs)"
paulson@11287
   680
apply (erule rev_mp, erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   681
apply (force, simp_all (no_asm_simp))
paulson@13922
   682
txt{*Fake*}
paulson@11287
   683
apply spy_analz
paulson@13922
   684
txt{*SpyKeys*}
paulson@11287
   685
apply force
paulson@11287
   686
apply (simp_all add: insert_absorb) 
paulson@13922
   687
txt{*ClientHello, ServerHello, ClientKeyExch: mostly freshness reasoning*}
paulson@11287
   688
apply (blast dest: Notes_Crypt_parts_spies)
paulson@11287
   689
apply (blast dest: Notes_Crypt_parts_spies)
paulson@11287
   690
apply (blast dest: Notes_Crypt_parts_spies)
paulson@13956
   691
txt{*ClientAccepts and ServerAccepts: because @{term "PMS \<notin> range PRF"}*}
paulson@11287
   692
apply force+
paulson@11287
   693
done
paulson@11287
   694
paulson@11287
   695
paulson@13922
   696
text{*If A sends ClientKeyExch to an honest B, then the MASTER SECRET
paulson@13922
   697
  will stay secret.*}
paulson@11287
   698
lemma Spy_not_see_MS:
paulson@11287
   699
     "[| Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   700
         evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   701
      ==> Nonce (PRF(PMS,NA,NB)) \<notin> analz (spies evs)"
paulson@11287
   702
apply (erule rev_mp, erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   703
apply (force, simp_all (no_asm_simp))
paulson@13922
   704
txt{*Fake*}
paulson@11287
   705
apply spy_analz
paulson@13922
   706
txt{*SpyKeys: by secrecy of the PMS, Spy cannot make the MS*}
paulson@11287
   707
apply (blast dest!: Spy_not_see_PMS)
paulson@11287
   708
apply (simp_all add: insert_absorb)
paulson@13922
   709
txt{*ClientAccepts and ServerAccepts: because PMS was already visible;
paulson@13922
   710
  others, freshness etc.*}
paulson@11287
   711
apply (blast dest: Notes_Crypt_parts_spies Spy_not_see_PMS 
paulson@11287
   712
                   Notes_imp_knows_Spy [THEN analz.Inj])+
paulson@11287
   713
done
paulson@11287
   714
paulson@11287
   715
paulson@11287
   716
paulson@13922
   717
subsubsection{*Weakening the Oops conditions for leakage of clientK*}
paulson@11287
   718
paulson@13922
   719
text{*If A created PMS then nobody else (except the Spy in replays)
paulson@13922
   720
  would send a message using a clientK generated from that PMS.*}
paulson@11287
   721
lemma Says_clientK_unique:
paulson@11287
   722
     "[| Says A' B' (Crypt (clientK(Na,Nb,PRF(PMS,NA,NB))) Y) \<in> set evs;
paulson@11287
   723
         Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   724
         evs \<in> tls;  A' \<noteq> Spy |]
paulson@11287
   725
      ==> A = A'"
paulson@11287
   726
apply (erule rev_mp, erule rev_mp)
paulson@11287
   727
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   728
apply (force, simp_all)
paulson@13922
   729
txt{*ClientKeyExch*}
paulson@11287
   730
apply (blast dest!: PMS_Crypt_sessionK_not_spied)
paulson@13922
   731
txt{*ClientFinished, ClientResume: by unicity of PMS*}
paulson@11287
   732
apply (blast dest!: Notes_master_imp_Notes_PMS 
paulson@11287
   733
             intro: Notes_unique_PMS [THEN conjunct1])+
paulson@11287
   734
done
paulson@11287
   735
paulson@11287
   736
paulson@13922
   737
text{*If A created PMS and has not leaked her clientK to the Spy,
paulson@13922
   738
  then it is completely secure: not even in parts!*}
paulson@11287
   739
lemma clientK_not_spied:
paulson@11287
   740
     "[| Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   741
