安卓依靠security provider保障網(wǎng)絡(luò)通信安全。然而有時(shí)默認(rèn)的security provider存在安全漏洞。為了防止這些漏洞被利用，Google Play services 提供了一個(gè)自動(dòng)更新設(shè)備的security provider的方法來(lái)對(duì)抗已知的漏洞。通過(guò)調(diào)用Google Play services方法，可以確保你的應(yīng)用運(yùn)行在可以抵抗已知漏洞的設(shè)備上。

舉個(gè)例子，OpenSSL的漏洞(CVE-2014-0224)會(huì)導(dǎo)致中間人攻擊，在通信雙方不知情的情況下解密流量。Google Play services 5.0提供了一個(gè)補(bǔ)丁，但是必須確保應(yīng)用安裝了這個(gè)補(bǔ)丁。通過(guò)調(diào)用Google Play services方法，可以確保你的應(yīng)用運(yùn)行在可抵抗攻擊的安全設(shè)備上。

注意：更新設(shè)備的security provider不是更新android.net.SSLCertificateSocketFactory.比起使用這個(gè)類(lèi)，我們更鼓勵(lì)應(yīng)用開(kāi)發(fā)者使用融入密碼學(xué)的高級(jí)方法。大多數(shù)應(yīng)用可以使用類(lèi)似HttpsURLConnection，HttpClient，AndroidHttpClient這樣的API，而不必去設(shè)置TrustManager或者創(chuàng)建一個(gè)SSLCertificateSocketFactory。

使用ProviderInstaller給Security Provider打補(bǔ)丁

使用providerinstaller類(lèi)來(lái)更新設(shè)備的security provider。你可以通過(guò)調(diào)用該類(lèi)的方法[installIfNeeded()]()(或者[ installifneededasync]())來(lái)驗(yàn)證security provider是否為最新的(必要的話(huà)更新它)。

當(dāng)你調(diào)用[installifneeded]()時(shí)，[providerinstaller]()會(huì)做以下事情：

如果設(shè)備的Provider成功更新(或已經(jīng)是最新的)，該方法返回正常。
如果設(shè)備的Google Play services 庫(kù)已經(jīng)過(guò)時(shí)了，這個(gè)方法拋出[googleplayservicesrepairableexception]()異常表明無(wú)法更新Provider。應(yīng)用程序可以捕獲這個(gè)異常并向用戶(hù)彈出合適的對(duì)話(huà)框提示更新Google Play services。
如果產(chǎn)生了不可恢復(fù)的錯(cuò)誤，該方法拋出[googleplayservicesnotavailableexception]()表示它無(wú)法更新[Provider]()。應(yīng)用程序可以捕獲異常并選擇合適的行動(dòng)，如顯示標(biāo)準(zhǔn)問(wèn)題解決流程圖。

[installifneededasync]()方法類(lèi)似，但它不拋出異常，而是通過(guò)相應(yīng)的回調(diào)方法，以提示成功或失敗。

如果[installifneeded]()需要安裝一個(gè)新的[Provider]()，可能耗費(fèi)30-50毫秒（較新的設(shè)備）到350毫秒（舊設(shè)備）。如果security provider已經(jīng)是最新的，該方法需要的時(shí)間量可以忽略不計(jì)。為了避免影響用戶(hù)體驗(yàn)：

線程加載后立即在后臺(tái)網(wǎng)絡(luò)線程中調(diào)用[installifneeded]()，而不是等待線程嘗試使用網(wǎng)絡(luò)。（多次調(diào)用該方法沒(méi)有害處，如果安全提供程序不需要更新它會(huì)立即返回。）
如果用戶(hù)體驗(yàn)會(huì)受線程阻塞的影響——比如從UI線程中調(diào)用，那么使用[installifneededasync()]()調(diào)用該方法的異步版本。（當(dāng)然，如果你要這樣做，在嘗試任何安全通信之前必須等待操作完成。[providerinstaller]()調(diào)用監(jiān)聽(tīng)者的[onproviderinstalled()]()方法發(fā)出成功信號(hào)。

警告：如果[providerinstaller]()無(wú)法安裝更新Provider，您的設(shè)備security provider會(huì)容易受到已知漏洞的攻擊。你的程序等同于所有HTTP通信未被加密。一旦[Provider]()更新，所有安全API（包括SSL API）的調(diào)用會(huì)經(jīng)過(guò)它(但這并不適用于[android.net.sslcertificatesocketfactory]()，面對(duì)[cve-2014-0224]()這種漏洞仍然是脆弱的)。

同步修補(bǔ)

修補(bǔ)security provider最簡(jiǎn)單的方法就是調(diào)用同步方法[installIfNeeded()](http://developer.android.com/reference/com/google/android/gms/security/ProviderInstaller.html##installIfNeeded(android.content.Context).如果用戶(hù)體驗(yàn)不會(huì)被線程阻塞影響的話(huà)，這種方法很合適。

舉個(gè)例子，這里有一個(gè)sync adapter會(huì)更新security provider。由于它運(yùn)行在后臺(tái)，因此在等待security provider更新的時(shí)候線程阻塞是可以的。sync adapter調(diào)用installifneeded()更新security provider。如果返回正常，sync adapter可以確保security provider是最新的。如果返回異常，sync adapter可以采取適當(dāng)?shù)男袆?dòng)（如提示用戶(hù)更新Google Play services）。


/**
 * Sample sync adapter using {@link ProviderInstaller}.
 */
public class SyncAdapter extends AbstractThreadedSyncAdapter {

  ...

