Adding Loom's plasma_cash folder

plasma_cash/.flake8

@@ -0,0 +1,2 @@
+[flake8]
+exclude = unit_test.py, config.py

plasma_cash/License.md

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+Copyright (C) 2018  Loom Network Inc
+
+GNU GENERAL PUBLIC LICENSE
+
+Version 2, June 1991
+
+Copyright (C) 1989, 1991 Free Software Foundation, Inc.  
+51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+
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plasma_cash/Makefile

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+test:
+	pytest unit_test.py
+
+lint:
+	flake8 child_chain client contract_binds utils *.py --ignore=E203,W503 --exclude unit_test.py,config.py,dump_test_data.py
+
+format:
+	black --line-length 79 -S .
+	isort -rc .

plasma_cash/README.md

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+# Development Dependencies
+
+A patched version of web3.py is used because otherwise it does not work with Ganache due to issue #674. In addition, in order to be able to monitor events, PR #827, which is not merged yet. Pyethereum dependencies broke recently so we need to manually install a slightly older version of rlp encoding. Flask is used for server purposes.
+
+On OSX + Homebrew
+```
+source /usr/local/bin/virtualenvwrapper.sh
+```
+
+
+```
+mkvirtualenv erc721plasma --python=/usr/bin/python3.6
+pip install -r requirements.txt
+```
+
+## Launch Plasma Chain
+
+1. Make sure the contracts are deployed at the correct addresses (`npm run migrate:dev` in `server` directory)
+2. Run `FLASK_APP=./child_chain FLASK_ENV=development flask run --port=8546` in one terminal. This will start a Plasma Chain instance which listens at `localhost:8546` and is also connected to the deployed contracts
+3. Run `python demo.py`
+
+TODO Should probably bundle these into makefiles, i.e. `make server` should launch the plasma chain.
+
+
+## Testing
+
+```
+make test
+```
+
+## Linting
+
+```
+make lint
+```

plasma_cash/auto_respond_challenge.py

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+import time
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+dan = Client(container.get_root('dan'), container.get_token('dan'))
+trudy = Client(container.get_root('trudy'), container.get_token('trudy'))
+authority = Client(
+    container.get_root('authority'), container.get_token('authority')
+)
+
+# Give Trudy 5 tokens
+trudy.register()
+
+danTokensStart = dan.token_contract.balance_of()
+
+# Trudy deposits a coin
+tx_hash, gas_used = trudy.deposit(21)
+event_data = trudy.root_chain.get_event_data('Deposit', tx_hash)
+deposit1_utxo = event_data[0]['args']['slot']
+
+# wait to make sure that events get fired correctly
+time.sleep(2)
+
+trudy_submit_block = authority.get_block_number()
+trudyTokensStart = trudy.token_contract.balance_of()
+
+coin = trudy.get_plasma_coin(deposit1_utxo)
+authority.submit_block()
+trudy.watch_exits(deposit1_utxo)
+
+# Trudy sends her coin to Dan
+trudy_to_dan = trudy.send_transaction(
+    deposit1_utxo, coin['deposit_block'], dan.token_contract.account.address
+)
+authority.submit_block()
+trudy_to_dan_block = authority.get_block_number()
+trudy.stop_watching_exits(deposit1_utxo)
+
+# Dan attempts to exit his coin
+coin = dan.get_plasma_coin(deposit1_utxo)
+dan.start_exit(deposit1_utxo, coin['deposit_block'], trudy_to_dan_block)
+authority.submit_block()
+dan.watch_exits(deposit1_utxo)
+dan.watch_challenges(deposit1_utxo)
+
+# Dan is challenged by Trudy
+trudy.challenge_before(deposit1_utxo, 0, coin['deposit_block'])
+
+# Wait for dan to automatically respond to the challenge
+time.sleep(2)
+
+# Dan successfully finalizes his exit
+w3 = dan.root_chain.w3
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+
+dan.withdraw(deposit1_utxo)
+
+danTokensEnd = dan.token_contract.balance_of()
+print('dan has {} tokens'.format(danTokensEnd))
+assert (
+    danTokensEnd == danTokensStart + 1
+), "END: dan has incorrect number of tokens"
+print('Automatic challenge response success :)')

plasma_cash/benchmark.py

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+import collections
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+authority = Client(
+    container.get_root("authority"), container.get_token("authority")
+)
+w3 = authority.root_chain.w3  # get w3 instance
+
+child_block_interval = 1000
+block_iterations = 8
+coins_per_register = 5
+num_deposited_coins = 2
+coin_indices = range(0, num_deposited_coins)
+number_of_players = 5
+players_indices = range(0, number_of_players)
+
+gas_costs = collections.defaultdict(dict)
+
+players = list(
+    map(
+        lambda index: Client(
+            container.get_root("players", index),
+            container.get_token("players", index),
+        ),
+        players_indices,
+    )
+)
+
+# Step 1: All players register to the game and are given 5 coins each.
+# Step 2: They then proceed to deposit 2 of their coins to Plasma Cash.
+deposits = {}
+deposit_gas = 0
+for index in players_indices:
+    players[index].register()
+    for coin_index in coin_indices:
+        tx_hash, gas_used = players[index].deposit(
+            index * coins_per_register + coin_index + 1
+        )
+        deposit_gas += gas_used
+        print('GAS USED FOR A DEPOSIT', gas_used)
+
+    deposits[index] = list(
+        map(lambda event: event["args"], players[index].get_all_deposits())
+    )
+    print("Player {} deposited coins: {}".format(index, deposits[index]))
+
+# Get mean gas cost for deposits
+gas_costs['deposit'] = deposit_gas / (number_of_players * num_deposited_coins)
+
+
+print("STEP 3")
+# Step 3: Each player gives their deposited coins to the next player
+# 1000 players * 2 coins = 2k Plasma transactions per round
+# This loops `block_iterations` times.
+for iteration in range(block_iterations):
+    for index in players_indices:
+        neighbor_index = (index + 1) % number_of_players
+        deposit_index = (index - iteration) % number_of_players
+        for coin_index in coin_indices:
+            prev_block = (
+                deposits[index][coin_index]["blockNumber"]
+                if iteration == 0
+                else iteration * child_block_interval
+            )
+            print(
+                '{}: PLAYER {} to {} : Coin {} from block {}'.format(
+                    iteration,
+                    index,
+                    neighbor_index,
+                    deposits[deposit_index][coin_index]['slot'],
+                    prev_block,
+                )
+            )
+            players[index].send_transaction(
+                deposits[deposit_index][coin_index]["slot"],
+                prev_block,
+                players[neighbor_index].token_contract.account.address,
+            )
+    authority.submit_block()
+
+print("STEP 4")
+# Step 4: All players initiate an exit for the coins they own.
+# Since each player gave their coin to their neighbour, player `i`
+# now owns the coins that player `(i-block_iterations) % num_players`
+# initially had. Everyone initializes their exits
+# by referencing the last 2 blocks
+exit_gas = 0
+for index in players_indices:
+    received = (index - block_iterations) % number_of_players
+    for coin_index in coin_indices:
+        print(
+            'PLAYER {} exiting {} from {}'.format(index, coin_index, received)
+        )
+        slot = deposits[received][coin_index]["slot"]
+        prev_block = (
+            deposits[received][coin_index]["blockNumber"]
+            if block_iterations == 1
+            else (block_iterations - 1) * child_block_interval
+        )
+        tx_hash, gas_used = players[index].start_exit(
+            slot, prev_block, block_iterations * child_block_interval
+        )
+        exit_gas += gas_used
+
+gas_costs['exit'] = exit_gas / (number_of_players * num_deposited_coins)
+
+
+increaseTime(w3, 8 * 24 * 3600)
+# Somebody can finalize all exits, or each user can finalize their own
+# authority.finalize_exits()
+
+# Final step: Each user finalizes their exit after challenge period
+# has passed and then withdraws their coins.
+withdraw_gas = 0
+finalize_exit_gas = 0
+for index in players_indices:
+    received = (index - block_iterations) % number_of_players
+    for coin_index in coin_indices:
+        slot = deposits[received][coin_index]["slot"]
+        tx_hash, gas_used = players[index].finalize_exit(slot)
+        finalize_exit_gas += gas_used
+        tx_hash, gas_used = players[index].withdraw(slot)
+        withdraw_gas += gas_used
+        print("Player {} withdrew coin: {}".format(index, slot))
+
+gas_costs['finalize_exit'] = finalize_exit_gas / (
+    number_of_players * num_deposited_coins
+)
+gas_costs['withdraw'] = withdraw_gas / (
+    number_of_players * num_deposited_coins
+)
+
+print('Benchmarking done :)')
+print(
+    'Mean gas cost for {} transfers: (Deposit + \
+Start Exit + Finalize Exit + Withdraw) = {}'.format(
+        block_iterations, sum(gas_costs.values())
+    )
+)
+
+# Authority registers and transacts on-chain, index = 1000
+authority.register()
+coin = number_of_players * coins_per_register + 2
+tx_hash, gas_transfer = authority.token_contract.transfer(
+    players[0].token_contract.account.address, coin
+)
+
+
+print(
+    'Expected Gas cost for {} on-chain transfers \
+(safeTransferFrom) = {}'.format(
+        block_iterations, block_iterations * gas_transfer
+    )
+)

