以前用 C++ 做过的 DRM 项目，现抽取出其中核心的代码, 演示一下如何借助 DRM 对流媒体文件进行保护。
虽然微软的 DRM 技术被破解了, 但那是以用户通过认证并下载证书为前提的。由是观之, 运用 DRM 对流媒体
文件施以保护仍有一定意义，这毕竟比什么都不做要强嘛!

/* drm.h*/
#ifndef __DRM_H__
#define __DRM_H__

#include <string>
#import "wmrmobjs.dll"

class DRMObject {
public:
  DRMObject(char* inFile, char* outFile, char* licenseURL, char* corpName);
  bool Encrypt();

public:
  std::string key;
  std::string seed;
  std::string keyID;
  std::string contentID;
  std::string publicKey;
  std::string privateKey;

private:
  std::string _inFile;
  std::string _outFile;
  std::string _corpName;
  std::string _licenseURL;
};

#endif

// drm.cxx
#include "drm.h"
#include <comdef.h>
#include <iostream>

DRMObject::DRMObject(char* inFile, char* outFile, char* licenseURL, char* corpName)
{
  _inFile = inFile;
  _outFile = outFile;
  _corpName = corpName;
  _licenseURL = licenseURL;
}

bool DRMObject::Encrypt()
{
  try {
    HRESULT hr;

// Initialize the COM library on the current thread
    hr = CoInitialize(NULL);
    if (FAILED(hr))
      _com_issue_error(hr);

WMRMOBJSLib::IWMRMKeysPtr    keysObj("Wmrmobjs.WMRMKeys");  
    WMRMOBJSLib::IWMRMHeaderPtr  headerObj("Wmrmobjs.WMRMHeader");
    WMRMOBJSLib::IWMRMProtectPtr protectObj("Wmrmobjs.WMRMProtect");

// Generate keyID,seed,contentID
    keyID = keysObj->GenerateKeyID();
    seed  = keysObj->GenerateSeed();
    contentID = keysObj->GenerateKeyID();

// Generate key
    keysObj->KeyID = keyID.c_str();
    keysObj->Seed  = seed.c_str();
    key = keysObj->GenerateKey();

// Set protected header
    headerObj->KeyID = keyID.c_str();
    headerObj->ContentID = contentID.c_str();
    headerObj->LicenseAcqURL = _licenseURL.c_str();
    headerObj->Attribute["Copyright"] = _corpName.c_str();

// verify the key
    headerObj->SetCheckSum(key.c_str());

//Generate public and private key 
    _variant_t privKey, pubKey;
    VariantInit(&privKey);
    VariantInit(&pubKey);
    keysObj->GenerateSigningKeys(&privKey, &pubKey);    
    headerObj->IndividualizedVersion = "2.2";

// Save private and public kyes
    privateKey = (_bstr_t)privKey;
    publicKey  = (_bstr_t)pubKey;

// Sign key
    headerObj->Sign((_bstr_t)privKey);

// Set protect object
    _bstr_t header;
    header = headerObj->Header;
    protectObj->Header = header;
    protectObj->Key = key.c_str();
    protectObj->V1KeyID = keyID.c_str();

// start encrypt
    protectObj->InputFile = _inFile.c_str();  
    protectObj->ProtectFile(_outFile.c_str());
  }
  catch (const _com_error& e) {
    std::cerr << "COM Exception: "
       << e.ErrorMessage()
       << std::endl;
    if (e.ErrorInfo())
      std::cerr << (char*)e.ErrorInfo()
  << std::endl;
    return false;
  }

CoUninitialize();
  return true;
}

// drm_test.cxx
#include "drm.h"
#include <iostream>
using namespace std;

int main() {
  DRMObject* drmObj = new DRMObject("d:\\test.wma",
        "d:\\test2.wma",
        "http://localhost/test.asp",
        "test corp");
  if (drmObj->Encrypt()) {
    cout << "KeyID: "
           << drmObj->keyID
           << endl;

cout << "Seed: "
            << drmObj->seed
            << endl;

cout << "Key: "
           << drmObj->key
           << endl;

cout << "ContentID: "
            << drmObj->contentID
            << endl;

cout << "Public Key: "
           << drmObj->publicKey
           << endl;

cout << "Private Key: "
           << drmObj->privateKey
           << endl;
  }
  delete drmObj;
}