         Says A Spy (Key (clientK(Na,Nb,PRF(PMS,NA,NB)))) \<notin> set evs;
paulson@11287
   742
         A \<notin> bad;  B \<notin> bad;
paulson@11287
   743
         evs \<in> tls |]
paulson@11287
   744
      ==> Key (clientK(Na,Nb,PRF(PMS,NA,NB))) \<notin> parts (spies evs)"
paulson@11287
   745
apply (erule rev_mp, erule rev_mp)
paulson@11287
   746
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   747
apply (force, simp_all (no_asm_simp))
paulson@13922
   748
txt{*ClientKeyExch*}
paulson@11287
   749
apply blast 
paulson@13922
   750
txt{*SpyKeys*}
paulson@11287
   751
apply (blast dest!: Spy_not_see_MS)
paulson@13922
   752
txt{*ClientKeyExch*}
paulson@11287
   753
apply (blast dest!: PMS_sessionK_not_spied)
paulson@13922
   754
txt{*Oops*}
paulson@11287
   755
apply (blast intro: Says_clientK_unique)
paulson@11287
   756
done
paulson@11287
   757
paulson@11287
   758
paulson@13922
   759
subsubsection{*Weakening the Oops conditions for leakage of serverK*}
paulson@11287
   760
paulson@13922
   761
text{*If A created PMS for B, then nobody other than B or the Spy would
paulson@13922
   762
  send a message using a serverK generated from that PMS.*}
paulson@11287
   763
lemma Says_serverK_unique:
paulson@11287
   764
     "[| Says B' A' (Crypt (serverK(Na,Nb,PRF(PMS,NA,NB))) Y) \<in> set evs;
paulson@11287
   765
         Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   766
         evs \<in> tls;  A \<notin> bad;  B \<notin> bad;  B' \<noteq> Spy |]
paulson@11287
   767
      ==> B = B'"
paulson@11287
   768
apply (erule rev_mp, erule rev_mp)
paulson@11287
   769
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   770
apply (force, simp_all)
paulson@13922
   771
txt{*ClientKeyExch*}
paulson@11287
   772
apply (blast dest!: PMS_Crypt_sessionK_not_spied)
paulson@13922
   773
txt{*ServerResume, ServerFinished: by unicity of PMS*}
paulson@11287
   774
apply (blast dest!: Notes_master_imp_Crypt_PMS 
paulson@11287
   775
             dest: Spy_not_see_PMS Notes_Crypt_parts_spies Crypt_unique_PMS)+
paulson@11287
   776
done
paulson@11287
   777
paulson@11287
   778
paulson@13922
   779
text{*If A created PMS for B, and B has not leaked his serverK to the Spy,
paulson@13922
   780
  then it is completely secure: not even in parts!*}
paulson@11287
   781
lemma serverK_not_spied:
paulson@11287
   782
     "[| Notes A {|Agent B, Nonce PMS|} \<in> set evs;
paulson@11287
   783
         Says B Spy (Key(serverK(Na,Nb,PRF(PMS,NA,NB)))) \<notin> set evs;
paulson@11287
   784
         A \<notin> bad;  B \<notin> bad;  evs \<in> tls |]
paulson@11287
   785
      ==> Key (serverK(Na,Nb,PRF(PMS,NA,NB))) \<notin> parts (spies evs)"
paulson@11287
   786
apply (erule rev_mp, erule rev_mp)
paulson@11287
   787
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   788
apply (force, simp_all (no_asm_simp))
paulson@13922
   789
txt{*Fake*}
paulson@11287
   790
apply blast 
paulson@13922
   791
txt{*SpyKeys*}
paulson@11287
   792
apply (blast dest!: Spy_not_see_MS)
paulson@13922
   793
txt{*ClientKeyExch*}
paulson@11287
   794
apply (blast dest!: PMS_sessionK_not_spied)
paulson@13922
   795
txt{*Oops*}
paulson@11287
   796
apply (blast intro: Says_serverK_unique)
paulson@11287
   797
done
paulson@11287
   798
paulson@11287
   799
paulson@13922
   800
subsubsection{*Protocol goals: if A receives ServerFinished, then B is present
paulson@11287
   801
     and has used the quoted values PA, PB, etc.  Note that it is up to A