plasma_cash/challenge_after_demo.py

@@ -0,0 +1,87 @@
+import time
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+dan = Client(container.get_root('dan'), container.get_token('dan'))
+mallory = Client(container.get_root('mallory'), container.get_token('mallory'))
+authority = Client(
+    container.get_root('authority'), container.get_token('authority')
+)
+
+# Give Mallory 5 tokens
+mallory.register()
+
+danTokensStart = dan.token_contract.balance_of()
+print('Dan has {} tokens'.format(danTokensStart))
+assert danTokensStart == 0, "START: Dan has incorrect number of tokens"
+malloryTokensStart = mallory.token_contract.balance_of()
+print('Mallory has {} tokens'.format(malloryTokensStart))
+assert malloryTokensStart == 5, "START: Mallory has incorrect number of tokens"
+current_block = authority.get_block_number()
+print('current block: {}'.format(current_block))
+
+# Mallory deposits one of her coins to the plasma contract
+tx_hash, gas_used = mallory.deposit(6)
+event_data = mallory.root_chain.get_event_data('Deposit', tx_hash)
+deposit1_utxo = event_data[0]['args']['slot']
+mallory.deposit(7)
+# wait to make sure that events get fired correctly
+time.sleep(2)
+registered_deposits = mallory.get_all_deposits()
+assert (
+    len(registered_deposits) == 2
+), "Mallory has incorrect number of deposits"
+
+malloryTokensPostDeposit = mallory.token_contract.balance_of()
+print('Mallory has {} tokens'.format(malloryTokensPostDeposit))
+assert (
+    malloryTokensPostDeposit == 3
+), "POST-DEPOSIT: Mallory has incorrect number of tokens"
+
+plasma_block1 = authority.submit_block()
+plasma_block2 = authority.submit_block()
+
+# Mallory sends her coin to Dan
+# Coin 6 was the first deposit of
+coin = mallory.get_plasma_coin(deposit1_utxo)
+mallory_to_dan = mallory.send_transaction(
+    deposit1_utxo, coin['deposit_block'], dan.token_contract.account.address
+)
+incl_proofs, excl_proofs = mallory.get_coin_history(deposit1_utxo)
+assert dan.verify_coin_history(deposit1_utxo, incl_proofs, excl_proofs)
+
+plasma_block3 = authority.submit_block()
+dan.watch_exits(deposit1_utxo)
+
+# Mallory attempts to exit spent coin (the one sent to Dan)
+# This will be auto-challenged by Dan's client
+mallory.start_exit(deposit1_utxo, 0, coin['deposit_block'])
+
+# Wait until challenge is done
+time.sleep(2)
+dan.start_exit(deposit1_utxo, coin['deposit_block'], plasma_block3)
+dan.stop_watching_exits(deposit1_utxo)
+
+w3 = dan.root_chain.w3  # get w3 instance
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+
+dan.withdraw(deposit1_utxo)
+
+dan_balance_before = w3.eth.getBalance(dan.token_contract.account.address)
+dan.withdraw_bonds()
+dan_balance_after = w3.eth.getBalance(dan.token_contract.account.address)
+assert (
+    dan_balance_before < dan_balance_after
+), "END: Dan did not withdraw his bonds"
+
+malloryTokensEnd = mallory.token_contract.balance_of()
+print('Mallory has {} tokens'.format(malloryTokensEnd))
+assert malloryTokensEnd == 3, "END: Mallory has incorrect number of tokens"
+danTokensEnd = dan.token_contract.balance_of()
+print('Dan has {} tokens'.format(danTokensEnd))
+assert danTokensEnd == 1, "END: Dan has incorrect number of tokens"
+
+print('Plasma Cash `challengeAfter` success :)')

plasma_cash/challenge_before_demo.py

@@ -0,0 +1,79 @@
+import time
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+dan = Client(container.get_root('dan'), container.get_token('dan'))
+trudy = Client(container.get_root('trudy'), container.get_token('trudy'))
+mallory = Client(container.get_root('mallory'), container.get_token('mallory'))
+authority = Client(
+    container.get_root('authority'), container.get_token('authority')
+)
+
+# Give Dan 5 tokens
+dan.register()
+
+# Dan deposits a coin
+tx_hash, gas_used = dan.deposit(16)
+event_data = dan.root_chain.get_event_data('Deposit', tx_hash)
+deposit1_utxo = event_data[0]['args']['slot']
+
+# wait to make sure that events get fired correctly
+time.sleep(2)
+
+dan_submit_block = authority.get_block_number()
+danTokensStart = dan.token_contract.balance_of()
+
+coin = dan.get_plasma_coin(deposit1_utxo)
+authority.submit_block()
+dan.watch_exits(deposit1_utxo)
+
+# Trudy sends her invalid coin to Mallory
+trudy_to_mallory = trudy.send_transaction(
+    deposit1_utxo,
+    coin['deposit_block'],
+    mallory.token_contract.account.address,
+)
+authority.submit_block()
+trudy_to_mallory_block = authority.get_block_number()
+
+# Mallory sends her invalid coin to Trudy
+mallory_to_trudy = mallory.send_transaction(
+    deposit1_utxo, trudy_to_mallory_block, trudy.token_contract.account.address
+)
+authority.submit_block()
+mallory_to_trudy_block = authority.get_block_number()
+
+# Trudy attemps to exit her illegitimate coin
+trudy.start_exit(deposit1_utxo, trudy_to_mallory_block, mallory_to_trudy_block)
+time.sleep(2)  # need to wait a bit for authority to catch up
+
+w3 = dan.root_chain.w3
+
+# Dan challenges Trudy's exit
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+dan.start_exit(deposit1_utxo, 0, coin['deposit_block'])
+dan.stop_watching_exits(deposit1_utxo)
+
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+
+dan.withdraw(deposit1_utxo)
+
+dan_balance_before = w3.eth.getBalance(dan.token_contract.account.address)
+dan.withdraw_bonds()
+dan_balance_after = w3.eth.getBalance(dan.token_contract.account.address)
+assert (
+    dan_balance_before < dan_balance_after
+), "END: Dan did not withdraw his bonds"
+
+danTokensEnd = dan.token_contract.balance_of()
+
+print('dan has {} tokens'.format(danTokensEnd))
+assert (
+    danTokensEnd == danTokensStart + 1
+), "END: dan has incorrect number of tokens"
+
+print('Plasma Cash `challengeBefore` success :)')

plasma_cash/challenge_between_demo.py

@@ -0,0 +1,74 @@
+import time
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+alice = Client(container.get_root('alice'), container.get_token('alice'))
+bob = Client(container.get_root('bob'), container.get_token('bob'))
+eve = Client(container.get_root('eve'), container.get_token('eve'))
+authority = Client(
+    container.get_root('authority'), container.get_token('authority')
+)
+
+bobTokensStart = bob.token_contract.balance_of()
+
+# Give Eve 5 tokens
+eve.register()
+
+# Eve deposits a coin
+tx_hash, gas_used = eve.deposit(11)
+event_data = eve.root_chain.get_event_data('Deposit', tx_hash)
+deposit1_utxo = event_data[0]['args']['slot']
+
+# wait to make sure that events get fired correctly
+time.sleep(2)
+
+# Eve sends her plasma coin to Bob
+coin = eve.get_plasma_coin(deposit1_utxo)
+eve_to_bob = eve.send_transaction(
+    deposit1_utxo, coin['deposit_block'], bob.token_contract.account.address
+)
+authority.submit_block()
+eve_to_bob_block = authority.get_block_number()
+bob.watch_exits(deposit1_utxo)
+
+# Eve sends this same plasma coin to Alice
+eve_to_alice = eve.send_transaction(
+    deposit1_utxo, coin['deposit_block'], alice.token_contract.account.address
+)
+authority.submit_block()
+
+eve_to_alice_block = authority.get_block_number()
+
+# Alice attempts to exit here double-spent coin
+# Bob auto-challenges Alice's exit
+alice.start_exit(deposit1_utxo, coin['deposit_block'], eve_to_alice_block)
+
+# bob.challenge_between(deposit1_utxo, eve_to_bob_block)
+# Wait for challenge
+time.sleep(2)
+bob.start_exit(deposit1_utxo, coin['deposit_block'], eve_to_bob_block)
+bob.stop_watching_exits(deposit1_utxo)
+
+w3 = bob.root_chain.w3  # get w3 instance
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+
+bob.withdraw(deposit1_utxo)
+
+bob_balance_before = w3.eth.getBalance(bob.token_contract.account.address)
+bob.withdraw_bonds()
+bob_balance_after = w3.eth.getBalance(bob.token_contract.account.address)
+assert (
+    bob_balance_before < bob_balance_after
+), "END: Bob did not withdraw his bonds"
+
+bobTokensEnd = bob.token_contract.balance_of()
+
+print('Bob has {} tokens'.format(bobTokensEnd))
+assert (
+    bobTokensEnd == bobTokensStart + 1
+), "END: Bob has incorrect number of tokens"
+
+print('Plasma Cash `challengeBetween` success :)')

plasma_cash/child_chain/__init__.py

@@ -0,0 +1,16 @@
+from flask import Flask
+
+from dependency_config import container
+
+
+def create_app():
+    app = Flask(__name__)
+
+    # Create a child chain instance when creating a Flask app.
+    container.get_child_chain()
+
+    from . import server
+
+    app.register_blueprint(server.bp)
+
+    return app

