  We describe a collection of techniques whereby audiovisual or other
recordings of significant events can be made in a way that hinders
falsification, pre-dating, or post-dating by interested parties, even by the
makers and operators of the recording equipment. A central feature of these
techniques is the interplay between private information, which by its nature is
untrustworthy and susceptible to suppression or manipulation by interested
parties, and public information, which is too widely known to be manipulated by
anyone. While authenticated recordings may be infeasible to falsify, they can
be abused in other ways, such as being used for blackmail or harassment; but
susceptibility to these abuses can be reduced by encryption and secret sharing.
