(* Simpler Yahalom protocol
Version of Burrows, Abadi, Needham, SRC039

Message 1 A -> B: A; Na 
Message 2 B -> S: B; Nb; {A; Na}Kbs 
Message 3 S -> A: Nb; {B; Kab; Na}Kas ; {A; Kab; Nb}Kbs 
Message 4 A -> B: {A; Kab; Nb}Kbs ; {Nb}Kab

*)

pred c/1 elimVar, decompData.

fun encrypt/2.
fun host/1.

query c:secretA[].
query c:secretB[].

not c:Kas[].

reduc

(* attacker *)

c:c[];
c:k -> c:host(k);
c:k & c:m -> c:encrypt(m,k);
c:k & c:encrypt(m,k) -> c:m;

(* A *)

c:(host(Kas[]), Na[]);
c:(nb, encrypt((b, k, Na[]), Kas[]), mb) -> c:(mb, encrypt(nb, k));
c:(nb, encrypt((host(Kas[]), k, Na[]), Kas[]), mb) -> c:encrypt(secretA[], k);

(* B *)

c:(a, na) -> c:(host(Kas[]), Nb[a, na], encrypt((a, na), Kas[]));
c:(encrypt((host(Kas[]), k, Nb[host(Kas[]), na]), Kas[]), encrypt(Nb[host(Kas[]), na], k)) -> c:encrypt(secretB[], k);

(* S *)

c:(host(kbs), nb, encrypt((host(kas), na), kbs)) -> c:(nb, encrypt((host(kbs), k[kas, kbs, na, nb], na), kas), encrypt((host(kas),  k[kas, kbs, na, nb], nb), kbs)).

(* EXPECTPV
RESULT goal unreachable: c:secretB[]
RESULT goal unreachable: c:secretA[]
0.008s (user 0.008s + system 0.000s), max rss 8568K
END *)
