  Active galactic nuclei (AGN) can launch and sustain powerful winds featuring
mildly relativistic velocity and wide opening angle. Such winds, known as
ultra-fast outflows (UFOs), can develop a bubble structure characterized by a
forward shock expanding in the host galaxy and a wind termination shock
separating the fast cool wind from the hot shocked wind. In this work we
explore whether diffusive shock acceleration can take place efficiently at the
wind termination shock of UFOs. We calculate the spectrum of accelerated
particles and find that protons can be energized up to the EeV range promoting
UFOs to promising candidates for accelerating ultra-high energy cosmic rays
(UHECRs). We also compute the associated gamma-ray and neutrino fluxes and
compare them with available data in the literature. We observe that high-energy
(HE) neutrinos are efficiently produced up to hundreds of PeV while the
associated gamma rays could be efficiently absorbed beyond a few tens of GeV by
the optical-ultraviolet AGN photon field. By assuming a typical source density
of non-jetted AGN we expect that UFOs could play a dominant role as diffuse
sources of UHECRs and HE neutrinos. We finally apply our model to the recently
observed NGC1068 and we find out that under specific parametric conditions an
obscured UFO could provide a sizeable contribution to the observed gamma-ray
flux while only contributing up to ~10 per cent to the associated neutrino
flux.
