  Respecting that any consistent quantum field theory in curved space-time must
include black hole radiation, in this paper, we examine the Krein-Gupta-Bleuler
(KGB) formalism as an inevitable quantization scheme in order to follow the
guideline of the covariance of minimally coupled massless scalar field and
linear gravity on de Sitter (dS) background in the sense of
Wightman-G\"{a}rding approach, by investigating thermodynamical aspects of
black holes. The formalism is interestingly free of pathological large distance
behavior. In this construction, also, no infinite term appears in the
calculation of expectation values of the energy-momentum tensor (we have an
automatic and covariant renormalization) which results in the vacuum energy of
the free field vanishes. However, the existence of an effective potential
barrier, intrinsically created by black holes gravitational field, gives a
Casimir-type contribution to the vacuum expectation value of the
energy-momentum tensor. On this basis, by evaluating the Casimir
energy-momentum tensor for a conformally coupled massless scalar field in the
vicinity of a non-rotating black hole event horizon through the KGB
quantization, in this work, we explicitly prove that the hole produces
black-body radiation which its temperature exactly coincides with the result
obtained by Hawking for black hole radiation.
