# Paulson's strengthened version of Yahalom
#
# Modelled after the description in the SPORE library
# http://www.lsv.ens-cachan.fr/spore/yahalomPaulson.html
#
#

const Fresh: Function;
const Compromised: Function;

usertype SessionKey;

protocol yahalom-Paulson(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, Nr, {R,Kir,Ni}k(I,S), T );
        send_4(I,R, T, {Nr}Kir );

        claim_I1(I, Secret,Kir);
        claim_I2(I, Nisynch);
        claim_I3(I, Empty, (Fresh,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, Nr, {I,Ni}k(R,S) );
        read_4(I,R, {I,R, Kir, Nr}k(R,S) , {Nr}Kir );

        claim_R1(R, Secret,Kir);
        claim_R2(R, Nisynch);
        claim_R3(R, Empty, (Fresh,Kir));
    }

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

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