CS171 Final Project: Distributed Blockchain Money Transfer

Overview

Fault-tolerant decentralized system that implements Paxos to create a peer-to-peer money exchange backed by blockchain encryption.

How to run

• Start five peers with ids=1, 2, 3, 4, 5
• Example shown below: Full debug (prints debugging), not loading previous state

# Terminal 1 
python3 client.py --id 1 --load False --debug full

# Terminal 2
python3 client.py --id 2 --load False --debug full

...

# Terminal 5
python3 client.py --id 2 --load False --debug full

Sample workflow

>> printBalance
{1: 100, 2: 100, 3: 100, 4: 100, 5: 100}

>> moneyTransfer(1,2,10)
Done.

>> printBalance
{1: 90, 2: 110, 3: 100, 4: 100, 5: 100}

>> printBlockchain
Block(Tx=(1, 2, 10), Nonce=My4oLp2Q, Hash=3bd955b1be731db12c3f27782314157878c05ae1c1198c2d959df66499b53ee2, PrevHash=None)

Commands

1. moneyTransfer(debit node, credit node, amount)

   Transfers amount of money from debit node to credit node.

2. failProcess

   Kills the process to which the input is provided.

3. fixProcess

   Restarts the process after it has failed.

4. printBlockchain

   Prints the copy of blockchain on that node.

5. printBalance

   Prints the balance of all 5 accounts on that node.

6. debugMessage(client id, message)

   Sends a debug message to the specified client which echoes it.

Features

Debug Output Options

• None: Only interface output
• Basic: Debug outputs with only event types
• Full: Debug outputs with full events
  Usage: --debug None / Basic / Full, (default=None)

Load From File

• False: Starts a fresh peer.
• True: Loads peer state from it's saved backup.
  Usage: --load False / True, (default=False)

Failure Recovery

A peer that has been put into a dead state using the failProcess command will not reply to incoming messages.
When a user enters FixProcess on the terminal, the peer will query all other peers for the required data to bring itself up to date.
The peer will adopt the reply with the longest blockchain depth.

On The Fly Recovery

If a peer receives an 'Accept' message from an elected proposer with a higher depth than its own, it'll initate recovery from that proposer.
Once the peer brings itself up to date with the proposer, it'll resume the Paxos process.

Cryptographic Verification

All blocks that are appended onto a peer's blockchain, and all full blockchains that are adopted during recovery, are cryptographically verified.

Communication Protocol

1. Fire and Forget Send
   Messages are sent without waiting for a reply.

2. Listener Thread
   Listener Deamon Thread listens for incoming messages.

3. FIFO Worker
   Worker Thread handles requests enqueued by the Listener Thread in FIFO order.