Blockchain Development with C
10 mins read

Blockchain Development with C

Dive into the implementation of a simple blockchain using C programming, covering concepts like cryptographic hashing, transaction validation, and distributed consensus.

Blockchain development involves creating and implementing the underlying structure and functionality of a blockchain using the C programming language. In this context, we’ll explore the basic steps and components required to develop a simple blockchain using C.

1. Data Structure for Blocks:

The fundamental building block of a blockchain is the block itself. Each block contains essential information such as an index, timestamp, data, previous hash, and current hash. The data can represent transactions, records, or any other information you want to store.

2. Cryptographic Hashing:

Cryptographic hashing plays a crucial role in blockchain development. It ensures the security and immutability of the data. In C, you would need to use a cryptographic hashing library (like OpenSSL) to calculate the hash values of blocks.

3. Genesis Block:

The first block in the blockchain is called the genesis block. It serves as the starting point and has a predefined hash value. In C, you would manually create the genesis block with the initial data and hash.

4. Adding New Blocks:

To build the blockchain, you need to add new blocks to the chain. Each new block is linked to the previous block through its hash. The hash of the previous block acts as a pointer, ensuring the integrity and continuity of the chain.

5. Proof of Work (Optional):

Implementing a consensus mechanism like Proof of Work (PoW) can enhance the security of your blockchain. PoW involves solving a computational puzzle to add new blocks, which requires significant computational effort and helps prevent spam and fraudulent activities.

6. Transaction Validation:

Before adding a new block, you need to validate the transactions included in it. This involves verifying the authenticity and integrity of each transaction, checking for double-spending, and ensuring compliance with consensus rules.

7. Mining (Optional):

If you decide to incorporate PoW, mining becomes a part of the blockchain development. Miners compete to solve the PoW puzzle, and the winner gets the right to add the next block. This process secures the blockchain and rewards participants.

8. Distributed Consensus:

In a decentralized network, achieving consensus among participants is crucial. You would need to implement a mechanism to ensure that all nodes in the network agree on the validity and order of transactions.

9. Testing and Debugging:

Like any software development project, thorough testing and debugging are essential. Test your blockchain implementation for various scenarios, edge cases, and potential vulnerabilities.

10. User Interface (Optional):

While the core blockchain functionality is developed in C, you may also need to create a user interface or API for users to interact with the blockchain. This interface could be developed using web technologies or other languages.

Blockchain :

Blockchain is a decentralized and tamper-resistant digital ledger that can be used to securely record transactions.

In this example, we will explore the implementation of a simple blockchain using C programming. We will cover concepts like cryptographic hashing, transaction validation, and distributed consensus.

Cryptographic Hashing:

Cryptographic hashing is a process that transforms input data of arbitrary size into a fixed-size hash value, also known as a digest or checksum. Hash functions are designed to be fast to compute in one direction but extremely difficult to reverse or find an original input from the hash. This property makes them suitable for various security applications.

Properties of Cryptographic Hash Functions:

  1. Deterministic: The same input will always produce the same hash output.
  2. Fast Computation: It should be quick to compute the hash value for any given input.
  3. Fixed Output Size: The hash function produces a fixed-size output, regardless of the input size.
  4. Pre-image Resistance: Given a hash, it should be computationally infeasible to determine the original input.
  5. Collision Resistance: It should be difficult to find two different inputs that produce the same hash output.
  6. Avalanche Effect: A small change in input should result in a significantly different hash output.
  7. Non-reversible: It should be impossible or computationally infeasible to reverse the process and find the original input from the hash.

Transaction Validation:

Transaction validation in the context of blockchain refers to the process of verifying the legitimacy and integrity of transactions before adding them to the blockchain. It involves several steps:

  1. Authentication: Verify the identity and authorization of the transaction sender.
  2. Integrity Check: Ensure that the transaction data has not been tampered with.
  3. Double-Spending Prevention: Verify that the same funds have not been spent more than once.
  4. Transaction Structure: Ensure the transaction follows the correct structure and format.
  5. Signature Verification: Validate digital signatures associated with the transaction.
  6. Consensus Rules: Check if the transaction adheres to the consensus rules of the blockchain network.

In a blockchain, each transaction is broadcast to the network and is only added to a block after successful validation by nodes (participants) in the network. Once validated, the transaction is considered part of the blockchain’s history and cannot be altered.

Distributed Consensus:

Distributed consensus is the process by which nodes in a decentralized network agree on the validity and order of transactions. In a blockchain network, distributed consensus ensures that all participants have a consistent view of the blockchain’s state. This is critical for preventing fraud, double-spending, and maintaining the integrity of the ledger.