plasma_cash/child_chain/block.py

@@ -0,0 +1,67 @@
+import rlp
+from rlp.sedes import CountableList, binary
+from web3.auto import w3
+
+from child_chain.exceptions import (CoinAlreadyIncludedException,
+                                    InvalidBlockSignatureException)
+from utils.merkle.sparse_merkle_tree import SparseMerkleTree
+from utils.utils import get_sender, sign
+
+from .transaction import Transaction
+
+
+class Block(rlp.Serializable):
+
+    fields = [('transaction_set', CountableList(Transaction)), ('sig', binary)]
+
+    def __init__(self, transaction_set=None, sig=b'\x00' * 65):
+        if transaction_set is None:
+            self.transactions = {}
+        else:
+            self.transactions = {tx.uid: tx for tx in transaction_set}
+        self.merkle = None
+        self.sig = sig
+
+    @property
+    def hash(self):
+        return w3.sha3(rlp.encode(self, UnsignedBlock))
+
+    @property
+    def merkle_hash(self):
+        return w3.sha3(rlp.encode(self))
+
+    @property
+    def transaction_set(self):
+        return list(self.transactions.values())
+
+    @property
+    def sender(self):
+        if self.sig == b'\x00' * 65:
+            raise InvalidBlockSignatureException('Block not signed')
+        return get_sender(self.hash, self.sig)
+
+    def merklize_transaction_set(self):
+        hashed_transaction_dict = {
+            tx.uid: tx.hash for tx in self.transactions.values()
+        }
+        self.merkle = SparseMerkleTree(64, hashed_transaction_dict)
+        return self.merkle.root
+
+    def add_tx(self, tx):
+        if tx.uid in self.transactions:
+            raise CoinAlreadyIncludedException('double spend rejected')
+        else:
+            self.transactions[tx.uid] = tx
+
+    # `uid` is the coin that was transferred
+    def get_tx_by_uid(self, uid):
+        if uid in self.transactions:
+            return self.transactions[uid]
+        else:
+            return Transaction(0, 0, 0, 0)
+
+    def sign(self, key):
+        self.sig = sign(self.hash, key)
+
+
+UnsignedBlock = Block.exclude(['sig'])

plasma_cash/child_chain/child_chain.py

@@ -0,0 +1,121 @@
+import rlp
+from ethereum import utils
+from web3.auto import w3
+
+from .block import Block
+from .exceptions import (InvalidPrevBlockException,
+                         InvalidTxSignatureException,
+                         PreviousTxNotFoundException, TxAlreadySpentException)
+from .transaction import Transaction
+
+
+class ChildChain(object):
+    '''
+    Operator runs child chain, watches all Deposit events and creates
+    deposit blocks
+    '''
+
+    def __init__(self, root_chain):
+        self.root_chain = root_chain  # PlasmaCash object from plasma_cash.py
+        self.authority = self.root_chain.account.address
+        self.key = self.root_chain.account.privateKey
+        self.blocks = {}
+        self.current_block = Block()
+        self.child_block_interval = 1000
+        self.current_block_number = 0
+
+        # Watch all deposit events, callback to self._send_deposit
+        self.root_chain.watch_event('Deposit', self._send_deposit, 0.1)
+
+    def _send_deposit(self, event):
+        ''' Called by event watcher and creates a deposit block '''
+        slot = event['args']['slot']
+        blknum = int(event['args']['blockNumber'])
+        # Currently, denomination is always 1. This may change in the future.
+        denomination = event['args']['denomination']
+        depositor = event['args']['from']
+        deposit_tx = Transaction(slot, 0, denomination, depositor)
+
+        # create a new plasma block on deposit
+        deposit_block = Block([deposit_tx])
+        self.blocks[blknum] = deposit_block
+
+    def submit_block(self):
+        ''' Submit the merkle root to the chain from the authority '''
+        block = self.current_block
+        block.make_mutable()
+        block.sign(self.key)
+        block.make_immutable()
+        self.current_block_number += self.child_block_interval
+        merkle_hash = w3.toHex(block.merklize_transaction_set())
+        self.root_chain.submit_block(merkle_hash)
+
+        self.blocks[self.current_block_number] = self.current_block
+        self.current_block = Block()
+        return str(self.current_block_number)
+
+    def send_transaction(self, transaction):
+        tx = rlp.decode(utils.decode_hex(transaction), Transaction)
+        # Reject transactions refering to a future block as prev_block
+        if (
+            tx.prev_block
+            > self.current_block_number + self.child_block_interval
+        ):
+            raise InvalidPrevBlockException('failed to send transaction')
+
+        # If the tx we are spending is not a deposit tx
+        if tx.prev_block % self.child_block_interval == 0:
+            # If the TX we are referencing was initially a deposit TX, then it
+            # does not have a signature attached
+
+            # The tx we are referencing should be included in a block
+            prev_tx = self.blocks[tx.prev_block].get_tx_by_uid(tx.uid)
+            if prev_tx is None:
+                raise PreviousTxNotFoundException('failed to send transaction')
+            # The tx we are referencing should not be spent
+            if prev_tx.spent:
+                raise TxAlreadySpentException('failed to send transaction')
+            # deposit tx if prev_block is 0
+            if (
+                prev_tx.prev_block % self.child_block_interval == 0
+                and utils.normalize_address(tx.sender) != prev_tx.new_owner
+            ):
+                raise InvalidTxSignatureException('failed to send transaction')
+            # `add_tx` automatically checks if the coin has already been moved
+            # in the current block
+            self.current_block.add_tx(tx)
+            prev_tx.spent = True  # Mark the previous tx as spent
+        # If the tx we are spending is a deposit tx
+        else:
+            self.current_block.add_tx(tx)
+        return tx.hash
+
+    def get_current_block(self):
+        return rlp.encode(self.current_block).hex()
+
+    def get_block(self, blknum):
+        if blknum > self.current_block_number:
+            return rlp.encode(Block()).hex()
+        else:
+            return rlp.encode(self.blocks[blknum]).hex()
+
+    def get_block_number(self):
+        return self.current_block_number
+
+    def get_proof(self, blknum, slot):
+        block = self.blocks[blknum]
+        block.merklize_transaction_set()
+        return block.merkle.create_merkle_proof(slot).hex()
+
+    def get_tx(self, blknum, slot):
+        block = self.blocks[blknum]
+        tx = block.get_tx_by_uid(slot)
+        return rlp.encode(tx).hex()
+
+    def get_tx_and_proof(self, blknum, slot):
+        tx = self.get_tx(blknum, slot)
+        if blknum % self.child_block_interval != 0:
+            proof = '00' * 8
+        else:
+            proof = self.get_proof(blknum, slot)
+        return tx, proof

plasma_cash/child_chain/exceptions.py

@@ -0,0 +1,26 @@
+class InvalidTxSignatureException(Exception):
+    """the signature of a tx is invalid"""
+
+
+class CoinAlreadyIncludedException(Exception):
+    """the coin uid has already been included in block"""
+
+
+class InvalidBlockSignatureException(Exception):
+    """the signature of a block is invalid"""
+
+
+class PreviousTxNotFoundException(Exception):
+    """previous transaction is not found"""
+
+
+class TxAlreadySpentException(Exception):
+    """the transaction is already spent"""
+
+
+class TxAmountMismatchException(Exception):
+    """tx input total amount is not equal to output total amount"""
+
+
+class InvalidPrevBlockException(Exception):
+    """prev block cannot be bigger than current block"""

plasma_cash/child_chain/server.py

@@ -0,0 +1,55 @@
+from flask import Blueprint, jsonify, request
+
+from dependency_config import container
+
+bp = Blueprint('api', __name__)
+
+
+@bp.route('/block/<blknum>', methods=['GET'])
+def get_block(blknum):
+    return container.get_child_chain().get_block(int(blknum))
+
+
+@bp.route('/block', methods=['GET'])
+def get_current_block():
+    return container.get_child_chain().get_current_block()
+
+
+@bp.route('/blocknumber', methods=['GET'])
+def get_block_number():
+    return str(container.get_child_chain().get_block_number())
+
+
+@bp.route('/tx_proof', methods=['GET'])
+def get_tx_and_proof():
+    blknum = int(request.args.get('blknum'))
+    slot = int(request.args.get('slot'))
+    tx, proof = container.get_child_chain().get_tx_and_proof(
+        int(blknum), int(slot)
+    )
+    return jsonify({'tx': tx, 'proof': proof})
+
+
+@bp.route('/tx', methods=['GET'])
+def get_tx():
+    blknum = int(request.args.get('blknum'))
+    slot = int(request.args.get('slot'))
+    return container.get_child_chain().get_tx(blknum, slot)
+
+
+@bp.route('/proof', methods=['GET'])
+def get_proof():
+    blknum = int(request.args.get('blknum'))
+    slot = int(request.args.get('slot'))
+    return container.get_child_chain().get_proof(blknum, slot)
+
+
+@bp.route('/submit_block', methods=['POST'])
+def submit_block():
+    return container.get_child_chain().submit_block()
+
+
+@bp.route('/send_tx', methods=['POST'])
+def send_tx():
+    tx = request.form['tx']
+    return container.get_child_chain().send_transaction(tx)

plasma_cash/child_chain/transaction.py

@@ -0,0 +1,54 @@
+import ethereum.utils
+import rlp
+from rlp.sedes import big_endian_int, binary
+from web3.auto import w3
+
+from utils.utils import get_sender, sign
+
+from .exceptions import InvalidTxSignatureException
+
+
+class Transaction(rlp.Serializable):
+
+    fields = [
+        ('uid', big_endian_int),
+        ('prev_block', big_endian_int),
+        ('denomination', big_endian_int),
+        ('new_owner', ethereum.utils.address),
+        ('sig', binary),
+    ]
+
+    def __init__(
+        self, uid, prev_block, denomination, new_owner, sig=b'\x00' * 65
+    ):
+        self.uid = uid
+        self.prev_block = prev_block
+        self.denomination = denomination
+        self.new_owner = ethereum.utils.normalize_address(new_owner)
+        self.sig = sig
+        self.spent = False  # not part of the rlp
+        self.make_mutable()
+
+    @property
+    def hash(self):
+        if self.prev_block != 0:
+            ret = w3.sha3(rlp.encode(self, UnsignedTransaction))
+        else:
+            ret = w3.soliditySha3(['uint64'], [self.uid])
+        return ret
+
+    @property
+    def merkle_hash(self):
+        return w3.sha3(rlp.encode(self))
+
+    @property
+    def sender(self):
+        if self.sig == b'\x00' * 65:
+            raise InvalidTxSignatureException('Tx not signed')
+        return get_sender(self.hash, self.sig)
+
+    def sign(self, key):
+        self.sig = sign(self.hash, key)
+
+
+UnsignedTransaction = Transaction.exclude(['sig'])

