ExBlock - Simple Blockchain in Elixir

A simple blockchain implementation in Elixir based on the guide from Writing a Simple Blockchain in Elixir.

Overview

This project implements a basic blockchain with the following features:

• Block Structure: Each block contains data, timestamp, previous hash, and its own hash
• Cryptographic Hashing: Uses SHA256 for block validation and chain integrity
• Chain Validation: Ensures the entire blockchain is valid by verifying hash connections
• Immutable: Once data is added to a block, it cannot be changed without invalidating the chain

Project Structure

lib/
├── block.ex       # Block structure and validation
├── crypto.ex      # Cryptographic hashing functions
├── blockchain.ex  # Blockchain operations (create, insert, validate)
└── ex_block.ex    # Main module (generated)

Modules

Block

Defines the block structure and validation:

• new/2 - Creates a new block with data and previous hash
• zero/0 - Creates the genesis block
• valid?/1 and valid?/2 - Validates block integrity

Crypto

Handles cryptographic operations:

• hash/1 - Calculates SHA256 hash of a block
• put_hash/1 - Adds the calculated hash to a block

Blockchain

Main blockchain operations:

• new/0 - Creates a new blockchain with genesis block
• insert/2 - Adds new data as a block to the chain
• valid?/1 - Validates the entire blockchain

Usage

Installation

mix deps.get
mix compile

Testing

Run the test script to see the blockchain in action:

mix run test_blockchain.exs

Interactive Session

Start an interactive Elixir session:

iex -S mix

Then try the blockchain:

# Create a new blockchain
chain = Blockchain.new()

# Add some data
chain = Blockchain.insert(chain, "Hello, World!")
chain = Blockchain.insert(chain, "Another message")

# Validate the chain
Blockchain.valid?(chain)  # Should return true

Example Output

=== Simple Blockchain Test ===

1. Creating a new blockchain...
2. Inserting 'MESSAGE 1'...
3. Inserting 'MESSAGE 2' and 'MESSAGE 3'...
4. Validating the blockchain...
Blockchain is valid: true

5. Block details:
Block 0: ZERO_DATA (Hash: EF475D8687640B5D...)
Block 1: MESSAGE 1 (Hash: 68D4C1D238A4A706...)
Block 2: MESSAGE 2 (Hash: 6F6F0B06163ECA14...)
Block 3: MESSAGE 3 (Hash: 0E45ECC20596D432...)

Features Not Implemented

This is a simplified blockchain for educational purposes. Production blockchains would include:

• Public-key cryptography and digital signatures
• Proof-of-work or other consensus mechanisms
• Network communication and node synchronization
• Persistent storage
• Transaction handling
• Merkle trees for efficient validation

Dependencies

• poison - JSON encoding/decoding for hash calculations

Credits

Based on the excellent tutorial by Sheharyar Naseer: Writing a Simple Blockchain in Elixir