(* Title: HOL/Auth/NS_Public_Bad
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1996 University of Cambridge
Inductive relation "ns_public" for the Needham-Schroeder Public-Key protocol.
Flawed version, vulnerable to Lowe's attack.
From page 260 of
Burrows, Abadi and Needham. A Logic of Authentication.
Proc. Royal Soc. 426 (1989)
*)
NS_Public_Bad = Public +
consts lost :: agent set (*No need for it to be a variable*)
ns_public :: event list set
inductive ns_public
intrs
(*Initial trace is empty*)
Nil "[]: ns_public"
(*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: ns_public; B ~= Spy;
X: synth (analz (sees lost Spy evs)) |]
==> Says Spy B X # evs : ns_public"
(*Alice initiates a protocol run, sending a nonce to Bob*)
NS1 "[| evs: ns_public; A ~= B; Nonce NA ~: used evs |]
==> Says A B (Crypt (pubK B) {|Nonce NA, Agent A|})
# evs : ns_public"
(*Bob responds to Alice's message with a further nonce*)
NS2 "[| evs: ns_public; A ~= B; Nonce NB ~: used evs;
Says A' B (Crypt (pubK B) {|Nonce NA, Agent A|}) : set evs |]
==> Says B A (Crypt (pubK A) {|Nonce NA, Nonce NB|})
# evs : ns_public"
(*Alice proves her existence by sending NB back to Bob.*)
NS3 "[| evs: ns_public; A ~= B;
Says A B (Crypt (pubK B) {|Nonce NA, Agent A|}) : set evs;
Says B' A (Crypt (pubK A) {|Nonce NA, Nonce NB|}) : set evs |]
==> Says A B (Crypt (pubK B) (Nonce NB)) # evs : ns_public"
(**Oops message??**)
rules
(*Spy has access to his own key for spoof messages*)
Spy_in_lost "Spy: lost"
end