This repo contains the General Purpose Atomic Crosschain Transactions (GPACT) protocol reference implementation. It contains Solidity contracts, Java library code, test code, and example code. This is an implementation of this paper: https://arxiv.org/abs/2011.12783.
The General Purpose Atomic Crosschain Transaction protocol is a blockchain technology that allows function calls across blockchains that either updates state on all blockchains or discards state updates on all blockchains. The function calls can update state on each blockchain and return values across blockchains. The protocol enables applications to access information and utilise functionality that resides on one blockchain from other blockchains. Unlike previous atomic crosschain protocols that only offer atomic asset swaps, this protocol allows for general purpose application logic.
The figure above shows a logical representation of a crosschain call graph using the protocol.
A trade finance application creates a crosschain function
call that goes across five contracts on five blockchains to execute a trade for a shipment of goods.
The Root Transaction executes the entry point function, the executeTrade function in the
Trade Wallet contract on the Wallet blockchain. The Trade Wallet contract could be a
multi-signatory wallet that parties to a shipment have to submit a transaction to, indicating that they agree
a shipment for a certain quantity of goods has been made and should be paid for. The
executeTrade function calls the shipment function in the Logic contract on the Terms blockchain
to determine the price that should be paid and to affect the transfer of stock and payment. The
shipment function calls the getPrice function on the Oracle contract on the Price Oracle
blockchain to determine the price that should be paid for the goods, then calls the transfer
function on the Balances contract on the Finance blockchain to affect the payment, and finally
calls the delivery function on the Stock contract on the Logistics blockchain to register the
changed ownership of the goods.
It could be argued that some of the contracts could exist on the one blockchain, thus reducing
the need for crosschain transactions. However, the Finance blockchain and the Logistics
blockchain in particular could be consortium blockchains involving different participants.
The Price Oracle blockchain could be operated by a consortium that charged for access to the
information. Government regulators could require the logic on the Terms blockchain visible to
them, but the participants in the trade wallet on the Wallet blockchain may wish to remain
anonymous. A crosschain transaction capability is needed to meet these requirements.