Initial implementation of a single server-side "Operator" service (with some extra functionality for testing) and v0.1 smart contract for Ethereum blockchain that can be used to enforce proper behavior in case of disputes.
At the moment the groundwork is done (convenience functions + cryptography) in smart contract to continue writing required processes "Start -> (Challenge?) -> Complete".
Implemented challenges:
- Deposit -> No deposit published in Plasma chain? -> Start withdrawing for deposit? -> Challenge deposit withdraw? -> Finalize"
- Deposit -> Do few transactions -> Start UTXO withdraw -> Express withdraw / Normal withdraw"
Required challenges:
- Proof of double spending (start withdrawing and then spending on Plasma or vice-versa)
- Plain double spend attack
- Proof of funding transaction in Plasma without corresponding deposit in Ethereum network (or duplicate funding TX)
- Proof of incorrectly signed TX
- Other to follow...
The task is to make blockchain transactions as fast as they can be applied virtually to any application.
One of the possible solutions is Plasma - the prominent upgrade to Ethereum blockchain. Our approach is based on this conception.
From a technical point of view Plasma blockchain - is just another blockchain, that can be efficiently settled to parent Ethereum chain and is well protected from the misbehavior of both Plasma operator and Plasma blockchain participants by smart-contract on Ethererum network.
Plasma chain itself has a straightforward structure with assets being undividable and transferred in full from the previous owner to the next one. The transaction has inputs and outputs, with few different types of transactions depending on the required function. For example, we propose type "Merge" to connect two inputs into one output in order to reduce the number of UTXOs that will be followed by the client. Full description will be given when the design is more stable. All chain logic is made using Ethereum crypto primitives - sha3, secp256k1 and 65-byte signatures allowing the use of ecrecover.
Block in Plasma network has a structure of Header: [BlockNumber, NumberOfTransactions, ParentHash, MerkleTreeRoot, PlasmaOperatorSignature], where
ParentHashreferences to the previous block (by number)MerkleTreeRootis root hash of a Merkle treeNumberOfTransactionstransactions in this Plasma block and an array of transactions.
The header is submitted by Plasma network operator to the smart-contract on Ethereum chain. Blocks can only be sent one by one, with sequence numbering is enforced by contract. Any user of Ethereum network can deposit ETH to contract that will trigger, event and will allow Plasma network operator to make a funding transaction in a Plasma chain. Then users can freely transact in Plasma chain, with headers pushed to a parent contract in Ethereum.
When a user wants to settle one of his transactions to the main network, he initiates a withdraw on Ethereum network by providing the reference to the transaction (in the form of BlockNumber, TxNumberInBlock, OutputNumberInTX), full transaction and Merkle proof that this transaction was indeed included in that block. Parent contract checks a proof versus submitted root hash for this block. If validation was sucessefull the process of withdrawing starts. After 24 hours it can be finalized. There is a particular kind of transaction in Plasma network that can speed up a process by efficiently burning the input (sending it to 0x0). If this block is not published by the operator, withdrawing can go as usual.
The concept is implemented using JS with conjunction on Web3 and ethereumjs/testrpc on a backend. For the sake of simplicity, all necessary functions are wrapped in REST API calls doing signatures on behalf of a predefined set of the address on a server. Further work will allow users to use wallet apps such as Metamask to initiate transactions in a Plasma network by making a signature on a client side and interacting with a parent contract on Ethereum network as usual.
Here at BankEx, we believe in the efficiency of offloading of some transactions from Ethereum blockchain to Plasma chains especially if the proper incentive is present for Plasma operators to behave appropriately (such incentive can be presented in the form of competing with other operators for obtaining end-users). Another advantage is a flexibility of Plasma chain implementation as long as it can be effectively cross-checked by contract on a parent chain. With the new cryptographic primitive added in Metropolis fork, one can extend our PoC implementation with transactions utilizing ring signatures of zkSNARKs for the privacy of end user.
- Ubuntu or similar is preferable but can also be run on Mac OS X or Windows as well
- NodeJS version >= 8.9. Tested on 9.0
git clone https://github.com/BankEx/PlasmaETHexchange.git
cd PlasmaETHexchangenpm install
npm run serverBackend localhost:8000/
Insomnia.json is an Insomnia workspace file with various testing functions, play with it.
!! May require some parameter changes in existing requests to comply with new output numbering.
User 1: 0xf62803ffaddda373d44b10bf6bb404909be0e66b
User 2: 0xcf78f18299eac0e0a238db7f4742ef433f98c85e
Operator (oracle): 0x405aaaa4bdcda14a0af295f3669459b6b0fc8104
Will be filled later