author | paulson |
Fri, 05 Sep 1997 12:24:13 +0200 | |
changeset 3659 | eddedfe2f3f8 |
parent 3519 | ab0a9fbed4c0 |
child 3683 | aafe719dff14 |
permissions | -rw-r--r-- |
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(* Title: HOL/Auth/Yahalom2 |
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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 "yahalom" for the Yahalom protocol, Variant 2. |
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This version trades encryption of NB for additional explicitness in YM3. |
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Also in YM3, care is taken to make the two certificates distinct. |
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From page 259 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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Yahalom2 = Shared + |
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consts yahalom :: event list set |
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inductive "yahalom" |
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intrs |
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(*Initial trace is empty*) |
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Nil "[]: yahalom" |
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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: yahalom; B ~= Spy; |
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X: synth (analz (sees Spy evs)) |] |
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==> Says Spy B X # evs : yahalom" |
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(*Alice initiates a protocol run*) |
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YM1 "[| evs1: yahalom; A ~= B; Nonce NA ~: used evs1 |] |
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==> Says A B {|Agent A, Nonce NA|} # evs1 : yahalom" |
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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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YM2 "[| evs2: yahalom; B ~= Server; Nonce NB ~: used evs2; |
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Says A' B {|Agent A, Nonce NA|} : set evs2 |] |
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==> Says B Server |
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{|Agent B, Nonce NB, Crypt (shrK B) {|Agent A, Nonce NA|}|} |
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# evs2 : yahalom" |
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(*The Server receives Bob's message. He responds by sending a |
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new session key to Alice, with a certificate for forwarding to Bob. |
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Fields are reversed in the 2nd certificate to prevent attacks!! *) |
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YM3 "[| evs3: yahalom; A ~= B; A ~= Server; Key KAB ~: used evs3; |
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Says B' Server {|Agent B, Nonce NB, |
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Crypt (shrK B) {|Agent A, Nonce NA|}|} |
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: set evs3 |] |
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==> Says Server A |
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{|Nonce NB, |
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Crypt (shrK A) {|Agent B, Key KAB, Nonce NA|}, |
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Crypt (shrK B) {|Nonce NB, Key KAB, Agent A|}|} |
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# evs3 : yahalom" |
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(*Alice receives the Server's (?) message, checks her Nonce, and |
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uses the new session key to send Bob his Nonce.*) |
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YM4 "[| evs4: yahalom; A ~= Server; |
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Says S A {|Nonce NB, Crypt (shrK A) {|Agent B, Key K, Nonce NA|}, |
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X|} : set evs4; |
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Says A B {|Agent A, Nonce NA|} : set evs4 |] |
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==> Says A B {|X, Crypt K (Nonce NB)|} # evs4 : yahalom" |
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(*This message models possible leaks of session keys. The nonces |
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identify the protocol run. Quoting Server here ensures they are |
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correct. *) |
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Oops "[| evso: yahalom; A ~= Spy; |
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Says Server A {|Nonce NB, |
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Crypt (shrK A) {|Agent B, Key K, Nonce NA|}, |
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X|} : set evso |] |
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==> Says A Spy {|Nonce NA, Nonce NB, Key K|} # evso : yahalom" |
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end |