src/HOL/Auth/OtwayRees_Bad.thy

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Auth/OtwayRees_Bad.thy	Mon Sep 23 17:41:57 1996 +0200
@@ -0,0 +1,79 @@
+(*  Title:      HOL/Auth/OtwayRees_Bad
+    ID:         $Id$
+    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1996  University of Cambridge
+
+Inductive relation "otway" for the Otway-Rees protocol.
+
+The FAULTY version omitting encryption of Nonce NB, as suggested on page 247 of
+  Burrows, Abadi and Needham.  A Logic of Authentication.
+  Proc. Royal Soc. 426 (1989)
+*)
+
+OtwayRees_Bad = Shared + 
+
+consts  otway   :: "event list set"
+inductive otway
+  intrs 
+         (*Initial trace is empty*)
+    Nil  "[]: otway"
+
+         (*The enemy MAY say anything he CAN say.  We do not expect him to
+           invent new nonces here, but he can also use NS1.  Common to
+           all similar protocols.*)
+    Fake "[| evs: otway;  B ~= Enemy;  X: synth (analz (sees Enemy evs)) |]
+          ==> Says Enemy B X  # evs : otway"
+
+         (*Alice initiates a protocol run*)
+    OR1  "[| evs: otway;  A ~= B;  B ~= Server |]
+          ==> Says A B {|Nonce (newN evs), Agent A, Agent B, 
+                         Crypt {|Nonce (newN evs), Agent A, Agent B|} 
+                               (shrK A) |} 
+                 # evs : otway"
+
+         (*Bob's response to Alice's message.  Bob doesn't know who 
+	   the sender is, hence the A' in the sender field.
+           We modify the published protocol by NOT encrypting NB.*)
+    OR2  "[| evs: otway;  B ~= Server;
+             Says A' B {|Nonce NA, Agent A, Agent B, X|} : set_of_list evs |]
+          ==> Says B Server 
+                  {|Nonce NA, Agent A, Agent B, X, Nonce (newN evs), 
+                    Crypt {|Nonce NA, Agent A, Agent B|} (shrK B)|}
+                 # evs : otway"
+
+         (*The Server receives Bob's message and checks that the three NAs
+           match.  Then he sends a new session key to Bob with a packet for
+           forwarding to Alice.*)
+    OR3  "[| evs: otway;  B ~= Server;
+             Says B' Server 
+                  {|Nonce NA, Agent A, Agent B, 
+                    Crypt {|Nonce NA, Agent A, Agent B|} (shrK A), 
+                    Nonce NB, 
+                    Crypt {|Nonce NA, Agent A, Agent B|} (shrK B)|}
+               : set_of_list evs |]
+          ==> Says Server B 
+                  {|Nonce NA, 
+                    Crypt {|Nonce NA, Key (newK evs)|} (shrK A),
+                    Crypt {|Nonce NB, Key (newK evs)|} (shrK B)|}
+                 # evs : otway"
+
+         (*Bob receives the Server's (?) message and compares the Nonces with
+	   those in the message he previously sent the Server.*)
+    OR4  "[| evs: otway;  A ~= B;  B ~= Server;
+             Says S B {|Nonce NA, X, Crypt {|Nonce NB, Key K|} (shrK B)|}
+               : set_of_list evs;
+             Says B Server {|Nonce NA, Agent A, Agent B, X', Nonce NB, X''|}
+               : set_of_list evs |]
+          ==> Says B A {|Nonce NA, X|} # evs : otway"
+
+         (*This message models possible leaks of session keys.  Alice's Nonce
+           identifies the protocol run.*)
+    Reveal "[| evs: otway;  A ~= Enemy;
+               Says B' A {|Nonce NA, Crypt {|Nonce NA, Key K|} (shrK A)|}
+                 : set_of_list evs;
+               Says A  B {|Nonce NA, Agent A, Agent B, 
+                           Crypt {|Nonce NA, Agent A, Agent B|} (shrK A)|}
+                 : set_of_list evs |]
+            ==> Says A Enemy {|Nonce NA, Key K|} # evs : otway"
+
+end