Protocol: BilateralKeyExchange

Types: Agent A,B;
       Number NA,NB;
       Symmetric_key K;
       Function pk,f

Knowledge: A: A,B,pk(A),pk(B),inv(pk(A)),f;
	   B: A,B,pk(A),pk(B),inv(pk(B)),pk,f



Actions:
B->A: B,{NB,B}pk(A)
A->B: {f(NB),NA,A,K}pk(B)
B->A: {|f(NA)|}K

Goals:
A *->* B: K