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blockchain

Description

Simple blockchain implementation with wallets, transactions and mining system.

How this code works?

  1. Create 3 wallets: Genesis Wallet (as GW), Wallet A (as A) and Wallet B (as B)
    Hardcode first transaction in GW
    Create transaction (without block) and we have e.g. 100 unit on GW.
    Current transactions data counter: GW transaction: inputs = 0 , outputs = 1 -> UTXOs = 1

  2. Send 100 unit from GW to A
    Create new transaction (as T) and add to new block
    Add 1 output transaction from UTXOs to input transactions of current T
    Current transaction data counter: T: inputs = 1, outputs = 0
    Add two T outputs -> T(recipient, value, T.id) and T(sender, value, T.id)
    Current transaction data counter: T: inputs = 1, outputs = 2
    Add these two outputs to UTXOs -> UTXOs = 3
    Remove current T input from UTXOs -> UTXOs = 2

  3. Whenever we sending units (e.g. money) and creating transactions we adding a new block to blockchain and next transaction to UTXOs. Every next block in blockchain knows about previous.

What is UTXO?

A UTXO is an unspent transaction output. In an accepted transaction in a valid blockchain payment system (such as Bitcoin), only unspent outputs can be used as inputs to a transaction. When a transaction takes place, inputs are deleted and outputs are created as new UTXOs that may then be consumed in future transactions.

source: https://www.r3.com/blog/what-is-a-uxto/

Tools

Java

Features

  • blocks
  • wallets
  • transactions
  • mining system
  • digital signatures

Build/Run

mvn clean compile assembly:single exec:java

Actual version output

Creating genesis wallet and first transaction..
Mining block: 09d946dfa8d9ccafc23d362e09ec036bfbdf49aed67e9cde8649e4b73f62abaa

Validating blockchain.. OK

Test #1 Sending '40' from Wallet A to Wallet B
-----------------------------------------------
Sender wallet balance = 100.0
Recipient wallet balance = 0.0
Processing transaction..
Mining block: f9b35a09fe2e6ab3b4510dcf88e23bd33816eaa9018ee8721c1a0c1e0245f138
Sender wallet balance = 60.0
Recipient wallet balance = 40.0

Validating blockchain.. OK

Test #2 Sending '1000' from Wallet A to Wallet B
-----------------------------------------------
Sender wallet balance = 60.0
Recipient wallet balance = 40.0
Error: Not enough funds
Mining block: 6fc0b114c5c9cbb56beab0d4150a08367914d7e3c8636da6b79ae406dafa4dc4
Sender wallet balance = 60.0
Recipient wallet balance = 40.0

Validating blockchain.. OK

Test #3 Sending '20' from Wallet B to Wallet A
-----------------------------------------------
Sender wallet balance = 40.0
Recipient wallet balance = 60.0
Processing transaction..
Mining block: 3215f84bb27e5f1e2a31ae791f9ae3a0033217c117969e5baa18e27108d36da1
Sender wallet balance = 20.0
Recipient wallet balance = 80.0

Validating blockchain.. OK

Test #4 Sending '30' from Wallet A to Wallet C
-----------------------------------------------
Sender wallet balance = 80.0
Recipient wallet balance = 0.0
Processing transaction..
Mining block: 858846fe5aad2a75be98a98b6e1a91ce27eb855509bbcbd38b283a59b2230fb3
Sender wallet balance = 50.0
Recipient wallet balance = 30.0

Validating blockchain.. OK