EleCa: a Monte Carlo code for the propagation of extragalactic photons
  at ultra-high energy
  Ultra high energy photons play an important role as an independent probe of
the photo-pion production mechanism by UHE cosmic rays. Their observation, or
non-observation, may constrain astrophysical scenarios for the origin of UHECRs
and help to understand the nature of the flux suppression observed by several
experiments at energies above 10$^{19.5}$ eV. Whereas the interaction length of
UHE photons above 10$^{17}$ eV is only of a few hundred kpc up to tenths of
Mpc, photons can interact with the extragalactic background radiation leading
to the development of electromagnetic cascades which affect the fluxes of
photons observed at Earth. The interpretation of the current experimental
results rely on the simulations of the UHE photon propagation. In this
contribution, we present the novel Monte Carlo code "EleCa" to simulate the
\emph{Ele}ctromagnetic \emph{Ca}scading initiated by high-energy photons and
electrons. The distance within which we expect to observe UHE photons is
discussed and the flux of GZK photons at Earth is investigated in several
astrophysical scenarios.
