c++实现EVP_aes_256_cbc大文件加密与解密

EVP_aes_256_cbc是OpenSSL库提供的一种加密算法，可以用于对大文件进行加密和解密。下面是c++实现EVP_aes_256_cbc大文件加密与解密的示例代码：

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

using namespace std;

int aes_encrypt(const char *key, const char *iv, const char *infile, const char *outfile)
{
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    if (!ctx) {
        cerr << "Error: EVP_CIPHER_CTX_new() failed" << endl;
        return -1;
    }

    // 初始化加密上下文
    if (EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, (const unsigned char *)key, (const unsigned char *)iv) != 1) {
        cerr << "Error: EVP_EncryptInit_ex() failed" << endl;
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 打开输入文件
    ifstream fin(infile, ios::binary);
    if (!fin.is_open()) {
        cerr << "Error: Cannot open input file" << endl;
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 打开输出文件
    ofstream fout(outfile, ios::binary);
    if (!fout.is_open()) {
        cerr << "Error: Cannot create output file" << endl;
        fin.close();
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 读取输入文件并加密
    const int BUFSIZE = 1024 * 1024;
    unsigned char inbuf[BUFSIZE];
    unsigned char outbuf[BUFSIZE + EVP_CIPHER_block_size(EVP_aes_256_cbc())];
    int inlen, outlen;
    while (!fin.eof()) {
        fin.read((char *)inbuf, BUFSIZE);
        inlen = fin.gcount();
        if (EVP_EncryptUpdate(ctx, outbuf, &outlen, inbuf, inlen) != 1) {
            cerr << "Error: EVP_EncryptUpdate() failed" << endl;
            fin.close();
            fout.close();
            EVP_CIPHER_CTX_free(ctx);
            return -1;
        }
        fout.write((char *)outbuf, outlen);
    }

    // 结束加密
    if (EVP_EncryptFinal_ex(ctx, outbuf, &outlen) != 1) {
        cerr << "Error: EVP_EncryptFinal_ex() failed" << endl;
        fin.close();
        fout.close();
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }
    fout.write((char *)outbuf, outlen);

    // 关闭文件和加密上下文
    fin.close();
    fout.close();
    EVP_CIPHER_CTX_free(ctx);

    return 0;
}

int aes_decrypt(const char *key, const char *iv, const char *infile, const char *outfile)
{
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    if (!ctx) {
        cerr << "Error: EVP_CIPHER_CTX_new() failed" << endl;
        return -1;
    }

    // 初始化解密上下文
    if (EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, (const unsigned char *)key, (const unsigned char *)iv) != 1) {
        cerr << "Error: EVP_DecryptInit_ex() failed" << endl;
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 打开输入文件
    ifstream fin(infile, ios::binary);
    if (!fin.is_open()) {
        cerr << "Error: Cannot open input file" << endl;
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 打开输出文件
    ofstream fout(outfile, ios::binary);
    if (!fout.is_open()) {
        cerr << "Error: Cannot create output file" << endl;
        fin.close();
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }

    // 读取输入文件并解密
    const int BUFSIZE = 1024 * 1024 + EVP_CIPHER_block_size(EVP_aes_256_cbc());
    unsigned char inbuf[BUFSIZE];
    unsigned char outbuf[BUFSIZE];
    int inlen, outlen;
    while (!fin.eof()) {
        fin.read((char *)inbuf, BUFSIZE);
        inlen = fin.gcount();
        if (EVP_DecryptUpdate(ctx, outbuf, &outlen, inbuf, inlen) != 1) {
            cerr << "Error: EVP_DecryptUpdate() failed" << endl;
            fin.close();
            fout.close();
            EVP_CIPHER_CTX_free(ctx);
            return -1;
        }
        fout.write((char *)outbuf, outlen);
    }

    // 结束解密
    if (EVP_DecryptFinal_ex(ctx, outbuf, &outlen) != 1) {
        cerr << "Error: EVP_DecryptFinal_ex() failed" << endl;
        fin.close();
        fout.close();
        EVP_CIPHER_CTX_free(ctx);
        return -1;
    }
    fout.write((char *)outbuf, outlen);

    // 关闭文件和解密上下文
    fin.close();
    fout.close();
    EVP_CIPHER_CTX_free(ctx);

    return 0;
}

int main()
{
    const char *key = "0123456789abcdef0123456789abcdef";
    const char *iv = "0123456789abcdef";
    const char *infile = "input.txt";
    const char *outfile = "output.txt";

    // 加密
    if (aes_encrypt(key, iv, infile, outfile) != 0) {
        cerr << "Error: Encryption failed" << endl;
        return -1;
    }
    cout << "Encryption succeeded" << endl;

    // 解密
    if (aes_decrypt(key, iv, outfile, "input_decrypted.txt") != 0) {
        cerr << "Error: Decryption failed" << endl;
        return -1;
    }
    cout << "Decryption succeeded" << endl;

    return 0;
}

这个示例代码中，我们使用了OpenSSL库提供的EVP_aes_256_cbc加密算法，对给定的输入文件进行加密和解密。在实际使用中，你需要根据自己的需求修改参数，比如加密算法、密钥、向量、输入文件和输出文件等。