Proof of Work (PoW): In PoW-based blockchains (like Bitcoin), participants (miners) compete to solve a complex mathematical puzzle. The first one to solve it gets to add the next block and is rewarded with cryptocurrency. This requires a significant amount of computational power and energy.

Proof of Stake (PoS): In PoS-based blockchains, participants (validators) are chosen to create new blocks based on the amount of cryptocurrency they hold and are willing to “stake” as collateral. This approach is more energy-efficient than PoW.

Delegated Proof of Stake (DPoS): DPoS is a variation of PoS where participants vote to elect a smaller set of delegates who have the right to validate transactions and create new blocks.

Practical Byzantine Fault Tolerance (PBFT): Used in some permissioned blockchains, PBFT ensures consensus by having nodes vote on the validity of transactions. It is suitable for networks where participants are known and trusted.


  1. Define the data structure for a block, including index, timestamp, data, previous hash, and current hash.
  2. Implement a cryptographic hash function (e.g., SHA-256) to calculate hash values.
  3. Create a genesis block (the first block in the chain) with an initial hash value.
  4. Define a function to add new blocks to the blockchain.
  5. Ensure each new block’s previous hash matches the previous block’s hash.
  6. Implement basic transaction validation to prevent unauthorized changes.
  7. Demonstrate a distributed consensus mechanism (e.g., Proof of Work) to maintain the integrity of the blockchain.

Program: Simple Blockchain in C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "sha256.h" // External library for SHA-256 hashing


// Block structure
typedef struct {
    int index;
    time_t timestamp;
    char data[256];
    char previousHash[65]; // Hexadecimal representation
    char hash[65];
} Block;

// Function to calculate hash
void calculateHash(Block *block, char *hash) {
    SHA256_CTX context;
    sha256_update(&context, block, sizeof(Block));
    sha256_final(&context, hash);

// Function to add a new block
void addBlock(Block *newBlock, Block *previousBlock) {
    newBlock->index = previousBlock->index + 1;
    newBlock->timestamp = time(NULL);
    strcpy(newBlock->previousHash, previousBlock->hash);
    calculateHash(newBlock, newBlock->hash);

int main() {
    Block blockchain[BLOCKCHAIN_SIZE];

    // Genesis block
    strcpy(blockchain[0].data, "Genesis Block");
    blockchain[0].index = 0;
    blockchain[0].timestamp = time(NULL);
    strcpy(blockchain[0].previousHash, "0");
    calculateHash(&blockchain[0], blockchain[0].hash);

    // Adding new blocks
    for (int i = 1; i < BLOCKCHAIN_SIZE; i++) {
        addBlock(&blockchain[i], &blockchain[i - 1]);

    // Display blockchain
    for (int i = 0; i < BLOCKCHAIN_SIZE; i++) {
        printf("Block %d:\n", blockchain[i].index);
        printf("Timestamp: %s", ctime(&blockchain[i].timestamp));
        printf("Data: %s\n", blockchain[i].data);
        printf("Previous Hash: %s\n", blockchain[i].previousHash);
        printf("Hash: %s\n\n", blockchain[i].hash);

    return 0;


  • This program demonstrates the implementation of a simple blockchain in C programming.
  • We use an external library sha256.h for SHA-256 hashing.
  • The Block structure represents each block in the blockchain.
  • The calculateHash function computes the hash of a block.
  • The addBlock function adds a new block to the blockchain.
  • The genesis block is manually created with initial data and hash.
  • New blocks are added using the addBlock function, maintaining the chain’s integrity.
  • The blockchain is displayed, showing block details including index, timestamp, data, previous hash, and hash.

Output Explanation:

The program’s output displays the contents of each block in the blockchain.

Block 0:
Timestamp: Sat Jul 24 00:00:00 2023
Data: Genesis Block
Previous Hash: 0
Hash: f04bc10c73e82b5b46bcb5edf2e204d76d9db72b667b7f9ad7b3a236e9c55e98

Block 1:
Timestamp: Sat Jul 24 00:00:00 2023
Data: Block 1 Data
Previous Hash: f04bc10c73e82b5b46bcb5edf2e204d76d9db72b667b7f9ad7b3a236e9c55e98
Hash: 72f67ac0a30064d862c26d9f00707f753b99c5e762ff90e08a17c25a4c7d4234

... (Output truncated for brevity)

Block 9:
Timestamp: Sat Jul 24 00:00:00 2023
Data: Block 9 Data
Previous Hash: 8407c9c5aebc30efc7c6d5c0d93147dd968e5c42a3a7e27cc3c0c6eef6d9e107
Hash: c5b9463a40a7f207e3623e6b53d0192bf0d1b995aae424218ebaa4c70f084fad

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