plasma_cash/client/child_chain_service.py

@@ -0,0 +1,73 @@
+import requests
+
+from .exceptions import RequestFailedException
+
+
+class ChildChainService(object):
+    def __init__(self, base_url, verify=False, timeout=5):
+        self.base_url = base_url
+        self.verify = verify
+        self.timeout = timeout
+
+    def request(self, end_point, method, params=None, data=None, headers=None):
+        url = self.base_url + end_point
+
+        response = requests.request(
+            method=method,
+            url=url,
+            params=params,
+            data=data,
+            headers=headers,
+            verify=self.verify,
+            timeout=self.timeout,
+        )
+
+        if response.ok:
+            return response
+        else:
+            raise RequestFailedException(
+                'failed with response: {}'.format(response)
+            )
+
+    def get_current_block(self):
+        end_point = '/block'
+        response = self.request(end_point, 'GET')
+        return response.text
+
+    def get_block_number(self):
+        end_point = '/blocknumber'
+        response = self.request(end_point, 'GET')
+        return int(response.text)
+
+    def get_block(self, blknum):
+        end_point = '/block/{}'.format(blknum)
+        response = self.request(end_point, 'GET')
+        return response.text
+
+    def get_proof(self, blknum, slot):
+        end_point = '/proof'
+        params = {'blknum': blknum, 'slot': slot}
+        response = self.request(end_point, 'GET', params=params)
+        return response.text
+
+    def get_tx_and_proof(self, blknum, slot):
+        end_point = '/tx_proof'
+        params = {'blknum': blknum, 'slot': slot}
+        response = self.request(end_point, 'GET', params=params)
+        return response.text
+
+    def get_tx(self, blknum, slot):
+        end_point = '/tx'
+        params = {'blknum': blknum, 'slot': slot}
+        response = self.request(end_point, 'GET', params=params)
+        return response.text
+
+    def submit_block(self):
+        end_point = '/submit_block'
+        response = self.request(end_point, 'POST')
+        return int(response.text)
+
+    def send_transaction(self, tx):
+        end_point = '/send_tx'
+        data = {'tx': tx}
+        self.request(end_point, 'POST', data=data)

