Request for comment: Bridge instances introduction

[hackfisher]

Bridge Instances

Introduction

Each Bridge Instance is combined of a tuple with four components (Source::Truth, Source:Message, Target:Message, Target:Truth).

Bridges Cases

1. darwinia parachain <> Thirdparty standalone substrate chain. (s2s grandpa finality pallet, s2s message pallet, s2s parachain grandpa finality pallet)
2. darwinia parachain <> EVM chain. (Ethereum/BSC/Heco) (parachain gandpa finlaity solidity, our beefy design)
3. darwinia standalone <> Thirdparty standalone (s2s finality pallet)
4. darwinia standalone <> Thirdparty parachain (s2s parachain finality pallet)
5. darwinia parachain(Polkadot) <> Thirdparty parachain(Kusama) (s2s parachain finality pallet)
6. darwinia parachain(Polkadot) <> Thirdparty parachain(Polkadot) , use Polkadot XCMP.

Components:

1. Truth Layer

   1. Grandpa finality pallet (For substrate standalone), with two implementations: [Substrate_Pallet, EVM_Solidity]
   2. Parachain Grandpa finality pallet (For parachain, via Relay chain), with two implementations: [Substrate_Pallet, EVM_Solidity]
   3. Legacy eth1 pow finality pallet (For pow eth1)
   4. BSC finality pallet
   5. Eth2 consensus finality(For eth2 execution layer via eth2 consensus)

2. Message Layer

   Note that Darwinia standalone will be both compatible with substrate and evm.

   • Substrate Message Pallet(For substrate chains)
   • EVM Message Solidity(For evm chains)

   And current combinations are mainly about:

   1. (Source:Message, Target:Message) = (substrate_message_pallet, substrate_message_pallet)
   2. (Source:Message, Target:Message) = (evm_message_solidity, evm_message_solidity)

Implementation

A. Darwinia Standalone Chain as Hub (Current Approach)

Source	Target	Source::Truth	Source::Message	Target:Message	Target::Truth
Darwinia standalone	Substrate standalone chain	Grandpa finality pallet	Substrate Message Pallet	Substrate Message Pallet	Grandpa finality pallet
Darwinia standalone	EVM-like chain	Grandpa & BEEFY(Custom commitment) Lang: Solidity	EVM Message Solidity	EVM Message Solidity	Chain specific Consensus Finality
Darwinia standalone	Moonbeam	Grandpa & BEEFY(Custom commitment) Lang: Solidity	EVM Message Solidity	EVM Message Solidity	Parachain grandpa finality pallet(Via Polkadot)
Darwinia standalone	Polkadot’s Other Parachain	Grandpa finality pallet	Substrate Message pallet	Substrate Message pallet	Parachain grandpa finality pallet(Via Polkadot)
Darwinia parachain	Polkadot’s other parachain	Polkadot Consensus (Relay Chain)	XCMP	XCMP	Polkadot Consensus(Relay Chain)
Darwinia standalone	Darwinia Parachain	Grandpa finality pallet	Substrate Message pallet	Substrate Message pallet	Parachain grandpa finality pallet(Via Polkadot)
Darwinia parachain	Substrate standalone chain	NaN	Route through Darwinia standalone	Route through Darwinia standalone	NaN
Darwinia parachain	EVM-like chain	NaN	Route through Darwinia standalone	Route through Darwinia standalone	NaN
Darwinia standalone	Polkadot’s other parachain	NaN	Route through Darwinia parachain and XCMP	Route through Darwinia parachain XCMP	NaN

B. Darwinia Parachain as Hub(Not used)

Source	Target	Source::Truth	Source::Message	Target:Message	Target::Truth
Darwinia standalone	Substrate standalone chain	NaN	Route through Darwinia Parachain	Route through Darwinia Parachain	NaN
Darwinia standalone	EVM-like chain	NaN	Route through Darwinia Parachain	Route through Darwinia Parachain	NaN
Darwinia parachain	Substrate standalone chain	Parachain grandpa finality pallet(Via Polkadot)	Substrate Message pallet	Substrate Message pallet	Grandpa finality pallet
Darwinia parachain	EVM-like chain	Polkadot Grandpa & BEEFY + Darwinia Digest( Message Commitment) Lang: Solidity	Substrate Message Pallet / EVM Message Solidity(If parachain support EVM) [TBD]	EVM Message Solidity	Chain specific Consensus Finality
Darwinia Parachain	Darwinia standalone	Parachain grandpa finality pallet(Via Polkadot)	Substrate Message pallet	Substrate Message pallet	Grandpa finality pallet
Darwinia parachain	Polkadot’s other parachain	Polkadot Consensus(Relay Chain)	XCMP	XCMP	Polkadot Consensus(Relay Chain)
Darwinia standalone	Polkadot’s other parachain	NaN	Route through Darwinia Parachain	Route through Darwinia Parachain	NaN

For the bridge instances for (Darwinia parachain, Substrate standalone chain) and (Darwinia parachain, EVM-like chain), when the parachain connect or disconnect from Relay chain, the related Truth components required to be upgraded or replaced.