paulson@13956
   802
     to compare PA with what she originally sent.*}
paulson@11287
   803
paulson@13922
   804
text{*The mention of her name (A) in X assures A that B knows who she is.*}
paulson@11287
   805
lemma TrustServerFinished [rule_format]:
paulson@11287
   806
     "[| X = Crypt (serverK(Na,Nb,M))
paulson@11287
   807
               (Hash{|Number SID, Nonce M,
paulson@11287
   808
                      Nonce Na, Number PA, Agent A,
paulson@11287
   809
                      Nonce Nb, Number PB, Agent B|});
paulson@11287
   810
         M = PRF(PMS,NA,NB);
paulson@11287
   811
         evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   812
      ==> Says B Spy (Key(serverK(Na,Nb,M))) \<notin> set evs -->
paulson@11287
   813
          Notes A {|Agent B, Nonce PMS|} \<in> set evs -->
paulson@11287
   814
          X \<in> parts (spies evs) --> Says B A X \<in> set evs"
paulson@11287
   815
apply (erule ssubst)+
paulson@11287
   816
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   817
apply (force, simp_all (no_asm_simp))
paulson@13922
   818
txt{*Fake: the Spy doesn't have the critical session key!*}
paulson@11287
   819
apply (blast dest: serverK_not_spied)
paulson@13922
   820
txt{*ClientKeyExch*}
paulson@11287
   821
apply (blast dest!: PMS_Crypt_sessionK_not_spied)
paulson@11287
   822
done
paulson@11287
   823
paulson@13922
   824
text{*This version refers not to ServerFinished but to any message from B.
paulson@11287
   825
  We don't assume B has received CertVerify, and an intruder could
paulson@11287
   826
  have changed A's identity in all other messages, so we can't be sure
paulson@11287
   827
  that B sends his message to A.  If CLIENT KEY EXCHANGE were augmented
paulson@13922
   828
  to bind A's identity with PMS, then we could replace A' by A below.*}
paulson@11287
   829
lemma TrustServerMsg [rule_format]:
paulson@11287
   830
     "[| M = PRF(PMS,NA,NB);  evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   831
      ==> Says B Spy (Key(serverK(Na,Nb,M))) \<notin> set evs -->
paulson@11287
   832
          Notes A {|Agent B, Nonce PMS|} \<in> set evs -->
paulson@11287
   833
          Crypt (serverK(Na,Nb,M)) Y \<in> parts (spies evs)  -->
paulson@11287
   834
          (\<exists>A'. Says B A' (Crypt (serverK(Na,Nb,M)) Y) \<in> set evs)"
paulson@11287
   835
apply (erule ssubst)
paulson@11287
   836
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   837
apply (force, simp_all (no_asm_simp) add: ex_disj_distrib)
paulson@13922
   838
txt{*Fake: the Spy doesn't have the critical session key!*}
paulson@11287
   839
apply (blast dest: serverK_not_spied)
paulson@13922
   840
txt{*ClientKeyExch*}
paulson@11287
   841
apply (clarify, blast dest!: PMS_Crypt_sessionK_not_spied)
paulson@13922
   842
txt{*ServerResume, ServerFinished: by unicity of PMS*}
paulson@11287
   843
apply (blast dest!: Notes_master_imp_Crypt_PMS 
paulson@11287
   844
             dest: Spy_not_see_PMS Notes_Crypt_parts_spies Crypt_unique_PMS)+
paulson@11287
   845
done
paulson@11287
   846
paulson@11287
   847
paulson@13922
   848
subsubsection{*Protocol goal: if B receives any message encrypted with clientK
paulson@13922
   849
      then A has sent it*}
paulson@13922
   850
paulson@13922
   851
text{*ASSUMING that A chose PMS.  Authentication is
paulson@11287
   852
     assumed here; B cannot verify it.  But if the message is
paulson@13922
   853
     ClientFinished, then B can then check the quoted values PA, PB, etc.*}
