4.1.1.4 创建/使用内部活动-安卓应用安全指南(Android Application Secure Design/Secure Coding Guidebook)

4.1.1.4 创建/使用内部活动

内部活动是禁止其他内部应用以外的应用使用的活动。它们用于内部开发的应用，以便安全地共享信息和功能。

第三方应用可能会读取用于启动活动的意图。因此，如果你将敏感信息放入用于启动活动的意图中，有必要采取对策来确保它不会被恶意第三方读取。

下面展示了创建内部活动的示例代码。

要点（创建活动）：

定义内部签名权限。
不要指定taskAffinity。
不要指定launchMode。
需要内部签名权限。
不要定义意图过滤器，并将导出属性显式设为true。
确认内部签名权限是由内部应用的。
尽管意图是从内部应用发送的，仔细和安全地处理接收到的意图。
由于请求的应用是内部的，因此可以返回敏感信息。
导出 APK 时，请使用与目标应用相同的开发人员密钥对 APK 进行签名。

AndroidManifest.xml


<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.jssec.android.activity.inhouseactivity" >
    
    <!-- *** POINT 1 *** Define an in-house signature permission -->
    <permission
    android:name="org.jssec.android.activity.inhouseactivity.MY_PERMISSION"
    android:protectionLevel="signature" />
    
    <application
        android:allowBackup="false"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        
        <!-- In-house Activity -->
        <!-- *** POINT 2 *** Do not specify taskAffinity -->
        <!-- *** POINT 3 *** Do not specify launchMode -->
        <!-- *** POINT 4 *** Require the in-house signature permission -->
        <!-- *** POINT 5 *** Do not define the intent filter and explicitly set the exported attribute to
        true -->
        <activity
            android:name="org.jssec.android.activity.inhouseactivity.InhouseActivity"
            android:exported="true"
            android:permission="org.jssec.android.activity.inhouseactivity.MY_PERMISSION" />
    </application>
</manifest>

InhouseActivity.java

package org.jssec.android.activity.inhouseactivity;

import org.jssec.android.shared.SigPerm;
import org.jssec.android.shared.Utils;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class InhouseActivity extends Activity {

    // In-house Signature Permission
    private static final String MY_PERMISSION = "org.jssec.android.activity.inhouseactivity.MY_PERMISSION";
    // In-house certificate hash value
    private static String sMyCertHash = null;
    
    private static String myCertHash(Context context) {
        if (sMyCertHash == null) {
            if (Utils.isDebuggable(context)) {
                // Certificate hash value of "androiddebugkey" in the debug.keystore.
                sMyCertHash = "0EFB7236 328348A9 89718BAD DF57F544 D5CCB4AE B9DB34BC 1E29DD26 F77C8255";
            } else {
                // Certificate hash value of "my company key" in the keystore.
                sMyCertHash = "D397D343 A5CBC10F 4EDDEB7C A10062DE 5690984F 1FB9E88B D7B3A7C2 42E142CA";
            }
        }
        return sMyCertHash;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        // *** POINT 6 *** Verify that the in-house signature permission is defined by an in-house application.
        if (!SigPerm.test(this, MY_PERMISSION, myCertHash(this))) {
            Toast.makeText(this, "The in-house signature permission is not declared by in-house application.",
            Toast.LENGTH_LONG).show();
            finish();
            return;
        }
        // *** POINT 7 *** Handle the received intent carefully and securely, even though the intent was sent from an in-house application.
        // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
        String param = getIntent().getStringExtra("PARAM");
        Toast.makeText(this, String.format("Received param: ¥"%s¥"", param), Toast.LENGTH_LONG).show();
    }
    
    public void onReturnResultClick(View view) {
        // *** POINT 8 *** Sensitive information can be returned since the requesting application is inhouse.
        Intent intent = new Intent();
        intent.putExtra("RESULT", "Sensitive Info");
        setResult(RESULT_OK, intent);
        finish();
    }
}

