Android 4.2.2 系统签名

这里有原生系统的签名文件platform.pk8和platform.x509.pem以及Signapk工具 。
如果是自己编译的Android系统那么密钥文件在如下位置：

 /build/target/product/security/

java -jar signapk.jar  platform.x509.pem platform.pk8 input.apk output.apk

这样编译出来的APK就具有的系统签名，无论是装到/system/app中还是/data/app中都会是。

可以通过以下代码检测本应用是否为系统签名的应用：(来自：https://pankajchunchun.wordpress.com/2014/07/08/how-to-check-if-application-is-system-app-or-not-by-signed-signature/)

import android.content.Context;import android.content.pm.ApplicationInfo;import android.content.pm.PackageInfo;import android.content.pm.PackageManager;import android.content.pm.PackageManager.NameNotFoundException;public class AppUtility {    private static final String SYSTEM_PACKAGE_NAME = "android";    private PackageManager mPackageManager = null;    public AppUtility(Context context) {        mPackageManager = (PackageManager) context.getPackageManager();    }    /**     * Match signature of application to identify that if it is signed by system     * or not.     *      * @param packageName     *            package of application. Can not be blank.     * @return <code>true</code> if application is signed by system certificate,     *         otherwise <code>false</code>     */    public boolean isSystemApp(String packageName) {        try {            // Get packageinfo for target application            PackageInfo targetPkgInfo = mPackageManager.getPackageInfo(                    packageName, PackageManager.GET_SIGNATURES);            // Get packageinfo for system package            PackageInfo sys = mPackageManager.getPackageInfo(                    SYSTEM_PACKAGE_NAME, PackageManager.GET_SIGNATURES);            // Match both packageinfo for there signatures            return (targetPkgInfo != null && targetPkgInfo.signatures != null && sys.signatures[0]                    .equals(targetPkgInfo.signatures[0]));        } catch (PackageManager.NameNotFoundException e) {            return false;        }    }    /**     * Check if application is preloaded. It also check if the application is     * signed by system certificate or not.     *      * @param packageName     *            package name of application. Can not be null.     * @return <code>true</code> if package is preloaded and system.     */    public boolean isAppPreLoaded(String packageName) {        if (packageName == null) {            throw new IllegalArgumentException("Package name can not be null");        }        try {            ApplicationInfo ai = mPackageManager.getApplicationInfo(                    packageName, 0);            // First check if it is preloaded.            // If yes then check if it is System app or not.            if (ai != null                    && (ai.flags & (ApplicationInfo.FLAG_SYSTEM | ApplicationInfo.FLAG_UPDATED_SYSTEM_APP)) != 0) {                // Check if signature matches                if (isSystemApp(packageName) == true) {                    return true;                } else {                    return false;                }            }        } catch (NameNotFoundException e) {            e.printStackTrace();        }        return false;    }}