  This paper formulates time-dependent, force-free, degenerate electrodynamics
as a hyperbolic system of conservation laws. It is shown that this system has
four characteristic modes, a pair of fast waves propagating with the speed of
light and a pair of Alfven waves. All these modes are linearly degenerate. The
results of this analytic study can be used in developing upwind numerical
schemes for the electrodynamics of black holes and pulsar magnetospheres. As an
example, this paper describes a simple one-dimensional numerical scheme based
on linear and exact Riemann solvers.
