用c++实现基于openssl的大文件的签名并将签名写入文件中以及验证签名

好的，我将为您提供一个基于openssl的C++程序，实现对大文件进行数字签名并将签名写入文件中，以及验证签名。

首先，您需要安装openssl库和头文件，以便在您的程序中使用openssl的函数。接下来，您可以使用以下代码实现数字签名：

#include <openssl/evp.h>
#include <openssl/sha.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

#define KEY_LENGTH 2048
#define SIGN_LENGTH 256

bool sign_file(const char* file_path, const char* private_key_path, const char* signature_path) {
    ifstream file(file_path, ios::binary | ios::ate);
    if (!file.is_open()) {
        cout << "Failed to open file" << endl;
        return false;
    }
    int file_size = file.tellg();
    file.seekg(0, ios::beg);

    unsigned char* file_data = new unsigned char[file_size];
    file.read((char*)file_data, file_size);
    file.close();

    EVP_PKEY* pkey = NULL;
    FILE* fp = fopen(private_key_path, "rb");
    if (!fp) {
        cout << "Failed to open private key file" << endl;
        return false;
    }
    pkey = PEM_read_PrivateKey(fp, NULL, NULL, NULL);
    fclose(fp);

    if (!pkey) {
        cout << "Failed to read private key" << endl;
        return false;
    }

    EVP_MD_CTX* mdctx = EVP_MD_CTX_new();
    if (!mdctx) {
        cout << "Failed to create md context" << endl;
        return false;
    }

    if (!EVP_SignInit(mdctx, EVP_sha256())) {
        cout << "Failed to initialize signing" << endl;
        return false;
    }

    if (!EVP_SignUpdate(mdctx, file_data, file_size)) {
        cout << "Failed to update signing" << endl;
        return false;
    }

    unsigned char* signature = new unsigned char[SIGN_LENGTH];
    unsigned int signature_length = SIGN_LENGTH;
    if (!EVP_SignFinal(mdctx, signature, &signature_length, pkey)) {
        cout << "Failed to finalize signing" << endl;
        return false;
    }

    ofstream signature_file(signature_path, ios::binary | ios::trunc);
    if (!signature_file.is_open()) {
        cout << "Failed to create signature file" << endl;
        return false;
    }
    signature_file.write((char*)signature, signature_length);
    signature_file.close();

    delete[] file_data;
    delete[] signature;
    EVP_MD_CTX_free(mdctx);
    EVP_PKEY_free(pkey);
    return true;
}

此函数将读取指定的文件，并使用提供的私钥对其进行数字签名。签名将写入指定的文件中。请注意，此函数使用SHA256哈希算法进行加密。您可以根据需要更改哈希算法。

接下来，您可以使用以下代码验证签名：

bool verify_signature(const char* file_path, const char* public_key_path, const char* signature_path) {
    ifstream file(file_path, ios::binary | ios::ate);
    if (!file.is_open()) {
        cout << "Failed to open file" << endl;
        return false;
    }
    int file_size = file.tellg();
    file.seekg(0, ios::beg);

    unsigned char* file_data = new unsigned char[file_size];
    file.read((char*)file_data, file_size);
    file.close();

    EVP_PKEY* pkey = NULL;
    FILE* fp = fopen(public_key_path, "rb");
    if (!fp) {
        cout << "Failed to open public key file" << endl;
        return false;
    }
    pkey = PEM_read_PUBKEY(fp, NULL, NULL, NULL);
    fclose(fp);

    if (!pkey) {
        cout << "Failed to read public key" << endl;
        return false;
    }

    ifstream signature_file(signature_path, ios::binary | ios::ate);
    if (!signature_file.is_open()) {
        cout << "Failed to open signature file" << endl;
        return false;
    }
    int signature_size = signature_file.tellg();
    signature_file.seekg(0, ios::beg);

    unsigned char* signature = new unsigned char[signature_size];
    signature_file.read((char*)signature, signature_size);
    signature_file.close();

    EVP_MD_CTX* mdctx = EVP_MD_CTX_new();
    if (!mdctx) {
        cout << "Failed to create md context" << endl;
        return false;
    }

    if (!EVP_VerifyInit(mdctx, EVP_sha256())) {
        cout << "Failed to initialize verification" << endl;
        return false;
    }

    if (!EVP_VerifyUpdate(mdctx, file_data, file_size)) {
        cout << "Failed to update verification" << endl;
        return false;
    }

    int result = EVP_VerifyFinal(mdctx, signature, signature_size, pkey);
    if (result != 1) {
        cout << "Failed to verify signature" << endl;
        return false;
    }

    delete[] file_data;
    delete[] signature;
    EVP_MD_CTX_free(mdctx);
    EVP_PKEY_free(pkey);
    return true;
}

此函数将读取指定的文件和签名文件，并使用提供的公钥验证签名是否有效。如果签名有效，则返回true，否则返回false。

请注意，此程序中使用的密钥长度为2048位。您可以根据需要更改密钥长度。此外，此程序中使用的哈希算法为SHA256。您可以根据需要更改哈希算法。

希望这能帮到您！