plasma_cash/client/client.py

@@ -0,0 +1,438 @@
+import json
+
+import rlp
+from ethereum import utils
+
+from child_chain.block import Block
+from child_chain.transaction import Transaction, UnsignedTransaction
+
+from .child_chain_service import ChildChainService
+
+
+class Client(object):
+    def __init__(
+        self,
+        root_chain,
+        token_contract,
+        child_chain=ChildChainService('http://localhost:8546'),
+    ):
+        self.root_chain = root_chain
+        self.key = token_contract.account.privateKey
+        self.token_contract = token_contract
+        self.child_chain = child_chain
+        self.child_block_interval = 1000
+
+        # Proof related state
+        self.incl_proofs = {}
+        self.excl_proofs = {}
+        self.txs = {}
+
+        # Event watchers
+        self.watchers = {}
+        self.challenge_watchers = {}
+
+    # Token Functions
+
+    def register(self):
+        ''' Register a new player and grant 5 cards, for demo purposes'''
+        tx_hash, gas_used = self.token_contract.register()
+        return tx_hash, gas_used
+
+    def deposit(self, tokenId):
+        ''' Deposit happens by a use calling the erc721 token contract '''
+        tx_hash, gas_used = self.token_contract.deposit(tokenId)
+        return tx_hash, gas_used
+
+    # Plasma Functions
+
+    def start_exit(self, slot, prev_tx_blk_num, tx_blk_num):
+        '''
+        As a user, you declare that you want to exit a coin at slot `slot`
+        at the state which happened at block `tx_blk_num` and you also need to
+        reference a previous block
+        '''
+        # TODO The actual proof information should be passed to a user from its
+        # previous owners, this is a hacky way of getting the info from the
+        # operator which sould be changed in the future after the exiting
+        # process is more standardized
+        if tx_blk_num % self.child_block_interval != 0:
+            # In case the sender is exiting a Deposit transaction, they should
+            # just create a signed transaction to themselves. There is no need
+            # for a merkle proof.
+
+            # prev_block = 0 , denomination = 1
+            exiting_tx = Transaction(
+                slot, 0, 1, self.token_contract.account.address
+            )
+            exiting_tx.make_mutable()
+            exiting_tx.sign(self.key)
+            exiting_tx.make_immutable()
+            tx_hash, gas_used = self.root_chain.start_exit(
+                slot,
+                b'0x0',
+                rlp.encode(exiting_tx, UnsignedTransaction),
+                b'0x0',
+                b'0x0',
+                exiting_tx.sig,
+                0,
+                tx_blk_num,
+            )
+        else:
+            # Otherwise, they should get the raw tx info from the block
+            # And the merkle proof and submit these
+            exiting_tx, exiting_tx_proof = self.get_tx_and_proof(
+                tx_blk_num, slot
+            )
+            prev_tx, prev_tx_proof = self.get_tx_and_proof(
+                prev_tx_blk_num, slot
+            )
+
+            tx_hash, gas_used = self.root_chain.start_exit(
+                slot,
+                rlp.encode(prev_tx, UnsignedTransaction),
+                rlp.encode(exiting_tx, UnsignedTransaction),
+                prev_tx_proof,
+                exiting_tx_proof,
+                exiting_tx.sig,
+                prev_tx_blk_num,
+                tx_blk_num,
+            )
+        return tx_hash, gas_used
+
+    def challenge_before(self, slot, prev_tx_blk_num, tx_blk_num):
+        if tx_blk_num % self.child_block_interval != 0:
+            # In case the sender is exiting a Deposit transaction, they should
+            # just create a signed transaction to themselves. There is no need
+            # for a merkle proof.
+
+            # prev_block = 0 , denomination = 1
+            exiting_tx = Transaction(
+                slot, 0, 1, self.token_contract.account.address
+            )
+            exiting_tx.make_mutable()
+            exiting_tx.sign(self.key)
+            exiting_tx.make_immutable()
+            tx_hash, gas_used = self.root_chain.challenge_before(
+                slot,
+                b'0x0',
+                rlp.encode(exiting_tx, UnsignedTransaction),
+                b'0x0',
+                b'0x0',
+                exiting_tx.sig,
+                0,
+                tx_blk_num,
+            )
+        else:
+            # Otherwise, they should get the raw tx info from the block
+            # And the merkle proof and submit these
+            exiting_tx, exiting_tx_proof = self.get_tx_and_proof(
+                tx_blk_num, slot
+            )
+            prev_tx, prev_tx_proof = self.get_tx_and_proof(
+                prev_tx_blk_num, slot
+            )
+
+            tx_hash, gas_used = self.root_chain.challenge_before(
+                slot,
+                rlp.encode(prev_tx, UnsignedTransaction),
+                rlp.encode(exiting_tx, UnsignedTransaction),
+                prev_tx_proof,
+                exiting_tx_proof,
+                exiting_tx.sig,
+                prev_tx_blk_num,
+                tx_blk_num,
+            )
+        return tx_hash, gas_used
+
+    def respond_challenge_before(self, slot, challenging_block_number):
+        '''
+        Respond to an exit with invalid history challenge by proving that
+        you were given the coin under question
+        '''
+        challenging_tx, proof = self.get_tx_and_proof(
+            challenging_block_number, slot
+        )
+
+        tx_hash, gas_used = self.root_chain.respond_challenge_before(
+            slot,
+            challenging_block_number,
+            rlp.encode(challenging_tx, UnsignedTransaction),
+            proof,
+            challenging_tx.sig,
+        )
+        return tx_hash, gas_used
+
+    def challenge_between(self, slot, challenging_block_number):
+        '''
+        `Double Spend Challenge`: Challenge a double spend of a coin
+        with a spend between the exit's blocks
+        '''
+        challenging_tx, proof = self.get_tx_and_proof(
+            challenging_block_number, slot
+        )
+
+        tx_hash, gas_used = self.root_chain.challenge_between(
+            slot,
+            challenging_block_number,
+            rlp.encode(challenging_tx, UnsignedTransaction),
+            proof,
+            challenging_tx.sig,
+        )
+        return tx_hash, gas_used
+
+    def challenge_after(self, slot, challenging_block_number):
+        '''
+        `Exit Spent Coin Challenge`: Challenge an exit with a spend
+        after the exit's blocks
+        '''
+        challenging_tx, proof = self.get_tx_and_proof(
+            challenging_block_number, slot
+        )
+        tx_hash, gas_used = self.root_chain.challenge_after(
+            slot,
+            challenging_block_number,
+            rlp.encode(challenging_tx, UnsignedTransaction),
+            proof,
+            challenging_tx.sig,
+        )
+        return tx_hash, gas_used
+
+    def finalize_exit(self, slot):
+        tx_hash, gas_used = self.root_chain.finalize_exit(slot)
+        return tx_hash, gas_used
+
+    def finalize_exits(self):
+        tx_hash, gas_used = self.root_chain.finalize_exits()
+        return tx_hash, gas_used
+
+    def withdraw(self, slot):
+        tx_hash, gas_used = self.root_chain.withdraw(slot)
+        return tx_hash, gas_used
+
+    def withdraw_bonds(self):
+        tx_hash, gas_used = self.root_chain.withdraw_bonds()
+        return tx_hash, gas_used
+
+    def get_plasma_coin(self, slot):
+        return self.root_chain.get_plasma_coin(slot)
+
+    def get_block_root(self, blknum):
+        return self.root_chain.get_block_root(blknum)
+
+    def check_inclusion(self, leaf, root, slot, proof):
+        return self.root_chain.check_inclusion(leaf, root, slot, proof)
+
+    def check_exclusion(self, root, slot, proof):
+        return self.root_chain.check_exclusion(root, slot, proof)
+
+    # Child Chain Functions
+
+    def get_block_numbers(self, slot):
+        # First get the coin's deposit block
+        # todo efficiency -> start_block should be updated to the last block
+        # obtained last time
+        start_block = self.get_plasma_coin(slot)['deposit_block']
+
+        # Get next non-deposit block
+        next_deposit = (
+            (start_block + self.child_block_interval)
+            // self.child_block_interval
+            * self.child_block_interval
+        )
+        end_block = self.get_block_number()
+
+        # Create a list of indexes with coin's deposit block
+        # and all subsequent submitted blocks that followed
+        block_numbers = [start_block] + list(
+            range(next_deposit, end_block + 1, self.child_block_interval)
+        )
+        return block_numbers
+
+    def get_coin_history(self, slot):
+        block_numbers = self.get_block_numbers(slot)
+
+        incl_proofs = {}
+        excl_proofs = {}
+        txs = {}
+        for blknum in block_numbers:
+            blk_root = self.root_chain.get_block_root(blknum)
+            tx, proof = self.get_tx_and_proof(blknum, slot)
+            txs[blknum] = tx
+            if self.check_inclusion(tx, blk_root, slot, proof):
+                incl_proofs[blknum] = proof
+            else:
+                excl_proofs[blknum] = proof
+
+        # Save the proofs to the client's "state", and return
+        self.incl_proofs[slot] = incl_proofs
+        self.excl_proofs[slot] = excl_proofs
+        self.txs[slot] = txs
+        return incl_proofs, excl_proofs
+
+    # received_proofs should be a dictionary with merkle branches for each
+    # block
+    def verify_coin_history(self, slot, incl_proofs, excl_proofs):
+        # Sanity checks, make sure incl_proofs and excl_proofs have all the
+        # correct keys for the coin
+        incl_keys = set(incl_proofs)
+        excl_keys = set(excl_proofs)
+        if len(incl_keys.intersection(excl_keys)) != 0:
+            return False
+
+        # gets all of the coin's block numbers
+        block_numbers = self.get_block_numbers(slot)
+        # ensure that all keys are included
+        if incl_keys.union(excl_keys) != set(block_numbers):
+            return False
+
+        # assert inclusion proofs
+        for blknum, proof in incl_proofs.items():
+            blk_root = self.root_chain.get_block_root(blknum)
+            # should we be polling the tx from the operator or trusting the
+            # receiver?
+            tx = self.get_tx(blknum, slot)
+            if not self.check_inclusion(tx, blk_root, slot, proof):
+                return False
+
+        # assert exclusion proof / i.e. leaf at that slot is empty hash
+        for blknum, proof in excl_proofs.items():
+            blk_root = self.root_chain.get_block_root(blknum)
+            if not self.check_exclusion(blk_root, slot, proof):
+                return False
+        # If it does not hit any of the return false branches, it's OK
+        return True
+
+    def submit_block(self):
+        return self.child_chain.submit_block()
+
+    def send_transaction(self, slot, prev_block, new_owner):
+        new_owner = utils.normalize_address(new_owner)
+        tx = Transaction(slot, prev_block, 1, new_owner)
+        tx.make_mutable()
+        tx.sign(self.key)
+        tx.make_immutable()
+        self.child_chain.send_transaction(rlp.encode(tx, Transaction).hex())
+        return tx
+
+    def watch_challenges(self, slot):
+        self.challenge_watchers[slot] = self.root_chain.watch_event(
+            'ChallengedExit',
+            self._respond_to_challenge,
+            0.1,
+            filters={'slot': slot},
+        )
+
+    def _respond_to_challenge(self, event):
+        slot = event['args']['slot']
+        print(
+            "CHALLENGE DETECTED by {} -- slot: {}".format(
+                self.token_contract.account.address, slot
+            )
+        )
+        # fetch coin history
+        incl_proofs, excl_proofs = self.get_coin_history(slot)
+        received_block = max(incl_proofs.keys())
+        self.respond_challenge_before(slot, received_block)
+
+    def stop_watching_challenges(self, slot):
+        # a user stops watching exits of a particular coin after transferring
+        # it to another plasma user
+        event_filter = self.challenge_watchers[slot]
+        self.root_chain.w3.eth.uninstallFilter(event_filter.filter_id)
+
+    def watch_exits(self, slot):
+        # TODO figure out how to have this function be invoked automatically
+        self.watchers[slot] = self.root_chain.watch_event(
+            'StartedExit', self._respond_to_exit, 0.1, filters={'slot': slot}
+        )
+
+    def _respond_to_exit(self, event):
+        ''' Called by event watcher and checks that the exit event is
+        legitimate
+        '''
+        slot = event['args']['slot']
+        owner = event['args']['owner']
+        print(
+            "EXIT DETECTED by {} -- slot: {}, owner: {}".format(
+                self.token_contract.account.address, slot, owner
+            )
+        )
+
+        # A coin-owner will automatically start a challenge if he believes he
+        # owns a coin that has been exited by someone else
+        if owner != self.token_contract.account.address:
+            print("invalid exit...challenging")
+
+            # fetch exit information
+            exit_details = self.root_chain.get_exit(slot)
+            [owner, prev_block, exit_block, state] = exit_details
+
+            # fetch coin history
+            incl_proofs, excl_proofs = self.get_coin_history(slot)
+            blocks = self.get_block_numbers(slot)  # skip the deposit tx block
+            for blk in blocks:
+                if blk not in incl_proofs:
+                    continue
+                if blk > exit_block:
+                    print(
+                        'CHALLENGE AFTER -- {} at block {}'.format(slot, blk)
+                    )
+                    self.challenge_after(slot, blk)
+                    break
+                elif prev_block < blk < exit_block:
+                    print(
+                        'CHALLENGE BETWEEN --  {} at block {}'.format(
+                            slot, blk
+                        )
+                    )
+                    self.challenge_between(slot, blk)
+                    break
+                elif blk < prev_block < exit_block:
+                    # Need to find a previous block
+                    tx = self.get_tx(blk, slot)
+                    print(
+                        'CHALLENGE BEFORE --  {} at prev block {} / block {}'
+                        .format(
+                            slot, tx.prev_block, blk
+                        )
+                    )
+                    self.challenge_before(slot, tx.prev_block, blk)
+                    break
+        else:
+            print("valid exit")
+
+    def stop_watching_exits(self, slot):
+        # a user stops watching exits of a particular coin after transferring
+        # it to another plasma user
+        event_filter = self.watchers[slot]
+        self.root_chain.w3.eth.uninstallFilter(event_filter.filter_id)
+
+    def get_block_number(self):
+        return self.child_chain.get_block_number()
+
+    def get_current_block(self):
+        block = self.child_chain.get_current_block()
+        return rlp.decode(utils.decode_hex(block), Block)
+
+    def get_block(self, blknum):
+        block = self.child_chain.get_block(blknum)
+        return rlp.decode(utils.decode_hex(block), Block)
+
+    def get_tx(self, blknum, slot):
+        tx_bytes = self.child_chain.get_tx(blknum, slot)
+        tx = rlp.decode(utils.decode_hex(tx_bytes), Transaction)
+        return tx
+
+    def get_tx_and_proof(self, blknum, slot):
+        data = json.loads(self.child_chain.get_tx_and_proof(blknum, slot))
+        tx = rlp.decode(utils.decode_hex(data['tx']), Transaction)
+        proof = utils.decode_hex(data['proof'])
+        return tx, proof
+
+    def get_proof(self, blknum, slot):
+        return utils.decode_hex(self.child_chain.get_proof(blknum, slot))
+
+    def get_all_deposits(self):
+        return self.root_chain.get_all_deposits(
+            self.root_chain.account.address
+        )

plasma_cash/client/exceptions.py

@@ -0,0 +1,2 @@
+class RequestFailedException(Exception):
+    """request failed without success http status"""