SigPerm.java

package org.jssec.android.shared;

import android.content.Context;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.PermissionInfo;

public class SigPerm {

    public static boolean test(Context ctx, String sigPermName, String correctHash) {
        if (correctHash == null) return false;
        correctHash = correctHash.replaceAll(" ", "");
        return correctHash.equals(hash(ctx, sigPermName));
    }

    public static String hash(Context ctx, String sigPermName) {
        if (sigPermName == null) return null;
        try {
            // Get the package name of the application which declares a permission named sigPermName.
            PackageManager pm = ctx.getPackageManager();
            PermissionInfo pi;
            pi = pm.getPermissionInfo(sigPermName, PackageManager.GET_META_DATA);
            String pkgname = pi.packageName;
            // Fail if the permission named sigPermName is not a Signature Permission
            if (pi.protectionLevel != PermissionInfo.PROTECTION_SIGNATURE) return null;
            // Return the certificate hash value of the application which declares a permission named sigPermName.
            return PkgCert.hash(ctx, pkgname);
        } catch (NameNotFoundException e) {
            return null;
        }
    }
}

PkgCert.java

package org.jssec.android.shared;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.Signature;

public class PkgCert {
    public static boolean test(Context ctx, String pkgname, String correctHash) {
        if (correctHash == null) return false;
        correctHash = correctHash.replaceAll(" ", "");
        return correctHash.equals(hash(ctx, pkgname));
    }
    
    public static String hash(Context ctx, String pkgname) {
        if (pkgname == null) return null;
        try {
            PackageManager pm = ctx.getPackageManager();
            PackageInfo pkginfo = pm.getPackageInfo(pkgname, PackageManager.GET_SIGNATURES);
            if (pkginfo.signatures.length != 1) return null; // Will not handle multiple signatures.
            Signature sig = pkginfo.signatures[0];
            byte[] cert = sig.toByteArray();
            byte[] sha256 = computeSha256(cert);
            return byte2hex(sha256);
        } catch (NameNotFoundException e) {
            return null;
        }
    }
    
    private static byte[] computeSha256(byte[] data) {
        try {
            return MessageDigest.getInstance("SHA-256").digest(data);
        } catch (NoSuchAlgorithmException e) {
            return null;
        }
    }
    
    private static String byte2hex(byte[] data) {
        if (data == null) return null;
        final StringBuilder hexadecimal = new StringBuilder();
        for (final byte b : data) {
            hexadecimal.append(String.format("%02X", b));
        }
        return hexadecimal.toString();
    }
}

要点 9：导出 APK 时，请使用与目标应用相同的开发人员密钥对 APK 进行签名。

使用内部活动的代码如下：

要点（使用活动）：

声明你要使用内部签名权限。
确认内部签名权限是由内部应用定义的。
验证目标应用是否使用内部证书签名。
由于目标应用是内部的，所以敏感信息只能由putExtra()发送。
使用显式意图调用内部活动。
即使数据来自内部应用，也要小心并安全地处理接收到的数据。
导出 APK 时，请使用与目标应用相同的开发人员密钥对 APK 进行签名。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.jssec.android.activity.inhouseuser" >
    
    <!-- *** POINT 10 *** Declare to use the in-house signature permission -->
    <uses-permission
    android:name="org.jssec.android.activity.inhouseactivity.MY_PERMISSION" />
    
    <application
        android:allowBackup="false"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        
        <activity
            android:name="org.jssec.android.activity.inhouseuser.InhouseUserActivity"
            android:label="@string/app_name"
            android:exported="true" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

InhouseUserActivity.java

package org.jssec.android.activity.inhouseuser;

import org.jssec.android.shared.PkgCert;
import org.jssec.android.shared.SigPerm;
import org.jssec.android.shared.Utils;
import android.app.Activity;
import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class InhouseUserActivity extends Activity {

    // Target Activity information
    private static final String TARGET_PACKAGE = "org.jssec.android.activity.inhouseactivity";
    private static final String TARGET_ACTIVITY = "org.jssec.android.activity.inhouseactivity.InhouseActivity";
    // In-house Signature Permission
    private static final String MY_PERMISSION = "org.jssec.android.activity.inhouseactivity.MY_PERMISSION";
    // In-house certificate hash value
    private static String sMyCertHash = null;
    
    private static String myCertHash(Context context) {
        if (sMyCertHash == null) {
            if (Utils.isDebuggable(context)) {
                // Certificate hash value of "androiddebugkey" in the debug.keystore.
                sMyCertHash = "0EFB7236 328348A9 89718BAD DF57F544 D5CCB4AE B9DB34BC 1E29DD26 F77C8255";
            } else {
                // Certificate hash value of "my company key" in the keystore.
                sMyCertHash = "D397D343 A5CBC10F 4EDDEB7C A10062DE 5690984F 1FB9E88B D7B3A7C2 42E142CA";
            }
        }
        return sMyCertHash;
    }
    
