author | paulson |
Mon, 14 Jul 1997 12:47:21 +0200 | |
changeset 3519 | ab0a9fbed4c0 |
parent 3465 | e85c24717cad |
child 3659 | eddedfe2f3f8 |
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 "[]: 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 "[| evs: otway; B ~= Spy; X: synth (analz (sees Spy evs)) |] |
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==> Says Spy B X # evs : otway" |
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(*Alice initiates a protocol run*) |
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OR1 "[| evs: otway; A ~= B; B ~= Server; Nonce NA ~: used evs |] |
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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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# evs : otway" |
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(*Bob's response to Alice's message. Bob doesn't know who |
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the sender is, hence the A' in the sender field. |
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We modify the published protocol by NOT encrypting NB.*) |
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OR2 "[| evs: otway; B ~= Server; Nonce NB ~: used evs; |
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Says A' B {|Nonce NA, Agent A, Agent B, X|} : set evs |] |
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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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# evs : 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 "[| evs: otway; B ~= Server; Key KAB ~: used evs; |
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Says B' 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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: set evs |] |
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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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# evs : 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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OR4 "[| evs: otway; A ~= B; |
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Says B Server {|Nonce NA, Agent A, Agent B, X', Nonce NB, X''|} |
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: set evs; |
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Says S' B {|Nonce NA, X, Crypt (shrK B) {|Nonce NB, Key K|}|} |
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: set evs |] |
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==> Says B A {|Nonce NA, X|} # evs : 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 "[| evs: otway; B ~= Spy; |
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Says Server B {|Nonce NA, X, Crypt (shrK B) {|Nonce NB, Key K|}|} |
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: set evs |] |
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==> Says B Spy {|Nonce NA, Nonce NB, Key K|} # evs : otway" |
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end |