5.4.1 示例代码

你可以通过下面的图表(图 5.4-1)找出你应该实现的 HTTP / HTTPS 通信类型。

当发送或接收敏感信息时,将使用 HTTPS 通信,因为其通信通道使用 SSL / TLS 加密。 以下敏感信息需要 HTTPS 通信。

  • Web 服务的登录 ID /密码。
  • 保持认证状态的信息(会话 ID,令牌,Cookie 等)
  • 取决于 Web 服务的重要/机密信息(个人信息,信用卡信息等)

具有网络通信的智能手机应用是“系统”和 Web 服务器的一部分。 而且你必须根据整个“系统”的安全设计和编码,为每个通信选择 HTTP 或 HTTPS。 表 5.4-1 用于比较 HTTP 和 HTTPS。 表 5.4-2 是示例代码的差异。

表 5.4-1 HTTP 与 HTTPS 通信方式的比较

HTTP HTTPS
特性 URL http://开头 https://开头
加密内容
内容的篡改检测 不可能 可能
对服务器进行认证 不可能 可能
损害的风险 由攻击者读取内容
由攻击者修改内容
应用访问了伪造的服务器

表 5.4-2 HTTP/HTTPS 通信示例代码的解释

示例代码 通信 收发敏感信息 服务器证书
通过 HTTP 的通信 HTTP 不适用 -
通过 HTTPS 的通信 HTTPS OK 服务器证书由可信第三方机构签署,例如 Cybertrust 和 VeriSign
通过 HTTPS 使用私有证书的通信 HTTTPS OK 私有证书(经常能在内部服务器或测试服务器上看到的操作)

Android 支持java.net.HttpURLConnection / javax.net.ssl.HttpsURLConnection作为 HTTP / HTTPS 通信 API。 在 Android 6.0(API Level 23)版本中,另一个 HTTP 客户端库 Apache HttpClient 的支持已被删除。

5.4.1.1 通过 HTTP 进行通信

它基于两个前提,即通过 HTTP 通信发送/接收的所有内容都可能被攻击者嗅探和篡改,并且你的目标服务器可能被攻击者准备的假服务器替换。 只有在没有造成损害或损害在允许范围内的情况下,才能使用 HTTP 通信,即使在本地也是如此。 如果应用无法接受该前提,请参阅“5.4.1.2 通过 HTTPS 进行通信”和“5.4.1.3 通过 HTTPS 使用私有证书进行通信”。

以下示例代码显示了一个应用,它在 Web 服务器上执行图像搜索,获取结果图像并显示它。与服务器的 HTTP 通信在搜索时执行两次。第一次通信是搜索图像数据,第二次是获取它。它使用AsyncTask创建用于通信过程的工作线程,来避免在 UI 线程上执行通信。与服务器的通信中发送/接收的内容,在这里不被认为是敏感的(例如,用于搜索的字符串,图像的 URL 或图像数据)。因此,接收到的数据,如图像的 URL 和图像数据,可能由攻击者提供。为了简单地显示示例代码,在示例代码中没有采取任何对策,通过将接收到的攻击数据视为可容忍的。此外,在 JSON 解析或显示图像数据期间,可能出现异常的处理将被忽略。根据应用规范,有必要正确处理例外情况。

要点:

  1. 发送的数据中不得包含敏感信息。
  2. 假设收到的数据可能来自攻击者。

HttpImageSearch.java

package org.jssec.android.https.imagesearch;

import android.os.AsyncTask;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

public abstract class HttpImageSearch extends AsyncTask<String, Void, Object> {

    @Override
    protected Object doInBackground(String... params) {
        byte[] responseArray;
        // --------------------------------------------------------
        // Communication 1st time: Execute image search
        // --------------------------------------------------------
        // *** POINT 1 *** Sensitive information must not be contained in send data.
        // Send image search character string
        StringBuilder s = new StringBuilder();
        for (String param : params){
            s.append(param);
            s.append('+');
        }
        s.deleteCharAt(s.length() - 1);
        String search_url = "http://ajax.googleapis.com/ajax/services/search/images?v=1.0&q=" +
        s.toString();
        responseArray = getByteArray(search_url);
        if (responseArray == null) {
            return null;
        }
        // *** POINT 2 *** Suppose that received data may be sent from attackers.
        // This is sample, so omit the process in case of the searching result is the data from an attacker.
        // This is sample, so omit the exception process in case of JSON purse.
        String image_url;
        try {
            String json = new String(responseArray);
            image_url = new JSONObject(json).getJSONObject("responseData")
                .getJSONArray("results").getJSONObject(0).getString("url");
        } catch(JSONException e) {
            return e;
        }
        // --------------------------------------------------------
        // Communication 2nd time: Get images
        // --------------------------------------------------------
        // *** POINT 1 *** Sensitive information must not be contained in send data.
        if (image_url != null ) {
            responseArray = getByteArray(image_url);
            if (responseArray == null) {
                return null;
            }
        }
        // *** POINT 2 *** Suppose that received data may be sent from attackers.
        return responseArray;
    }
    
