Simple implementation of regular blockchain and redactable blockchain

This repository contains a Makefile and associated C source files for a blockchain project focusing on hashing and redactability features. The project demonstrates different aspects of blockchain technology, including performance metrics for hash computations and the capability to edit blockchain elements under controlled conditions.

Executables

The Makefile in this project automates the compilation and linking process for creating four distinct executables:

1. redactable_blockchain: Implements a simple editable blockchain that incorporates chameleon hash functions to allow post-hoc modifications while maintaining the blockchain's integrity.

2. blockchain: A basic blockchain implementation using SHA256 hashing to ensure data integrity and security.

3. redact_time: Measures the time taken to compute hashes and handle collisions within the editable blockchain, providing essential data for analyzing the efficiency and security of the redactable features.

4. sha256_time: Focuses on measuring the computation time of SHA256 hashes, used to evaluate the performance of traditional blockchain hashing.

Makefile Usage

Compilation

To compile all the programs listed above, use the following command in your terminal:

$ make all

You can also compile individual programs by specifying their corresponding target:

$ make time_redact # measure time for redaction
$ make time_sha256 # measure time for sha256
$ make redact      # redactable blockchain example 
$ make sha256      # normal blockchain example

Running the Programs

After compilation, each executable can be run from the command line as follows:

$ ./redactable_blockchain
$ ./blockchain
$ ./redact_time
$ ./sha256_time

blockchain commands

• Generate Block (g): Allows the user to add a new block to the blockchain by specifying the block's message.

Enter command: g
Enter block message(less than 50 words): first block's message
Enter command: g
Enter block message(less than 50 words): second block

• Print Blockchain (p): Displays all the blocks in the blockchain, showing each block's data and hash.

Enter command: p

# output
Blockchain:
-----------------------
Index:    0
Timestamp:1714978172
Data:     first block's message
PrevHash: 0000000000000000000000000000000000000000000000000000000000000000
Hash:     82f3b8db79e5a73cb4ec2f32e0504bb2a3fe63a7e45508eb92caf71da421114d
-----------------------
Index:    1
Timestamp:1714978364
Data:     second block
PrevHash: 82f3b8db79e5a73cb4ec2f32e0504bb2a3fe63a7e45508eb92caf71da421114d
Hash:     12b44029317acd0e6e854be10b612179aef804b8fd211ef5c7de3f8dd7b834a1

• Verify Blockchain (v): Recomputes the hashes for all blocks to ensure that the chain's integrity is maintained. It checks if the blockchain is valid based on the current data.

Enter command: v

# output
Index: 0, Hash:     82f3b8db79e5a73cb4ec2f32e0504bb2a3fe63a7e45508eb92caf71da421114d
Index: 1, prevHash: 82f3b8db79e5a73cb4ec2f32e0504bb2a3fe63a7e45508eb92caf71da421114d
-----------------------
Blockchain validated successfully.

• Modify Block (m): Enables the user to alter the data of a specified block. Note that modifying a block will change its hash and may invalidate the blockchain.

Enter command: m
Choose the index of the block you want to modify: 0
Enter the message you want to modify: modify block 0

# try to validate blockchain after modify block 0
Enter command: v

# output
Index: 0, Hash:     4afb832ed37d1e88ca664a8adc5e0bdfec79c0d1aaf303039f13173858a8690e
Index: 1, prevHash: 82f3b8db79e5a73cb4ec2f32e0504bb2a3fe63a7e45508eb92caf71da421114d
-----------------------
Invalid hash
Blockchain validation failed.
(quit process)

• Quit (q): Exits the blockchain application process.

System Requirements

Make sure to have the necessary dependencies, such as the cryptographic library (crypto), installed on your system to ensure the programs run successfully.

sudo apt install libssl-dev

Acknowledgments

This project makes extensive use of components developed by Thiago Leucz Astrizi, found in his blockchain_tests repository on GitHub. Specific files utilized include:

• sha256_time Implementation: We use the sha256.c file from Thiago's repository to test computation times, critical for assessing our blockchain solution's efficiency.

• redact_time: The classical_redactable_blockchain.c provided insight into implementing redactable features in blockchains, allowing modifications under certain conditions without compromising integrity.

• Chameleon Hash Function: The files chameleon_hash_ateniese04a.c and preimage_chameleon_hash.h are utilized as APIs in our project to develop a simple editable blockchain. This feature is vital for allowing post-hoc adjustments in the blockchain while maintaining security and verifiability.

I am deeply thankful to thiagoharry for his contributions to the open-source community.