Blockchain in Python

Learning about blockchains from Jeiwan and porting to Python.

DISCLAIMER

This repository is for personal experimentation and mainly for fun (you may even find a joke or two written throughout the code!). There is no set process for testing, so code in the master branch has no guarantees of running correctly.

Current State

• Persistence is accomplished using the Plyvel library. Previously this was done using shelve. Moving from Shelve to Plyvel, we lost the convenience of letting the database handle serialization of blocks, UTXOs, and wallets. However, Plyvel should be a more robust and efficient database, giving us snapshots, sorted iterators, write batches, and more!
• Public/Private key cryptography (verifying/signing) is accomplished through the ecdsa library. See their README for security considerations.
• Blocks only support PTPKH transactions. No scripting. Just locking and unlocking outputs.
• P2P testing so far has been limited (only 4 peers, no bad actors).
• Since block times are so low, the blockchain will often fork. The network handles this gracefully and always reaches consensus.

Tests

See the README in the tests directory

Quick Start

Single Node Using Docker

$ docker build -t pychain .
...
# -it lets you input characters (CTRL-C, and 'q' to quit)
# --rm deletes the container upon exit (i.e. deleting your databases)
$ docker run -it --rm pychain

P2P Network Using Docker-Compose

It's recommended you use the provided deployment scripts

$ cd scripts
$ ./deploy_network --num-nodes=3

Alternatively, you can roll your own docker-compose setup.

$ docker build -t pychain .

# you will need a valid docker-compose.yml file for this to work. You can use the template in this repo as a reference.
$ docker-compose up --scale p2p=3

Node CLI

The following commands can be ran on a single Pychain node.

Creating Wallets

Command:

create-wallet

$ ./gucci_main.py c
New address: 17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh
$ ./gucci_main.py c
New address: 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r

List Addresses

Command:

list-addresses

$ ./gucci_main.py l
1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r
17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh

Creating a Blockchain

Command:

init-blockchain

$ ./gucci_main.py i --address 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r

Done

Printing the Blockchain

Command:

print-blockchain

$ ./gucci_main.py p --full y
{
  "hash": "000006a4c3c01d76ac261a2cd5c6ac6297b2bd4dc4984bbef91d5d9d624e6e78",
  "prevHash": "0000000000000000000000000000000000000000000000000000000000000000",
  "timestamp": 1530423399,
  "height": 0,
  "nonce": 370089,
  "merkleRoot": "af24b2c82707d87a608fe21c830a11a63960fc585816d972cc7d42725a7799ac",
  "txs": [
    {
      "id": "5fbac38f51bc0daa4b2d261a8d49a15cd8a68e4c10ab3e0c9d33093a756561b5",
      "inputs": [
        {
          "refTxId": "",
          "refOutIdx": -1,
          "signature": "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
          "pubKey": "1995389d31069c544da983a95027e9319d93cbf81fd38c3786f115f9a9938547d2df7272d1258bb3"
      }
      ],
      "outputs": [
        {
          "idx": 0,
          "value": 50,
          "pubKeyHash": "9f9a193d56e9599090417053ed6450ff93fed822"
        }
      ]
    }
  ]
}

Get Wallet balance

Command:

get-balance

$ ./gucci_main.py g --address 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r
Balance of '1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r': 50

Send Coins

Command:

send

# cannot send more than you have
$ ./gucci_main.py s --from 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r --to 17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh --amount 51
Not enough funds!

# for now, the sender mines the coinbase reward
$ ./gucci_main.py s --from 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r --to 17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh --amount 50

Success!

# sender sent all 50 of his coins, then received the 50 miner reward
$ ./gucci_main.py g --address 1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r
Balance of '1Fmjs3MCtDswPeLry1BBabFk5A1SEURc4r': 50

# sendee has all 50 of the sender's coins
$ ./gucci_main.py g --address 17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh
Balance of '17vsuqM11VJ7RYy6m6y5dZ2yk9LDMF91Wh': 50

Join Network

Command:

up

$ ./gucci_main.py up --address 13jXEksSr4khBY1bRg4pZtWod9Z3kud26S
This node is mining and will receive rewards to 13jXEksSr4khBY1bRg4pZtWod9Z3kud26S
My host: 172.17.0.2
My mining address 13jXEksSr4khBY1bRg4pZtWod9Z3kud26S

# this message will appear if your local
# blockchain hasn't been initialized yet
Empty blockchain. Creating genesis.
Created coinbase with reward going to 13jXEksSr4khBY1bRg4pZtWod9Z3kud26S
Merkle root e477945230fb23da77b2cfc7402494368cae487bbcbebe85f3ef1bb96819e075
Gensis block hash: 00007faa2e194e877c1caf6aa853e3054ef386ce12338d04e3415381de21e157

Starting server
Press 'q' or 'CTRL-C' to quit.