Extract the X509Certificate used to sign the app from the APK

ApkCertificate.java

package com.example.alessio.testapp;

import android.content.Context;
import android.content.pm.ApplicationInfo;

import java.io.IOException;
import java.io.InputStream;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;

public class ApkCertificate {

	public static X509Certificate getApkCertificate(Context context) throws Exception {
		ZipFile apk = null;
		InputStream in = null;
		try {
			ApplicationInfo ai = context.getPackageManager().getApplicationInfo(context.getPackageName(), 0);
			apk = new ZipFile(ai.sourceDir);
			ZipEntry entry = apk.getEntry("META-INF/CERT.RSA");
			in = apk.getInputStream(entry);
			CertificateFactory factory = CertificateFactory.getInstance("X.509");
			return (X509Certificate) factory.generateCertificate(in);
		} finally {
			if (in != null) {
				try {
					in.close();
				} catch (IOException ignore) {
				}
			}
			if (apk != null) {
				try {
					apk.close();
				} catch (IOException ignore) {
				}
			}
		}
	}
	
}