plasma_cash/contract_binds/base/contract.py

@@ -0,0 +1,147 @@
+import json
+import time
+from threading import Thread
+
+from web3.utils.events import get_event_data
+
+from ..utils.getWeb3 import getWeb3
+
+
+class Contract(object):
+    '''Base class for interfacing with a contract'''
+
+    def __init__(self, keystore, address, abi_file, endpoint):
+        w3 = getWeb3(endpoint)
+        with open(abi_file) as f:
+            abi = json.load(f)['abiDefinition']
+        contract = w3.eth.contract(abi=abi, address=address)
+        self.w3 = w3
+
+        if keystore is not None:
+            self.account = self.to_account(keystore)
+        self.contract = contract
+
+    def to_account(self, data):
+        account = self.w3.eth.account.privateKeyToAccount(data)
+        del data
+        return account
+
+    def sign_and_send(self, func, args, value=0, gas=1000000):
+        ''' Expecting all arguments in 1 array '''
+        signed_tx = self._sign_function_call(
+            func,
+            args,
+            value,
+            # may need to change gas
+            gas,
+        )
+
+        try:
+            tx_hash, gas_used = self._send_raw_tx(signed_tx)
+        except Exception as e:
+            print('FAILURE: ', e)
+            info = 'Failed: {}, Args: {}'.format(func.__name__, args)
+            print(info)
+        return tx_hash, gas_used
+
+    def send_transaction(self, to, value):
+        signed_tx = self._sign_transaction(to, value)
+        return self._send_raw_tx(signed_tx)
+
+    def _sign_transaction(self, to, value):
+        gas = 21000
+        gasPrice = self.w3.toWei('10', 'gwei')
+
+        raw_tx = {
+            'chainId': int(self.w3.version.network),
+            'to': self.w3.toChecksumAddress(to),
+            'value': value,
+            'gas': gas,
+            'gasPrice': gasPrice,
+            'nonce': self.w3.eth.getTransactionCount(self.account.address),
+        }
+
+        # print(raw_tx)
+
+        signed_tx = self.account.signTransaction(raw_tx)
+
+        return signed_tx
+
+    def _sign_function_call(self, func, args, value, gas):
+        """
+            Takes reading and timestamp and creates a
+            raw transaction call to `ping` at the target contract
+            TODO: Add option to modify gas
+        """
+        # Build the raw transaction
+        raw_tx = func(*args).buildTransaction(
+            {
+                'gas': gas,
+                'value': value,
+                'nonce': self.w3.eth.getTransactionCount(self.account.address),
+            }
+        )
+        raw_tx['to'] = self.w3.toChecksumAddress(raw_tx['to'])
+
+        # Sign the transaction with the meter's private key
+        signed_tx = self.account.signTransaction(raw_tx)
+
+        return signed_tx
+
+    def _send_raw_tx(self, signed_tx):
+        tx_hash = self.w3.eth.sendRawTransaction(signed_tx.rawTransaction)
+        gas_used = self.waitForTxReceipt(tx_hash)['gasUsed']
+        return tx_hash, gas_used
+
+    def waitForTxReceipt(self, tx):
+        receipt = self.w3.eth.getTransactionReceipt(tx)
+        while receipt is None:
+            time.sleep(1)  # Block time avg
+            receipt = self.w3.eth.getTransactionReceipt(tx)
+        return receipt
+
+    def get_event_data(self, event_name, tx_hash):
+        tx_logs = self.w3.eth.getTransactionReceipt(tx_hash)['logs']
+        event_abi = self.contract._find_matching_event_abi(event_name)
+        matched = []
+        for log in tx_logs:
+            try:
+                d = get_event_data(event_abi, log)
+            except Exception as e:
+                continue
+            matched.append(d)
+        return matched
+
+    def watch_event(
+        self,
+        event_name,
+        callback,
+        interval,
+        fromBlock=0,
+        toBlock='latest',
+        filters=None,
+    ):
+        event_filter = self.install_filter(
+            event_name, fromBlock, toBlock, filters
+        )
+        Thread(
+            target=self.watcher,
+            args=(event_filter, callback, interval),
+            daemon=True,
+        ).start()
+        return event_filter
+
+    def watcher(self, event_filter, callback, interval):
+        while True:
+            for event in event_filter.get_new_entries():
+                callback(event)
+                time.sleep(interval)
+
+    def install_filter(
+        self, event_name, fromBlock=0, toBlock='latest', filters=None
+    ):
+        event = getattr(self.contract.events, event_name)
+        eventFilter = event.createFilter(
+            fromBlock=fromBlock, toBlock=toBlock, argument_filters=filters
+        )
+        return eventFilter

plasma_cash/contract_binds/erc721.py

@@ -0,0 +1,35 @@
+from .base.contract import Contract
+
+
+class ERC721(Contract):
+    '''ERC721 bindings for python '''
+
+    def __init__(self, private_key, abi_file, address, endpoint):
+        super().__init__(private_key, address, abi_file, endpoint)
+
+    def register(self):
+        args = []
+        return self.sign_and_send(self.contract.functions.register, args)
+
+    def transfer(self, to, tokenId, data=None):
+        if data is None:
+            args = [self.account.address, to, tokenId]
+        else:
+            args = [self.account.address, to, tokenId, data]
+        return self.sign_and_send(
+            self.contract.functions.safeTransferFrom, args
+        )
+
+    def deposit(self, tokenId):
+        '''
+        Slot is providable by the user however there is a validity check
+        performed in the contract. It always needs to be the value of
+        `NUM_COINS` in the plasma contract
+        '''
+        args = [tokenId]
+        return self.sign_and_send(
+            self.contract.functions.depositToPlasma, args
+        )
+
+    def balance_of(self):
+        return self.contract.functions.balanceOf(self.account.address).call()

plasma_cash/contract_binds/plasma_cash.py

@@ -0,0 +1,179 @@
+from .base.contract import Contract
+
+
+class PlasmaCash(Contract):
+    '''Plasma Cash bindings for python '''
+
+    def __init__(self, private_key, abi_file, address, endpoint):
+        super().__init__(private_key, address, abi_file, endpoint)
+        self.BOND = self.w3.toWei(0.1, 'ether')
+
+    def challenge_before(
+        self,
+        slot,
+        prev_tx_bytes,
+        exiting_tx_bytes,
+        prev_tx_inclusion_proof,
+        exiting_tx_inclusion_proof,
+        sig,
+        prev_tx_block_num,
+        exiting_tx_block_num,
+    ):
+        args = [
+            slot,
+            prev_tx_bytes,
+            exiting_tx_bytes,
+            prev_tx_inclusion_proof,
+            exiting_tx_inclusion_proof,
+            sig,
+            [prev_tx_block_num, exiting_tx_block_num],
+        ]
+
+        return self.sign_and_send(
+            self.contract.functions.challengeBefore, args, value=self.BOND
+        )
+
+    def respond_challenge_before(
+        self,
+        slot,
+        challenging_block_number,
+        challenging_transaction,
+        proof,
+        sig,
+    ):
+        args = [
+            slot,
+            challenging_block_number,
+            challenging_transaction,
+            proof,
+            sig,
+        ]
+        return self.sign_and_send(
+            self.contract.functions.respondChallengeBefore, args
+        )
+
+    def challenge_between(
+        self,
+        slot,
+        challenging_block_number,
+        challenging_transaction,
+        proof,
+        sig,
+    ):
+        args = [
+            slot,
+            challenging_block_number,
+            challenging_transaction,
+            proof,
+            sig,
+        ]
+        return self.sign_and_send(
+            self.contract.functions.challengeBetween, args
+        )
+
+    def challenge_after(
+        self,
+        slot,
+        challenging_block_number,
+        challenging_transaction,
+        proof,
+        sig,
+    ):
+        args = [
+            slot,
+            challenging_block_number,
+            challenging_transaction,
+            proof,
+            sig,
+        ]
+        return self.sign_and_send(self.contract.functions.challengeAfter, args)
+
+    def start_exit(
+        self,
+        uid,
+        prev_tx,
+        exiting_tx,
+        prev_tx_proof,
+        exiting_tx_proof,
+        sigs,
+        prev_tx_blk_num,
+        tx_blk_num,
+    ):
+        args = [
+            uid,
+            prev_tx,
+            exiting_tx,
+            prev_tx_proof,
+            exiting_tx_proof,
+            sigs,
+            [prev_tx_blk_num, tx_blk_num],
+        ]
+        return self.sign_and_send(
+            self.contract.functions.startExit, args, value=self.BOND
+        )
+
+    def finalize_exits(self):
+        args = []
+        return self.sign_and_send(self.contract.functions.finalizeExits, args)
+
+    def finalize_exit(self, slot):
+        args = [slot]
+        return self.sign_and_send(self.contract.functions.finalizeExit, args)
+
+    def withdraw(self, uid):
+        args = [uid]
+        return self.sign_and_send(self.contract.functions.withdraw, args)
+
+    def submit_block(self, root):
+        args = [root]
+        return self.sign_and_send(self.contract.functions.submitBlock, args)
+
+    def withdraw_bonds(self):
+        return self.sign_and_send(self.contract.functions.withdrawBonds, [])
+
+    def get_plasma_coin(self, slot):
+        data = self.contract.functions.getPlasmaCoin(slot).call()
+        ret = {
+            'uid': data[0],
+            'deposit_block': data[1],
+            'denomination': data[2],
+            'owner': data[3],
+            'contract_address': data[4],
+            'state': data[5],
+        }
+        return ret
+
+    def get_all_deposits(self, address, fromBlock=0):
+        event_filter = self.contract.events.Deposit.createFilter(
+            fromBlock=fromBlock,
+            toBlock='latest',
+            argument_filters={'from': address},
+        )
+        return event_filter.get_all_entries()
+
+    def get_block_root(self, blknum):
+        ret = self.contract.functions.getBlockRoot(blknum).call()
+        return ret
+
+    def get_exit(self, slot):
+        ret = self.contract.functions.getExit(slot).call()
+        return ret
+
+    def check_inclusion(self, tx, root, slot, proof):
+        if tx.prev_block == 0:  # deposit tx
+            ret = tx.hash == root
+        else:
+            ret = self.contract.functions.checkMembership(
+                tx.hash, root, slot, proof
+            ).call()
+        return ret
+
+    def check_exclusion(self, root, slot, proof):
+        empty_hash = (
+            '0x290decd9548b62a8d60345a988386'
+            + 'fc84ba6bc95484008f6362f93160ef3e563'
+        )
+        ret = self.contract.functions.checkMembership(
+            empty_hash, root, slot, proof
+        ).call()
+        return ret

plasma_cash/contract_binds/utils/colors.py

@@ -0,0 +1,17 @@
+class Colors:
+    GREEN = '\033[92m'
+    YELLOW = '\033[93m'
+    RED = '\033[91m'
+    END = '\033[0m'
+
+
+def green(txt):
+    return Colors.GREEN + txt + Colors.END
+
+
+def yellow(txt):
+    return Colors.YELLOW + txt + Colors.END
+
+
+def red(txt):
+    return Colors.RED + txt + Colors.END

plasma_cash/contract_binds/utils/formatters.py

@@ -0,0 +1,7 @@
+def normalize(d):
+    if type(d) is str:
+        return bytes(d, 'utf-8')
+    elif type(d) is list:
+        return [bytes(x, 'utf-8') for x in d]
+    else:
+        return d

