def proof_of_work(self, block: Block) -> str:
'''Proof-of-Work to verify a valid block and find the corresponding nonce value'''
block.nonce = 0
computed_hash = block.compute_hash()
# Keep trying and increasing the nonce value
# until the new hash value meets the difficulty level restriction (Solve the hash puzzle)
while not computed_hash.startswith('0' * block.difficulty):
block.nonce += 1
computed_hash = block.compute_hash()
return computed_hash
def lightweight():
fullchain = [json.loads(block) for block in blockchain.chain]
lightweight = []
for block in fullchain:
block_object = Block(block['index'], block['transaction'], block['timestamp'], block['previous_hash'])
block_object.merkle_root = block['merkle_root']
block_object.nonce = block['nonce']
block_object.difficulty = block['difficulty']
lightweight.append(block_object.to_dict())
response = {
'chain': json.dumps(lightweight),
'length': len(lightweight)
}
return jsonify(response), 200
def valid_chain(self, chain: List[str]) -> bool:
'''check if a blockchain (all blocks) is valid'''
current_index = 0
chain = json.loads(chain)
# load and check every block from the blockchain
while current_index < len(chain):
block = json.loads(chain[current_index])
current_block = Block(block['index'], block['transaction'],
block['timestamp'], block['previous_hash'])
current_block.merkle_root = block['merkle_root']
current_block.nonce = block['nonce']
current_block.difficulty = block['difficulty']
# if the current block is NOT the last block
if current_index + 1 < len(chain):
# if the hash value of the current block != previous block's hash value of the next block, then reject
if current_block.compute_hash() != json.loads(
chain[current_index + 1])['previous_hash']:
return False
# check if the current block is an instance from the list of chain
if isinstance(current_block.transaction, list):
for transaction in current_block.transaction:
transaction = json.loads(transaction)
# Skip block reward because it does not have signature
if transaction['sender'] == 'Block_Reward':
continue
current_transaction = Transaction(transaction['sender'],
transaction['recipient'],
transaction['value'])
current_transaction.signature = transaction['signature']
# check if digital signature of each transaction is valid, if not then reject
if not current_transaction.verify_transaction_signature():
return False
# check if hash value of the current block is not valid, if yes then reject
if not self.is_valid_proof(current_block, block['hash']):
return False
current_index += 1
return True