Crackcoin is a very basic blockchain-free cryptocurrency PoC in Python. It's a project for discovering cryptocurrencies.

Note that this is a PoC that runs only on local networks and does not provide proper security. The code should only be used to get familiar with the building blocks for a cryptocurrency. Also, crackcoin should not be confused with the (dead) currency CrackCoin (CRACK) from 2014.

This project was created as an exercise after reading "Mastering Bitcoin: unlocking digital cryptocurrencies".

• Transaction-based mining as a PoC for a blockchain-free cryptocurrency
• Threading in Python
• Working with sockets in Python (UDP)
• ECC crypto / ECC public key compression/decompression
• Base58 encoding like bitcoin
• Having the whole thing work (wallet, crypto, validation, networking, mining, etc)

Most cryptocurrencies use a blockchain to validate transactions among other things. After years of running these networks it's beginning to look like blockchain-based currencies naturally evolve into a centralised network, because it's in the best interest of the participants to combine computing power to calculate solutions for blocks.

An interesting framework for a blockchain-free protocol is discussed in the paper "Blockchain-Free Cryptocurrencies: A Framework for Truly Decentralised Fast Transactions", which can be found here:

https://eprint.iacr.org/2016/871.pdf

Do note that crackcoin doesn't implement nearly as complex a protocol as described in the paper. But the transaction-based mining method was used as an inspiration for implementing the 'core' for crackcoin.

• First run python crackcoin.py
• Then type h to see options and communicate with other crackcoin-nodes on the network

• Run python generateGenesis.py until a cool address pops up
• Edit crackcoinBase.sql: replace the address for the transaction with transactionHash d34db33f in transactions_outputs with your generated address
• Run crackcoin and wait until a confirmation is generated for d34db33f with a higher difficulty (>6) than the one in crackcoinBase.sql
• Replace the confirmation for d34db33f
• Share code on other nodes
• Manually replace your wallet keys and address with the address and keys generated by generateGenesis.py. This will allow you to 'spend' the genesis cash.

• Wallets

  • A wallet consists of a public/private keypair and an address. The address is derived from the public key.

• Transactions

  • A transaction contains inputs, outputs and a unique identifier (called 'hash').
  • An output has a unique identifier and is just an amount and a 'to'-address.
  • An input points to a previous output, and uses the coins from that output. It must contain a compressed public key and a signature. This way nodes can identify that the 'to'-address from the previous output, which can be generated with the public key, is owned by the spender.

• The GUI

  • When you create a transaction, a confirmation is created and both the transaction and the confirmation are shared on the network (UDP broadcast).
  • When using the broadcast option b, your crackcoin node will broadcast a request packet on the network. Any crackcoin node receiving the request will send all transactions and confirmations to you. This is so new nodes can 'sync'.

• Network server (UDP)

  • When the server receives a new transaction, it checks if the transaction is valid and adds it to the database ('ledger').
  • When a confirmation is received, the transaction's confirmation is updated if the received difficulty is higher than the existing difficulty.

• Mining and confirmations

  • Confirmations are proof of work hashes for a transaction.
  • The mining component simply creates confirmations for some transaction.
  • Mining is done by hardening the transaction confirmation with the least difficulty.