src/HOL/Auth/Yahalom2.thy

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+++ b/src/HOL/Auth/Yahalom2.thy	Fri Oct 18 11:43:14 1996 +0200
@@ -0,0 +1,72 @@
+(*  Title:      HOL/Auth/Yahalom
+    ID:         $Id$
+    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1996  University of Cambridge
+
+Inductive relation "yahalom" for the Yahalom protocol, Variant 2.
+
+This version trades encryption of NB for additional explicitness in YM3.
+
+From page 259 of
+  Burrows, Abadi and Needham.  A Logic of Authentication.
+  Proc. Royal Soc. 426 (1989)
+*)
+
+Yahalom2 = Shared + 
+
+consts  yahalom   :: "agent set => event list set"
+inductive "yahalom lost"
+  intrs 
+         (*Initial trace is empty*)
+    Nil  "[]: yahalom lost"
+
+         (*The spy 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: yahalom lost;  B ~= Spy;  
+             X: synth (analz (sees lost Spy evs)) |]
+          ==> Says Spy B X  # evs : yahalom lost"
+
+         (*Alice initiates a protocol run*)
+    YM1  "[| evs: yahalom lost;  A ~= B |]
+          ==> Says A B {|Agent A, Nonce (newN evs)|} # evs : yahalom lost"
+
+         (*Bob's response to Alice's message.  Bob doesn't know who 
+	   the sender is, hence the A' in the sender field.*)
+    YM2  "[| evs: yahalom lost;  B ~= Server;
+             Says A' B {|Agent A, Nonce NA|} : set_of_list evs |]
+          ==> Says B Server 
+                  {|Agent B, Nonce (newN evs), 
+                    Crypt {|Agent A, Nonce NA|} (shrK B)|}
+                 # evs : yahalom lost"
+
+         (*The Server receives Bob's message.  He responds by sending a
+            new session key to Alice, with a packet for forwarding to Bob.*)
+    YM3  "[| evs: yahalom lost;  A ~= Server;
+             Says B' Server 
+                  {|Agent B, Nonce NB, Crypt {|Agent A, Nonce NA|} (shrK B)|}
+               : set_of_list evs |]
+          ==> Says Server A
+               {|Nonce NB, 
+                 Crypt {|Agent B, Key (newK evs), Nonce NA|} (shrK A),
+                 Crypt {|Agent A, Key (newK evs), Nonce NB, Nonce NB|} (shrK B)|}
+                 # evs : yahalom lost"
+
+         (*Alice receives the Server's (?) message, checks her Nonce, and
+           uses the new session key to send Bob his Nonce.*)
+    YM4  "[| evs: yahalom lost;  A ~= B;  
+             Says S A {|Nonce NB, Crypt {|Agent B, Key K, Nonce NA|} (shrK A),
+                        X|}
+               : set_of_list evs;
+             Says A B {|Agent A, Nonce NA|} : set_of_list evs |]
+          ==> Says A B {|X, Crypt (Nonce NB) K|} # evs : yahalom lost"
+
+         (*This message models possible leaks of session keys.  The Nonce NA
+           identifies the protocol run.  We can't be sure about NB.*)
+    Revl "[| evs: yahalom lost;  A ~= Spy;
+             Says S A {|Nonce NB, Crypt {|Agent B, Key K, Nonce NA|} (shrK A),
+                        X|}
+               : set_of_list evs |]
+          ==> Says A Spy {|Nonce NA, Key K|} # evs : yahalom lost"
+
+end