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  BEP: 333
  Title: BNB Chain Fusion
  Status: Candidate
  Type: Standards
  Created: 2023-11-29

BEP-333: BNB Chain Fusion

BEP-333: BNB Chain Fusion

1. Summary

This BEP proposes to securely and smoothly transit the BNB Beacon Chain and BNB Smart Chain (BSC) from a dual-chain structure into a single chain structure and decommission the Beacon Chain.

2. Abstract

BNB Chain Fusion (BC Fusion) is a major achievement for BNB Chain. It helps overcome legacy services and technical debt, enabling faster iteration and development. BC Fusion includes three sub-BEPs:

This BEP primarily proposes strategic planning and coordination for organizing these BEPs. The goal is to facilitate the secure and seamless implementation of BC Fusion.

3. Status

This BEP is a draft.

4. Motivation

BNB Beacon Chain is a blockchain developed by the BNB Chain community that implements a vision of a decentralized exchange (DEX) for digital assets. Besides this, Beacon Chain and BSC is a dual-chain structure: Beacon Chain helps to enhance the security of BSC as a staking and governance layer. With the rise of various other forms of Dex, order-book based decentralized exchange was decommissioned in BEP151. With the quick evolution of BSC, the Beacon Chain has become a burden. The cross-chain bridge that connects the two chains slows down the development iteration and always exposes BNB to a certain level of security vulnerabilities. It's time to take a step further and migrate the functionality of Beacon Chain to BSC, allowing Beacon Chain to retire.

5. Specification

5.1 Introduction

The Beacon Chain currently possesses several key functionalities:

  1. Cryptocurrency management platform. The Beacon Chain mainnet currently supports a hundred kinds of BEP2 and BEP8 tokens. These tokens have value and can be circulated on the Beacon Chain or transferred across different chains using protocols such as BEP3.

  2. The staking layer of BSC. The BSC utilizes the POSA consensus algorithm. It delegates staking election and reward distribution functions to the Beacon Chain. This design choice was based on the fact that the Beacon Chain is built on the cosmos-sdk architecture, which already includes a well-developed staking module that can be reused.

  3. The governance layer of BSC. For similar reasons, the governance functionality of BSC is delegated to the Beacon Chain as well. The governance vote and tally happen on Beacon Chain, and the execution plan is delivered to the BSC through cross chain communication protocol.

Therefore, we have three separate BEPs that discuss how to migrate these functionalities or valuable assets to BSC.

  1. BEP-299: This BEP presents a secure and trustless way for users to recover their assets on the BSC once the Beacon chain stops running.

  2. BEP-294: This BEP allows BNB holders to stake BNB to the specified validators and get staking rewards on the BSC side directly. To ensure network security, the migration of Staking voting power is designed to be seamless. This means that both the Beacon Chain and BSC's staking modules will coexist and function simultaneously during the migration process.

  3. BEP297: This BEP allows community members to submit proposals directly on the BSC network. The governance module is fully compatible with Tally.

5.2 Multiple Phases

To accomplish BC Fusion, there will be several preparation and post-action steps involved, connecting these BEPs together. Thus, BC Fusion is divided into multiple stages:

multiple phases

5.2.1 First Sunset Fork

Due to the requirement of returning cryptocurrency to the user's wallet in order to migrate funds to BSC through BEP-299. The Beacon Chain will disable specific types of transactions to encourage users to keep their funds in their own wallets. The following types of Beacon chain transactions will be disabled: TimeLockMsg, TimeRelockMsg, FreezeMsg, IssueMsg, MintMsg, IssueMiniMsg, HTLTMsg, DepositHTLTMsg.

During the migration process, Beacon Chain prohibits the creation and editing of validators to prevent conflicts with validators created on BSC side. New delegations will also be prohibited. The following types of Beacon chain transactions will be disabled: MsgCreateValidatorOpen, MsgCreateSideChainValidator, MsgCreateSideChainValidatorWithVoteAddr, MsgEditSideChainValidatorWithVoteAddr, MsgSideChainDelegate, MsgSideChainReDelegate.

To ensure that the voting power migration process is not maliciously manipulated, the Governance module will be automatically disabled when the voting power is below 5M BNB.

The above-mentioned features will be enabled in Beacon Chain FirstSunsetFork.

5.2.2 BSC Feynman Hardfork

BEP-294, BEP-297 and BEP-299 will be deployed in the BSC Feynman hard fork.

  1. BEP-294 will take effect immediately. Validators created on BSC will receive triple voting power when staking an equal amount of BNB. This encourages the transfer of voting power from the Beacon Chain to BSC.

  2. The BEP-297 governance functionality will not be activated immediately after the hardfork. It will only be automatically enabled once more than 10 million BNB are migrated to BSC.

  3. The smart contract of BEP-299 is not available as the merkel root in the smart contract is still empty at this time. Only after the Beacon Chain comes to a complete halt, the Token Migration feature will be initiated by setting the Merkle root for balance dump through governance.

  4. Cross-chain re-delegation, which allows users to un-delegate their stakes from Beacon Chain and then delegate them on BSC in one Beacon Chain transaction, will be enabled after governance opening the related cross-chain channel.

An important wallet will be introduced in this hardfork: AssetProtector. AssetProtector is a multi-signature wallet controlled by the core dev team at the beginning. It can:

  • Pause and unpause the staking, governance and token migration contract in emergency situations.

  • Forbidden a specific account to perform any operations in the staking contract.

5.2.3 Second Sunset Fork

After transferring more than two-thirds of the voting power to BSC, the Beacon Chain must restrict additional transaction types and automatically execute specific logic to ensure the return of funds to users' wallets. The following transactions will be disabled: MsgSideChainSubmitProposal.

All TimeLock and AtomicSwap will automatically be refunded to the user's wallet. All the BSC delegation will be undelegated automatically, if the delegation comes through BEP153, the funds will be sent back to the BSC network.

5.2.4 Final Sunset Fork

Before executing Final Sunset, users still have the opportunity to transfer funds across chains. However, after Final Sunset, cross-chain communication between the Beacon Chain and BSC will be completely stopped.

After Sunset Fork, the validators in the Beacon Chain community will gradually shut down, and the entire chain will no longer accept new transactions or propose new blocks.

Some of the funds will be permanently locked:

  1. The total amount of staking funds for validators on the Beacon Chain itself is approximately 110k BNB.

  2. On the Beacon Chain, the BEP2/BEP8 tokens that are not mirrored or bound to BSC.

  3. The BEP153 staking reward that is less than 0.1BNB or staked value which is less than 0.01BNB will be locked forever.

All these funds are not recoverable after the Final Sunset Fork.

5.2.5 Post BC Fusion

  • The core dev team will dump the ledger of Beacon Chain and generate a merkle tree. The data will be publicly reviewed for about 1 month.

  • A governance proposal will be submitted to set the merkel root and approver account of the token migration contract.

  • A dapp will be provided for token migration from Beacon Chain to BSC.

  • All the blockchain data of Beacon Chain will be uploaded to Greenfield, Filecoin and Arweave for archive.

6. License

The content is licensed under CC0.