Cryptography in C++: Encryption and Hashing — A Complete Guide

Cryptography in C++: Encryption and Hashing — Complete Guide

Cryptography is the fundamental basis of security for modern applications. In C++, developers have access to powerful libraries that enable data encryption, decryption, and hashing. In this article, we will take a detailed look at two popular libraries: OpenSSL and Crypto++, and also examine key concepts: symmetric encryption (AES), asymmetric encryption (RSA), and cryptographic hash functions (SHA-256).

1. Basic Concepts of Cryptography

Before moving to code, it is important to understand the basic terms:

• Symmetric encryption — one key is used for both encryption and decryption. Examples: AES, DES, ChaCha20.
• Asymmetric encryption — a pair of keys: public (for encryption) and private (for decryption). Examples: RSA, ECC.
• Hash functions — irreversible transformation of data into a fixed-length string. Examples: SHA-256, MD5 (deprecated), BLAKE2.
• Salt — random data added to a password before hashing to protect against rainbow tables.

2. OpenSSL Library in C++

OpenSSL is a cross-platform open-source library that implements SSL/TLS protocols and a wide range of cryptographic algorithms. To work with it in C++, you need to include header files and link with the libssl and libcrypto libraries.

Example 1: SHA-256 Hashing with OpenSSL

#include <iostream>#include <openssl/sha.h>#include <cstring>

std::string sha256(const std::string& input) {    unsigned char hash[SHA256_DIGEST_LENGTH];    SHA256_CTX sha256;    SHA256_Init(&sha256);    SHA256_Update(&sha256, input.c_str(), input.length());    SHA256_Final(hash, &sha256);

    std::string output;    for(int i = 0; i < SHA256_DIGEST_LENGTH; i++) {        char buf[3];        sprintf(buf, "%02x", hash[i]);        output += buf;    }    return output;}

int main() {    std::string data = "PythonLib - cryptography in C++";    std::cout << "SHA-256: " << sha256(data) << std::endl;    return 0;}

This code demonstrates basic usage of the SHA256 context. The SHA256_Init function initializes the context, SHA256_Update adds data (can be called multiple times for streaming processing), and SHA256_Final completes the computation and writes the result.

Example 2: AES-256-CBC Symmetric Encryption

#include <iostream>#include <openssl/evp.h>#include <vector>#include <cstring>

std::vector<unsigned char> aes_encrypt(const std::string& plaintext,                                        const unsigned char* key,                                        const unsigned char* iv) {    EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();    EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key, iv);

    std::vector<unsigned char> ciphertext(plaintext.size() + EVP_CIPHER_block_size(EVP_aes_256_cbc()));    int len = 0;    int ciphertext_len = 0;

    EVP_EncryptUpdate(ctx, ciphertext.data(), &len,                      reinterpret_cast<const unsigned char*>(plaintext.c_str()), plaintext.size());    ciphertext_len = len;

    EVP_EncryptFinal_ex(ctx, ciphertext.data() + len, &len);    ciphertext_len += len;    ciphertext.resize(ciphertext_len);

    EVP_CIPHER_CTX_free(ctx);    return ciphertext;}

int main() {    // 256-bit key (32 bytes) and 128-bit IV (16 bytes)    unsigned char key[32] = "01234567890123456789012345678901";    unsigned char iv[16] = "0123456789012345";

    std::string message = "Secret data for PythonLib";