用c++实现基于openssl的对称加密与解密

以下是一个简单的示例代码，实现了基于 OpenSSL 的对称加密和解密：

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

#define KEY_SIZE 32
#define IV_SIZE 16

int aes_encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
                unsigned char *iv, unsigned char *ciphertext) {
    EVP_CIPHER_CTX *ctx;
    int len, ciphertext_len;

    if (!(ctx = EVP_CIPHER_CTX_new())) return -1;

    if (1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key, iv))
        return -1;

    if (1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
        return -1;
    ciphertext_len = len;

    if (1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) return -1;
    ciphertext_len += len;

    EVP_CIPHER_CTX_free(ctx);

    return ciphertext_len;
}

int aes_decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
                unsigned char *iv, unsigned char *plaintext) {
    EVP_CIPHER_CTX *ctx;
    int len, plaintext_len, ret;

    if (!(ctx = EVP_CIPHER_CTX_new())) return -1;

    if (1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key, iv))
        return -1;

    if (1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
        return -1;
    plaintext_len = len;

    ret = EVP_DecryptFinal_ex(ctx, plaintext + len, &len);
    EVP_CIPHER_CTX_free(ctx);

    if (ret > 0) {
        plaintext_len += len;
        return plaintext_len;
    } else {
        return -1;
    }
}

int main() {
    unsigned char key[KEY_SIZE], iv[IV_SIZE];
    unsigned char plaintext[] = "Hello, world!";
    unsigned char ciphertext[sizeof(plaintext) + AES_BLOCK_SIZE];
    unsigned char decryptedtext[sizeof(plaintext)];
    int decryptedtext_len, ciphertext_len;

    // Generate random key and iv
    RAND_bytes(key, KEY_SIZE);
    RAND_bytes(iv, IV_SIZE);

    // Encrypt the plaintext
    ciphertext_len = aes_encrypt(plaintext, sizeof(plaintext), key, iv, ciphertext);

    // Decrypt the ciphertext
    decryptedtext_len = aes_decrypt(ciphertext, ciphertext_len, key, iv, decryptedtext);

    // Print the results
    std::cout << "Plaintext: " << plaintext << std::endl;
    std::cout << "Ciphertext: " << ciphertext << std::endl;
    std::cout << "Decrypted text: " << decryptedtext << std::endl;

    return 0;
}

该代码使用了 AES-256-CBC 对称加密算法，生成一个随机的 256 位密钥和 128 位 IV。加密和解密时使用相同的密钥和 IV。注意，此代码中的明文和密文都不包括终止符。