private byte[] getSign(Context context) {
 PackageManager pm = context.getPackageManager();
 List<PackageInfo> apps = pm
  .getInstalledPackages(PackageManager.GET_SIGNATURES);
 Iterator<PackageInfo> iter = apps.iterator();
 while (iter.hasNext()) {
  PackageInfo info = iter.next();
  String packageName = info.packageName;
  //按包名 取签名
  if (packageName.equals("com.test.test")) {
  return info.signatures[0].toByteArray();
  } 
 }
 return null;
}

public static String getPublicKey(byte[] signature) {
try {
  CertificateFactory certFactory = CertificateFactory
   .getInstance("X.509");
  X509Certificate cert = (X509Certificate) certFactory
   .generateCertificate(new ByteArrayInputStream(signature));
  String publickey = cert.getPublicKey().toString();
  publickey = publickey.substring(publickey.indexOf("modulus: ") + 9,
   publickey.indexOf("\n", publickey.indexOf("modulus:")));
  Log.d("TRACK", publickey);
  return publickey;
 } catch (CertificateException e) {
  e.printStackTrace();
 }
 return null;
}