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period_1/04-blockchain_class/405_HW3_Tamper-Proof_Chain/BlockChain.py
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#!/usr/bin/env python3 #!/usr/bin/env python3
"""Block Integrity -> Tamper Proof Chain: Homework """Block Integrity -> Tamper Proof Chain: Homework
The goal of this homework is to extend the behavior of a block to created a chain and securely link The goal of this homework is to extend the behavior of a block to created a chain and securely link
them together using cryptography. In general, each block is used to hold a batch of transactions. In addition a cryptographic them together using cryptography. In general, each block is used to hold a batch of transactions. In addition a cryptographic
hash of the previous block in the chain and some other needed values for computation. hash of the previous block in the chain and some other needed values for computation.
In this homework each block will hold: In this homework each block will hold:
* a string message (data) * a string message (data)
* its own block hash value * its own block hash value
* hash value of the previous block * hash value of the previous block
* nonce value which will be incremented when a block is mined * nonce value which will be incremented when a block is mined
Your task is to: Your task is to:
* locate the TODOs in this file * locate the TODOs in this file
* complete the missing part from the code * complete the missing part from the code
* run the test of this exercise located in same folder. * run the test of this exercise located in same folder.
To test run 'Blockchain_t.py' in your command line To test run 'Blockchain_t.py' in your command line
Notes: Notes:
* do not change class structure or method signature to not break unit tests * do not change class structure or method signature to not break unit tests
* visit this url for more information on this topic: * visit this url for more information on this topic:
https://cryptography.io/en/latest/hazmat/primitives/cryptographic-hashes/ https://cryptography.io/en/latest/hazmat/primitives/cryptographic-hashes/
""" """
from cryptography.hazmat.backends import default_backend from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes from cryptography.hazmat.primitives import hashes
class CBlock: class CBlock:
# TODO 1: Initialize the values of a block # TODO 1: Initialize the values of a block
# Make sure you distinguish between the genesis block and other blocks # Make sure you distinguish between the genesis block and other blocks
def __init__(self, data, previousBlock): def __init__(self, data, previousBlock):
if previousBlock == None : if previousBlock == None :
self.previousHash = None self.previousHash = None
self.previousBlock = None self.previousBlock = None
self.data = data self.data = data
else: else:
self.previousBlock = previousBlock self.previousBlock = previousBlock
self.previousHash = self.previousBlock.computeHash() self.previousHash = self.previousBlock.computeHash()
self.data = data self.data = data
self.blockHash = None self.blockHash = None
self.nonce = 0 self.nonce = 0
# TODO 2: Compute the cryptographic hash of the current block. # TODO 2: Compute the cryptographic hash of the current block.
# Be sure which values must be considered to compute the hash properly. # Be sure which values must be considered to compute the hash properly.
# return the digest value # return the digest value
def computeHash(self): def computeHash(self):
digest = hashes.Hash(hashes.SHA256(), backend=default_backend()) digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
if self.previousHash != None: if self.previousHash != None:
digest.update(self.previousHash) digest.update(self.previousHash)
try: try:
digest.update(str(self.data).encode()) digest.update(str(self.data).encode())
except: except:
digest.update(self.data) digest.update(self.data)
digest.update(str(self.nonce).encode()) digest.update(str(self.nonce).encode())
return digest.finalize() return digest.finalize()
# TODO 3: Mine the current value of a block # TODO 3: Mine the current value of a block
# Calculates a digest based on required values from the block, such as: # Calculates a digest based on required values from the block, such as:
# data, previousHash, nonce # data, previousHash, nonce
# Make sure to compute the hash value of the current block and store it properly # Make sure to compute the hash value of the current block and store it properly
def mine(self, leading_zeros): def mine(self, leading_zeros):
self.nonce = 0 self.nonce = 0
if self.previousBlock: while True:
self.previousHash = self.previousBlock.blockHash digest = self.computeHash()
else:
self.previousHash = None if digest[:leading_zeros] == b'\x00' * leading_zeros:
self.blockHash = digest
while True: print(self.nonce) # Output.txt file has printed nonce values
digest = self.computeHash() break
if digest[:leading_zeros] == b'\x00' * leading_zeros: self.nonce += 1
self.blockHash = digest
print(self.nonce) # Output.txt file has printed nonce values # TODO 4: Check if the current block contains valid hash digest values
break # Make sure to distinguish between the genesis block and other blocks
# Make sure to compare both hash digest values:
self.nonce += 1 # The computed digest of the current block
# The stored digest of the previous block
# TODO 4: Check if the current block contains valid hash digest values # return the result of all comparisons as a boolean value
# Make sure to distinguish between the genesis block and other blocks def is_valid_hash(self):
# Make sure to compare both hash digest values: if(self.previousBlock == None):
# The computed digest of the current block return True
# The stored digest of the previous block
# return the result of all comparisons as a boolean value if(self.computeHash() != self.blockHash or self.previousBlock.blockHash != self.previousBlock.computeHash()):
# def is_valid_hash(self): return False
# if(self.previousBlock == None): return self.previousBlock.is_valid_hash()
# return True
# if(self.computeHash() != self.blockHash or self.previousBlock.blockHash != self.previousBlock.computeHash()):
# return False
# return self.previousBlock.is_valid_hash()
def is_valid_hash(self):
if self.previousBlock:
self.previousHash = self.previousBlock.computeHash()
return self.computeHash() == self.blockHash