cat rsa.f
/* rsa.f May 3, 1987 */
rsa(m,e,n) /* Raises m to the e th power modulo n.  Leaves result in m. */
char *m, *e, *n ;
{       char *j, *z, *l  ;
        j = q + 180 ;
        z = q + 195 ;
        l = q + 210 ;
        copy(e,j) ;
        copy(one,z) ;
        copy(m,l) ;
        while(strcmp(xero,j) < 0 )
        {       if(halve(j) == 1) multiply(z,l,n) ;
                multiply(l,l,n) ;
        }
        copy(z,m) ;
}

$