kerberos-rddm.spdl

/*
 * Scyther description of Kerberos as in RDDM'07
 *
 */

usertype Sessionkey;
usertype Text;
secret ktk: Function;
secret kck: Function;
secret kst: Function;

protocol @swapkey-ktk(I,R)
{
    # Protocol added to work around the symmetry problems where k(I,R) != k(R,I)
    role I
    {
        var T:Ticket;


        recv_!X1(R,I,{T}ktk(I,R));
        send_!X2(I,R,{T}ktk(R,I));
    }
    role R
    {
    }
}
protocol @swapkey-kck(I,R)
{
    # Protocol added to work around the symmetry problems where k(I,R) != k(R,I)
    role I
    {
        var T:Ticket;


        recv_!X1(R,I,{T}kck(I,R));
        send_!X2(I,R,{T}kck(R,I));
    }
    role R
    {
    }
}
protocol @swapkey-kst(I,R)
{
    # Protocol added to work around the symmetry problems where k(I,R) != k(R,I)
    role I
    {
        var T:Ticket;


        recv_!X1(R,I,{T}kst(I,R));
        send_!X2(I,R,{T}kst(R,I));
    }
    role R
    {
    }
}

protocol kerberos(C,K,T,S) {

	role C {
		fresh n1: Nonce;
		fresh n2: Nonce;
		var tgt: Ticket;
		var st: Ticket;
		var AKey: Sessionkey;
		var SKey: Sessionkey;
		fresh t: Text;

		send_1(C,K, C,T,n1);
		recv_2(K,C, tgt, { AKey,n1,T }kck(C,K) );

		// Stage boundary
		
		send_3(C,T, tgt, { C }AKey,C,S,n2 );
		recv_4(T,C, C, st, { SKey, n2, S }AKey );
		
		// Stage boundary
		
		send_5(C,S, st, { C,t }SKey );
		recv_6(S,C, { t }SKey );

		// Theorem 5 (a)
                // If C,K are honest
                claim(C,Reachable);
		// Theorem 6 (a)
		// If C,K,T are all honest
		claim(C,Secret,AKey);
		// Theorem 7 (a)
		// If C,K,S are all honest
		claim(C, Reachable);
		// Theorem 8
		// If C,K,S are all honest
                claim(C, Secret, SKey);
	}
	role K {
		var n1: Nonce;
		fresh AKey: Sessionkey;

		recv_1(C,K, C,T,n1);
		send_2(K,C, { AKey, C }ktk(T,K), { AKey,n1,T }kck(C,K) );
		// Theorem 6 (a)
		// If C,K,T are all honest
		claim_K1(K,Secret,AKey);
	}

	role T {
		var AKey: Sessionkey;
		var n2: Nonce;
		fresh SKey: Sessionkey;

		recv_3(C,T, { AKey, C }ktk(T,K), { C }AKey,C,S,n2 );
		send_4(T,C, C,{ SKey, C }kst(S,T), { SKey, n2, S }AKey );

		// Theorem 5 (a)
                // If C,K are honest
                claim(T,Reachable);
		// Theorem 6 (a)
		// If C,K,T are all honest
		claim(T,Secret,AKey);

		// My own
		claim(T,Secret,SKey);
	}
	role S {
		var t: Text;
		var SKey: Sessionkey;

		recv_5(C,S, { SKey, C }kst(S,T), { C,t }SKey );
		send_6(S,C, { t }SKey );
		// Theorem 7 (b)
		// If C,K,S,T are honest
		claim(S, Reachable);

		// My own
		claim(S, Secret, t);
		claim(S, Secret, SKey);
	}
}

const Alice,Bob,Charlie,Eve: Agent;

// C untrusted

// K untrusted

// T untrusted

// S untrusted