blockchain.py

import binascii
import hashlib
import json
from collections import OrderedDict
from time import time
from urllib.parse import urlparse
from uuid import uuid4

import Crypto
import Crypto.Random  # noqa: F401
import requests
from Crypto.Hash import SHA
from Crypto.PublicKey import RSA
from Crypto.Signature import PKCS1_v1_5

MINING_SENDER = "THE BLOCKCHAIN"
MINING_REWARD = 1
MINING_DIFFICULTY = 2


class Blockchain:
    def __init__(self):
        self.chain = []
        self.transactions = []
        self.nodes = set()
        self.node_id = str(uuid4()).replace("-", "")
        self.new_block(0, "00")

    def new_block(self, nonce: int, previous_hash: str) -> dict:
        """
        Create a new Block in the Blockchain
        :param proof: <int> The proof given by the Proof of Work algorithm
        :param previous_hash: (Optional) <str> Hash of previous Block
        :return: <dict> New Block
        """

        block = {
            "index": len(self.chain) + 1,
            "timestamp": time(),
            "transactions": self.transactions,
            "nonce": nonce,
            "previous_hash": previous_hash or self.hash(self.chain[-1]),
        }

        # Reset the current list of transactions
        self.transactions = []

        self.chain.append(block)
        return block

    def new_transaction(self, sender: str, recipient: str, amount: int) -> int:
        """
        Creates a new transaction to go into the next mined Block
        :param sender: <str> Address of the Sender
        :param recipient: <str> Address of the Recipient
        :param amount: <int> Amount
        :return: <int> The index of the Block that will hold this transaction
        """
        self.transactions.append(
            {"sender": sender, "recipient": recipient, "amount": amount}
        )

        return self.last_block["index"] + 1

    @staticmethod
    def hash(block: dict) -> str:
        """
        Creates a SHA-256 hash of a Block
        :param block: <dict> Block
        :return: <str>
        """
        # We must make sure that the Dictionary is Ordered, or we'll have inconsistent hashes

        block_string = json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(block_string).hexdigest()

    @property
    def last_block(self):
        """
        Returns the last Block in the chain.
        """
        return self.chain[-1]

    def proof_of_work(self) -> int:
        """
        Simple Proof of Work Algorithm:
         - Find a number p' such that hash(pp') contains leading 4 zeroes, where p is the previous p'
         - p is the previous proof, and p' is the new proof
        :param last_proof: <int>
        :return: <int>
        """
        last_block = self.chain[-1]
        last_hash = self.hash(last_block)

        nonce = 0
        while self.valid_proof(self.transactions, last_hash, nonce) is False:
            nonce += 1

        return nonce

    @staticmethod
    def valid_proof(transactions, last_hash, nonce, difficulty=MINING_DIFFICULTY):
        """
        Check if a hash value satisfies the mining conditions. This function is used within the proof_of_work function.
        """
        guess = (str(transactions) + str(last_hash) + str(nonce)).encode()
        guess_hash = hashlib.sha256(guess).hexdigest()
        return guess_hash[:difficulty] == "0" * difficulty

    def register_node(self, address: str) -> None:
        """
        Add a new node to the list of nodes
        :param address: <str> Address of node. Eg. 'http://192.168.0.5:5000'
        :return: None
        """
        parsed_url = urlparse(address)
        if parsed_url.netloc:
            self.nodes.add(parsed_url.netloc)
        elif parsed_url.path:
            # Accepts an URL without scheme like '192.168.0.5:5000'.
            self.nodes.add(parsed_url.path)
        else:
            raise ValueError("Invalid URL")

    @staticmethod
    def verify_transaction_signature(sender_address, signature, transaction):
        """
        Check that the provided signature corresponds to transaction
        signed by the public key (sender_address)
        """
        public_key = RSA.importKey(binascii.unhexlify(sender_address))
        verifier = PKCS1_v1_5.new(public_key)

        hash = SHA.new(str(transaction).encode("utf8"))
        return verifier.verify(hash, binascii.unhexlify(signature))

    def submit_transaction(self, sender_address, recipient_address, value, signature):
        """Add a transaction to transactions array if the signature verified"""
        transaction = OrderedDict(
            {
                "sender_address": sender_address,
                "recipient_address": recipient_address,
                "value": value,
            }
        )

        if sender_address == MINING_SENDER:
            self.transactions.append(transaction)
            return len(self.chain) + 1
        else:
            transaction_verification = self.verify_transaction_signature(
                sender_address, signature, transaction
            )
            if transaction_verification:
                self.transactions.append(transaction)
                return len(self.chain) + 1
            else:
                return False

    def valid_chain(self, chain: list) -> bool:
        """
        Determine if a given blockchain is valid
        :param chain: <list> A blockchain
        :return: <bool> True if valid, False if not
        """
        last_block = chain[0]
        current_index = 1

        while current_index < len(chain):
            block = chain[current_index]

            if block["previous_hash"] != self.hash(last_block):
                return False

            transactions = block["transactions"][:-1]
            transaction_elements = ["sender_address", "recipient_address", "value"]
            transactions = [
                OrderedDict((k, transaction[k]) for k in transaction_elements)
                for transaction in transactions
            ]

            if not self.valid_proof(
                transactions, block["previous_hash"], block["nonce"], MINING_DIFFICULTY
            ):
                return False

            last_block = block
            current_index += 1

        return True

    def resolve_conflicts(self) -> bool:
        """
        This is our Consensus Algorithm, it resolves conflicts
        by replacing our chain with the longest one in the network.
        :return: <bool> True if our chain was replaced, False if not
        """

        neighbours = self.nodes
        new_chain = None

        # We're only looking for chains longer than ours
        max_length = len(self.chain)

        # Grab and verify the chains from all the nodes in our network
        for node in neighbours:
            response = requests.get(f"http://{node}/chain")

            if response.status_code == 200:
                length = response.json()["length"]
                chain = response.json()["chain"]

                # Check if the length is longer and the chain is valid
                if length > max_length and self.valid_chain(chain):
                    max_length = length
                    new_chain = chain

        # Replace our chain if we discovered a new, valid chain longer than ours
        if new_chain:
            self.chain = new_chain
            return True

        return False