PkgCert.java

```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();
    }
}

android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class PartnerUserActivity extends Activity {

    // *** POINT 7 *** Verify if the certificate of a target application has been registered in a whitelist.
    private static PkgCertWhitelists sWhitelists = null;
    
    private static void buildWhitelists(Context context) {
        boolean isdebug = Utils.isDebuggable(context);
        sWhitelists = new PkgCertWhitelists();
        // Register the certificate hash value of partner application org.jssec.android.activity.partner
        activity
            .sWhitelists.add("org.jssec.android.activity.partneractivity", isdebug ?
            // The certificate hash value of "androiddebugkey" is in debug.keystore.
            "0EFB7236 328348A9 89718BAD DF57F544 D5CCB4AE B9DB34BC 1E29DD26 F77C8255" :
            // The certificate hash value of "my company key" is in the keystore.
            "D397D343 A5CBC10F 4EDDEB7C A10062DE 5690984F 1FB9E88B D7B3A7C2 42E142CA");
            // Register the other partner applications in the same way.
    }
    
    private static boolean checkPartner(Context context, String pkgname) {
        if (sWhitelists == null) buildWhitelists(context);
        return sWhitelists.test(context, pkgname);
    }
    
    private static final int REQUEST_CODE = 1;
    // Information related the target partner activity
    private static final String TARGET_PACKAGE = "org.jssec.android.activity.partneractivity";
    private static final String TARGET_ACTIVITY = "org.jssec.android.activity.partneractivity.PartnerActivity";
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    
    public void onUseActivityClick(View view) {
        // *** POINT 7 *** Verify if the certificate of the target application has been registered in the own white list.
        if (!checkPartner(this, TARGET_PACKAGE)) {
            Toast.makeText(this, "Target application is not a partner application.", Toast.LENGTH_LONG).show();
            return;
        }
        try {
            // *** POINT 8 *** Do not set the FLAG_ACTIVITY_NEW_TASK flag for the intent that start an activity.
            Intent intent = new Intent();
            // *** POINT 9 *** Only send information that is granted to be disclosed to a Partner Activity only by putExtra().
            intent.putExtra("PARAM", "Info for Partner Apps");
            // *** POINT 10 *** Use explicit intent to call a Partner Activity.
            intent.setClassName(TARGET_PACKAGE, TARTER_ACTIVITY);
            // *** POINT 11 *** Use startActivityForResult() to call a Partner 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 12 *** Handle the received data carefully and securely,
                // even though the data comes from a partner 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;
        }
    }
}

package org.jssec.android.shared;

import java.util.HashMap;
import java.util.Map;
import android.content.Context;

public class PkgCertWhitelists {
    private Map<String, String> mWhitelists = new HashMap<String, String>();
    
    public boolean add(String pkgname, String sha256) {
        if (pkgname == null) return false;
``` ```
if (sha256 == null) return false;
sha256 = sha256.replaceAll(" ", "");
if (sha256.length() != 64) return false; // SHA-256 -> 32 bytes -> 64 chars
sha256 = sha256.toUpperCase();
if (sha256.replaceAll("[0-9A-F]+", "").length() != 0) return false; // found non hex char
mWhitelists.put(pkgname, sha256);
return true;
}

public boolean test(Context ctx, String pkgname) {
// Get the correct hash value which corresponds to pkgname.
String correctHash = mWhitelists.get(pkgname);
// Compare the actual hash value of pkgname with the correct hash value.
return PkgCert.test(ctx, pkgname, correctHash);
}

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.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();
    }
}