  A mathematical approach to investigate particle acceleration at shock waves
moving at arbitrary speed in a medium with arbitrary scattering properties was
first discussed in (Vietri 2003) and (Blasi & Vietri 2005}. We use this method
and somewhat extend it in order to include the effect of a large scale magnetic
field in the upstream plasma, with arbitrary orientation with respect to the
direction of motion of the shock. We also use this approach to investigate the
effects of anisotropic scattering on spectra and anisotropies of the
distribution function of the accelerated particles.
