# Andrew Secure RPC
#
# Modelled after the description in the SPORE library
# http://www.lsv.ens-cachan.fr/spore/andrew.html
#
# Note:
# The shared key between I and R is modelled as k(I,R) currently
# there is no way to express that this key is equal to k(R,I)
# So it is possile that certain attacks that use this property are not found
#

usertype SessionKey;
const succ: Function;
const Fresh: Function;

protocol andrew(I,R)
{
    role I
    {
        fresh ni: Nonce;
        var nr,nr2: Nonce;
        var kir: SessionKey;

        send_1(I,R, I,{ni}k(I,R) );
        recv_2(R,I, {succ(ni),nr}k(I,R) );
        send_3(I,R, {succ(nr)}k(I,R) );
        recv_4(R,I, {kir,nr2}k(I,R) );
        claim_I1(I,Secret,kir);
        claim_I2(I,Nisynch);
        claim_I3(I,Niagree);
        claim_I4(I,Empty,(Fresh,kir));
    }    
    
    role R
    {
        var ni: Nonce;
        fresh nr,nr2: Nonce;
        fresh kir: SessionKey;

        recv_1(I,R, I,{ni}k(I,R) );
        send_2(R,I, {succ(ni),nr}k(I,R) );
        recv_3(I,R, {succ(nr)}k(I,R) );
        send_4(R,I, {kir,nr2}k(I,R) );
        claim_R1(R,Secret,kir);
        claim_R2(R,Nisynch);
        claim_R3(R,Niagree);
        claim_R4(R,Empty,(Fresh,kir));
    }
}