  // This is called each time a sync is attempted; this is okay, since the
  // overhead is negligible if the security provider is up-to-date.
  @Override
  public void onPerformSync(Account account, Bundle extras, String authority,
      ContentProviderClient provider, SyncResult syncResult) {
    try {
      ProviderInstaller.installIfNeeded(getContext());
    } catch (GooglePlayServicesRepairableException e) {

      // Indicates that Google Play services is out of date, disabled, etc.

      // Prompt the user to install/update/enable Google Play services.
      GooglePlayServicesUtil.showErrorNotification(
          e.getConnectionStatusCode(), getContext());

      // Notify the SyncManager that a soft error occurred.
      syncResult.stats.numIOExceptions++;
      return;

    } catch (GooglePlayServicesNotAvailableException e) {
      // Indicates a non-recoverable error; the ProviderInstaller is not able
      // to install an up-to-date Provider.

      // Notify the SyncManager that a hard error occurred.
      syncResult.stats.numAuthExceptions++;
      return;
    }

    // If this is reached, you know that the provider was already up-to-date,
    // or was successfully updated.
  }
}

異步修補(bǔ)

更新security provider可能耗費(fèi)350毫秒（舊設(shè)備）。如果在一個(gè)會(huì)直接影響用戶(hù)體驗(yàn)的線程中更新，如UI線程，那么你不會(huì)希望進(jìn)行同步更新，因?yàn)檫@可能導(dǎo)致應(yīng)用程序或設(shè)備凍結(jié)直到操作完成。因此你應(yīng)該使用異步方法[installifneededasync()](http://developer.android.com/reference/com/google/android/gms/security/ProviderInstaller.html#installIfNeededAsync(android.content.Context, com.google.android.gms.security.ProviderInstaller.ProviderInstallListener)。方法通過(guò)調(diào)用回調(diào)函數(shù)來(lái)反饋其成功或失敗。例如，下面是一些關(guān)于更新security provider在UI線程中的活動(dòng)的代碼。調(diào)用installifneededasync()來(lái)更新security provider，并指定自己為監(jiān)聽(tīng)器接收成功或失敗的通知。如果security provider是最新的或更新成功，會(huì)調(diào)用[onproviderinstalled()](http://developer.android.com/reference/com/google/android/gms/security/ProviderInstaller.ProviderInstallListener.html#onProviderInstalled()方法，并且知道通信是安全的。如果security provider無(wú)法更新，會(huì)調(diào)用[onproviderinstallfailed()](http://developer.android.com/reference/com/google/android/gms/security/ProviderInstaller.ProviderInstallListener.html#onProviderInstallFailed(int, android.content.Intent)方法，并采取適當(dāng)?shù)男袆?dòng)（如提示用戶(hù)更新Google Play services）

/**
 * Sample activity using {@link ProviderInstaller}.
 */
public class MainActivity extends Activity
    implements ProviderInstaller.ProviderInstallListener {

  private static final int ERROR_DIALOG_REQUEST_CODE = 1;

  private boolean mRetryProviderInstall;

  //Update the security provider when the activity is created.
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ProviderInstaller.installIfNeededAsync(this, this);
  }

  /**
   * This method is only called if the provider is successfully updated
   * (or is already up-to-date).
   */
  @Override
  protected void onProviderInstalled() {
    // Provider is up-to-date, app can make secure network calls.
  }

  /**
   * This method is called if updating fails; the error code indicates
   * whether the error is recoverable.
   */
  @Override
  protected void onProviderInstallFailed(int errorCode, Intent recoveryIntent) {
    if (GooglePlayServicesUtil.isUserRecoverableError(errorCode)) {
      // Recoverable error. Show a dialog prompting the user to
      // install/update/enable Google Play services.
      GooglePlayServicesUtil.showErrorDialogFragment(
          errorCode,
          this,
          ERROR_DIALOG_REQUEST_CODE,
          new DialogInterface.OnCancelListener() {
            @Override
            public void onCancel(DialogInterface dialog) {
              // The user chose not to take the recovery action
              onProviderInstallerNotAvailable();
            }
          });
    } else {
      // Google Play services is not available.
      onProviderInstallerNotAvailable();
    }
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode,
      Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == ERROR_DIALOG_REQUEST_CODE) {
      // Adding a fragment via GooglePlayServicesUtil.showErrorDialogFragment
      // before the instance state is restored throws an error. So instead,
      // set a flag here, which will cause the fragment to delay until
      // onPostResume.
      mRetryProviderInstall = true;
    }
  }

  /**
   * On resume, check to see if we flagged that we need to reinstall the
   * provider.
   */
  @Override
  protected void onPostResume() {
    super.onPostResult();
    if (mRetryProviderInstall) {
      // We can now safely retry installation.
      ProviderInstall.installIfNeededAsync(this, this);
    }
    mRetryProviderInstall = false;
  }

  private void onProviderInstallerNotAvailable() {
    // This is reached if the provider cannot be updated for some reason.
    // App should consider all HTTP communication to be vulnerable, and take
    // appropriate action.
  }
}

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