    private byte[] getByteArray(String strUrl) {
        byte[] buff = new byte[1024];
        byte[] result = null;
        HttpURLConnection response;
        BufferedInputStream inputStream = null;
        ByteArrayOutputStream responseArray = null;
        int length;
        try {
            URL url = new URL(strUrl);
            response = (HttpURLConnection) url.openConnection();
            response.setRequestMethod("GET");
            response.connect();
            checkResponse(response);
            inputStream = new BufferedInputStream(response.getInputStream());
            responseArray = new ByteArrayOutputStream();
            while ((length = inputStream.read(buff)) != -1) {
                if (length > 0) {
                    responseArray.write(buff, 0, length);
                }
            }
            result = responseArray.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // This is sample, so omit the exception process
                }
            }
            if (responseArray != null) {
                try {
                    responseArray.close();
                } catch (IOException e) {
                    // This is sample, so omit the exception process
                }
            }
        }
        return result;
    }
    
    private void checkResponse(HttpURLConnection response) throws IOException {
        int statusCode = response.getResponseCode();
        if (HttpURLConnection.HTTP_OK != statusCode) {
            throw new IOException("HttpStatus: " + statusCode);
        }
    }
}

ImageSearchActivity.java

package org.jssec.android.https.imagesearch;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;

public class ImageSearchActivity extends Activity {

    private EditText mQueryBox;
    private TextView mMsgBox;
    private ImageView mImgBox;
    private AsyncTask<String, Void, Object> mAsyncTask ;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mQueryBox = (EditText)findViewById(R.id.querybox);
        mMsgBox = (TextView)findViewById(R.id.msgbox);
        mImgBox = (ImageView)findViewById(R.id.imageview);
    }
    
    @Override
    protected void onPause() {
        // After this, Activity may be deleted, so cancel the asynchronization process in advance.
        if (mAsyncTask != null) mAsyncTask.cancel(true);
        super.onPause();
    }
    
    public void onHttpSearchClick(View view) {
        String query = mQueryBox.getText().toString();
        mMsgBox.setText("HTTP:" + query);
        mImgBox.setImageBitmap(null);
        // Cancel, since the last asynchronous process might not have been finished yet.
        if (mAsyncTask != null) mAsyncTask.cancel(true);
        // Since cannot communicate by UI thread, communicate by worker thread by AsynchTask.
        mAsyncTask = new HttpImageSearch() {
        
            @Override
            protected void onPostExecute(Object result) {
                // Process the communication result by UI thread.
                if (result == null) {
                    mMsgBox.append("¥nException occurs¥n");
                } else if (result instanceof Exception) {
                    Exception e = (Exception)result;
                    mMsgBox.append("¥nException occurs¥n" + e.toString());
                } else {
                    // Exception process when image display is omitted here, since it's sample.
                    byte[] data = (byte[])result;
                    Bitmap bmp = BitmapFactory.decodeByteArray(data, 0, data.length);
                    mImgBox.setImageBitmap(bmp);
                }
            }
        }.execute(query); 
        // pass search character string and start asynchronous process
    }
    
    public void onHttpsSearchClick(View view) {
        String query = mQueryBox.getText().toString();
        mMsgBox.setText("HTTPS:" + query);
        mImgBox.setImageBitmap(null);
        // Cancel, since the last asynchronous process might not have been finished yet.
        if (mAsyncTask != null) mAsyncTask.cancel(true);
        // Since cannot communicate by UI thread, communicate by worker thread by AsynchTask.
        mAsyncTask = new HttpsImageSearch() {
            @Override
            protected void onPostExecute(Object result) {
                // Process the communication result by UI thread.
                if (result instanceof Exception) {
                    Exception e = (Exception)result;
                    mMsgBox.append("¥nException occurs¥n" + e.toString());
                } else {
                    byte[] data = (byte[])result;
                    Bitmap bmp = BitmapFactory.decodeByteArray(data, 0, data.length);
                    mImgBox.setImageBitmap(bmp);
                }
            }
        }.execute(query); 
        // pass search character string and start asynchronous process
    }
}

