android verify signature of file with .der public key

' - Signature Verification Sample Program' tutorial was cited in a StackOverflow forum post in 2012.

The - Signature Verification Sample Program tutorial was cited in a StackOverflow forum post in 2012.

Subject: android verify signature of file with .der public key
Date: Dec. 10, 2012
Author: Josh

I'm trying to verify the signature of a file. I followed these
instruction to generate a certificate:

// generate a private key with size of 2048 bits
openssl genrsa -out private_key.pem 2048

// derive a public key from the above private key
openssl rsa -in private_key.pem -out public_key.pem -outform PEM

// iOS will not import PEM encoded data so it needs to be converted
// to DER encoded data
openssl rsa -pubin -inform PEM -outform DER -in public_key.pem
   -out public_key.der

// generate a self-signed certificate for testing
openssl req -new -x509 -key private_key.pem -out test_cert.pem
   -days 1095

// show the content of the original certificate
openssl x509 -in test_cert.pem -text -noout
// convert the certificate to DER format
openssl x509 -in test_cert.pem -outform der -out test_cert.der
// show the content of the new certificate
openssl x509 -in test_cert.der -inform der -text -noout

I used the example at this link to hash some data and verify that
everything was all good (I did steps 2 - 5).

Now I'm trying to put the .der file, the signature file, and the data
file into an Android application and basically verify it's all good
again. I'm not getting any errors, but I'm not getting false.. Below
 is the code I've written:

import android.os.Bundle;
import android.os.Environment;
import android.util.Base64;
import android.util.Log;
import android.widget.TextView;


// Most of the below is taken from:
// /Digital-Signature-JcaVerify-Signature-Verification-Program.html
public class MyActivity extends Activity {

String input = Environment.getExternalStorageDirectory() + "/data.txt";
String signFile = Environment.getExternalStorageDirectory() + "/signature";
String signAlgo = "SHA1withRSA";
int keyFile = R.raw.test_cert_josh;
String TAG = "VERIFY";

public void onCreate(Bundle savedInstanceState) {

    TextView textView = (TextView) findViewById(;

    try {
        PublicKey pubKey = readPublicKey(keyFile);
        byte[] sign = readSignature(signFile);
        textView.setText(verify(input, signAlgo, sign, pubKey) + "");
    } catch (Exception e) {

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