  A recent trend in multi-party computation is to achieve cryptographic
fairness via monetary penalties, i.e. each honest player either obtains the
output or receives a compensation in the form of a cryptocurrency. We pioneer
another type of fairness, financial fairness, that is closer to the real-world
valuation of financial transactions. Intuitively, a penalty protocol is
financially fair if the net present cost of participation (the total value of
cash inflows less cash outflows, weighted by the relative discount rate) is the
same for all honest participants, even when some parties cheat.
  We formally define the notion, show several impossibility results based on
game theory, and analyze the practical effects of (lack of) financial fairness
if one was to run the protocols for real on Bitcoin using Bloomberg's dark pool
trading.
  For example, we show that the ladder protocol (CRYPTO'14), and its variants
(CCS'15 and CCS'16), fail to achieve financial fairness both in theory and in
practice, while the penalty protocols of Kumaresan and Bentov (CCS'14) and
Baum, David and Dowsley (FC'20) are financially fair.
  This version contains formal definitions, detailed security proofs, demos and
experimental data in the appendix.
