  The differential cross section for elastic electron proton scattering has
been calculated taking into account the two photon exchange within the
phenomenological description of the electromagnetic electron proton
interactions. The calculation is based on the consistent evaluation of the
matrix elements of the proton current in a diagonal spin basis, which makes it
possible to naturally obtain expressions for the generalized Sachs form
factors. A new method has been proposed to independently measure these form
factors in the elastic $e \vec{p} \to e \vec{p}$ process in the case where the
initial proton at rest is fully polarized along the direction of the motion of
the final proton.
