README.md

ABSTRACT

This repository should emulate a blockchain on one computer. Each node runs in its own thread. The purpose is to get a better understanding of the blockchain technology and to be able to simulate and understand certain scenarios without the use of several computers.

This repository is not complete yet and blockchain enthusiastic contributors are welcome!

SIMPLE EXAMPLE

Here is a simple example of what is already possible:

from Network import Network
from Miner import Miner

network = Network()
network.new_miners(3, 10) # add 3 new trusfull miners with a computing power of 10

network.start_working(blocks=6) # let the nodes mine for 6 blocks

MINER 2  FOUND BLOCK
MINER 1  FOUND BLOCK
MINER 1  FOUND BLOCK
MINER 1  FOUND BLOCK
MINER 1  FOUND BLOCK
MINER 1  FOUND BLOCK

network.consensus() # check if all nodes have the same chain and the same ledger

True

network.nodes[0].show_ledger()

LEDGER OF MINER 0: 
  MINER 2 (e25db...): 1
  MINER 1 (53c2b...): 5

network.nodes[0].show_chain()

 +---------------------+  +---------------------+  +---------------------+  +---------------------+
 | BLOCK NR: 0         |  | BLOCK NR: 1         |  | BLOCK NR: 2         |  | BLOCK NR: 3         |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | PROOF: ifrt153ouh   |  | PROOF: wabhyco48j   |  | PROOF: 5yqgstsy31   |  | PROOF: lk639by7ob   |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | TRANSACTIONS: 0     |  | TRANSACTIONS: 1     |  | TRANSACTIONS: 1     |  | TRANSACTIONS: 1     |
 + - - - - - - - - - - +  |                     |  |                     |  |                     |
 | DIFF: 1             |  | from: rewar         |  | from: rewar         |  | from: rewar         |
 + - - - - - - - - - - +  | to: e25db...        |  | to: 53c2b...        |  | to: 53c2b...        |
 | PREV_H: genes...    |  | amount: 1           |  | amount: 1           |  | amount: 1           |
 +---------------------+  + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
                          | DIFF: 2             |  | DIFF: 2             |  | DIFF: 2             |
                          + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
                          | PREV_H: b'def2f'... |  | PREV_H: b'31bc4'... |  | PREV_H: b'ad46e'... |
                          +---------------------+  +---------------------+  +---------------------+

 +---------------------+  +---------------------+  +---------------------+
 | BLOCK NR: 4         |  | BLOCK NR: 5         |  | BLOCK NR: 6         |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | PROOF: 00fq0tywq3   |  | PROOF: kz1rq3f0wd   |  | PROOF: x3kiwkxsku   |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | TRANSACTIONS: 1     |  | TRANSACTIONS: 1     |  | TRANSACTIONS: 1     |
 |                     |  |                     |  |                     |
 | from: rewar         |  | from: rewar         |  | from: rewar         |
 | to: 53c2b...        |  | to: 53c2b...        |  | to: 53c2b...        |
 | amount: 1           |  | amount: 1           |  | amount: 1           |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | DIFF: 2             |  | DIFF: 2             |  | DIFF: 2             |
 + - - - - - - - - - - +  + - - - - - - - - - - +  + - - - - - - - - - - +
 | PREV_H: b'4ffd4'... |  | PREV_H: b'97c4e'... |  | PREV_H: b'6de48'... |
 +---------------------+  +---------------------+  +---------------------+

51% ATTACK

Here is a simple demonstration for a 51% Attack:

from Network import Network
from Miner import Miner
from Evil_Miner import Evil_Miner

network = Network()
# 3 honest miners with a power of 6
miner_0 = Miner(network, 6) 
miner_1 = Miner(network, 6)
miner_2 = Miner(network, 6)
# 1 evil Miner with a power of 50
evil_miner_3 = Evil_Miner(network, 50, secret_working=False) 

network.add_node(miner_0)
network.add_node(miner_1)
network.add_node(miner_2)
network.add_node(evil_miner_3)

# mine 10 blocks
network.start_working(blocks=10)

MINER 1  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
MINER 2  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK

network.consensus() # everything fine so far

True

network.nodes[0].show_ledger()

LEDGER OF MINER 0: 
   MINER 1 (fe047... ): 1
   MINER 3 (07459... ): 8
   MINER 2 (6dbf9... ): 1

# send to miner_0 an amout of 8
evil_miner_3.send(miner_0.public_key, 8)

# from now on work secretly own chain. Find blocks but dont broadcast them
evil_miner_3.secret_working = True

len(evil_miner_3.transactions)

2

del evil_miner_3.transactions[1]

len(evil_miner_3.transactions)

1

evil_miner_3.transactions

[{'sender': '',
  'to': '0745903784bf1547aa8aca26fcd000d34d03b88b7ef9ace36b6e9c19ea5bdf53ae76233320dc7eea3df98177bc23afcec44a816f8d5ee6f58bd23b0089f3cca5',
  'amount': 1,
  'signature': '72d9f41f9770953604a57d7dce351fc9722ce522128fb270eeedc6022688ac0acf579e99dc6f61c0ac4bc0d503d09a4e27d59d78cc097fd87377480ff611d6a9'}]

network.start_working(blocks=100, time=30)

EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
MINER 0  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK
EVIL_MINER 3  FOUND BLOCK

network.consensus()

True

len(miner_0.chain)

12

len(evil_miner_3.chain), len(evil_miner_3.secret_chain)

(12, 17) // evil miner has a longer secret chain

network.nodes[0].show_ledger() # correct chain

LEDGER OF MINER 0: 
   MINER 1 (fe047... ): 1
   MINER 3 (07459... ): 0
   MINER 2 (6dbf9... ): 1
   MINER 0 (4302d... ): 9   

# no send the secret chain as broadcast to the other nodes
evil_miner_3.send_broadcast({"type": "pow", "chain": evil_miner_3.secret_chain})

len(miner_0.chain)

17

miner_0.show_ledger()

LEDGER OF MINER 0: 
   MINER 1 (fe047... ): 1
   MINER 3 (07459... ): 14
   MINER 2 (6dbf9... ): 1

the first transaction was reset