Simple Blockchain Implementation in C

By Irvin Cardoza

This project implements a basic blockchain structure in C language, using linked lists to store blocks and the SHA-256 hashing algorithm from CommonCrypto for hashing. We use CommonCrypto as it is convinient for Macos users.

Why use this project?

• Unlike other projects, this has all the code in one single file and no external pip/bash installs needed. It can be copy pasted and run easily. This projects is mainly to give an understanding as to how the blockchain works and teaches us to use the hash algorithm.

Features

• Blockchain Structure: Implemented using a linked list of blocks.
• Hashing: Utilizes SHA-256 hashing algorithm to secure block integrity.
• User Interaction: Allows users to add data interactively to the blockchain.

Requirements

• C Compiler: Ensure you have a C compiler installed on your system.
• CommonCrypto Library: This program uses the CommonCrypto library for SHA-256 hashing. Make sure it's available on your development environment.

How to Use

1. Compile the Program:

   • Open a terminal or command prompt.
   • Navigate to the directory containing blockchain.c.
   • Compile the program by running using GCC.
   • The convinience of using CommonCrypto is by just importing library we can directly run code without any installatioms.

2. Run the Program:

   • Ideally run on VSCode with gcc compiler preinstalled.

3. Interact with the Blockchain:

   • Follow the prompts to add blocks to the blockchain.
   • Enter data for each block when prompted.
   • Continue adding blocks as desired.

4. View Blockchain Contents:

   • Once you finish adding blocks, the program will display the contents of the blockchain.
   • Each block's index, timestamp, data, previous hash, and hash will be shown.

5. Clean Up:

   • The program automatically frees allocated memory when it exits.
   • No additional clean-up steps are required after running the program.

Example

Here's a brief example of the program in action:

Example

$ ./blockchain
Enter data for the new block: First block
Block added to blockchain.
Do you want to add another block? (y/n): y
Enter data for the new block: Second block
Block added to blockchain.
Do you want to add another block? (y/n): n
Blockchain contents:
Block: 0
Timestamp: [timestamp]
Data: First block
Previous Hash: 0
Hash: [hash]

Block: 1
Timestamp: [timestamp]
Data: Second block
Previous Hash: [hash of first block]
Hash: [hash]

Notes:

• Replace [timestamp], [hash], and other placeholders with actual values displayed by your program during runtime.
• This example demonstrates the interactive nature of the program where users can add blocks to the blockchain sequentially.
• The blockchain contents section displays each block's index, timestamp, data, previous hash, and hash after adding blocks as described.

Problems encountered:

• The main issue I had was using the openssl to use sha.h library. I then found CommonCrypto to solve my issues.