Simple plasma implementation

Plasma consists of three major parts.

1. Plasma chain: A simple proof-of-authority chain where the actual transactions take place.
2. Plasma contract: A smart contract deployed on root chain which handles the deposits and withdrawals for the child chain (plasma chain).
3. Ethereum blockchain: The root chain which only records the block headers of the plasma chain.

The complete cycle of interacting with plasma is made up of three stages.

Deposit

Participants deposit to the plasma contract on the root chain. Then the operator at the plasma chain will construct a deposit transaction according to the contract event when building a new block.

Transact

Participants could transact with each other on the plasma chain without notifying the root chain. Only when every block is created by the operator, it will submit the block header to the plasma contract on the root chain.

Withdraw

A withdrawal is initiated by calling the plasma contract. After creating a withdrawal, user needs to wait 7 days for other participants to challenge it. If anyone could prove the given withdrawal that has been spent later on the plasma chain, the withdrawal will be canceled. Otherwise, after 7 days and without any other withdrawals with higher priority, user could withdraw his funds back to the root chain.

Prerequisite

1. Truffle: An Ethereum development framework which helps us compiling, deploying, and interacting with smart contract.
2. Testrpc: A test Ethereum RPC client for fast development. Here, we use ganache-cli. If you prefer a GUI version, you could replace it with ganache. Note that you could also launch an Ethereum private chain (geth) to replace testrpc.

Run

1. Install dependency

npm install

2. Run ganache

ganache-cli

Testrpc will generate ten default accounts for us. For convenience, you could specify a HD wallet mnemonic to get fixed addresses. For example:

ganache-cli -m pink two example move shop length clean crop cheese tent strike field

The corresponding initial addresses are:

(0) 0x0bf5f0f213b0b752858e9352fd6081f5d730dc17
(1) 0x87dbd8ab1bd9d4fce07db12743594a5f456435ff
(2) 0x3b0ba3134ac12cc065d4dba498a60cba5ef16098
(3) 0x6c7f749d0e21aa6478af8e7adc362a8bf76be826
(4) 0x9a404f89ad853e592d7b48242b4745c17a8ee852
(5) 0x34d5e94fc3e7ecac3859a03176cb57534f30b71c
(6) 0x8c0e1d37680a03eeb4c85880ffe1edf61ffa76f4
(7) 0x6017db4acdfed284da94485d715a0f758048ac0b
(8) 0x239ddceb1d7cebf07435a52f569b86f310af9cad
(9) 0x1166d1f78f44c79e8e3f0d74419940e521790d7c

3. Compile contracts

truffle compile

4. Deploy contracts

truffle migrate

If you need to deploy contracts on this testrpc again, don't forget to add the --reset argument.

5. Set the contract configuration (config.js).
   1. After deploying contracts, fill in the PlasmaChainManager contract address.
   2. Choose one of the initial addresses as the operator address, for example, 0x87dbd8ab1bd9d4fce07db12743594a5f456435ff.
6. Run the plasma chain.

npm start

or

node main.js [options]

the available options are:

Option	Description
--port	Specify HTTP API port, default 3001
--contract	Specify contract address, otherwise use value in config.js
--operator	Specify operator address, otherwise use value in config.js

Testing

1. Run ganache

ganache-cli

2. Run tests

truffle test

HTTP API

Block related

Get blockchain

Get the whole blockchain.

Parameter

None

Sample

curl http://localhost:3001/blocks

Mine blocks

Miner mines a new block.

Parameter

None

Sample

curl -X POST http://localhost:3001/mineBlock

Transaction related

Create a transaction

Create a transaction to other participants. User could specify at most two UTXOs to spend. Also note that the units used in field amount is ether.

Parameter

Name	Type	Required	Description
from	Address	Yes	Transfer funds from whom
to	Address	Yes	Transfer funds to whom
amount	Decimal	Yes	How much ether (in ether)

Sample

curl -H "Content-type:application/json" --data '{"from": "0x6C7f749d0E21aA6478aF8e7Adc362a8bF76Be826", "to": "0x3B0bA3134Ac12Cc065d4dBa498a60cba5Ef16098", "amount": 2}' http://localhost:3001/transact

Deposit related

Deposit

Deposit funds to Plasma smart contract.

Parameter

Name	Type	Required	Description
address	Address	Yes	Deposit from whom
amount	Integer	Yes	How much funds to deposit

Sample

curl -H "Content-type:application/json" --data '{"address": "0x6C7f749d0E21aA6478aF8e7Adc362a8bF76Be826", "amount": 4}' http://localhost:3001/deposit

Withdrawal related

Create withdrawal

Create a new withdrawal.

Parameter

Name	Type	Required	Description
blkNum	Integer	Yes	The position of the UTXO user wants to withdraw
txIndex	Integer	Yes	The position of the UTXO user wants to withdraw
oIndex	Integer	Yes	The position of the UTXO user wants to withdraw
from	Address	Yes	The owner of the UTXO

Sample

curl -H "Content-type:application/json" --data '{"blkNum": 3, "txIndex": 1, "oIndex": 0, "from": "0x6C7f749d0E21aA6478aF8e7Adc362a8bF76Be826"}' http://localhost:3001/withdraw/create

Challenge withdrawal

Create a withdrawal challenge.

Parameter

Name	Type	Required	Description
withdrawalId	Integer	Yes	The withdrawal ID user wants to challenge
blkNum	Integer	Yes	The position of the UTXO user wants to challenge
txIndex	Integer	Yes	The position of the UTXO user wants to challenge
oIndex	Integer	Yes	The position of the UTXO user wants to challenge
from	Address	Yes	The owner of the UTXO

curl -H "Content-type:application/json" --data '{"withdrawalId": 4000000000, "blkNum": 4, "txIndex": 2, "oIndex": 1, "from": "0x6C7f749d0E21aA6478aF8e7Adc362a8bF76Be826"}' http://localhost:3001/withdraw/challenge

Finalize withdrawal

Finalize withdrawals manually.

Parameter

Name	Type	Required	Description
from	Address	Yes	Who initiates the withdrawal finalization

Sample

curl -H "Content-type:application/json" --data '{"from": "0x6C7f749d0E21aA6478aF8e7Adc362a8bF76Be826"}' http://localhost:3001/withdraw/finalize