示例 C 程序：设置和获取会话密钥参数

以下示例创建一个随机会话密钥，获取并打印该键的一些默认参数，在原始键上设置新参数，然后获取并打印该新参数的值。 它通过销毁会话密钥并释放加密上下文进行清理。

此示例演示了以下任务和函数的用法：

• 使用 CryptAcquireContext 访问 CSP。
• 使用 CryptGenRandom 使用随机字节来归档缓冲区。
• 使用 CryptGenKey 创建会话密钥。
• 使用 CryptGetKeyParam 获取键参数的值。
• 使用 CryptSetKeyParam 更改密钥生成过程。
• 使用 CryptDestroyKey 销毁密钥。
• 使用 CryptReleaseContext 释放 CSP。

此示例使用 函数 MyHandleError。 此示例中包含此函数的代码。 此函数和其他辅助函数的代码也列在常规用途函数下。

//-------------------------------------------------------------------
// Copyright (C) Microsoft.  All rights reserved.

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

// Link with the Crypt32.lib file.
#pragma comment (lib, "Crypt32")

void MyHandleError(PCTSTR psz);

void main()
{
    HCRYPTPROV hProv;
    HCRYPTKEY hKey;
    DWORD dwMode;
    BYTE pbData[16];
    BYTE pbRandomData[8];
    DWORD dwCount;
    DWORD i;

    // Acquire a cryptographic provider context handle.
    if(!CryptAcquireContext(
        &hProv, 
        NULL, 
        NULL, 
        PROV_RSA_FULL, 
        0)) 
    {
        MyHandleError(TEXT("Error during CryptAcquireContext."));
    }

    //  Generate eight bytes of random data into pbRandomData.
    if( CryptGenRandom(
            hProv,
            8,
            pbRandomData))
    {
        _tprintf(TEXT("Eight bytes of random data have been generated.\n"));
    }
    else
    {
        MyHandleError(TEXT("Random bytes were not correctly generated."));
    }

    // Create a random block cipher session key.
    if(!CryptGenKey(
            hProv, 
            CALG_RC4, 
            CRYPT_EXPORTABLE, 
            &hKey)) 
    {
        MyHandleError(TEXT("Error during CryptGenKey."));
    }

    // Read the cipher mode.
    dwCount = sizeof(DWORD);
    if(CryptGetKeyParam(
        hKey, 
        KP_MODE, 
        (PBYTE)&dwMode, 
        &dwCount, 
        0))
    {
        // Print the cipher mode.
        _tprintf(TEXT("Default cipher mode: %d\n"), dwMode);
    }
    else
    {
        MyHandleError(TEXT("Error during CryptGetKeyParam."));
    }

    // Read the initialization vector.

    //  Get the length of the initialization vector.
    if(!CryptGetKeyParam(
        hKey, 
        KP_IV, 
        NULL,     
        &dwCount, 
        0)) 
    {
        MyHandleError(TEXT("Error getting the IV length"));
    }

    // Get the initialization vector, itself.
    if(CryptGetKeyParam(
        hKey, 
        KP_IV, 
        pbData, 
        &dwCount, 
        0))
    {
        // Print the initialization vector.
        _tprintf(TEXT("Default IV:"));
        for(i = 0; i < dwCount; i++) 
        {
            _tprintf(TEXT("%2.2x "),pbData[i]);
        }

        _tprintf(TEXT("\n"));
    }
    else
    {
        MyHandleError(TEXT("Error getting the IV."));
    }

    //  Reset the initialization vector.
    if(CryptSetKeyParam(
        hKey,
        KP_IV,
        pbRandomData,
        0))
    {
        _tprintf(TEXT("New initialization vector is set.\n"));
    }
    else
    {
        MyHandleError(TEXT("The new IV was not set."));
    }

    // Read the new initialization vector.

    //  Get the length of the new initialization vector.
    if(!CryptGetKeyParam(
        hKey, 
        KP_IV, 
        NULL,     
        &dwCount, 
        0)) 
    {
        MyHandleError(TEXT("Error getting the IV length"));
    }

    // Get the initialization vector, itself.
    if(CryptGetKeyParam(
        hKey, 
        KP_IV, 
        pbData, 
        &dwCount, 
        0))
    {
        // Print the initialization vector.
        _tprintf(TEXT("RE-set IV:"));
        for(i = 0; i < dwCount; i++) 
        {
            _tprintf(TEXT("%2.2x "),pbData[i]);
        }
        
        _tprintf(TEXT("\n"));
    }
    else
    {
        MyHandleError(TEXT("Error getting the IV."));
    }

    //  Clean up.

    //  Destroy the session key.
    if(hKey)
    { 
        CryptDestroyKey(hKey);
    }

    // Release the provider handle.
    if(hProv)
    { 
        CryptReleaseContext(hProv, 0);
    }
} // End of main.

//-------------------------------------------------------------------
//    This example uses the function MyHandleError, a simple error
//    handling function, to print an error message to the standard  
//    error (stderr) file and exit the program. 
//    For most applications, replace this function with one 
//    that does more extensive error reporting.

void MyHandleError(PTSTR psz)
{
    _ftprintf(stderr, TEXT("An error occurred in the program. \n"));
    _ftprintf(stderr, TEXT("%s\n"), psz);
    _ftprintf(stderr, TEXT("Error number %x.\n"), GetLastError());
    _ftprintf(stderr, TEXT("Program terminating. \n"));
    exit(1);
} // End of MyHandleError.