# Yahalom
#
# Modelled after the description in the SPORE library
# http://www.lsv.ens-cachan.fr/spore/yahalom.html
#
#

usertype SessionKey;

protocol yahalom(I,R,S)
{
    role I
    {
        fresh Ni: Nonce;
        var Nr: Nonce;
        var T: Ticket;
        var Kir: SessionKey;

        send_1(I,R, I,Ni);
        read_3(S,I, {R,Kir,Ni,Nr}k(I,S), T );
        send_4(I,R, T, {Nr}Kir );

        claim_I1(I, Secret,Kir);
    }

    role R
    {
        fresh Nr: Nonce;
        var Ni: Nonce;
        var T: Ticket;
        var Kir: SessionKey;

        read_1(I,R, I,Ni);
        send_2(R,S, R, {I,Ni,Nr}k(R,S) );
        read_4(I,R, {I,Kir}k(R,S) , {Nr}Kir );

        claim_R1(R, Secret,Kir);
    }

    role S
    {
        fresh Kir: SessionKey;
        var Ni,Nr: Nonce;

        read_2(R,S, R, {I,Ni,Nr}k(R,S) );
        send_3(S,I, {R,Kir,Ni,Nr}k(I,S), {I,Kir}k(R,S) );

        claim(S, Secret, Ni);
        claim(S, Secret, Nr);
    }
}