(* 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.
From page 257 of
Burrows, Abadi and Needham. A Logic of Authentication.
Proc. Royal Soc. 426 (1989)
*)
Yahalom = 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,
Crypt {|Agent A, Nonce NA, Nonce (newN evs)|} (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, Crypt {|Agent A, Nonce NA, Nonce NB|} (shrK B)|}
: set_of_list evs |]
==> Says Server A
{|Crypt {|Agent B, Key (newK evs),
Nonce NA, Nonce NB|} (shrK A),
Crypt {|Agent A, Key (newK evs)|} (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 {|Crypt {|Agent B, Key K, Nonce NA, Nonce NB|} (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 Nonces
identify the protocol run.*)
Revl "[| evs: yahalom lost; A ~= Spy;
Says S A {|Crypt {|Agent B, Key K, Nonce NA, Nonce NB|} (shrK A),
X|}
: set_of_list evs |]
==> Says A Spy {|Nonce NA, Nonce NB, Key K|} # evs : yahalom lost"
end