LandPoS

A land management system using Proof of Stake consensus based blockchain

Group 14

ID	Name
2019A7PS0164H	Nandan H R
2019A7PS0033H	T V Chandra Vamsi
2019A7PS0158H	Vraj Ketan Gandhi

Running the blockchain network

Requirements

• Python 3.10
• pip

Folder contents

The root folder consists of:

• blockchain, network and utils directories
• Two python files, main.py and demo.py.
• requirements.txt

Running main.py gives a command line interface to execute your own commands in the network.
demo.py contains a sample test case containing three nodes and covering all possible operations that can be performed in the network.

Steps to run program

1. From the root directory, run pip install -r requirements.txt
2. To execute demo.py, run python demo.py
3. To use the command line interface, execute main.py with the command python main.py <file_name>
   where <file_name> is optional and contains the state of the blockchain network. blockchain.net contains the sample state of the network from demo.py.
4. After starting the main.py program, type help and hit enter to get a list of commands that can be performed in the network.

Blockchain and Proof of Stake

A Blockchain is a distributed ledger containing immutable transactions. It is a set of blocks cryptographically linked to each other. Each block contains a number of transactions. Each transaction is a transfer of value in the blockchain

This blockchain is used to track ownerships and transfers of lands

The blockchain supports 4 types of transactions

1. Receive Coins When a new node is connected, it is the amount of coins provided to it by the network ( specified by the user during node creation)
   
2. Land Declaration The transaction that a user uses to register a new land under their name
   
3. Land Transfer The transaction that a user uses to transfer ownership of a land they own to another user
   
4. Stake Increase The transaction used by a user to increase their stake in the network

Proof of Stake Consensus

A validator is selected from the set of nodes in the network. This is done by using the coinage of the nodes.

• Stake - The amount of coins staked by a node in the network
• Age - The number of blocks since the last block minted by a node
• Coinage - The product of stake and age A node is randomly chosen as a validator (Weighted by their coinages)

The validator node validates the transactions and puts the validated transaction into a block. This is called minting or forging a block. The block is then broadcasted to all nodes who then add it to their respective blockchains.

The structure of a block is given as

Block Header

• ID: The height of the block
• Timestamp: The timestamp when the block was minted
• Prev. block hash: The hash of the previous block
• Merkle Root: The merkle root of the transactions in the block
• Validator: The ID of the validator of the block

Block Data

• The list of transactions validated in this block

Function Definitions

Network

This folder holds the code implementation for the representation of the blockchain network. Network is essentially a simulation of a P2P environment.

network.py

The Network class represents a blockchain network. It manages all communications between nodes.

Function	Definition
connectNode()	Connects a new node to the network
start()	Starts the blockchain network which listens to the user inputs
run()	Run a specified command on the network
nodeExists()	A helper function to check if a given node (or for atleast one node) exists on the network
handle()	Handle user commands
printCommands()	Displays all the available commands
broadcastTransaction()	Broadcasts the new transaction to all nodes
broadcastBlock()	Broadcasts the new minted block to all nodes
getValidator()	This contains the implementation for the PoS consensus. The probability of a validator being selected is directly dependent on the stake the node holds in the blockchain. The validator mints the new block.This function will return the validator node's ID.
mint()	This function calls the validator on all the transactions in the transaction pool
validate()	This function actually validates all the transactions passed to it and returns a boolean based on whether the transaction is valid
addBlock()	Once all the transactions are validated, this function will mint and return the new block. The broadcastBlock() function will then broadcast the block to all nodes.

node.py

This file contains the implementation of all the commands pertaining to operating a node as well as the Proof of Stake consensus algorithm

Function	Definition
registerCoins()	Inititates a transaction to set the node's initial balance
registerLand()	Initates a new transaction to register a new land under the node
buyLand()	Initiates a new transaction for buying a land
sellLand()	Initiates a new transaction for selling a land
stake()	Initiate a new transaction to increase the stake of a node
addTransaction()	Adds a transaction to the transaction pool
getValidator()	This contains the implementation for the PoS consensus. The probability of a validator being selected is directly dependent on the stake the node holds in the blockchain. The validator mints the new block.This function will return the validator node's ID.
mint()	The validator chosen validates all transactions and mints a block
validate()	This function validates all the transactions passed to it and returns a boolean based on whether the transaction is valid
addBlock()	Adds a block to the transaction and empties the transaction pool

Blockchain

This folder contains the blockchain implementation of the code

block.py

This file contains implementation for the block of the blockchain

Function	Definition
hashBlock()	Hashes a given block using the SHA256 algorithm
genesis()	Generates the genesis block
createBlock()	Creates and returns a new block
serialize()	Serializes the block

blockchain.py

The Blockchain class is used to represent a blockchain which is a series of cryptographically linked blocks. The Blockchain is the single source of truth for all data in a distributed network.

Function	Definition
addBlock()	Appends a block to the blockchain
getLength()	Returns the length of the blockchain
getTransaction()	Returns transaction based on transaction ID
getLandHistory()	Gets history of the buyers and sellers of the land
getLandOwner()	Returns the landowner of the land ID given
getLandOwners()	Returns a list of all the lands and their owners
getBlockFromHeight()	Returns a block based on the block height
getLastBlock()	Returns the last block of the blockchain
getStakes()	Returns a list of the stakes of all nodes
getAges()	Get the coin ages of all nodes
getBalance()	Get wallet balance of a node
getAllBalances()	Get wallet balances of all nodes

transaction.py

The Transaction class represents a transaction in the blockchain. A transaction is a transfer of value in a blockchain.

Function	Definition
newRCTransaction()	Create a new Receive Coins transaction
newLDTransaction()	Create a new Land Declaration transaction
newLTTransaction()	Create a new Land Transfer transaction
newSTTransaction()	Create a new Stake Increase transaction
generateTransaction()	Generates a transaction in the correct structure
serialize()	Serializes the transaction object

merkle_tree.py

A MerkleTree is a tree in which every leaf node is a hash of a data block and every inner node is the hash of its child nodes. This class provides a function called getMerkleRoot() to get the Merkle Root given a list of transactions