用c++实现基于openssl的大文件的对称加密与解密包括密钥管理

以下是一个基本的示例代码，用于使用 OpenSSL 对称加密和解密大文件。该代码使用 AES 算法并支持 CBC 模式。

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

using namespace std;

void encryptFile(string inputFile, string outputFile, string keyFile) {
    ifstream fin(inputFile, ios::binary);
    ofstream fout(outputFile, ios::binary);

    // 读取密钥
    ifstream keyIn(keyFile, ios::binary);
    char key[AES_BLOCK_SIZE];
    keyIn.read(key, AES_BLOCK_SIZE);

    // 生成随机 IV
    unsigned char iv[AES_BLOCK_SIZE];
    RAND_bytes(iv, AES_BLOCK_SIZE);

    // 写入 IV
    fout.write(reinterpret_cast<const char*>(iv), AES_BLOCK_SIZE);

    // 初始化加密上下文
    AES_KEY aesKey;
    AES_set_encrypt_key(reinterpret_cast<const unsigned char*>(key), 8 * AES_BLOCK_SIZE, &aesKey);

    // 加密数据
    char inputBuffer[AES_BLOCK_SIZE];
    char outputBuffer[AES_BLOCK_SIZE];
    int bytesRead = 0;
    while (fin.read(inputBuffer, AES_BLOCK_SIZE)) {
        AES_cbc_encrypt(reinterpret_cast<const unsigned char*>(inputBuffer), reinterpret_cast<unsigned char*>(outputBuffer), AES_BLOCK_SIZE, &aesKey, iv, AES_ENCRYPT);
        fout.write(reinterpret_cast<const char*>(outputBuffer), AES_BLOCK_SIZE);
        bytesRead += AES_BLOCK_SIZE;
    }

    // 加密数据块的余数
    int remainingBytes = fin.gcount();
    if (remainingBytes > 0) {
        memset(inputBuffer + remainingBytes, 0, AES_BLOCK_SIZE - remainingBytes);
        AES_cbc_encrypt(reinterpret_cast<const unsigned char*>(inputBuffer), reinterpret_cast<unsigned char*>(outputBuffer), AES_BLOCK_SIZE, &aesKey, iv, AES_ENCRYPT);
        fout.write(reinterpret_cast<const char*>(outputBuffer), remainingBytes);
        bytesRead += remainingBytes;
    }

    fin.close();
    fout.close();
    keyIn.close();
}

void decryptFile(string inputFile, string outputFile, string keyFile) {
    ifstream fin(inputFile, ios::binary);
    ofstream fout(outputFile, ios::binary);

    // 读取密钥
    ifstream keyIn(keyFile, ios::binary);
    char key[AES_BLOCK_SIZE];
    keyIn.read(key, AES_BLOCK_SIZE);

    // 读取 IV
    unsigned char iv[AES_BLOCK_SIZE];
    fin.read(reinterpret_cast<char*>(iv), AES_BLOCK_SIZE);

    // 初始化解密上下文
    AES_KEY aesKey;
    AES_set_decrypt_key(reinterpret_cast<const unsigned char*>(key), 8 * AES_BLOCK_SIZE, &aesKey);

    // 解密数据
    char inputBuffer[AES_BLOCK_SIZE];
    char outputBuffer[AES_BLOCK_SIZE];
    int bytesRead = 0;
    while (fin.read(inputBuffer, AES_BLOCK_SIZE)) {
        AES_cbc_encrypt(reinterpret_cast<const unsigned char*>(inputBuffer), reinterpret_cast<unsigned char*>(outputBuffer), AES_BLOCK_SIZE, &aesKey, iv, AES_DECRYPT);
        fout.write(reinterpret_cast<const char*>(outputBuffer), AES_BLOCK_SIZE);
        bytesRead += AES_BLOCK_SIZE;
    }

    // 解密数据块的余数
    int remainingBytes = fin.gcount();
    if (remainingBytes > 0) {
        memset(inputBuffer + remainingBytes, 0, AES_BLOCK_SIZE - remainingBytes);
        AES_cbc_encrypt(reinterpret_cast<const unsigned char*>(inputBuffer), reinterpret_cast<unsigned char*>(outputBuffer), AES_BLOCK_SIZE, &aesKey, iv, AES_DECRYPT);
        fout.write(reinterpret_cast<const char*>(outputBuffer), remainingBytes);
        bytesRead += remainingBytes;
    }

    fin.close();
    fout.close();
    keyIn.close();
}

int main(int argc, char* argv[]) {
    if (argc < 4) {
        cerr << "Usage: " << argv[0] << " <input file> <output file> <key file>" << endl;
        return 1;
    }

    string inputFile = argv[1];
    string outputFile = argv[2];
    string keyFile = argv[3];

    encryptFile(inputFile, outputFile, keyFile);
    decryptFile(outputFile, "decrypted_" + inputFile, keyFile);

    return 0;
}

此代码需要 OpenSSL 库的支持。您可以使用以下命令编译代码：

g++ -o encrypt_decrypt_file encrypt_decrypt_file.cpp -lssl -lcrypto

该代码的基本思路是使用 CBC 模式将输入文件分成多个块，每个块大小为 AES 块大小（16 字节）。加密时，对于每个块，使用 AES 加密算法对其进行加密，并将结果写入输出文件中。解密时，对于每个块，使用 AES 解密算法对其进行解密，并将结果写入输出文件中。

此代码还需要密钥管理。在本示例中，我们将密钥存储在一个单独的文件中，并在加密和解密过程中读取它。在实际应用中，您可以使用其他密钥管理方案来保护密钥。