How to read the Android apk file signature

In the open platform, such as Application API key and secret often need to use the APK file signature, then how to read it?

The following paste the relevant reading source:

Altogether two documents Mainactivity and MD5,

Package Com.lcg.gensinature;import Android.app.activity;import Android.app.alertdialog;import Android.content.context;import Android.content.dialoginterface;import Android.content.pm.packageinfo;import Android.content.pm.packagemanager;import Android.content.pm.packagemanager.namenotfoundexception;import Android.content.pm.signature;import Android.os.bundle;import Android.text.clipboardmanager;import Android.text.editable;import Android.text.textutils;import Android.util.log;import Android.view.View;import Android.view.view.onclicklistener;import Android.widget.button;import Android.widget.edittext;import Android.widget.textview;import Android.widget.toast;public class Mainactivity extends activity{private Button  MCOPYBTN;  Private Button mgenbtn;  Private EditText Mpackageet;  Private TextView Md5signtv;      public static byte[] Getsign (Context paramcontext, String paramstring) {PackageInfo localpackageinfo;      int i;      Byte[] Arrayofbyte; try {LocalpAckageinfo = Paramcontext.getpackagemanager (). Getpackageinfo (paramstring, 64);        i = 0;        if (i >= localPackageInfo.signatures.length) {return null;        } System.out.println (i);        Arrayofbyte = Localpackageinfo.signatures[i].tobytearray ();        System.out.println (Arrayofbyte);      return arrayofbyte;      } catch (Packagemanager.namenotfoundexception localnamenotfoundexception) {return null;    }} protected void OnCreate (Bundle parambundle) {super.oncreate (parambundle);    Setcontentview (R.layout.activity_main);    This.mpackageet = ((EditText) Findviewbyid (R.id.pkgnameet));    THIS.MGENBTN = (Button) Findviewbyid (R.ID.GETBTN)); This.mGenBtn.setOnClickListener (New View.onclicklistener () {public void OnClick (View paramview) {Str        ing str1 = MainActivity.this.mPackageEt.getText (). toString ();        if (Textutils.isempty (str1));         Byte[] Arrayofbyte;       Arrayofbyte = Mainactivity.getsign (MainActivity.this.getApplicationContext (), str1);        String str2 = "";          try {str2 = Md5.hexdigest (arrayofbyte);          LOG.D ("Gensinature", "Gen md5=" + str2);          System.out.println (STR2);                    MainActivity.this.md5SignTv.setText (STR2);    Clipboardmanager CMB = (Clipboardmanager) MainActivity.this.getSystemService (MainActivity.this.CLIPBOARD_SERVICE);   Cmb.settext (STR2);          Toast.maketext (Mainactivity.this, "copied to clipboard", 1). Show ();        Return        } catch (Exception e) {e.printstacktrace ();    }      }    });        This.md5signtv = ((TextView) Findviewbyid (R.ID.RESULTTV));  ShowDialog ();    private void ShowDialog () {Alertdialog.builder localbuilder = new Alertdialog.builder (this);    Localbuilder.setcancelable (FALSE); Localbuilder.settitle ("Warning?").    Setmessage ("will read app information");    Localbuilder.setpositivebutton ("reject", null); LocalBuilder.setnegativebutton ("Consent", new Dialoginterface.onclicklistener () {public void OnClick (Dialoginterface paramd      ialoginterface, int paramint) {MainActivity.this.finish ();    }    });  Localbuilder.show ();  }}

Package Com.lcg.gensinature;import Java.security.messagedigest;public class md5{private static final char[] Hexdigits =  {48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 97, 98, 99, 100, 101, 102};      public static string Hexdigest (String paramstring) {try {string str = Hexdigest (Paramstring.getbytes ());    return str;  } catch (Exception localexception) {} return null; } public static String hexdigest (byte[] paramarrayofbyte) {try {messagedigest localmessagedigest = messaged      Igest.getinstance ("MD5");      System.out.println (Paramarrayofbyte);      Localmessagedigest.update (Paramarrayofbyte);      byte[] Arrayofbyte = Localmessagedigest.digest ();            System.out.println (Arrayofbyte);      char[] Arrayofchar = new CHAR[32];      int i = 0;      int j = 0;      for (i=0;i<16;i++) {int k = arrayofbyte[i];      int L = j + 1;      ARRAYOFCHAR[J] = hexdigits[(0xF & K >>> 4)];      j = L + 1; ARRAYOFCHAR[L] = Hexdigits[(K & 0xF)];    } if (I >=) return new String (Arrayofchar);    } catch (Exception e) {e.printstacktrace ();  } return null;  }}

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How to read the Android apk file signature