(* Title: HOL/Auth/OtwayRees
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1996 University of Cambridge
Inductive relation "otway" for the Otway-Rees protocol.
Simplified version with minimal encryption but explicit messages
From page 11 of
Abadi and Needham. Prudent Engineering Practice for Cryptographic Protocols.
IEEE Trans. SE 22 (1), 1996
*)
OtwayRees_AN = Shared +
consts otway :: "agent set => event list set"
inductive "otway lost"
intrs
(*Initial trace is empty*)
Nil "[]: otway 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: otway lost; B ~= Spy;
X: synth (analz (sees lost Spy evs)) |]
==> Says Spy B X # evs : otway lost"
(*Alice initiates a protocol run*)
OR1 "[| evs: otway lost; A ~= B; B ~= Server |]
==> Says A B {|Agent A, Agent B, Nonce (newN evs)|}
# evs : otway lost"
(*Bob's response to Alice's message. Bob doesn't know who
the sender is, hence the A' in the sender field.*)
OR2 "[| evs: otway lost; B ~= Server;
Says A' B {|Agent A, Agent B, Nonce NA|} : set_of_list evs |]
==> Says B Server {|Agent A, Agent B, Nonce NA, Nonce (newN evs)|}
# evs : otway lost"
(*The Server receives Bob's message. Then he sends a new
session key to Bob with a packet for forwarding to Alice.*)
OR3 "[| evs: otway lost; B ~= Server; A ~= B;
Says B' Server {|Agent A, Agent B, Nonce NA, Nonce NB|}
: set_of_list evs |]
==> Says Server B
{|Crypt {|Nonce NA, Agent A, Agent B, Key(newK evs)|} (shrK A),
Crypt {|Nonce NB, Agent A, Agent B, Key(newK evs)|} (shrK B)|}
# evs : otway lost"
(*Bob receives the Server's (?) message and compares the Nonces with
those in the message he previously sent the Server.*)
OR4 "[| evs: otway lost; A ~= B; B ~= Server;
Says S B {|X,
Crypt {|Nonce NB, Agent A, Agent B, Key K|} (shrK B)|}
: set_of_list evs;
Says B Server {|Agent A, Agent B, Nonce NA, Nonce NB|}
: set_of_list evs |]
==> Says B A X # evs : otway lost"
(*This message models possible leaks of session keys. Alice's Nonce
identifies the protocol run.*)
Revl "[| evs: otway lost; A ~= Spy;
Says B' A (Crypt {|Nonce NA, Agent A, Agent B, Key K|} (shrK A))
: set_of_list evs;
Says A B {|Agent A, Agent B, Nonce NA|} : set_of_list evs |]
==> Says A Spy {|Nonce NA, Key K|} # evs : otway lost"
end