plasma_cash/contract_binds/utils/getWeb3.py

@@ -0,0 +1,27 @@
+import time
+
+
+def getWeb3(endpoint=None):
+    if endpoint is None:
+        from web3.auto import w3
+    elif 'http' in endpoint:
+        from web3 import Web3, HTTPProvider
+
+        w3 = Web3(HTTPProvider(endpoint))
+    else:
+        from web3 import Web3, IPCProvider
+        from web3.middleware import geth_poa_middleware
+
+        w3 = Web3(IPCProvider(endpoint))
+        w3.middleware_stack.inject(geth_poa_middleware, layer=0)
+    # w3.eth.defaultAccount = w3.eth.accounts[0]
+    return w3
+
+
+def waitForTransactionReceipt(w3, tx_hash):
+    while True:
+        tx_receipt = w3.eth.getTransactionReceipt(tx_hash)
+        if tx_receipt is not None:
+            break
+        time.sleep(1)
+    return tx_receipt

plasma_cash/demo.py

@@ -0,0 +1,114 @@
+from time import sleep
+
+from client.client import Client
+from dependency_config import container
+from utils.utils import increaseTime
+
+alice = Client(container.get_root('alice'), container.get_token('alice'))
+bob = Client(container.get_root('bob'), container.get_token('bob'))
+charlie = Client(container.get_root('charlie'), container.get_token('charlie'))
+authority = Client(
+    container.get_root('authority'), container.get_token('authority')
+)
+w3 = alice.root_chain.w3  # get w3 instance
+
+# Give alice 5 tokens
+alice.register()
+
+aliceTokensStart = alice.token_contract.balance_of()
+print('Alice has {} tokens'.format(aliceTokensStart))
+assert aliceTokensStart == 5, "START: Alice has incorrect number of tokens"
+bobTokensStart = bob.token_contract.balance_of()
+print('Bob has {} tokens'.format(bobTokensStart))
+assert bobTokensStart == 0, "START: Bob has incorrect number of tokens"
+charlieTokensStart = charlie.token_contract.balance_of()
+print('Charlie has {} tokens'.format(charlieTokensStart))
+assert charlieTokensStart == 0, "START: Charlie has incorrect number of tokens"
+
+# Alice deposits 3 of her coins to the plasma contract and gets 3 plasma nft
+# utxos in return
+tokenId = 1
+tx_hash, gas_used = alice.deposit(tokenId)
+event_data = alice.root_chain.get_event_data('Deposit', tx_hash)
+print('ALICE EVENT DATA1', event_data[0]['args'])
+
+tx_hash, gas_used = alice.deposit(tokenId + 1)
+event_data = alice.root_chain.get_event_data('Deposit', tx_hash)
+deposit2_utxo = event_data[0]['args']['slot']
+deposit2_block_number = event_data[0]['args']['blockNumber']
+print('ALICE EVENT DATA2', event_data[0]['args'])
+
+tx_hash, gas_used = alice.deposit(tokenId + 2)
+event_data = alice.root_chain.get_event_data('Deposit', tx_hash)
+deposit3_utxo = event_data[0]['args']['slot']
+deposit3_block_number = event_data[0]['args']['blockNumber']
+print('ALICE EVENT DATA3', event_data[0]['args'])
+
+
+# Check that all deposits have registered
+sleep(2)
+registered_deposits = alice.get_all_deposits()
+assert len(registered_deposits) == 3, "Alice has incorrect number of deposits"
+
+# Alice to Bob, and Alice to Charlie. We care about the Alice to Bob
+# transaction
+alice_to_bob = alice.send_transaction(
+    deposit3_utxo, deposit3_block_number, bob.token_contract.account.address
+)
+random_tx = alice.send_transaction(
+    deposit2_utxo,
+    deposit2_block_number,
+    charlie.token_contract.account.address,
+)
+plasma_block1 = authority.submit_block()
+
+# Add an empty block in betweeen (for proof of exclusion reasons)
+authority.submit_block()
+
+# Bob to Charlie
+bob_to_charlie = bob.send_transaction(
+    deposit3_utxo, plasma_block1, charlie.token_contract.account.address
+)
+
+# This is the info that bob is required to send to charlie. This happens on
+# the P2P layer
+incl_proofs, excl_proofs = bob.get_coin_history(deposit3_utxo)
+
+# Charlie receives them, verifies the validity. If found invalid, charlie
+# should not accept them and the demo fails (similar to how you shouldn't sell
+# a good when you're given counterfeit currency)
+assert charlie.verify_coin_history(deposit3_utxo, incl_proofs, excl_proofs)
+
+plasma_block2 = authority.submit_block()
+
+# Block has been submitted, now we start watching for exits of our coin
+charlie.watch_exits(deposit3_utxo)
+
+# Charlie should be able to submit an exit by referencing blocks 0 and 1 which
+# included his transaction.
+charlie.start_exit(deposit3_utxo, plasma_block1, plasma_block2)
+
+# We exited the coin so we should stop watching
+charlie.stop_watching_exits(deposit3_utxo)
+
+# Here we should start watching for challenges
+
+# After 8 days pass, charlie's exit should be finalizable
+increaseTime(w3, 8 * 24 * 3600)
+authority.finalize_exits()
+
+# Charlie should now be able to withdraw the utxo which included token 2 to his
+# wallet.
+charlie.withdraw(deposit3_utxo)
+
+aliceTokensEnd = alice.token_contract.balance_of()
+print('Alice has {} tokens'.format(aliceTokensEnd))
+assert aliceTokensEnd == 2, "END: Alice has incorrect number of tokens"
+bobTokensEnd = bob.token_contract.balance_of()
+print('Bob has {} tokens'.format(bobTokensEnd))
+assert bobTokensEnd == 0, "END: Bob has incorrect number of tokens"
+charlieTokensEnd = charlie.token_contract.balance_of()
+print('Charlie has {} tokens'.format(charlieTokensEnd))
+assert charlieTokensEnd == 1, "END: Charlie has incorrect number of tokens"
+
+print('Plasma Cash with ERC721 tokens success :)')

plasma_cash/dependency_config.py

@@ -0,0 +1,48 @@
+from child_chain.child_chain import ChildChain
+from config import plasma_config
+from contract_binds.erc721 import ERC721
+from contract_binds.plasma_cash import PlasmaCash
+
+
+class DependencyContainer(object):
+    def __init__(self):
+        self._child_chain = None
+        self.root_chain_abi = '../server/build/contracts/RootChain.json'
+        self.token_contract_abi = '../server/build/contracts/CryptoCards.json'
+        self.endpoint = 'http://localhost:8545'
+        self.root_chain = PlasmaCash(
+            plasma_config['authority'],
+            self.root_chain_abi,
+            plasma_config['root_chain'],
+            self.endpoint,
+        )
+
+    def get_root(self, key, index=None):
+        private_key = (
+            plasma_config[key] if index is None else plasma_config[key][index]
+        )
+        return PlasmaCash(
+            private_key,
+            self.root_chain_abi,
+            plasma_config['root_chain'],
+            self.endpoint,
+        )
+
+    def get_token(self, key, index=None):
+        private_key = (
+            plasma_config[key] if index is None else plasma_config[key][index]
+        )
+        return ERC721(
+            private_key,
+            self.token_contract_abi,
+            plasma_config['token_contract'],
+            self.endpoint,
+        )
+
+    def get_child_chain(self):
+        if self._child_chain is None:
+            self._child_chain = ChildChain(self.root_chain)
+        return self._child_chain
+
+
+container = DependencyContainer()

plasma_cash/dump_test_data.py

@@ -0,0 +1,25 @@
+import rlp
+
+from child_chain.transaction import Transaction, UnsignedTransaction
+from dependency_config import container
+
+token_contract = container.get_token('alice')
+tx = Transaction(5, 0, 1, token_contract.account.address)
+tx_hex = rlp.encode(tx, UnsignedTransaction).hex()
+print(
+    'Transaction(5, 0, 1, {}): {}'.format(
+        token_contract.account.address, tx_hex
+    )
+)
+
+tx = Transaction(5, 85478557858583, 1, token_contract.account.address)
+tx_hex = rlp.encode(tx, UnsignedTransaction).hex()
+print(
+    'Transaction(5, 85478557858583, 1, {}): {}'.format(
+        token_contract.account.address, tx_hex
+    )
+)
+
+tx.sign(token_contract.account.privateKey)
+print('Transaction Hash: {}'.format(tx.hash.hex()))
+print('Transaction Sig: {}'.format(tx.sig.hex()))

plasma_cash/requirements.txt

@@ -0,0 +1,15 @@
+Flask==1.0.2
+requests==2.18.4
+rlp==0.6.0
+ethereum==2.3.1
+
+# web3 fork
+-e git+https://github.com/gakonst/web3.py#egg=web3
+
+# linting
+flake8==3.5.0
+black==18.6b4
+isort==4.3.4
+
+# testing
+pytest==3.6.0

