author | paulson |
Tue, 27 Feb 2001 16:13:23 +0100 | |
changeset 11185 | 1b737b4c2108 |
parent 6333 | b1dec44d0018 |
child 11251 | a6816d47f41d |
permissions | -rw-r--r-- |
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(* Title: HOL/Auth/OtwayRees_Bad |
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ID: $Id$ |
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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Copyright 1996 University of Cambridge |
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Inductive relation "otway" for the Otway-Rees protocol. |
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The FAULTY version omitting encryption of Nonce NB, as suggested on page 247 of |
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Burrows, Abadi and Needham. A Logic of Authentication. |
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Proc. Royal Soc. 426 (1989) |
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*) |
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OtwayRees_Bad = Shared + |
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consts otway :: event list set |
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inductive otway |
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intrs |
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(*Initial trace is empty*) |
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Nil "[] \\<in> otway" |
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(*The spy MAY say anything he CAN say. We do not expect him to |
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invent new nonces here, but he can also use NS1. Common to |
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all similar protocols.*) |
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Fake "[| evsf \\<in> otway; X \\<in> synth (analz (knows Spy evsf)) |] |
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==> Says Spy B X # evsf \\<in> otway" |
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(*A message that has been sent can be received by the |
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intended recipient.*) |
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Reception "[| evsr \\<in> otway; Says A B X \\<in> set evsr |] |
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==> Gets B X # evsr \\<in> otway" |
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(*Alice initiates a protocol run*) |
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OR1 "[| evs1 \\<in> otway; Nonce NA \\<notin> used evs1 |] |
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==> Says A B {|Nonce NA, Agent A, Agent B, |
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Crypt (shrK A) {|Nonce NA, Agent A, Agent B|} |} |
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# evs1 \\<in> otway" |
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(*Bob's response to Alice's message. |
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This variant of the protocol does NOT encrypt NB.*) |
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OR2 "[| evs2 \\<in> otway; Nonce NB \\<notin> used evs2; |
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Gets B {|Nonce NA, Agent A, Agent B, X|} \\<in> set evs2 |] |
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==> Says B Server |
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{|Nonce NA, Agent A, Agent B, X, Nonce NB, |
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Crypt (shrK B) {|Nonce NA, Agent A, Agent B|}|} |
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# evs2 \\<in> otway" |
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(*The Server receives Bob's message and checks that the three NAs |
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match. Then he sends a new session key to Bob with a packet for |
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forwarding to Alice.*) |
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OR3 "[| evs3 \\<in> otway; Key KAB \\<notin> used evs3; |
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Gets Server |
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{|Nonce NA, Agent A, Agent B, |
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Crypt (shrK A) {|Nonce NA, Agent A, Agent B|}, |
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Nonce NB, |
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Crypt (shrK B) {|Nonce NA, Agent A, Agent B|}|} |
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\\<in> set evs3 |] |
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==> Says Server B |
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{|Nonce NA, |
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Crypt (shrK A) {|Nonce NA, Key KAB|}, |
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Crypt (shrK B) {|Nonce NB, Key KAB|}|} |
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# evs3 \\<in> otway" |
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(*Bob receives the Server's (?) message and compares the Nonces with |
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those in the message he previously sent the Server. |
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Need B ~= Server because we allow messages to self.*) |
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OR4 "[| evs4 \\<in> otway; B ~= Server; |
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Says B Server {|Nonce NA, Agent A, Agent B, X', Nonce NB, |
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Crypt (shrK B) {|Nonce NA, Agent A, Agent B|}|} |
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\\<in> set evs4; |
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Gets B {|Nonce NA, X, Crypt (shrK B) {|Nonce NB, Key K|}|} |
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\\<in> set evs4 |] |
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==> Says B A {|Nonce NA, X|} # evs4 \\<in> otway" |
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(*This message models possible leaks of session keys. The nonces |
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identify the protocol run.*) |
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Oops "[| evso \\<in> otway; |
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Says Server B {|Nonce NA, X, Crypt (shrK B) {|Nonce NB, Key K|}|} |
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\\<in> set evso |] |
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==> Notes Spy {|Nonce NA, Nonce NB, Key K|} # evso \\<in> otway" |
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end |