  It was recently argued by Almheiri et al that black hole complementarity
strains the basic rules of quantum information theory, such as monogamy of
entanglement. Motivated by this argument, we develop a practical framework for
describing black hole evaporation via unitary time evolution, based on a
holographic perspective in which all black hole degrees of freedom live on the
stretched horizon. We model the horizon as a unitary quantum system with finite
entropy, and do not postulate that the horizon geometry is smooth. We then show
that, with mild assumptions, one can reconstruct local effective field theory
observables that probe the black hole interior, and relative to which the state
near the horizon looks like a local Minkowski vacuum. The reconstruction makes
use of the formalism of quantum error correcting codes, and works for black
hole states whose entanglement entropy does not yet saturate the
Bekenstein-Hawking bound. Our general framework clarifies the black hole final
state proposal, and allows a quantitative study of the transition into the
"firewall" regime of maximally mixed black hole states.
