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EVM Storage proofs generic bridge - 4K$ worth of G$+Fuse tokens




in over 262 years



4000 USD



The GoodDollar protocol needs a secure and robust bridge to the Fuse network, for scaling TXs and also Voting. Also having a generic evm bridge would make supporting other EVM based blockchains easier.

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See proposal on Fuse forum for more context:

Part 1 - Block headers registry contract - 1000$

The purpose of the contract is to store on Fuse, block headers from different blockchains signed by the Fuse validators.

  • [x] Most write methods to this contract should be limited to current validators
  • [x] The contract should hold validator signatures per blockhash (ie mapping blockhash -> SignedBlock)
  • [x] The contract should hold mapping from blockchain+block_number -> array<blockhashes>
SignedBlock {
 cycleEnd: uint256, //just for fuse
validators: address[],//just for fuse
 hasValidatorSigned: mapping<address> -> bool, //to prevent double signatures
  • [ ] the contract will hold a mapping of blockhash -> BlockHeader
Header {
  parent_hash: bytes32
  timestamp: uint256,
  number: uint256,
  author: address,
  transactions_root: bytes32,
  uncles_hash: bytes32,
  extra_data: bytes,
  state_root: bytes32,
  receipts_root: bytes32,
  log_bloom: bytes,
  gas_used: uint256,
  gas_limit: uint256,
  difficulty: uint256,
Block {
 header: BlockHeader,
 rlpHeader: bytes,
 signature: bytes,
 blockchainId: uint256,
 blockHash: bytes32,
 validators: address[],
 cycleEnd: uint256
  • [x] internal method _addSignedBlock(blockchainid,blockheader,blockhash,signature)
    • if blockhash doesnt exists yet, verify hash(blockheader) = blockhash and store header
    • verify signature is of the blockhash and by the msg.sender validator
    • verify validator didnt already submit this block (probably need another mapping for that)
    • add the validator signature for that specific blockhash
    • add blockhash to (blockchain+blocknumber) -> blockhashes mapping
  • [x] view getSignedBlock(blockchain,block number):(rlpHeader, Array<signatures>, Array<validators>, cycleEnd) - returns the data for the block with most signatures
  • [x] internal method `_addFuseSignedBlock(blockheader,blockhash,validators,cycleend,signature)
    • should perform the same as addSignedBlock just with added logic
    • key for blockhash mapping is defined as hash(blockhash,validators,cycleEnd)
    • signature is also expected to match digest of hash(blockhash,validators,cycleEnd)
  • [x] method addSignedBlocks(Block[] blocks) - the main entry to bulk add blocks
  • [x] method addBlockchain(blockchainId, rpc: string) onlyvoting - keeps a list of blockchains that validators should read blocks from
  • [ ] unit tests

Part 2 - Extend Fuse validators' nodejs app - 1500$

  • [ ] read list of extra blockchains + RPCs from registry contract. By default fuse+ethereum+bsc are always enabled no matter if they are in the list or not
  • [x] create provider connections and listen to new blocks (for example etherjs provider.on("block") -
  • [x] on each incoming sign the blockhash and push block data (see data type Block) to an array
    • for fuse read from consensus the cycleEnd value and the current validators value
    • notice that for fuse sealFields is instead of mixhash/digest and nonce
    • notice that for different blockchains the author/mixdigest fields can be named differently, coinbase,miner etc..
  • [x] set timer for every X seconds to publish the signed blocks
    • clone the blocks array
    • reset the original array
    • call addSignedBlocks
  • [ ] error handling
    • listen to provider errors and try to reconnect
    • catch fuse read/write tx errors and add a retry (ie something like the package @jsier/retrier
  • [ ] unit tests

Part 3 - Custom Bridge POC - 1500$

Create a smart contract that is able to verify a new Fuse signed block data and also that is able to verify some other block was signed by X validators in the past using storage proofs on latest block

  • [ ] initialize - initialize the contract with a given set of validators
  • [ ] method to set the latest Fuse block. setLatestBlock(BlockHeader,validators,cycleEnd, signatures)
    • require that block number > last blocknumber
    • require signatures are:
      • of digest (blockhash,validators,cycleEnd)
      • signed by validator in existing validator set
      • 66% validators in set

    • if blocknumber > stored cycleEnd then update the validator set
    • store latest block, cycleEnd
  • [ ] method to prove a past block was signed by X validators. provePastBlock(blockhash, validators, cycleEnd, storageProof)
    • use storage proofs to prove that last block submited contains in the SignedBlock mapping an entry for hash(blockhash,validators,cycleEnd) and that this entry signatures field length >= 66% validators