\\ Algo p. 12  :  Section 1.3.5
Computing public keys: isogen
\\implantation de la fonction isogen_\ell
isogen_ell(E0, s_Pl, s_Ql, s_skl, s_Pm, s_Qm, s_Rm, e_l, l)= 
{ 
        my(Ecurr, P_m, Q_m, R_m, s_Sl, i, s_Pint, iso);
        
        Ecurr = E0;

	P_m = s_Pm;
        Q_m = s_Qm;
        R_m = s_Rm;
        
        s_Sl = ellmul(E0, s_Ql, s_skl);
        s_Sl = elladd(E0, s_Pl, s_Sl); 
        
        for (i = 0, e_l - 1,
                s_I     = ellmul(Ecurr, s_Sl, l ^ (e_l - i - 1));
                iso     = ellisogeny(Ecurr, s_I);
                Ecurr   = ellinit(iso[1]);
                s_Sl    = ellisogenyapply(iso[2], s_Sl);
                P_m     = ellisogenyapply(iso[2], P_m);
                Q_m     = ellisogenyapply(iso[2], Q_m);
                R_m     = ellisogenyapply(iso[2], R_m);
        );	
        [P_m, Q_m, R_m, Ecurr]
}
isoex_ell(Ecurr0, s_skl, Pm, Qm, Rm, s_el, l) = 
{
        my(Ecurr, s_Pint, s_S,u);
                
        \\ Calcul de la courbe ou sont les points
        \\Ecurr = curve_from_public_key(u, x_Pm, x_Qm, x_Rm);
        Ecurr = Ecurr0;
        
        \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
        \\ La fonction précedente ne marche pas :
        \\ Les points ne sont pas sur la courbe
        \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
        s_Pm=Pm;
        s_Qm=Qm;

        \\ Point S
        s_S = ellmul(Ecurr, s_Qm, s_skl);
        s_S = elladd(Ecurr, s_Pm, s_S); 

        for (i = 0, s_el - 1,
        s_Pint  = ellmul(Ecurr, s_S, l ^ (s_el - i - 1));
        u       = ellisogeny(Ecurr, s_Pint);
        Ecurr   = ellinit(u[1]);
        s_S     =ellisogenyapply(u[2],s_S);
        );
        Ecurr.j
}