利用CryptoAPI加/解密文件

CryptoAPI是Windows平台上的一种加密API，可以用于加密和解密文件。下面是一个简单的示例，演示如何使用CryptoAPI加密和解密文件：

加密文件：

#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>

#pragma comment(lib, "crypt32.lib")

void EncryptFile(LPCWSTR lpszSourceFile, LPCWSTR lpszDestinationFile, LPCWSTR lpszPassword)
{
    HCRYPTPROV hProv = NULL;
    HCRYPTKEY hKey = NULL;
    HCRYPTHASH hHash = NULL;
    DWORD dwLen;
    DWORD dwCount;
    BYTE* pbBuffer = NULL;
    HANDLE hSourceFile = INVALID_HANDLE_VALUE;
    HANDLE hDestinationFile = INVALID_HANDLE_VALUE;

    // 打开源文件
    hSourceFile = CreateFile(
        lpszSourceFile,
        GENERIC_READ,
        FILE_SHARE_READ,
        NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        NULL
    );
    if (hSourceFile == INVALID_HANDLE_VALUE)
    {
        printf("Error: cannot open source file.\n");
        goto Exit;
    }

    // 创建目标文件
    hDestinationFile = CreateFile(
        lpszDestinationFile,
        GENERIC_WRITE,
        0,
        NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL
    );
    if (hDestinationFile == INVALID_HANDLE_VALUE)
    {
        printf("Error: cannot create destination file.\n");
        goto Exit;
    }

    // 获取密码哈希
    if (!CryptCreateHash(
        hProv,
        CALG_MD5,
        0,
        0,
        &hHash))
    {
        printf("Error: cannot create hash.\n");
        goto Exit;
    }

    if (!CryptHashData(
        hHash,
        (BYTE*)lpszPassword,
        (DWORD)wcslen(lpszPassword) * sizeof(WCHAR),
        0))
    {
        printf("Error: cannot hash password.\n");
        goto Exit;
    }

    // 获取加密密钥
    if (!CryptDeriveKey(
        hProv,
        CALG_RC4,
        hHash,
        0,
        &hKey))
    {
        printf("Error: cannot derive key.\n");
        goto Exit;
    }

    // 加密数据
    dwLen = GetFileSize(hSourceFile, NULL);
    pbBuffer = new BYTE[dwLen];
    if (!ReadFile(hSourceFile, pbBuffer, dwLen, &dwCount, NULL))
    {
        printf("Error: cannot read source file.\n");
        goto Exit;
    }

    if (!CryptEncrypt(
        hKey,
        NULL,
        TRUE,
        0,
        pbBuffer,
        &dwLen,
        dwLen))
    {
        printf("Error: cannot encrypt data.\n");
        goto Exit;
    }

    // 写入加密后的数据到目标文件
    if (!WriteFile(hDestinationFile, pbBuffer, dwLen, &dwCount, NULL))
    {
        printf("Error: cannot write destination file.\n");
        goto Exit;
    }

Exit:
    if (hSourceFile != INVALID_HANDLE_VALUE)
    {
        CloseHandle(hSourceFile);
    }
    if (hDestinationFile != INVALID_HANDLE_VALUE)
    {
        CloseHandle(hDestinationFile);
    }
    if (hHash != NULL)
    {
        CryptDestroyHash(hHash);
    }
    if (hKey != NULL)
    {
        CryptDestroyKey(hKey);
    }
    if (hProv != NULL)
    {
        CryptReleaseContext(hProv, 0);
    }
    if (pbBuffer != NULL)
    {
        delete[] pbBuffer;
    }
}

解密文件：

#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>

#pragma comment(lib, "crypt32.lib")

void DecryptFile(LPCWSTR lpszSourceFile, LPCWSTR lpszDestinationFile, LPCWSTR lpszPassword)
{
    HCRYPTPROV hProv = NULL;
    HCRYPTKEY hKey = NULL;
    HCRYPTHASH hHash = NULL;
    DWORD dwLen;
    DWORD dwCount;
    BYTE* pbBuffer = NULL;
    HANDLE hSourceFile = INVALID_HANDLE_VALUE;
    HANDLE hDestinationFile = INVALID_HANDLE_VALUE;

    // 打开源文件
    hSourceFile = CreateFile(
        lpszSourceFile,
        GENERIC_READ,
        FILE_SHARE_READ,
        NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        NULL
    );
    if (hSourceFile == INVALID_HANDLE_VALUE)
    {
        printf("Error: cannot open source file.\n");
        goto Exit;
    }

    // 创建目标文件
    hDestinationFile = CreateFile(
        lpszDestinationFile,
        GENERIC_WRITE,
        0,
        NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL
    );
    if (hDestinationFile == INVALID_HANDLE_VALUE)
    {
        printf("Error: cannot create destination file.\n");
        goto Exit;
    }

    // 获取密码哈希
    if (!CryptCreateHash(
        hProv,
        CALG_MD5,
        0,
        0,
        &hHash))
    {
        printf("Error: cannot create hash.\n");
        goto Exit;
    }

    if (!CryptHashData(
        hHash,
        (BYTE*)lpszPassword,
        (DWORD)wcslen(lpszPassword) * sizeof(WCHAR),
        0))
    {
        printf("Error: cannot hash password.\n");
        goto Exit;
    }

    // 获取解密密钥
    if (!CryptDeriveKey(
        hProv,
        CALG_RC4,
        hHash,
        0,
        &hKey))
    {
        printf("Error: cannot derive key.\n");
        goto Exit;
    }

    // 解密数据
    dwLen = GetFileSize(hSourceFile, NULL);
    pbBuffer = new BYTE[dwLen];
    if (!ReadFile(hSourceFile, pbBuffer, dwLen, &dwCount, NULL))
    {
        printf("Error: cannot read source file.\n");
        goto Exit;
    }

    if (!CryptDecrypt(
        hKey,
        NULL,
        TRUE,
        0,
        pbBuffer,
        &dwLen))
    {
        printf("Error: cannot decrypt data.\n");
        goto Exit;
    }

    // 写入解密后的数据到目标文件
    if (!WriteFile(hDestinationFile, pbBuffer, dwLen, &dwCount, NULL))
    {
        printf("Error: cannot write destination file.\n");
        goto Exit;
    }

Exit:
    if (hSourceFile != INVALID_HANDLE_VALUE)
    {
        CloseHandle(hSourceFile);
    }
    if (hDestinationFile != INVALID_HANDLE_VALUE)
    {
        CloseHandle(hDestinationFile);
    }
    if (hHash != NULL)
    {
        CryptDestroyHash(hHash);
    }
    if (hKey != NULL)
    {
        CryptDestroyKey(hKey);
    }
    if (hProv != NULL)
    {
        CryptReleaseContext(hProv, 0);
    }
    if (pbBuffer != NULL)
    {
        delete[] pbBuffer;
    }
}

要使用这些功能，只需调用EncryptFile和DecryptFile函数，并传递源文件路径、目标文件路径和加密/解密密码即可。请注意，这只是一个简单的示例，实际应用中需要考虑更多的安全问题。