GOST Protocol

GOST is a protocol for executing cross-chain confirmations of events between the GoChain and Ethereum blockchains. By leveraging the trust in GoChain's network of reputable signers, contracts deployed on GoChain can securely and confidently confirm events from Ethereum logs, and vice-versa. This simple primitive unlocks powerful interoperability which can be used to build more complex solutions, like cross-chain token transfers of ERC20 and GO20 tokens.

https://medium.com/gochain/gost-protocol-cross-chain-transactions-between-ethereum-and-gochain-39180811301d

Status

This project is still in development.

1. Alpha (devnets)
2. Beta (testnets)
3. Production (mainnets)

How it Works

The GOST protocol relies on GoChain's network of reputable signers to monitor and manage a Confirmations contract on each network. Users (humans or other contracts) request confirmation of events by specifying block number, log index, and an event hash - which uniquely identifies a particular event. The GoChain signers monitor for requested events, and once the block has been confirmed as canonical they vote to confirm an event as either valid or invalid with majority consensus.

Cross-Chain Confirmations

The IConfirmations interface defines the public set of functions available to users, and the Confirmations contract implements and extends the set with administrative functions. Event hashes are content based identifiers derived from the source contract address which emitted the event and the event parameters (topics and data).

// Event hash pseudocode. Note that the first topic will be the event ID.
hash = keccak256(abi.encode(source, topics..., data))

This allows contracts to not only confirm a particular event, but also to operate on the values of the event's parameters. In the case of token transfers, the event can specify the amount and recipient address for the receiving contract code to use.

Cross-Chain Token Transfers

One application of cross-chain event confirmations is the ability to manage cross-chain token transfers. By confirming events emitted when tokens are frozen or burned on one network, we can securely unfreeze or mint tokens on the other network. The Transfers contract defines a GOSTTransfer event, and provides a function to compute event hashes:

event GOSTTransfer(address indexed addr, uint amount);

// Compute the event hash for a GOSTTransfer event from the source contract.
function transferEventHash(address addr, uint amount) public view returns (bytes32) {
    return keccak256(abi.encode(transferSourceContract, eventID, addr, amount));
}

The Custody and Proxy contracts use these building blocks to securely transfer tokens back and forth between networks. The Custody contract deployed to the origin network (where the ERC20/GO20 token is deployed) and the Proxy contract deployed to the other network both emit and confirm each others' GOSTTransfer events. The custody contract holds locked tokens which have been sent to the proxy network, and only unlocks them when return transfer events from the proxy network are confirmed. Similarly, the proxy contract mints tokens when incoming transfers are confirmed and burns them when outgoing transfers are initiated.

Origin to Proxy

How to transfer tokens from their origin network to the proxy network:

1. token.approve(): Approve the custody contract as a spender for the amount being transferred.
2. custody.proxyTransfer(): Initiate the transfer by freezing tokens in the custody contract and emitting a GOSTTransfer event.
3. proxyConfirmations.request(): Request confirmation of the event and deposit funds to cover confirmation gas fees.
4. proxyConfirmations.status(): Wait for confirmation from the signers that the event is valid (status Confirmed).
5. proxy.claimTransfer(): Claim the confirmed transfer to receive minted tokens.

Proxy to Origin

How to transfer tokens from the proxy network back to the origin network:

1. proxy.originTransfer(): Initiate the transfer by burning tokens in the proxy contract and emitting a GOSTTransfer event.
2. originConfirmations.request(): Request confirmations of the event and deposit funds to cover confirmations gas fees.
3. originConfirmations.status(): Wait for confirmations from the signers that the event is valid (status Confirmed).
4. origin.claimTransfer(): Claim the confirmed transfer to receive unlocked tokens.

Contracts

TODO confirmations TODO proxy and custody

Deployment

TODO deployment steps for proxy and custody contracts (just link command or script?)

Confirmations

Contract addresses for the Confirmations contracts manages by the GoChain signers:

Mainnet

Network	Address
GoChain	TBD
Ethereum	TBD

Testnet

Network	Address
GoChain	TBD
Ropsten	TBD

Tokens

Contract addresses for cross-chain tokens:

Token	Origin	Address	Custody	Proxy
SampleToken	Ethereum	0x0	0x1	0x2