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

Cryptography in C++: From Theory to Practice of Encryption and Hashing

Cryptography is the fundamental foundation of modern application security. In C++, developers have access to powerful libraries that allow implementing both symmetric/asymmetric encryption and cryptographic hashing. In this material, we will cover two key libraries: OpenSSL (the de facto standard) and Crypto++ (pure C++, convenient for integration). You will learn how to encrypt data, verify integrity, and protect passwords.

Basic Cryptographic Concepts

Before moving to code, it is important to understand three basic operations:

• Symmetric encryption (AES, ChaCha20) — one key for encryption and decryption. Fast, suitable for large volumes of data.
• Asymmetric encryption (RSA, ECC) — a pair of keys (public/private). Used for key exchange and digital signatures.
• Hashing (SHA-256, MD5) — irreversible transformation of data into a fixed-length string. Used for integrity verification and password storage.

1. Working with OpenSSL in C++

OpenSSL is a cross-platform C library accessible via linking. Installation: sudo apt install libssl-dev (Linux) or via vcpkg/conan for Windows.

Example: Symmetric AES-256-CBC Encryption

#include <iostream>#include <string>#include <openssl/evp.h>#include <openssl/rand.h>

std::string 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::string ciphertext(plaintext.size() + 16, '\\0');    int len = 0, ciphertext_len = 0;    EVP_EncryptUpdate(ctx, reinterpret_cast<unsigned char*>(&ciphertext[0]), &len,                      reinterpret_cast<const unsigned char*>(plaintext.data()), plaintext.size());    ciphertext_len = len;    EVP_EncryptFinal_ex(ctx, reinterpret_cast<unsigned char*>(&ciphertext[ciphertext_len]), &len);    ciphertext_len += len;    ciphertext.resize(ciphertext_len);    EVP_CIPHER_CTX_free(ctx);    return ciphertext;}

int main() {    unsigned char key[32], iv[16];    RAND_bytes(key, sizeof(key)); // Generate random key    RAND_bytes(iv, sizeof(iv));

    std::string data = "Secret message";    std::string encrypted = aes_encrypt(data, key, iv);    std::cout << "Encrypted: " << encrypted.size() << " bytes" << std::endl;    return 0;}

SHA-256 Hashing via OpenSSL

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

std::string sha256(const std::string& str) {    unsigned char hash[SHA256_DIGEST_LENGTH];    SHA256_CTX sha256;    SHA256_Init(&sha256);    SHA256_Update(&sha256, str.c_str(), str.size());    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::cout << "SHA-256: " << sha256("Hello, Crypto!") << std::endl;    return 0;}

2. Crypto++ Library (Pure C++ Implementation)

Crypto++ (cryptopp) is a full-featured C++ library with no external dependencies. Installation: sudo apt install libcrypto++-dev or download from cryptopp.com.

Example: RSA Encryption with Crypto++

#include <iostream>#include <string>#include <cryptopp/rsa.h>#include <cryptopp/osrng.h>#include <cryptopp/base64.h>

int main() {    using namespace CryptoPP;

    AutoSeededRandomPool rng;    Inve