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.jssec.android.https.imagesearch"
    android:versionCode="1"
    android:versionName="1.0">
    <uses-permission android:name="android.permission.INTERNET"/>
    <application
        android:icon="@drawable/ic_launcher"
        android:allowBackup="false"
        android:label="@string/app_name" >
        <activity
            android:name=".ImageSearchActivity"
            android:label="@string/app_name"
            android:theme="@android:style/Theme.Light"
            android:exported="true" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

5.4.1.2 使用 HTTPS 进行通信

在 HTTPS 通信中,检查服务器是否可信,以及传输的数据是否加密。 为了验证服务器,Android HTTPS 库验证“服务器证书”,它在 HTTPS 事务的握手阶段从服务器传输,其要点如下:

  • 服务器证书由可信的第三方证书机构签署
  • 服务器证书的期限和其他属性有效
  • 服务器的主机名匹配服务器证书的主题字段中的 CN(通用名称)或 SAN(主题备用名称)

如果上述验证失败,则会引发SSLException(服务器证书验证异常)。 这可能意味着中间人攻击或服务器证书缺陷。 你的应用必须根据应用规范,以适当的顺序处理异常。

下一个示例代码用于 HTTPS 通信,它使用可信的第三方证书机构颁发的服务器证书连接到 Web 服务器。 对于使用私有服务器证书的 HTTPS 通信,请参阅“5.4.1.3 通过 HTTPS 使用私有证书进行通信”。

以下示例代码展示了一个应用,它在 Web 服务器上执行图像搜索,获取结果图像并显示它。 与服务器的 HTTPS 通信在搜索时执行两次。 第一次通信是搜索图像数据,第二次是获取它。 它使用AsyncTask创建用于通信过程的工作线程,来避免在 UI 线程上执行通信。 与服务器的通信中发送/接收的所有内容,在这里被认为是敏感的(例如,用于搜索的字符串,图像的 URL 或图像数据)。 为了简单地显示示例代码,不会执行针对SSLException的特殊处理。 根据应用规范,有必要正确处理异常。 另外,下面的示例代码允许使用 SSLv3 进行通信。 通常,我们建议配置远程服务器上的设置来禁用 SSLv3,以避免针对 SSLv3 中的漏洞(称为 POODLE)的攻击。

要点:

  1. URI 以https://开头。
  2. 发送数据中可能包含敏感信息。
  3. 尽管数据是从通过 HTTPS 连接的服务器发送的,但要小心并安全地处理收到的数据。
  4. SSLException应该在应用中以适当的顺序处理。

HttpsImageSearch.java

package org.jssec.android.https.imagesearch;

import org.json.JSONException;
import org.json.JSONObject;
import android.os.AsyncTask;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

public abstract class HttpsImageSearch extends AsyncTask<String, Void, Object> {

    @Override
    protected Object doInBackground(String... params) {
        byte[] responseArray;
        // --------------------------------------------------------
        // Communication 1st time : Execute image search
        // --------------------------------------------------------
        // *** POINT 1 *** URI starts with https://.
        // *** POINT 2 *** Sensitive information may be contained in send data.
        StringBuilder s = new StringBuilder();
        for (String param : params){
            s.append(param);
            s.append('+');
        }
        s.deleteCharAt(s.length() - 1);
        String search_url = "https://ajax.googleapis.com/ajax/services/search/images?v=1.0&q=" +
        s.toString();
        responseArray = getByteArray(search_url);
        if (responseArray == null) {
            return null;
        }
        // *** POINT 3 *** Handle the received data carefully and securely,
        // even though the data was sent from the server connected by HTTPS.
        // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
        String image_url;
        try {
            String json = new String(responseArray);
            image_url = new JSONObject(json).getJSONObject("responseData")
                .getJSONArray("results").getJSONObject(0).getString("url");
        } catch(JSONException e) {
            return e;
        }
        // --------------------------------------------------------
        // Communication 2nd time : Get image
        // --------------------------------------------------------
        // *** POINT 1 *** URI starts with https://.
        // *** POINT 2 *** Sensitive information may be contained in send data.
        if (image_url != null ) {
            responseArray = getByteArray(image_url);
            if (responseArray == null) {
                return null;
            }
        }
        return responseArray;
    }
    
