(* Symmetric key encryption *)

type key.
fun senc(bitstring, key): bitstring.
reduc forall m: bitstring, k: key; sdec(senc(m,k),k) = m.

free c:channel.

free s:bitstring [private].
query attacker(s).

process 
	new k:key;
	out(c, senc(senc(s,k),k));
	in(c, x:bitstring);
	out(c, sdec(x,k)) 
