Introduction to Cryptography in C


Cryptography is the science of securing information by converting it into an unreadable format and later deciphering it. This guide provides an introduction to cryptography in C and offers sample code to illustrate key cryptographic concepts and techniques.

Why Use Cryptography in C?

Cryptography in C is important for various reasons:

  • Security: Cryptography ensures data confidentiality, integrity, and authenticity.
  • Privacy: It protects sensitive information from unauthorized access.
  • Data Exchange: Cryptography is essential for secure data transmission over networks.

Key Cryptographic Concepts

Understanding cryptography in C involves key concepts:

  • Encryption: Converting plaintext into ciphertext using an encryption algorithm.
  • Decryption: Converting ciphertext back into plaintext using a decryption algorithm.
  • Key Management: Securely storing and managing cryptographic keys.

Sample Code for Cryptography

Let's explore a basic example of encryption and decryption using the Advanced Encryption Standard (AES) algorithm in C. We'll use the OpenSSL library to demonstrate encryption and decryption:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/aes.h>
int main() {
// Key for AES encryption and decryption
unsigned char aes_key[16] = "mysecretkey12345";

// Data to encrypt
unsigned char plaintext[] = "Hello, Cryptography!";

// Initialize AES context
AES_KEY aes_key_struct;
AES_set_encrypt_key(aes_key, 128, &aes_key_struct);

// Encrypt the data
AES_encrypt(plaintext, plaintext, &aes_key_struct);

// Display the ciphertext
printf("Ciphertext: ");
for (int i = 0; i < sizeof(plaintext); i++) {
printf("%02X ", plaintext[i]);

// Decrypt the data
AES_set_decrypt_key(aes_key, 128, &aes_key_struct);
AES_decrypt(plaintext, plaintext, &aes_key_struct);

// Display the decrypted plaintext
printf("Decrypted: %s\n", plaintext);

return 0;

This code encrypts the plaintext using AES and then decrypts it. It demonstrates a simple cryptographic operation but can be expanded to handle more complex encryption and decryption tasks.


Cryptography in C is essential for securing sensitive data and communications. This guide introduced the basics of cryptography and provided sample code for encrypting and decrypting data using AES. By delving further into cryptographic algorithms and best practices, you can enhance data security in your applications.