paulson@11287
   854
paulson@11287
   855
lemma TrustClientMsg [rule_format]:
paulson@11287
   856
     "[| M = PRF(PMS,NA,NB);  evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   857
      ==> Says A Spy (Key(clientK(Na,Nb,M))) \<notin> set evs -->
paulson@11287
   858
          Notes A {|Agent B, Nonce PMS|} \<in> set evs -->
paulson@11287
   859
          Crypt (clientK(Na,Nb,M)) Y \<in> parts (spies evs) -->
paulson@11287
   860
          Says A B (Crypt (clientK(Na,Nb,M)) Y) \<in> set evs"
paulson@11287
   861
apply (erule ssubst)
paulson@11287
   862
apply (erule tls.induct, frule_tac [7] CX_KB_is_pubKB)
paulson@11287
   863
apply (force, simp_all (no_asm_simp))
paulson@13922
   864
txt{*Fake: the Spy doesn't have the critical session key!*}
paulson@11287
   865
apply (blast dest: clientK_not_spied)
paulson@13922
   866
txt{*ClientKeyExch*}
paulson@11287
   867
apply (blast dest!: PMS_Crypt_sessionK_not_spied)
paulson@13922
   868
txt{*ClientFinished, ClientResume: by unicity of PMS*}
paulson@11287
   869
apply (blast dest!: Notes_master_imp_Notes_PMS dest: Notes_unique_PMS)+
paulson@11287
   870
done
paulson@11287
   871
paulson@11287
   872
paulson@13922
   873
subsubsection{*Protocol goal: if B receives ClientFinished, and if B is able to
paulson@11287
   874
     check a CertVerify from A, then A has used the quoted
paulson@13956
   875
     values PA, PB, etc.  Even this one requires A to be uncompromised.*}
paulson@11287
   876
lemma AuthClientFinished:
paulson@11287
   877
     "[| M = PRF(PMS,NA,NB);
paulson@11287
   878
         Says A Spy (Key(clientK(Na,Nb,M))) \<notin> set evs;
paulson@11287
   879
         Says A' B (Crypt (clientK(Na,Nb,M)) Y) \<in> set evs;
paulson@11287
   880
         certificate A KA \<in> parts (spies evs);
paulson@11287
   881
         Says A'' B (Crypt (invKey KA) (Hash{|nb, Agent B, Nonce PMS|}))
paulson@11287
   882
           \<in> set evs;
paulson@11287
   883
         evs \<in> tls;  A \<notin> bad;  B \<notin> bad |]
paulson@11287
   884
      ==> Says A B (Crypt (clientK(Na,Nb,M)) Y) \<in> set evs"
paulson@11287
   885
by (blast intro!: TrustClientMsg UseCertVerify)
paulson@11287
   886
paulson@11287
   887
(*22/9/97: loads in 622s, which is 10 minutes 22 seconds*)
paulson@11287
   888
(*24/9/97: loads in 672s, which is 11 minutes 12 seconds [stronger theorems]*)
paulson@11287
   889
(*29/9/97: loads in 481s, after removing Certificate from ClientKeyExch*)
paulson@11287
   890
(*30/9/97: loads in 476s, after removing unused theorems*)
paulson@11287
   891
(*30/9/97: loads in 448s, after fixing ServerResume*)
paulson@11287
   892
paulson@11287
   893
(*08/9/97: loads in 189s (pike), after much reorganization,
paulson@11287
   894
           back to 621s on albatross?*)
paulson@11287
   895
paulson@11287
   896
(*10/2/99: loads in 139s (pike)
paulson@11287
   897
           down to 433s on albatross*)
paulson@11287
   898
paulson@11287
   899
(*5/5/01: conversion to Isar script
wenzelm@32960
   900
          loads in 137s (perch)
paulson@11287
   901
          the last ML version loaded in 122s on perch, a 600MHz machine:
wenzelm@32960
   902
                twice as fast as pike.  No idea why it's so much slower!
wenzelm@32960
   903
          The Isar script is slower still, perhaps because simp_all simplifies
wenzelm@32960
   904
          the assumptions be default.
paulson@11287
   905
*)
paulson@3474
   906
paulson@3474
   907
end