usertype Sessionkey;
usertype Macseed;
const m: Function;
secret unm: Function;
const f: Function;

inversekeys (m, unm);

/*
 * Boyd key agreement
 *
 * Boyd & Mathuria: Protocols for authentication and key establishment
 * (2003) p. 101
 *
 * Note that MAC_ks(x) has been interpreted as MAC(x,ks); this
 * assumption causes some possible false attacks.
 */

protocol boyd(I,R,S)
{
	role I
	{
		const ni: Nonce;
		var nr: Nonce;
		var ks: Macseed;

		send_1 (I,S, I,R, ni );
		read_3 (R,I, { I,R, ks }k(I,S), m(ni, m(ks,ni,nr)), nr );
		send_4 (I,R, m(nr, m(ks,ni,nr)) );

		claim_6 (I, Secret, m(ks,ni,nr) );
		claim_7 (I, Niagree);
		claim_8 (I, Nisynch);
	}	
	
	role R
	{
		var ni: Nonce;
		const nr: Nonce;
		var ks: Macseed;

		read_2 (S,R, { I,R, ks }k(I,S), { I,R, ks }k(R,S), ni );
		send_3 (R,I, { I,R, ks }k(I,S), m(ni, m(ks,ni,nr)), nr );
		read_4 (I,R, m(nr, m(ks,ni,nr)) );

		claim_10 (R, Secret, m(ks,ni,nr));
		claim_11 (R, Niagree);
		claim_12 (R, Nisynch);
	}

	role S
	{
		var ni,nr: Nonce;
		const ks: Macseed;

		read_1 (I,S, I,R, ni );
		send_2 (S,R, { I,R, ks }k(I,S), { I,R, ks }k(R,S), ni );
	}
}