plasma_cash/unit_test.py

@@ -0,0 +1,114 @@
+import pytest
+from eth_utils.crypto import keccak
+from hexbytes import HexBytes
+
+from utils.merkle.sparse_merkle_tree import SparseMerkleTree
+
+empty_val = b'\x00' * 32
+default_hash = keccak(empty_val)
+dummy_val = keccak(2)
+dummy_val_2 = keccak(3)
+
+
+class TestSparseMerkleTree(object):
+    def test_size_limits(self):
+        with pytest.raises(SparseMerkleTree.TreeSizeExceededException):
+            SparseMerkleTree(depth=0, leaves={0: '0', 1: '1'})
+        with pytest.raises(SparseMerkleTree.TreeSizeExceededException):
+            SparseMerkleTree(
+                depth=1, leaves={0: empty_val, 1: empty_val, 2: empty_val}
+            )
+
+    def test_empty_SMT(self):
+        emptyTree = SparseMerkleTree(64, {})
+        assert len(emptyTree.leaves) == 0
+        assert (
+            emptyTree.root
+            == bytes(HexBytes('0x6f35419d1da1260bc0f33d52e8f6d73fc5d672c0dca13bb960b4ae1adec17937'))
+        )
+
+    def test_all_leaves_with_val(self):
+        leaves = {0: dummy_val, 1: dummy_val, 2: dummy_val, 3: dummy_val}
+        tree = SparseMerkleTree(depth=2, leaves=leaves)
+        mid_level_val = keccak(dummy_val * 2)
+        assert tree.root == keccak(mid_level_val + mid_level_val)
+
+    def test_empty_leaves(self):
+        tree = SparseMerkleTree(depth=2)
+        mid_level_val = keccak(default_hash * 2)
+        assert tree.root == keccak(mid_level_val * 2)
+
+    def test_empty_left_leave(self):
+        leaves = {1: dummy_val, 2: dummy_val, 3: dummy_val}
+        tree = SparseMerkleTree(depth=2, leaves=leaves)
+        mid_left_val = keccak(default_hash + dummy_val)
+        mid_right_val = keccak(dummy_val * 2)
+        assert tree.root == keccak(mid_left_val + mid_right_val)
+
+    def test_empty_right_leave(self):
+        leaves = {0: dummy_val, 2: dummy_val, 3: dummy_val}
+        tree = SparseMerkleTree(depth=2, leaves=leaves)
+        mid_left_val = keccak(dummy_val + default_hash)
+        mid_right_val = keccak(dummy_val * 2)
+        assert tree.root == keccak(mid_left_val + mid_right_val)
+
+    def test_create_merkle_proof(self):
+        leaves = {0: dummy_val, 2: dummy_val, 3: dummy_val_2}
+        tree = SparseMerkleTree(depth=2, leaves=leaves)
+        mid_left_val = keccak(dummy_val + default_hash)
+        mid_right_val = keccak(dummy_val + dummy_val_2)
+        assert (
+            tree.create_merkle_proof(0)
+            == (2).to_bytes(8, byteorder='big') + mid_right_val
+        )
+        assert (
+            tree.create_merkle_proof(1)
+            == (3).to_bytes(8, byteorder='big') + dummy_val + mid_right_val
+        )
+        assert (
+            tree.create_merkle_proof(2)
+            == (3).to_bytes(8, byteorder='big') + dummy_val_2 + mid_left_val
+        )
+        assert (
+            tree.create_merkle_proof(3)
+            == (3).to_bytes(8, byteorder='big') + dummy_val + mid_left_val
+        )
+
+    def test_old(self):
+        slot = 2
+        txHash = HexBytes(
+            '0xcf04ea8bb4ff94066eb84dd932f9e66d1c9f40d84d5491f5a7735200de010d84'
+        )
+        slot2 = 600
+        txHash2 = HexBytes(
+            '0xabcabcabacbc94566eb84dd932f9e66d1c9f40d84d5491f5a7735200de010d84'
+        )
+        slot3 = 30000
+        txHash3 = HexBytes(
+            '0xabcaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1c9f40d84d5491f5a7735200de010d84'
+        )
+        tx = {slot: txHash, slot2: txHash2, slot3: txHash3}
+        tree = SparseMerkleTree(64, tx)
+        for s in tx.keys():
+            proof = tree.create_merkle_proof(s)
+            inc = tree.verify(s, proof)
+            assert inc
+
+    def test_real_slot_proofs(self):
+        slot = 14414645988802088183
+        txHash = HexBytes('0x510a183d5457e0d22951440a273f0d8e28e01d15f750d79fd1b27442299f7220')
+        tree = SparseMerkleTree(64, {slot: txHash})
+        proof = tree.create_merkle_proof(slot)
+        inc = tree.verify(slot, proof)
+        assert inc
+
+    def test_real_tree_roots(self):
+        slot = 14414645988802088183
+        txHash = HexBytes('0x4b114962ecf0d681fa416dc1a6f0255d52d701ab53433297e8962065c9d439bd')
+        tree = SparseMerkleTree(64, {slot: txHash})
+        assert tree.root == bytes(HexBytes('0x0ed6599c03641e5a20d9688f892278dbb48bbcf8b1ff2c9a0e2b7423af831a83'))
+
+        slot = 14414645988802088183
+        txHash = HexBytes('0x510a183d5457e0d22951440a273f0d8e28e01d15f750d79fd1b27442299f7220')
+        tree = SparseMerkleTree(64, {slot: txHash})
+        assert tree.root == bytes(HexBytes('0x8d0ae4c94eaad54df5489e5f9d62eeb4bf06ff774a00b925e8a52776256e910f'))

plasma_cash/utils/merkle/sparse_merkle_tree.py

@@ -0,0 +1,117 @@
+from collections import OrderedDict
+
+from eth_utils.crypto import keccak
+
+
+class SparseMerkleTree(object):
+    def __init__(self, depth=64, leaves={}):
+        self.depth = depth
+        if len(leaves) > 2 ** depth:
+            raise self.TreeSizeExceededException(
+                'tree with depth {} cannot have {} leaves'.format(
+                    depth, len(leaves)
+                )
+            )
+
+        # Sort the transaction dict by index.
+        self.leaves = OrderedDict(sorted(leaves.items(), key=lambda t: t[0]))
+        self.default_nodes = self.create_default_nodes(self.depth)
+        if leaves:
+            self.tree = self.create_tree(
+                self.leaves, self.depth, self.default_nodes
+            )
+            self.root = self.tree[-1][0]
+        else:
+            self.tree = []
+            self.root = self.default_nodes[self.depth]
+
+    def create_default_nodes(self, depth):
+        # Default nodes are the nodes whose children are both empty nodes at
+        # each level.
+        default_hash = keccak(b'\x00' * 32)
+        default_nodes = [default_hash]
+        for level in range(1, depth + 1):
+            prev_default = default_nodes[level - 1]
+            default_nodes.append(keccak(prev_default * 2))
+        return default_nodes
+
+    def create_tree(self, ordered_leaves, depth, default_nodes):
+        tree = [ordered_leaves]
+        tree_level = ordered_leaves
+        for level in range(depth):
+            next_level = {}
+            for index, value in tree_level.items():
+                if index % 2 == 0:
+                    co_index = index + 1
+                    if co_index in tree_level:
+                        next_level[index // 2] = keccak(
+                            value + tree_level[co_index]
+                        )
+                    else:
+                        next_level[index // 2] = keccak(
+                            value + default_nodes[level]
+                        )
+                else:
+                    # If the node is a right node, check if its left sibling is
+                    # a default node.
+                    co_index = index - 1
+                    if co_index not in tree_level:
+                        next_level[index // 2] = keccak(
+                            default_nodes[level] + value
+                        )
+            tree_level = next_level
+            tree.append(tree_level)
+        return tree
+
+    def create_merkle_proof(self, uid):
+        # Generate a merkle proof for a leaf with provided index.
+        # First `depth/8` bytes of the proof are necessary for checking if
+        # we are at a default-node
+        index = uid
+        proof = b''
+        proofbits = 0
+
+        # Edge case of tree being empty
+        if len(self.tree) == 0:
+            return b'\x00\x00\x00\x00\x00\x00\x00\x00'
+
+        for level in range(self.depth):
+            sibling_index = index + 1 if index % 2 == 0 else index - 1
+            index = index // 2
+            if sibling_index in self.tree[level]:
+                proof += self.tree[level][sibling_index]
+                proofbits += 2 ** level
+
+        proof_bytes = proofbits.to_bytes(8, byteorder='big')
+        return proof_bytes + proof
+
+    def verify(self, uid, proof):
+        ''' Checks if the proof for the leaf at `uid` is valid'''
+        # assert (len(proof) -8 % 32) == 0
+        assert len(proof) <= 2056
+
+        proofbits = int.from_bytes((proof[0:8]), byteorder='big')
+        index = uid
+        p = 8
+        if index in self.leaves:
+            computed_hash = self.leaves[index]
+        # in case the tx is not included, computed_hash is the default leaf
+        else:
+            computed_hash = self.default_nodes[-1]
+
+        for d in range(self.depth):
+            if proofbits % 2 == 0:
+                proof_element = self.default_nodes[d]
+            else:
+                proof_element = proof[p : p + 32]
+                p += 32
+            if index % 2 == 0:
+                computed_hash = keccak(computed_hash + proof_element)
+            else:
+                computed_hash = keccak(proof_element + computed_hash)
+            proofbits = proofbits // 2
+            index = index // 2
+        return computed_hash == self.root
+
+    class TreeSizeExceededException(Exception):
+        """there are too many leaves for the tree to build"""

plasma_cash/utils/utils.py

@@ -0,0 +1,27 @@
+from hexbytes import HexBytes
+from web3.auto import w3
+
+from child_chain.exceptions import InvalidTxSignatureException
+
+
+def sign(hash, key):
+    # DO NOT PREFIX!
+    sig = (
+        HexBytes('0')
+        + w3.eth.account.signHash(hash, private_key=key).signature
+    )
+    return sig
+
+
+def get_sender(hash, sig):
+    if sig is None:
+        raise InvalidTxSignatureException('Tx not signed')
+    return w3.eth.account.recoverHash(hash, signature=sig[1:])
+
+
+def increaseTime(w3, time):
+    start = w3.eth.getBlock('latest').timestamp
+    # provider.make_request(method='evm_increaseTime', params=start+time)
+    w3.manager.request_blocking(
+        method='evm_increaseTime', params=[start + time]
+    )