  SmB$_6$ has been predicted to be a Kondo Topological Insulator with
topologically protected conducting surface states. We have studied
quantitatively the electrical transport through surface states in high quality
single crystals of SmB$_6$. We observe a large non-local surface signal at
temperatures lower than the bulk Kondo gap scale. Measurements and finite
element simulations allow us to distinguish unambiguously between the
contributions from different transport channels. In contrast to general
expectations, the electrical transport properties of the surface channels was
found to be insensitive to high magnetic fields. Local and non-local
magnetoresistance measurements allowed us to identify definite signatures of
helical spin states and strong inter-band scattering at the surface.