    private byte[] getByteArray(String strUrl) {
        byte[] buff = new byte[1024];
        byte[] result = null;
        HttpURLConnection response;
        BufferedInputStream inputStream = null;
        ByteArrayOutputStream responseArray = null;
        int length;
        try {
            URL url = new URL(strUrl);
            response = (HttpURLConnection) url.openConnection();
            response.setRequestMethod("GET");
            response.connect();
            checkResponse(response);
            inputStream = new BufferedInputStream(response.getInputStream());
            responseArray = new ByteArrayOutputStream();
            while ((length = inputStream.read(buff)) != -1) {
                if (length > 0) {
                    responseArray.write(buff, 0, length);
                }
            }
            result = responseArray.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // This is sample, so omit the exception process
                }
            }
            if (responseArray != null) {
                try {
                    responseArray.close();
                } catch (IOException e) {
                    // This is sample, so omit the exception process
                }
            }
        }
        return result;
    }
    
    private void checkResponse(HttpURLConnection response) throws IOException {
        int statusCode = response.getResponseCode();
        if (HttpURLConnection.HTTP_OK != statusCode) {
            throw new IOException("HttpStatus: " + statusCode);
        }
    }
}

其他示例代码文件与“5.4.1.1 通过 HTTP 进行通信”相同,因此请参阅“5.4.1.1 通过 HTTP 进行通信”。

5.4.1.3 使用私有证书通过 HTTPS 进行通信

这部分展示了一个 HTTPS 通信的示例代码,其中包含私人颁发的服务器证书(私有证书),但不是可信的第三方机构颁发的服务器证书。 请参阅“5.4.3.1 如何创建私有证书并配置服务器”,来创建私有证书机构和私有证书的根证书,并在 Web 服务器中设置 HTTPS。 示例程序的资产中包含cacert.crt文件。 它是私有证书机构的根证书文件。

以下示例代码展示了一个应用,在 Web 服务器上获取图像并显示该图像。 HTTPS 用于与服务器的通信。 它使用AsyncTask创建用于通信过程的工作线程,来避免在 UI 线程上执行通信。 与服务器的通信中发送/接收的所有内容(图像的 URL 和图像数据)都被认为是敏感的。 为了简单地显示示例代码,不会执行针对SSLException的特殊处理。 根据应用规范,有必要正确处理异常。

要点:

  1. 使用私人证书机构的根证书来验证服务器证书。
  2. URI 以https://开头。
  3. 发送数据中可能包含敏感信息。
  4. 接收的数据可以像服务器一样被信任。
  5. SSLException应该在应用中以适当的顺序处理。

PrivateCertificathettpsGet.java

package org.jssec.android.https.privatecertificate;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.KeyStore;
import java.security.SecureRandom;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManagerFactory;
import android.content.Context;
import android.os.AsyncTask;

public abstract class PrivateCertificateHttpsGet extends AsyncTask<String, Void, Object> {

    private Context mContext;
    
    public PrivateCertificateHttpsGet(Context context) {
        mContext = context;
    }
    
    @Override
    protected Object doInBackground(String... params) {
        TrustManagerFactory trustManager;
        BufferedInputStream inputStream = null;
        ByteArrayOutputStream responseArray = null;
        byte[] buff = new byte[1024];
        int length;
        try {
            URL url = new URL(params[0]);
            // *** POINT 1 *** Verify a server certificate with the root certificate of a private certificate authority.
            // Set keystore which includes only private certificate that is stored in assets, to client.
            KeyStore ks = KeyStoreUtil.getEmptyKeyStore();
            KeyStoreUtil.loadX509Certificate(ks,
                mContext.getResources().getAssets().open("cacert.crt"));
            // *** POINT 2 *** URI starts with https://.
            // *** POINT 3 *** Sensitive information may be contained in send data.
            trustManager = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
            trustManager.init(ks);
            SSLContext sslCon = SSLContext.getInstance("TLS");
            sslCon.init(null, trustManager.getTrustManagers(), new SecureRandom());
            HttpURLConnection con = (HttpURLConnection)url.openConnection();
            HttpsURLConnection response = (HttpsURLConnection)con;
            response.setDefaultSSLSocketFactory(sslCon.getSocketFactory());
            response.setSSLSocketFactory(sslCon.getSocketFactory());
            checkResponse(response);
            // *** POINT 4 *** Received data can be trusted as same as the server.
            inputStream = new BufferedInputStream(response.getInputStream());
            responseArray = new ByteArrayOutputStream();
            while ((length = inputStream.read(buff)) != -1) {
                if (length > 0) {
                    responseArray.write(buff, 0, length);
                }
            }
            return responseArray.toByteArray();
        } catch(SSLException e) {
            // *** POINT 5 *** SSLException should be handled with an appropriate sequence in an application.
            // Exception process is omitted here since it's sample.
            return e;
        } catch(Exception e) {
            return e;
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (Exception e) {
                    // This is sample, so omit the exception process
                }
            }
            if (responseArray != null) {
                try {
                    responseArray.close();
                } catch (Exception e) {
                    // This is sample, so omit the exception process
                }
            }
        }
    }
    
