Library > 21 - Bringing Down the Complexity: Fast Composable Protocols for Card Games Without Secret State
21 - Bringing Down the Complexity: Fast Composable Protocols for Card Games Without Secret State
July/2018, ACISP'18
BLOCKCHAINCRYPTODISTRIBUTEDMPCPROTOCOL
While many cryptographic protocols for card games have
been proposed, all of them focus on card games where players have some
state that must be kept secret from each other, e.g closed cards and
bluffs in Poker. This scenario poses many interesting technical challenges,
which are addressed with cryptographic tools that introduce significant
computational and communication overheads (e.g. zero-knowledge proofs).
In this paper, we consider the case of games that do not require any secret
state to be maintained (e.g. Blackjack and Baccarat). Basically, in these
games, cards are chosen at random and then publicly advertised, allowing
for players to publicly announce their actions (before or after cards
are known). We show that protocols for such games can be built from
very lightweight primitives such as digital signatures and canonical random
oracle commitments, yielding constructions that far outperform all
known card game protocols in terms of communication, computational
and round complexities. Moreover, in constructing highly efficient protocols,
we introduce a new technique based on verifiable random functions
for extending coin tossing, which is at the core of our constructions. Besides
ensuring that the games are played correctly, our protocols support
financial rewards and penalties enforcement, guaranteeing that winners
receive their rewards and that cheaters get financially penalized. In order
to do so, we build on blockchain-based techniques that leverage the
power of stateful smart contracts to ensure fair protocol execution.