    private static final int REQUEST_CODE = 1;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    public void onUseActivityClick(View view) {
        // *** POINT 11 *** Verify that the in-house signature permission is defined by an in-house application.
        if (!SigPerm.test(this, MY_PERMISSION, myCertHash(this))) {
            Toast.makeText(this, "The in-house signature permission is not declared by in-house application.",
            Toast.LENGTH_LONG).show();
            return;
        }
        // ** POINT 12 *** Verify that the destination application is signed with the in-house certificate.
        if (!PkgCert.test(this, TARGET_PACKAGE, myCertHash(this))) {
            Toast.makeText(this, "Target application is not an in-house application.", Toast.LENGTH_LONG).show();
            return;
        }
        try {
            Intent intent = new Intent();
            // *** POINT 13 *** Sensitive information can be sent only by putExtra() since the destination application is in-house.
            intent.putExtra("PARAM", "Sensitive Info");

            // *** POINT 14 *** Use explicit intents to call an In-house Activity.
            intent.setClassName(TARGET_PACKAGE, TARGET_ACTIVITY);
            startActivityForResult(intent, REQUEST_CODE);
        } catch (ActivityNotFoundException e) {
            Toast.makeText(this, "Target activity not found.", Toast.LENGTH_LONG).show();
        }
    }
    
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode != RESULT_OK) return;
        switch (requestCode) {
            case REQUEST_CODE:
                String result = data.getStringExtra("RESULT");
                // *** POINT 15 *** Handle the received data carefully and securely,
                // even though the data came from an in-house application.
                // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
                Toast.makeText(this, String.format("Received result: ¥"%s¥"", result), Toast.LENGTH_LONG).show();
                break;
        }
    }
}

SigPerm.java

package org.jssec.android.shared;

import android.content.Context;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.PermissionInfo;

public class SigPerm {

    public static boolean test(Context ctx, String sigPermName, String correctHash) {
        if (correctHash == null) return false;
        correctHash = correctHash.replaceAll(" ", "");
        return correctHash.equals(hash(ctx, sigPermName));
    }
    
    public static String hash(Context ctx, String sigPermName) {
        if (sigPermName == null) return null;
        try {
            // Get the package name of the application which declares a permission named sigPermName.
            PackageManager pm = ctx.getPackageManager();
            PermissionInfo pi;
            pi = pm.getPermissionInfo(sigPermName, PackageManager.GET_META_DATA);
            String pkgname = pi.packageName;
            // Fail if the permission named sigPermName is not a Signature Permission
            if (pi.protectionLevel != PermissionInfo.PROTECTION_SIGNATURE) return null;
            // Return the certificate hash value of the application which declares a permission named sigPermName.
            return PkgCert.hash(ctx, pkgname);
        } catch (NameNotFoundException e) {
            return null;
        }
    }
}

PkgCert.java

package org.jssec.android.shared;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.Signature;

public class PkgCert {

    public static boolean test(Context ctx, String pkgname, String correctHash) {
        if (correctHash == null) return false;
        correctHash = correctHash.replaceAll(" ", "");
        return correctHash.equals(hash(ctx, pkgname));
    }
    
    public static String hash(Context ctx, String pkgname) {
        if (pkgname == null) return null;
        try {
            PackageManager pm = ctx.getPackageManager();
            PackageInfo pkginfo = pm.getPackageInfo(pkgname, PackageManager.GET_SIGNATURES);
            if (pkginfo.signatures.length != 1) return null; // Will not handle multiple signatures.
            Signature sig = pkginfo.signatures[0];
            byte[] cert = sig.toByteArray();
            byte[] sha256 = computeSha256(cert);
            return byte2hex(sha256);
        } catch (NameNotFoundException e) {
            return null;
        }
    }
    
    private static byte[] computeSha256(byte[] data) {
        try {
            return MessageDigest.getInstance("SHA-256").digest(data);
        } catch (NoSuchAlgorithmException e) {
            return null;
        }
    }
    
    private static String byte2hex(byte[] data) {
        if (data == null) return null;
        final StringBuilder hexadecimal = new StringBuilder();
        for (final byte b : data) {
            hexadecimal.append(String.format("%02X", b));
        }
        return hexadecimal.toString();
    }
}

要点 16：导出 APK 时，请使用与目标应用相同的开发人员密钥对 APK 进行签名。

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