    private void checkResponse(HttpURLConnection response) throws IOException {
        int statusCode = response.getResponseCode();
        if (HttpURLConnection.HTTP_OK != statusCode) {
            throw new IOException("HttpStatus: " + statusCode);
        }
    }
}

KeyStoreUtil.java

package org.jssec.android.https.privatecertificate;

import java.io.IOException;
import java.io.InputStream;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Enumeration;

public class KeyStoreUtil {

    public static KeyStore getEmptyKeyStore() throws KeyStoreException,
        NoSuchAlgorithmException, CertificateException, IOException {
        KeyStore ks = KeyStore.getInstance("BKS");
        ks.load(null);
        return ks;
    }
    
    public static void loadAndroidCAStore(KeyStore ks)
    throws KeyStoreException, NoSuchAlgorithmException,
    CertificateException, IOException {
        KeyStore aks = KeyStore.getInstance("AndroidCAStore");
        aks.load(null);
        Enumeration<String> aliases = aks.aliases();
        while (aliases.hasMoreElements()) {
            String alias = aliases.nextElement();
            Certificate cert = aks.getCertificate(alias);
            ks.setCertificateEntry(alias, cert);
        }
    }
    
    public static void loadX509Certificate(KeyStore ks, InputStream is)
        throws CertificateException, KeyStoreException {
        try {
            CertificateFactory factory = CertificateFactory.getInstance("X509");
            X509Certificate x509 = (X509Certificate)factory.generateCertificate(is);
            String alias = x509.getSubjectDN().getName();
            ks.setCertificateEntry(alias, x509);
        } finally {
            try { is.close(); } catch (IOException e) { /* This is sample, so omit the exception process
            */ }
        }
    }
}

PrivateCertificateHttpsActivity.java

package org.jssec.android.https.privatecertificate;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;

    public class PrivateCertificateHttpsActivity extends Activity {
    
    private EditText mUrlBox;
    private TextView mMsgBox;
    private ImageView mImgBox;
    private AsyncTask<String, Void, Object> mAsyncTask ;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mUrlBox = (EditText)findViewById(R.id.urlbox);
        mMsgBox = (TextView)findViewById(R.id.msgbox);
        mImgBox = (ImageView)findViewById(R.id.imageview);
    }
    
    @Override
    protected void onPause() {
        // After this, Activity may be discarded, so cancel asynchronous process in advance.
        if (mAsyncTask != null) mAsyncTask.cancel(true);
        super.onPause();
    }
    
    public void onClick(View view) {
        String url = mUrlBox.getText().toString();
        mMsgBox.setText(url);
        mImgBox.setImageBitmap(null);
        // Cancel, since the last asynchronous process might have not been finished yet.
        if (mAsyncTask != null) mAsyncTask.cancel(true);
        // Since cannot communicate through UI thread, communicate by worker thread by AsynchTask.
        mAsyncTask = new PrivateCertificateHttpsGet(this) {
            @Override
            protected void onPostExecute(Object result) {
                // Process the communication result through UI thread.
                if (result instanceof Exception) {
                    Exception e = (Exception)result;
                    mMsgBox.append("¥nException occurs¥n" + e.toString());
                } else {
                    byte[] data = (byte[])result;
                    Bitmap bmp = BitmapFactory.decodeByteArray(data, 0, data.length);
                    mImgBox.setImageBitmap(bmp);
                }
            }
        }.execute(url); 
        // Pass URL and start asynchronization process
    }
}

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