We propose and study the notion of concurrent ballot authorization for
coercion-resistant, end-to-end verifiable (E2E) internet voting.  A
central part of providing coercion resistance is the ability for an
election authority to filter out fake ballots from legitimate ones in
a way that is both private and universally verifiable.  This ballot
authorization process, however, can potentially come at a heavy
computational cost.  In previous proposals, the bulk of this
computation cannot be performed until the last ballot has been cast.
By contrast, concurrent ballot authorization allows ballots to be
authorized as they are submitted, allowing the tally to be declared
immediately after polls close.  An efficient tally is especially
important in the coercion-resistant internet voting setting, as it is
particularly vulnerable to denial of service attacks caused by floods
of fake ballots.  We present a proof-of-concept voting system, Cobra,
the first coercion-resistant system to offer concurrent ballot
authorization.  Although Cobra offers the fastest tallying relative to
the related work, it has a registration process that we consider to be
too slow to be viable; one that is quadratic in the number of eligible
voters.  We present Cobra as a first-step toward what we hope will
become a standard feature of coercion-resistant internet voting
schemes: concurrent ballot authorization.