Cryptography in C++: Encryption and Hashing with OpenSSL and Crypto++

Cryptography in C++: Encryption and Hashing with OpenSSL and Crypto++

Reliable data protection is a basic need of any modern application. C++ provides developers with powerful tools for implementing cryptographic algorithms: from simple hashing to complex asymmetric encryption schemes. In this article, we will cover the two most popular libraries — OpenSSL and Crypto++ — and show how to use them to solve typical tasks: hashing, symmetric encryption (AES), and asymmetric encryption (RSA).

1. OpenSSL: Universal Crypto Provider

OpenSSL is the de facto standard for cryptography in C/C++. The library supports all major algorithms, X.509 certificates, and TLS protocols. To work with it, you need to install the libssl-dev package (Linux) or download binary builds for Windows.

1.1 SHA-256 Hashing

The simplest task is to compute the hash of a string. We use the low-level API (EVP).

#include <iostream>#include <openssl/evp.h>#include <iomanip>

std::string sha256(const std::string& str) {    EVP_MD_CTX* ctx = EVP_MD_CTX_new();    EVP_DigestInit_ex(ctx, EVP_sha256(), nullptr);    EVP_DigestUpdate(ctx, str.data(), str.size());

    unsigned char hash[EVP_MAX_MD_SIZE];    unsigned int hash_len;    EVP_DigestFinal_ex(ctx, hash, &hash_len);    EVP_MD_CTX_free(ctx);

    std::stringstream ss;    for (unsigned int i = 0; i < hash_len; ++i)        ss << std::hex << std::setw(2) << std::setfill('0')            << (int)hash[i];    return ss.str();}

int main() {    std::cout << sha256("Hello, Crypto!") << std::endl;    return 0;}

1.2 Symmetric Encryption AES-256-CBC

To encrypt data with a single key, we use AES in CBC mode. Important: the key and IV (initialization vector) must be random.

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

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

    std::vector<unsigned char> ciphertext(plaintext.size() + 16);    int out_len, tmp_len;    EVP_EncryptUpdate(ctx, ciphertext.data(), &out_len, plaintext.data(), plaintext.size());    EVP_EncryptFinal_ex(ctx, ciphertext.data() + out_len, &tmp_len);    out_len += tmp_len;    ciphertext.resize(out_len);

    EVP_CIPHER_CTX_free(ctx);    return ciphertext;}

Decryption is performed similarly using EVP_DecryptInit_ex and EVP_DecryptUpdate.

1.3 Asymmetric Encryption RSA

RSA is used for key exchange or data signing. Generating a key pair:

#include <openssl/rsa.h>#include <openssl/pem.h>

RSA* generate_rsa_keypair(int bits = 2048) {    RSA* rsa = RSA_new();    BIGNUM* e = BN_new();    BN_set_word(e, 65537);    RSA_generate_key_ex(rsa, bits, e, nullptr);    BN_free(e);    return rsa;}

// Saving the public key in PEMvoid save_public_key(RSA* rsa, const char* filename) {    BIO* bio = BIO_new_file(filename, "w");    PEM_write_bio_RSA_PUBKEY(bio, rsa);    BIO_free(bio);}

2. Crypto++: C++-Oriented Alternative

Crypto++ (Wei Dai's library) offers a more "native" C++ interface: templates, RAII, streams. It requires no external dependencies.

2.1 SHA-256 Hashing in Crypto++

#include <cryptopp/sha.h>#include <cryptopp/hex.h>#include <iostream>

std::string sha256_cryptopp(const std::string& msg) {    CryptoPP::SHA256 hash;    byte digest[Cr