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