  We show how single system steering can be exhibited by classical light, a
feature originating from superposition in classical optics that also enables
entanglement and Bell-violation by classical light beams. Single system
steering is the temporal analogue of Einstein-Podolsky-Rosen (EPR) steering in
the quantum domain, enabling control of the state of a remote system, and can
hence be connected to the security of secret key generation between two remote
parties. We derive the steering criterion for a single mode coherent state when
displaced parity measurements are performed at two different times. The
security bound of the Bennett-Brassard 1984 (BB84) protocol under the gaussian
cloning attack is calculated to yield an, in principle, ideal and quantum-like
key rate using a fine-grained uncertainty relation corresponding to the
classical phase space.
